JumpJet .info · 2018. 12. 4. · THE WIRELESS CONSTRUCTOR July, 1925 CHOSEN BY EXPERTS MULLARD...

HOW TO MAKE:A DOUBLE -PURPOSE TWO -VALVE

RECEIVER.By D. J. S. Harli, B.Sc.

THE CRYSTOVALVE RECEIVER.By Percy W. Harris, M.I.R.E.

TWO INTERESTING CRYSTAL SETS.

HOW TO USE YOUR SEPARATE H.T.AND GRID -BIAS TERMINALS.

By Percy W. Harris, M. /. R. E.

FAULTS IN H.F. TRANSFORMERS.By G. P. Kendall, B.Sc.

THE SUNDAY PROGRAMMES.FOR THE NEW CONSTRUCTOR-WHAT

TOOLS TO BUY.

HUNDREDS OF PRACTICALHINTS AND TIPS FOR THE

BEGINNER.

THE WIRELESS CONSTRUCTOR July, 1925

CHOSEN BY EXPERTS

MULLARD DOUBLE WHITE RING MASTER VALVESALL wireless receivers need a superior detector. Perfect rectification is the firstessential for perfect rec.eption.

The use of general purpose valves or valves with H.F. or L.F. operation in addition torectification was satisfactory to many of the Radio public up till to -day, but

NOWas a result of improved apparatus, searching tests and expert experience

YOU can have A VALVE SPECIALLY FOR DETECTION ;this means that your radio rectification will be purer and stronger.MULLARD DOUBLE WHITE RING VALVES ARE REAL

MASTER DETECTORS.They are specially selected for the detector stage in YOUR set.Obtainable from all dealers in two types.MULLARD DOUBLE WHITE RING DETECTOR VALVESType D'3 for accumulators (I '6-2 volts) 141 -eachType D'06 for dry cells (2'5-3 volts) 10/beach

Ask your dealer, he knows best.YOU can also obtain Mallard Master Valves for H.F. and L.P. operations in the same types.

MullardTHE MASTEAVALVE

Advt. The Mullard Radio Valve Co., Ltd. (W.C)., Nightingale Works, Balham, S. W.12

THE WIRELESS CONSTRUCTORJuly, 1925

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Ipniu

I lkE LE-

z

ONSTRUCTOK--gdited by Percy -144 Hams

- .1_0 - wow - ea we.. 1B a . l, eel.'--------

VOL. 1. No.

CONTENTSA Double -Purpose Two-Valve.. Re-

ceiverBy D. J. S. HARTT.B.Se.One of a Rare Species " 801

Facts about your Tuning Condensers 802Faults in H.F. Transformers .. 804

By G. P. KENDALL, B.Sc.The Sunday Programmes .. 807

By "CARRIER -WAVE.'The " Comparison " Crystal Sot .. 814

By JOHN W. BARBER.How to use your H.T. and G.B.

Terminals 819By PERCY W. HARRIS. M.I.R.E.

JULY

"Outdoor Radio" ..Charging Accumulators at Home ..

By G. P. KENDALL. B.SC.The "Crystovalve " Receiver ..

By PERCY W. HARRIS, M.I.R E.Radio Press News ..John Anstruther's Wireless Talks ..Mr. Harris goes to America..Workshop Hints ..A Low -Loss Crystal Receiver

By W. H. FULLER.Great New Radio Press LaboratoriesTools for the Home Constructor ..

By JOHN UNDERDCWII.

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In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR. 793

THE WiRaESS CONSTRUCTOR

CONTINUOUSVERNIERC ONTTZ

This geared type squarelaw condenser makes thetuning of elusive stationseasy and certain.The movement of the controlknob is transmitted to the mov-ing vanes through a 6 : 1 reduc-tion gearing. Three completeturns of the knob are necessaryto cause the vanes to movethrough 180°, thus giving a con-tinuous vernier control through-out the entire scale.The actual movement of the vanesis registered by the dial, which isrigidly fixed to the spindle, and" back -lash " is entirely absent.

No. Capacity PRICE

R2720 '00025 E 1 : 3 : 0R2721 '0005 £1 : 6 : 6R2722, '001 E 1 :10 : 6

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Announcement of

STERLING TELEPHONE & ELECTRIC CO., LTD., Manufacturers of Telephones and Radio Apparatus, etc.210-212, TOTTENHAM COURT ROAD, LONDON, W.1 Works : DAGENHAM, ESSEX

794 In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.

J uly, 1925 THE WIRELFSS CONSTRUCTOR

\Scientific Adviser;

Prof. G. W.O. Howo,D.Sc., M.I.E.E.

Advisory Editors;, Prof. R.WHIDDINGTON

M.A., D.Sc.Prof. C. L. FORTESCUE,

M.A., M.I.E.E.

r

A (1 o

WIRELESSCONSTRUCTOR,

V01. 1. JULY, 1925.

err4

By D. J. S. HARTT, B.Sc.

////.vi

e

Stall tauors,E. H. CHAPMAN, M.A.,

D.Sc.A. D. COWPER, M.Sc.R. W. HALLows, M.AG. P. KENDALL, B.ScA. JOHNSON-RANDALLS. G. HArrEE, M. i.R.E

No. 9.

iNA 41.1 .t

Loud -speaker reception of the local station up to ten miles, and distant reception ontelephones,. by the turn of a switch,. are the chief features of this fascinating receiver.

ONE of the most useful circuitsit is possible to obtain usingtwo valves is undoubtedly

a simple detector circuit, with re-action on to the aerial, followed byone:stage of transformer -coupled low -frequency am -

By the use ofgood components and withthe help of a good outdooraerial, a well -deigned re-ceiver embodying this cir-cuit will give good loud-speaker ,strength from amain broadsting,, stationup to distances of about' i'omiles, this being a con-servative estimate of therange for this purpose, sincethe conditions prevailinglocally have considerablebearing on the useful loud-speaker range. Under goodconditions,and with carefultuning and judicious use ofreaction, a receiver of thistype will also prove veryuseful for tong -distance reception. . .

For reception on the tele-phohes of. more distantstations, however, a stageof high -frequency amplifi- When the H.F. and Detector Circuit is in use, notecation, followed by - a de- that the two coils should be kept at right angleS.

/ //

tector valve, is often to be preferred,in that it is possible to receive thesestations without undue forcing, ofthe set, to obtain greater selec-tiVity than with the co-bventionaldetector circuit, using reaction onto a direct coupled aerial circuit,and followed by one stage of L.E.amplification.

It occurred to the author thatthe functions of the two types ofreceiver discussed above could well

be combined in one set,without any appreciablesacrifice of efficiency, sothat it would be possibleto change instantly froman H.F. detector circuit toa detector and one stage oftransformer -coupled L.F.amplification.

The idea has been incor-porated in the receivershown in the accompanyingphotographs, and the re-sults ol...ained with theactual set are fully up toexpectations. The loCalstation is received at goodloud -speaker strength,while other British andmany Continental stationshave been heard at goodstrength on the 'phones

795

THE WIRELES:, CONSTRA,..:TOR July, 1925

even whil the local station wastransmitti5.z, and interesting com-parisons of reception on the twocircuits have been made.

Two Possible CircuitsThe two possible circuits which

are shown in separate diagramsmay be traced out from the theo-retical circuit diagram of the re-ceiver. It will be seen that whenthe double -pole double -throw switchS is in position 2, and the lead fromthe grid of the first valve pluggedinto the socket marked S1, thenthe resulting circuit consists ofone stage of H.F., employingtuned -anode, followed by a detec-tor valve in the ordinary way. Noreaction is introduced from theanode circuit of the detector valve,for the set will be found to oscillatequite freely without it, and theoscillation can be controlled, andthe set worked in its most sensitivecondition just off the oscillatingpoint by means of the potenti-ometer R5.

Switch PositionsWhen the switch is in position r,

and the lead from the grid. of thefirst valve plugged into S2 thedetector and note -magnifier circuitis obtained, and the potentiometerin this case can be used to controlthe potentiaL- on the grid of thedetector valve, but in general thebest results will be obtained withthe slider over towards the positiveside of the potentiometer winding.

ViE

-0.- S2

0490.5r F

CI

R

C3

Fig. 1.-A

O.P.

coil L,, and reaction controlled byadjusting the potentiometer. Itwill be noticed that separate high-tension tappings are provided foreach valve in both circuits and

anode tuning in the H.F. circuit.The potentiometer control knobis seen between the two condenserdials, while the two rheostats arelocated at the rear of the panel,

A near view of the panel. The terminals are arrangedat the back for convenience.

that provision is made for grid -bias.when using the second valve as alow -frequency amplifier, thus allow-ing the valves to be operated at thebest working conditions in eachcase.

Points of DesignThe photographs should give a

good idea of the design and layout

C4

.0003pF

eC.Boe

i_nCs OH.T.(02

.90-04 OH.T,Eei

OH.T.e0000Mo.s. r -T

C,;

complete diagram of the circuit employed, with theswitching arrangements clearly indicated.

The coil L, is coupled to the aerialcoil L, to obtain reaction in theordinary way, whereas in the caseof the H.F. detector circuit thecoil L in conjunction with thevariable, c-3ndenser C4, forms thetuned -anode circuit, and is thenkept at right -angles to the aerial

of the set, all the components ofwhich are mounted on a standard -sized panel arranged to fit hori-zontally into a suitable box. Thetuning condensers are located con-veniently at the front of the panel,that on the left being for aerialtuning, and on the right for the

where the coil -holder is also con-veniently placed on the left. Theswitch occupies the space betweenthe two valves, while the ter-minals for battery connections arearranged at the back of the panel,the aerial and the earth terminalsbeing on the left-hand side at theback, and those for telephones in acorresponding position on the right.Thus the controls are in convenientand accessible positions for easyAdjustment.

Compon eats NecessaryA complete list and specification

of the components actually usedin the receiver are given here, butthe discriminating constructor hasa wide field of choice if any depar-ture from this list is desired.,

One ebonite panel, 12 in. byo in. by f in., of guaranteed

quality (Paragon).One variable square -law conden-

ser, .000511F (Collinson's PrecisionScrew Co., Ltd.).

One variable square -law conden-ser, .000312F (Collinson's PrecisionScrew Co., Ltd.).

One L.F. transformer, " Success "(Beard & Fitch, Ltd.).

One D.P.D.T. " anti -capacity "switch (Gambrell Bros.).

Two filament resistances, Dualtype, centre fixing (L. McMichael,Ltd.),

One potentiometer (L. McMichael,Ltd.).

One two-way coil holder, one -hole fixing type (Hall & Brenard).

796

July, 1925

One .0003 t.LF fixed condenser(Paragon, Peter Curtis, Ltd.).

One -0o6 p.F fixed condenser(Paragon, Peter Curtis, Ltd.)..

One fixed condenser with clips (L.McMichael, Ltd.).;' the value of thiswill be referred to later in the text)..

Two valve holders, Type C(H.T.C. Electrical Co.). -

One .000311F fixed' condenserwith clips and two 2111 f grid leaks(both Dubilier).

One combined grid. condenser(00031/1?) and gridleak holder(Dorwood).

Two sockets and one plug fitting(Lisenin Wireless Co.).

Eleven terminals.Two condenser indicators (De cko) .

Square-s'eCtion tinned copper wirefor wiring.

Radio Press Panel Transfers.One suitable containing box

(Carrington Mfg. Co.).The first operation in the con-

struction Of the set is to preparethe panel for mounting the coinponents, and provided that oneof the guaranteed makes of ebonitehas been purchased the work ofmarking out and drilling may beattempted as soon as all the com-ponents have been obtained.

/4"

114114"-,1 .44341tL

THE WIRELESS CONSTRUCTOR

Showing : themounting of theTone -control con-denser and' con-nections to theL.F. Transformer.

Drilling and Tipping the HolesThe drilling centres should be

marked out carefully on the backof the panel with the help of thedimensioned diagram accompany-ing the article ; where templatesare supplied with the components,

as is the case with the valve holdersand the switch specified, theseshould be used to mark out thecorrect drilling centres. The centresare then all indented with a centrephnch and the necessary holescarefully drilled.

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Fig. 2.-A dimensioned front -of -panel drawing, showing how the various part. ore placed. Fullsize blueprint No. Cior6A may be obtained, krice i go host free.

797

"THE W/REL ESS CONSTRUCTOR" DOUBLE -PURPOSE 2 VALVE RECE/ VER.

RA D/O PRESS LT-'?, BUSH HOUSE, STRAND, W. C.2. BL UE PR /N r C. /0/6 b. PRICE/

"THE W/REL ESS CONSTRUCTOR" DOUBLE -PURPOSE 2 VALVE RECE/ VER.

RA D/O PRESS LT-'?, BUSH HOUSE, STRAND, W. C.2. BL UE PR /N r C. /0/6 b. PRICE/

1'HE WIRELESS CONSTRUCTOR

The only holes which requiretapping are those to take the twostops provided for the switch, butif the constructor is unable to do -this, two other stops requiring onlya plain hole through the panel andfixed by a back -nut, may be sub-stituted. The three holes for taking

, C,

0005,a. F.

Connections to the Coil HolderIn the actual set the connections

to the coil holder are made withsquare section wire passing throughsmall holes drilled in the panel,but the connections may be moreeasily made if thinner wire or flexis substituted. When the wiring

C4---

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L60003

R4

H.T. ED 2

H.T.

H.T e

R5

C3 .0196.,,Z4F:

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L.T.ePig 3.-The H.F. and detector circuit in simplified form. Note thatthe moving vanes of the variable condensers are marked with an

arrowhead.

the fixing screws for the switch maybe drilled 6 B.A. clearance, and

in. 6 B.A. countersunk -headscrews and nuts used for mountingthis component. The mounting ofthe remainder of the componentsis quite straightforward, and callsfor no further comment.

Wiring UpAs far as the wiring of the re-

...eiver is concerned, if the construc-tor possesses average ability insoldering, little difficulty should beencountered here, provided thatthe free blueprint given with thisissue is followed carefully in con-junction with the back -of -panelphotographs, which should give afair idea of the relative spacing anddisposition of the various wires. In

- particular, note carefully the con-nections to the Dorwood grid con-denser and grid leak mount.

Note also how the various fixedcondensers are mounted and con-nected. The soldering tags of thefirst grid condenser (a Dubilier)are inserted and soldered into theends of the I,isenin sockets, whilethe Paragon condensers across theprimary of the L.P. transformerand the potentiometer windinghave their tags soldered to con-venient wires and are, so to speak,suspended in the air. Clips to takea McMichael clip -in fixed condenserare secured under the fixing nutsof idle ieleplione terminals.

has been satisfactorily finished, theset may be completed by applyingthe panel transfers to mark thevarious terminals, etc.

When operating the set for thefirst time use the detector, L.F.circuit, plug in two suitable coils,and insert the two valves you intendusing. Then connect up the acme

C2,0003

ci2Mn R3

.0005 ur

E

Fig. 4.-The detector and note magnifier arrangement. The letteringcorresponds with that of the other two circuits.

July, 1925

grid -bias terminals may be shorted,and also the 'H.T.+ , and H.T.+,terminals joined with a wire- andconnected to the 6o -volt tappingon the H.T. battery. Then, havingconnected the aerial, the earthand the telephones to their re-spective terminals, set the twocoils at right angles, and adjustthe filament temperature of thevalves. Search for the local ornearest main station by varyingthe condenser C1 and having foundit verify that signals become louderas the coil L2 is moved graduallytowards L1, with a slight re -tuningon the condenser C1.

Reaction LeadsIf the set has been made as

specified, this should be the case,otherwise the leads to the reactioncoil L, may need reversing. Thereceiver will work well with generalpurpose valves, either bright ordull -emitter, or a small powervalve with a suitable value of H.T.voltage applied to terminal H.T.+2,with the appropriate grid -bias,may be used in the L.F. stage.If the set is used with a loud-speaker for reception of localbroadcasting, a tone -control con-denser of the clip -in type with avalue between ooi ti.F and about000 v.F, dependent on the loud-speaker used, may be requiredacross the telephone terminals, andthis condenser may be left in whenswitched over to the H.F. detectorcircuit.

It will be noticed when the

Its ooaperI.P.

0004

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2

EB2

H.T. EBI

H.T. e

R5

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mulator, and having ascertainedthat the L.T. circuit is in order,set the potentiometer to the positiveside, and connect the H.T. ter-minals to appropriate tappings onthe H.T. battery.

A Preliminary TestFor a preliminary test using, say,

general purpose valves, the two

* 1)Le

detector L.F. circuit is used, thatthe variable condenser C4, the gridcondenser C6 and the grid leak R1,all in series, are connected fromthe H.T.-f end of the reactioncoil to L.T.+. In actual practicethis is found to have no noticeableeffect whatever on the working ofthe receiver, whether the connection

798.

July, 1925

is complete or is broken by removingthe grid -leak from its mounting. .

Coil CouplingWhen the H.F. and detector

circuit is used, the coils L, and L2are always kept at right angles,and tuning -is effected by varyingthe condensers C, and C, simul-taneously. The II.T, voltage appliedto the first valve, and the filamenttemperature, should be so adjustedthat when the aerial and the anodecircuits are tuned to resonance,satisfactory control of oscillationis obtained by means of the poten-tiometer. It should be found possi-ble under these conditions to makethe receiver oscillate smoothly byturning the potentiometer contactmore towards the negative side ofthe windings, and to stop theoscillation as it is moved towardsthe positive.

Any difficulty in producing self -oscillation may be overcome bybringing the anode coil a littlecloser to the aerial coil.

Sizes of CoilsSuggested coil values, when using

the detector-L.F. circuit for thebroadcast band of wavelengths,are Nos. 35 or 5o (Gambrell A or B)for L1, and for L2 always choose thesmallest coil that will give amplereaction with adequate control.(No. 35 should be large enoughwith an aerial -earth system of lowresistance, but a No. 5o or evenNo. 75 may be required.) For 5XX


When in use, thebatteries are out ofsight behind the set.

use a No. 15o in the aerial, and forEiffel Tower a No. 200. With theH.F.-detector circuit try a No. 35or 5o for the aerial coil L1, and aNo. 5o or 75 (Gambrell B or C) forthe anode, these values being forthe broadcast band of wavelengths.A No. 15o for L,, and No. 200 for

The connections to the Dorwood Condenser may be followedfrom this photograph, which also gives a good idea of the

heights of the various wires.

L2. snould be suitable for 5XX,while a No. 200 for L, and No. 25oor 30o for L2 should be tried forEiffel Tower.

Results ObtainedWhen the receiver was tested

on a fairly good outdoor aerial,about 8 miles from zLO, very goodloud -speaker strength was obtainedon the detector-L.F. circuit fromthis station. 5XX also came invery well on the loud -speaker.Other stations heard on the circuitincluded Brussels (Radio-Belg.) andEiffel Tower at loud phone strength,Hilversum, Radio -Paris, EcoleSuperieure, Birmingham, andMadrid at good 'phone strength,while Newcastle, Glasgow andAberdeen were also heard at fairstrength in the 'phones. In addi-tion a German station workingon about 30o metres was receivedat quite good strength on the loud-speaker. Interference from 2L0when receiving stations on wave-lengths near to that of zLO was,of course, experienced, but in thecase of the H.F.-detector circuitthis was noticeably less and absentin some cases.

On the H.F.-detector circuitthe stations given above weir allreceived with Belfast in addition,and in general the strength of thenearer ones was less than with thedetector L.P. circuit, but signalswere "cleaner," -of better quality,and therefore more pleasant froma listening point of view, since lessreaction was required.

799


41:

41:

!-4

4

The " Twin -Valve " Receiver constructed byMr. Collins, whilst in hospital

am forwarding herewitha photograph of a " Twin -Valve "set constructed by Ex -WarrantOfficer Collins whilst a patient inhospital.

As a model of neatness' and ac-curacy it would he hard to beat,even if we put aside the fact thatMr. Collins cannot sit up.

You will notice very little devia-tion from Mr. John Scott-Taggart'soriginal design (WIRELESS CON-STRUCTOR, Vol. i, NO.,3), thereforeit is sure to work well, and you aresure to get an entlnisiastic reportlater on.

Yours faithfully,W. WATSON.

Harlesden.

SIR,-I have made the " TwinValve "set as described by Mr. JohnScott -Taggart in the January issueof your journal, and thought youmight be interested to know theresults obtained.

As instructions for making theset were completely ignored andthe panel arrangement was to myown liking, .I think that the resultsare marvellous. I am' situatedabout 3-3-, miles from Birmingham,and pick that station up at veryloud loud -speaker strength. Man-chester, Bournemouth, London,Cardiff and Glasgow are allmoderate loud -speaker strength,and most Continental stations comein at moderate loud -speakerstrength. On one evening I pickedup WGY, CKAC, and KDKA,WGY, and KDKA quite loudenough to work a small loud-speaker. The following weekI added a further L.F. valve tothe set. KDKA on 326 metreswas very good on loud-speakeL

also WGY. This is the best circuithat I have ever tried out, ank

Some Readers' Experiences

with the "Twin -Valve"

Loud -Speaker Receiver

This receiver, which employs a two -valve

reflex circuit, was described in the

January issue of this magazine

I can certainly recommend anyamateur wishing to:make a goodselective two -valuer to constructthis set.-Wishing you everysuccess,

- . Yours faithfully,Edgbaston, C. LAW.

Birmingham.

SIR,-May I congratulate youon your " Twin -Valve " loud-speaker set, as described by Mr.John Scott -Taggart in the Januaryissue of THE WIRELESS CON-STRUCTOR.

I have not placed the com-ponents as in your design, asI have put the L.F. transformer atthe other end of the panel, and amusing a '0002 1.LF. condenser insteadof a .0003, as stated in the article.rsing two home-made honeycombcoils, a 5o and a 65, and a Sterling" Dinkie " loud -speaker, Edin-burgh, Glasgow, Aberdeen andBirmingham come in clearly. Theset is also very selective, as I amwithin 300 yards of the Edinburghstation and can cut it clean outand get Glasgow at good volume,which can be heard all over thehouse. I use a Dutch for thefirst valve and a Cossor for thesecond, using respectively 42 and6o volts on the plates. When Iuse grid -bias the set won't stophowling-I don't know why-soI leave it alone. -I am only 15,and as I took " Hot -Wire's " hints(?)for soldering-but not his circuit-you can imagine the job.

However, the set gives excellentresults, and that is all I want.Thanking you again,

Yours faithfully,ALICK POLSON.

Edinburgh.[We do not advise any departure

from the instructions.-ED.]

SIR,-It may interest you toknow that I have built the " TwinValve " loud -speaker receiver fromdetails contained in THE WIRELESSCONSTRUCTOR, No. 3. At theoutset please allow me heartily tocongratulate Mr. Scott -Taggart onthe design of a " two-valver " ofsuch marked efficiency.

Cardiff (3o miles) and Bourne-mouth (6o miles) come in extra-ordinarily loud and clear, andGlasgow at 'phone strength is allthat could be desired. My -aerialis approximately a level 35 ft.high, P.O. pattern, and earthonly about 4 ft. from the set andvery efficient.

I use a -" Watmel " variablegrid leak in place of fixed one,McMichael H.P. transformer, andthe valves -are, Marconi OsramD.E.R. (Detector), and EdiswanA.R.D.E., (H.F.) ; plate voltage 35and 8o respectively.

I use ordinary basket coils andfind them satisfactory.

Altogether I am quite proud ofmy set, more so from the factthat this is my " very first " inwireless construction of any kind,which, I think, speaks volumesfor your lucid and understand-able " diagrams and drawings andthe instructions accompanyingthem.

I should say without hesitationthat the new way of showing wiringdiagrams by leaving out the semi-circles and giving the wiring bystages is much. preferable ; in fact,I fail to see any, difficulty whateverin wiring up from the presentmethod.

Yours faithfully,P. R. WOODLAND"

Bridgwater,Somerset.

800

July, 1925

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THE WIRELESS COik.STRUCTOR

ONE OF A RARE SPECIES

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THE WIRELISS CONSTRUCTOR

Facts About

Your

Tuning

Condensers

IT maymay seem a veryobvious point to theold hand, yet many

a novice is puzzled, andexcusably, as to whichposition of the vanes ofthe condenser really givesthe maximum capacityand which the minimum.Our first photographshows a condenser of acOrnmonly used typeadjusted tp the maximumcapacity position, whichis also the position ofinaxiinuin wavelengthwhen the instrument isused in a tuned circuit.

The minimum capacityis obtained when the mov-ing plates are turned asfar out from the fixedones as .possible, and

July, 1925

state of affairs is seen isthe second photograph.

Remember that no con-denser. gives you abso-lutely zero capacity inthis position, since therealways remains what isknown as the minimumcapacity of the condenser.

Some of the faults whichdevelop in variable con-densers manifest them-selves in the form of agrating or a scratching,noise when the dial isturned, and this is usuallydue to one of the movingplates touching the fixed

902

July, 1925 THE WIRELESS CONSTRUCTOR

ones as it revolves. Theeasiest way to discoverwhether this is happeningis to turn the movingplates to the maximumcapacity position, and thenhold up the condenser asshown in our third photo-graph with a sheet of white

paper behind it, so thatone can look throughand observe 'whether any-plates are touching.

. In extreme cases, atouching plate can be seenquite clearly without -theaid of the sheet of whitepaper, and such a .defec-tive specimen is shown inthe fourth picture. Hereit will be observed that thesecond moving plate,counting from the dialend, is touching the fixedone, as indicated by thearrow head.

AnOthenr possible cause ofnoises oiPreyolving a dialis dust, or other dirt, be-tween the plates and the

fifth photograph shows how a pipe cleanermay be used as a remedy: This opera-tion should be carried out with considerablecare, so as not to bend the plates about, andthe cleaner should be passed carefullybetween each pair of both fixed and movingplates, until it can be seen that both are -reasonably clean when held up againsta piece of white paper.

When a condenser has lust been mountedin a new set, some sort of mark -must bemade upon the panel to serve as an in-dicator. A good way of doing this isshown in the last photograph, and it will beobserved that .a scriber is used for the .pur-pose of making a short, deep scratch in thedesired position, this scratch being after-wards filled in with some white material,such as wax oreven certain brands of toothpaste. This last may, perhaps, sound softie -what unsatisfactory as a filling medium, butit must be remembered that once it has driedthere is little chance of it being rubbed out,and it actually proves quite effective in.nractice.


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8

8

July, 1925

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/->Faults in H.F. TransformersBy G. P. KENDALL, B.Sc., Staff Editor

When trouble develops in a receiver, the H.F. transformers often escape attention,

but the fau't may be located herein, and be'ow are given some useful hints ontesting these compone its

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OST of us, -4) think, arerather apt to take mostOf our plug-in units for

granted, and when something goeswrong with the set, they areoften the last compofients to besuspected. True, most such unitsare usually very reliable, andthere is always the feeling that ifone falls under suspicion it is avery . easy ,matter to replace itwith another ; but, nevertheless,the substitution test is not a veryeasy one as a rule, because one does_not generally possess,- for example,two plug-in high -frequency trans-formers for the same wavelengthrange, and therefore such com-parisons are difficult. As a result,most of us rather neglect suchthings, and I hope that the follow-ing notes will serve to show whata simple matter it is to ascertainwhether high -frequency trans-formers are in working order.

A Gammon FaultOne of the commonest faults

in high -frequency transformers isthat of a simple break in theprimary or secondary, and thelatter may, under certain circum-stances produce very puzzling re-sults. A break in the primarywinding, on the other hand, usuallystops the set from working- alto-gether and the matter, therefore,is a relatively simple one. Thosewho possess a milliammeter willhave no difficulty in identifyingthis fault, by adopting the followingprocedure : put the milliammeterin the usual position for measuringthe total anode current of theset, viz., between the high-tensionpositive terminal on the instrumentand the high-tension positive socketof the H.T. battery. With allthe valves alight, note the readingof the milliammeter, then replacethe suspected high -frequency trans-former with any other which youmay possess, regardless pf thewavelength range, and again takethe milliammeter reading. If ithas increased considerably, say,half or one milliampere, you may

be fairly sure that the suspectedhigh -frequency transformer has abroken-down winding. The breakMay be actually in the windingitself, but it will more usually befound where the wire is broughtout and connected to the two pins,either by soldering or screwingbeneath nuts.

A SImp:e TestThose who do not possess a

milliammeter can still test theirtransformers by means of theinvaluable " telephones and drycell " method. The procedure inthis case, is as follows : remove thetransformer from its socket, andpldce it upon the table with thelegs upwards. Now take a singledry cell and a pair of telephones,and screw one of the tags of the'phones under one terminal of thecell. Take a wire from the otherterminal of the cell with one hand,and the free tag of the 'phones inthe other, and touch these twoupon the two primary pins of thetransformer. If the 'phones areworn, a loud click should be heardupon doing this-practically asloud, in fact, as if the telephonetags had been connected straightacross the dry cell itself. It isto be noted that if there is abreakdown in the primary winding,it is probable that a faint clickwill still be heard, and it should,therefore, be made a rule thatunless a really loud click is ob-tained, the winding is to beassumed to have broken down.

Breaks in the Sezondal-yBreakdowns .in the secondary

winding are less easy to identify,and the symptoms of such a caseare sometimes very peculiar, rangingfrom complete deadness on thepart of the set to quite good signalsaccompanied by an extremely per-sistent tendency to oscillate. Thesimplest method is undoubtedlyto repeat the telephone and dry -cell test upon the secondary wind-ing in the manner- which we havejust considered ; but, as before,

do not be content with anythingbut a really clear and loud click,a faint one betokening troublejust as surely as complete silence.Having decided that there is abreak in the secondary circuit,it may be looked for in the sameplaces as were, mentioned in dealingwith the primary winding, and ifno break can be discovered, probablythe best thing to do is to return thetransformer to the makers.

InsulationIt is not often found that the

insulation- between the primaryand secondary is- defective, atany rate in those types of trans-former in which the primary andsecondary are wound in entirelyseparate slots ; but this fault is apossible one, and should, perhaps,be given a little attention. Thetelephdne and dry -cell test willvain serve our purpose, beingcarried out this time betweeneither of the primary pins andeither of the secondary pins.' Theresult should be practically com-plete silence on a good -trans -former.

The only other common faultaffecting high -frequency trans-formers is that sometimes metwith in the matched type, wheretwo or more are simultaneouslytuned by means of a double ortreble condenser, the fault inquestion being inaccurate matchifig.The symptoms are usually poorsignals, and in some cases greatdifficulty in making the set oscillate,with a Very flat tuning upon thetransformer tuning condenser.Probably the easiest method ofchecking the matching of a pairOf transformers is to take thein toa friend who possesses a set whichincorporates only one stage oftuned transformer high -frequencyamplification, and get him tosubstitute one of them for hisown, tune in a distant .and fairlyweak transmission, then pull outthe one transformer and insert theother, noting whether any seriousdifference' in the condenser readingresults.

804


LISSENIUMSeparating Chelmsfordand Radio -Paris

SEND FOR TEXT BOOK of Lissen Parts-free to readers of ''Wireless Constructor."

CHANGE OF ADDRESSOur works at Shepherd's Bush were quite inadequate for satis-fictorily dealing with our rapidly increasing production ofLISSEN PARTS. We have consequently acquired muchlarger and more convenient premises, from which we shall beable to give even better service and immediate delivery. Nowireless dealer should be without an ample stock of LISSENPARTS. and we should like any reader of this publicationwho experiences any difficulty in obtaining his requirementsto write to us mentioning the name of his usual wirelessdealer. Dealers also are asked to send for a copy of ourlatest TEXT BOOK.

OUR NEW ADDRESS IS--

LISSEN LIMITEDLISSENIUM WORKS,

30-32, FRIARS LANE,RICHMOND, SURREY,

'Phone: RICHMOND 2285 (4 /hiss).'Grams: LISSENIUM, LONDON.

Receiving Radio -Paris without interference fromthe high power station at Chelmsford haspreviously been very difficult at any positionwithin about 75 miles of Chelmsford. The highpower used by the British Station, has necessitatedthe use of a loose -coupled circuit, or otherselective device, with the attendant difficultiesof operation.

BY means of the new LISSENAGON "X" COIL No. 250, thenecessary selectivity can be obtained without any addition to theexisting tuning arrangements of the receiver. A very selective

circuit is obtained by using a LISSENAGON "X" COIL No. 250 in theanode circuit of the H.F. valve. Any tuned anode circuit can be alteredin a few moments by removing the wire connecting the plate of theH.F. valve to the anode coil, inserting the "X" Coil and connecting theplate of the H.F. valve to one of the tapping points on the "X" Coil.The connection from one side of the anode coil to the grid condenserof the next valve remains unaltered, whilst the other side of the coil isstill connected to H.T. Positive. It should be noted that the latterconnection should be to the socket of the LISSENAGON "X" COIL,and the connection from the plate of the H.F. valve should be tried oneach of the two terminals to prove which gives best results. The tuningcondenser remains across the whole of the coil and tuning is carriedout as usual.

The LISSENAGON "X" COIL can also be used as an aperiodic aerialcoil, and in cases where interference is exceptionally heavy a LISSEN-AGON "X- COIL can be used in both aerial and anode circuits. For useas an aperiodic aerial coil it is only necessary to plug the coil into theaerial coil holder and connect the aerial to one of the terminals on theside of the coil mount. Note that the socket of the coil should beconnected to earth.

In addition to the No. 250 LISSENAGON "X" COIL, we are alsomaking LISSENAGON "X" COILS Nos. 50, 60 and 75. Used asdescribed above, they give a great degree of selectivity, stability andsmoothness of reaction control on the broadcast band of wavelengths.The L1SSENAGON "X" COIL No. 60 covers the 300 to 600 metrebanc'l of wavelengths, but the No. 50 "X" Ccil is recommended for thelower band of wavelengths, and the No. 75 for the higher wa;lengths.

ASK FOR LISSENAGON COILS-THECOILS WHICH INTENSIFY TUN I Al;

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Brandesahe name to .know in Radio

Grandpa reflects. on how fine . it is to be quiet andrestful, -yet still finding a full measure of amusementfor the leisure hourS. ' _The armchair presses com-fortably against the back of his head ; his broadshoulders sink luxuriothly into its padded depths.Glancing down .the stem ,of his pipe he sees thedee.p, rich colour. of the, polished bowl, and justbeyond, into his uninterrupted line of vision, comesa glass-and a " finger " of mellow liquid with thethousands of tiny bubbles hurrying to the top.Across his head is the dark, comfortable -lookingheadband of a Brandes. The Matched Tone re-ceivers, clasped gently but firmly to his ears, bringthe world and its news ; its pleasures and achieve-ments. No need to have it bawled at ou acrossthe club smoking room by a choleric ex -colonel." Great !" he sighs contentedly.

Ask your Dealer for Brandes.Brandes Ltd. 296, Regent Street, London, IV. f. Works : Slon;n, Bucks.

aatcbsclrioneHeadphones

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The Bishop of London, whosesermon at St. Martin's was

recently broadcast.

THERE is possibly no greaterproblem faced by any enter-tainment manager than the

framing of a programme for thatday which " comes be-tween a Saturday and aMonday," as the old songhas it.

If he allows too manycomedy items, he gets intothe black books of thciewho may be able to in-terfere with his licence.If he keeps to the "straightand narrow path " ofreligious music only, lieopens to an empty house,so he is on the horns of adilemma.

The B.B.C.'s ProblemBut the B.B.C. has not

these difficulties to contendwith : there is -no. vitalquestion of pounds,shillings and pence totrouble its financial spirit,neither can its existencebe endangered by theantagonism of sects, andtherefore; had it but beencontent to provide enter-tainment for a listeningworld, this problem wouldnever have existed for it.

But having abrogatedto itself, rightly orwrongly, as opinion maydiffer, the right ofpropaganda, and to makeits studio an unconse-crated pulpit to millionsof people of varyingfaiths, the B.B.C. is

The SundayProgrammesAND THOSE WHO

CONTRIBUTETOWARDS THEM

By"CARRIER -WAVE"

faced with the problem of satisfyingall classes.

To the unprejudiced " onlooker,"the one who is supposed to see themost of the game, a wiser coursewould perhaps have been to givethe public what it so evidentlywants, the best in music and enter-tainment, and leave the clerics to

The Archbishop of Canter-bury, who has also been heard

at 2LO.

look after the moral welfare of theirown _flocks, thereby avoiding allschisms and arguments, The pleathat the Church is harmed by wire-

less does not really holdgood, for the averagechurch -goer does not findthe broadcast service anadequate substitute forpersonal attendance at hisusual place of worship.Wireless would no morekeep a devout church -goerat home when the bellsring out than it wouldfrom his business thefollowing morning, whileit is incongruous, to sa,.,the least of it, to thinkthat the average mancoming from the religiousatmosphere of the servicewould go across the road" one minute " later to arestaurant for its band,however good, or evenattend a concert of light

uric.

The Church of St. Martin's -in -the -Fields, Londonthe services from which are frequently heard by

listeners.

807

The Present ArrangementOn the whole, the

present arrangement leaveslittle to be desired. Whilethe service part of theprogramme does not keeplisteners from church, itundoubtedly brings religioninto thousands of homes,and the studio often be-comes the pulpit for someof the greatest preachers,who, in many cases, wouldotherwise never beheard.

THE WIRELESS CO.NSTRUCTOR July, 1925

To invalids, alSo, broadcastingprovides almost the only way ofkeeping in touch with .religiousservices.

The Clerical SideHowever, it is right to say that in

its efforts to make the entertain-ment -loving "lion" lay down withthe clerical "lamb," the B.B.C. hasriven the highest prelates and allacts opportunities never beforemade possible.

At WembleyPossibly one of the most inier-

ssting was tiie 'F,Mpire Thanks-giving Service in May .last 'year,when their Majesties the Ring andQueen were 'present at the firstBritish Empire Exhibition, and anaddress was given by his 'Grace theArchbishop of Canterbury, with amassed choir of 3,000 voices con-ducted -by Sir Henry WalfordDavies. Such an event is, ofcourse, of national moment.

Mr. Percy -.Edgar, the StationDirector at Birmingham, takes aprominent part in Sunday services.

A favourite service has beenfound, too. in that .of St. Martin's -in -the -Fields, theold Charing Crosschurch, fromwhere a sermonby the Rt. Rev.the Lord Bishopof London was re-cently broadcast.

21,0 has beenquite broad-minded as to sects,for it has givenus opportunitiesfrom time to timet hear -the famousdignitaries of all,sects- Methodist,Presbyterian,Catholic andnewish -andhaseven taken thetrouble to giveus the SalvationArmy and theservice conducted

Miss Dorothy Silk, a famous singer,has been heard several times.

at the Royal Albert Hall By GipsySmith last year.

In the ProvincesA high standard is, of coarse,

maintained in the provinces, andat BirMingham, Mr. -Percy Edgar,the Station Director, takes a veryprominent part. Services are re-la.yed from the Cathedral Church,Si:. Philip's, preceded by a broad-cast of the cathedral bells, whileapparently one of the most appre-ciated features of the evening pro-gramme is the reading by Mr. Edgar-of a poetical extract, immediatelybefore closing clown.

Relayed ServicesAt the other stations, services

have been relayed from . York

Blister, Bristol Cathedral, and quiterecently Canterbury Cathedral.Amongst the prelates whO havebsen heard over the aether by thismeans, in addition to the manypopular louil preachers, such asthe Rev. L. Sheppard, at St.Martin's, London, may be men-tioned the Rt. Rev. The Bishop ofHereford, the Lord Bishop ofLlandaff, the Bishop of Durham,and the Bishop Suffragan of Dover.

The Entertainment SideThis has been covered by means

of afternoon .and ,evening concertsof a more or less classical nature.

Frequent organ recitals are given,opportunity being first taken inLondon of using the .2Eolian Hallorgan, under Mr. Frank Arm-strong ; later came that of theNational Institute for the Blind,and here have been heard Mr.William \Volstenholme, the blindcomposer and organist, Reginald

Mr. Gipsy Smith, who conducteda service at the Albert Hall.

Goss -Custard, Whittaker Wilson,and, perhaps best of all, Mr. Stanton,Jeffreys, Assistant Director of

Music to theB B .C.

The Catterall String Quartet, led by Arthur Catterall, who was theleader of the Halle Orchestra.

808

The Vocal S actionFor this have

been found someof the finestartistes in thecountry, includingthe two greatWagnerian .andoratorio singers,Miss Carrie Tubb.and Mr. Horace.Stevens. Bothwere heard re-cently when atEaster, the "Mes-siah " was relayedandMendelssohn's'oratorio "Hymnof Praise " wasperformed at 2 LO-..

Miss 'DorothySilk is another


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Fit Ediswan Dull EmitterValves in Portable Sets,

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Ail Bakelite base. Low self -capacity. W ale collarat top (firm grip for inserting and withdrawinjvalve). Moulded rib on same side as anodepin (ready identificationof anode pin, bytouch. Obviates"burnout"due toincorrectinsertion).

Al

To get the best out of your set,put the best into your set. Fit theright valve for your individual needs.

The most efficient electrode system for onetype of valve is not necessarily the best forother types. The electrode system of each typeof the " Valve in the Purple Box" is the resultof scientific determination of the best design forthe conditions under which it is to be used.

A noteworthy example is

TYPE D. E. 3.a general purpose valve for use with drybatteries, or 4 -volt accumulators.

REDUCED PRICE 16/6Outstanding features :-

FILAMENT. GRID.

Although current consumption isonly .06 amp., electron emissionequals that of bright emitter takingover twelve times the current. Thefilament does not depend for itsemission on a substance coated onthe outside which rapidly wears

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July, 1925

favourite singer. She has made aspecial forte of Bach arias and oldfolk songs, many of which she hasunearthed from obseirrity. Shewas heard - at her best, perhaps,when Cardiff, pioneer of good pro-grammes, devoted a Sunday nightto the works of Gustave Hoist, andincluded his short opera "Savitri,"in which Miss Silk took thetitle role, and which she createdwhen the opera -was produced lastyear at Covent Garden.

Amongst the innumerablefavourite vocalists, too, may 1ementioned Miss Kate Winter, whose,voice, we believe, is most frequentlyrecognised iii query programmes,Miss Constance Willis and May

Miss Irene Scharrer, a well knownsolo pianist.

Blythe, both famous members of the13.N.O.C., while enthusiasm isalways expressed when the othermembers of this company, especiallyWalter Hyde,Frederic Collier,or Robert Rad-ford, are heard.

The InstrumentalElement

Naturally, clas-sical music hasbeen a vital factorin Sunday pro-grammes, and has

11 given listeners op-portunities to hearthe best players ofchamber music aswell 'as soloists,for the formerhave been repre-sented with theCatterall String "Quartet,. led byArthur Catterall,-late leader of the

The

THE WIMESS CONSTRUCTOR

Mr. De Groot, the leader of theOrchestra at the Piccadilly Hotel.

IIalle-Orchestra, the London StringQuartet, with its famous personnel(Messrs. James Levey, Thomas,Petre, H. ,Waldo Warner andC. Warwick Evans), the SpencerDyke, the Snow String, the KutcherString Quartets and the lEolianPlayers, all artists of highest note.

On the solo side, the piano hasbeen in-- the safe hands of suchplayers as Irene Scharrer,Mr. William Murdoch, the Australianpianist, Mr. Maurice Cole, one ofthe earliest of all pianists tobroadcast, and Mr. Gordon Bryan.The violin with Daisy Kennedy,Constance Izard and AlbertSammons are names to conjurewith at any great hall, the 'cellowith Cedric Sharpe, the harp withJeanne Chevreau, and the old-worldmusic of the Chaplin' Trio are allexamples of real music.

The Lighter SideIt is, however, in the evening

that to most people the real musicof the day begins, and it is thispart of the programme; if any, thatshould he extended.

The Military BandThe brass band has often been

described as "the national instru-ment." Certainly, England dearlylovesits military band, and hereagain we have had of the best,including the Royal Artillery, theRoyal Air Force, the Grenadiers,the Life Guards, Princess Patricia'sCanadian Light Infantry, theKneller Hall military bands, to say

Miss Kate Winter, a favouritesinger, is frequently recognised in

query programmes.nothing of 2.LO's " very own,"formed and conducted by Mr. DanGodfrey, and who should knowbetter than he how to make this agreat success .

There is, how -

famous De Groot Orchestra, whose musicenjoyed on Sundays.

is so thoroughly

ever, one providerof classical musicwhose name hasbecome a house-hold word, andthat is Mr. DeGroot, the violin-ist-conductOr ofthe fine orchestraat the PiccadillyHotel. " King ofmeal -time music "has he -well beencalled,for from thecutset he deter-mined that hewould not playjazz, but wouldmake his audienceenjoy\ the finestmusic and, likeOliver" ask for more.lii.

811

THE 'WIRELESS CONSTRUCTOR July, 1925

Well, too, has he suc-ceeded-Puccini, Leon-cavallo, Wagner,Tchalkowskv, Sibelius, toquote bet a few of thegreat composers, have allbeen" fed" to the patronsof the hOtel and of thenether, and right wellleave they appreciatedthe change.

The Studio MenuAt 2.140 also the studio

has given the finest inminiature orchestras, :forthe two most hardto equalJ. H. Squire's CelesteOctet, which came earlyin the musical history ofthe B.B.C., and Casauo'sOctet soon 'proved theirability to give the peblicjust What it wanted.

These, too, have givenopportenity to bring 'for-ward singers whose voiceshave since become -knownto every music -lover.

Prom the De Groot con-certs first came to us MissMavis 'Bennett and MissWynne Ajello, the freshness oftheirvoices and their ability to interpret

Miss Jeanne Chevreau, of theharp, which has been heard

B.N.O.C., with herover the aether.

coloratura music making the deepestimpression.

foreign"day ,Of

Favourite SingersFavourite .singers of

the studio 'have becomeMiss Kate Winter,Winifred 'Fisher, DorothyBennett, Elsie Suddaby,Roy Henderson, LeonardGowings, BertramAYrton, amidst a ;hostOf others, while !bestof all have 'been the studioperformances "all alongthe line " of the artists ofthe British NationalOpera -Company. Theirsolo performances, as wellas performance of operain studio and at CoventGarden _and their othertheatres, have done moreto revive the love of operathan any, foreign companyexistent.

These names representbut the tiniest part of thevast army of musicians:Who make the Sundayprogramme what it h;and redeem that :dayfrom being what it istermed by so manyvisitors --the nationalpenance."

Some causes of Poor ReceptionFaults in Crystal Receivers and How They Were Remedied

By H. BRAMFORD

ON several occasions I have hadreceivers handed to meaccompanied with the re-

mark, " I can't make this go ;I don't- know why. I carefullyfollowed. the instructions when I

-made it, -and it -ought to go ; I amsure I have done everything right,":and then, rather sceptically, " Per-haps it is no good." Such remarks,strange to say, often apply to suchsimple things as crystal receiversof the most elementary type.

ExamplesOn one occasion a set was handed

to me in this manner. On examin-ing the receiver I saw that alldetails had actually been faithfullycarried out, and was at a loss forthe moment to trace the fault.HoWever, on perceiving a -question-able make of variometer on thereceiver my suspicions immediatelyturned:in this direction. The rotorrevolved on a spindle and socket.but the adjustment was so loose

. that there was practically no con-tact taking place between the rotorspindle and stator bush as -wasessential with this style of instru-ment. On removing the fault andmaking -connection- secure, and

attaching aerial, earth and 'phonesto the set, results were excellent.

On another occasion I had a setto overhaul. In this case instruc-tions had -been badly followed.For one thing the aerial terminalwas a minus quantity. Also not asingle nut was firmly secured, andnot a single contact was good. Infact, a remarkable disregard hadbeen paid to small but essentialdetails. Having checked the con-nections, and tightened up gener-ally, results obtainable were verypoor. In this case, the variablecondenser was at fault. The fixedvanes were connected properly,but the moving vanes were not-connected at all.

FaxiitsThe best way to look for -or guard

against faults -in crystal receiversis as follows :--

. Be quite sure that all -connec-tions are correct.

2. Test continuity of connectionsor windings with a flashlampor buzzer and battery.

3. Where connections are securedunder nuts, see that the nutsare tight, and, if possible, add alock nut.

4. -See that no bare wires .aretouching one another.

5. Carefully examine rubbingcontact connections, such asare found on -variometers andvariable -condensers.

6. See that the moving vanes ofvariable condensers do nottouch the fixed vanes.

7. See that the aerial and earthare connected to the receiverwhen trying out.

The" Sharp Tuning -Single -Valve Receiver

will be interested toknow that I have made your single -valve "Sharp Tuning " receiverwhich was described in THE;WIRELESS CONSTRUCTOR, Marchissue, by Mr. Stanley G. Rattee,and I am. very pleased with it.

I have used a 2 megoluns gridleak and a .0005a.F. ordinary typevariable condenser; instead of therheostat I used a Lissen Minor.I have received the following-stations : Birmingham (almost tooloud), Manchester, London, -Liver-poOl, Nottingham, Stoke-on-Trent,and a French and German -station,bet I do not know which stationsthey were. All these were receivedon 5o, 75, 5o coils.

I -cites faithfully,Birmingham, H. HEYNES.

812

July, 1925

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National Physical Laboratory, Teddington

REPORTON TEST OF

SAMPLES OF EBONITE.Sent by-Messrs. Peter Curtis, Limited.Tested for-Messrs. Peter Curtis, Limited.Reference-Letter SLF/PMC, dated 8.4.25.

INSULATION RESISTANCE.

Resistivity :Sample. Megohms for a cen- Air

timetre cube. Temp.

(1) greater than 15° C.500,000,000

(2) greater than500,000,000

SURFACE RESISTIVITY.

Surface ResistivityMegohms per centi- Air

metre per centimetre. Temp.

(1) greater than 15° C.100,000,000

(2) greater than100,000,000

ELECTRIC STRENGTH.The test was made in accordance with

Admiralty Schedule 756 for Ebonite.

Electricay,

Specified MinimumHumpte. Strength it..ectric Strength:

R MH. Volts R.M.S. Volts pmper Millimetre. Millimetre,

(1) 77,000 80.000(2) 80,500 80,000

Reference : E.T.A. 92-64 E.T.D. 182-7.(Sgd.) J. E. PETAVEL, Director.

pp. H.C.B.

N.B.-The above, and certain other testsmade, prove PARAGON EBONITE to be from200 to over 500 per mt. better than_certain grades of " Ebonite" alleged tobe suitable (sic) for radio uses.

The uniform dead black, fine grain mattfinish perfect machinability and greatersuperfine area per lb. are other exclusivefeatures of

PARAGON EBONITEThe Proved Best Made

Sales Organisation:

PETER CURTIS, LTD.IN ASSOCIATION WITH

THE PARAGON RUBBER MFG. CO., LTD., HULL

75, CAMDEN ROAD, LONDON, N.W.1Telegrams-PARACURTEX" Telephone- NORTH 3112

BIRMINGHAM, 76, Newhall Street. - Telephone-Central 7236.MANCHESTER, 312, Deansgate. - Telephone --Central 5095.

EMIR\

dik

In replying to advertisers, please nzention THE WIRELESS CONSTRUCTOR, 813

THE WIREIXSS CONSTRUCTOR July, 19'25

S The "Comparison"

This instrument makes possibleof crystal, each specimen being

detector of the

:11111111111111111111111111111111111111111111111111111111

MANY crystal enthusiasts spenda great amount of time intrying out various specimens

of crystals in an endeavour to find" the best," and derive muchamusement and instruction there-from. It is, however, very advan-tageous if a " standard " is at handby means of which comparisonsmay be made, at the same timeproviding a means whereby thewhole receiving circuit may be usedas an ordinary crystal set shouldoccasion arise.

It is with these generalisations inmind that the crystal receiver Mus-

a.* trated herewith has been designed,and the writer has found the " con-traption " very useful for suchtests as arise from time to time, as,

JAA

L

Fig. r. The switch S1 determineswhich crystal is in use.

for example, when some enthu-siastic friend makes great claims(possibly unwarranted) for a " new"crystal which he has " discovered."

The Standard DetectorThe " standard " detector may

consist of any of the " permanent "types now on the market, but inthis particular function it is as wellif one which possesses no adjust-ment whatever is used, owing tothe fact that no comparisons of anyreal use can be made if the standardis by any means variable.

A receiver which is primarilyintended for the purpose of com-paring crystals must inevitablyinvolve apparatus for the testingof carborundum crystals, and as

ASP- these demand special treatment inrespect of applied voltage, andspecial metallic contact, it is es -

Crystal ReceiverBys JOHN W. BARBER

When not in use the lid may beclosed down, thus excluding dust.

sential that a separate detector ofthe carborundum variety be incor-porated. Considering the designof the outfit as a receiver for normalpurposes, some suitable containingbox must be provided. It is a well-known fact that one of the greatestenemies of sensitivity in crystalsis dust, so that the whole should becapable of being closed up when

the comparison of many formstried against a standard

permanent type

not in use in order to excludethis undesirable element Anotherpoint is that any apparatusfor testing or comparison purposesshould be as compact as possible,and these considerations have allbeen taken into account in thedesign of the " Comparison CrystalSet."

The Cabinet

The containing box has a lidwhich may be closed up, and thepanel measures 8 in. by 7 in. Thepermanent detector, .or standard,is mounted behind the panel, whilethe detector for comparing crystals,which may be of any good makeincorporating a micrometer. adjust-ment, is mounted in a convenientposition on the left of the panel,For the carborundum detector Iany indebted to D. J. S. Hartt,B.Sc., of the Radio Press staff, the

* LOA

4/4(

/VG (Oa 4 +I .1

441

--tI I

A

7Z-

4 JIONOFF;

_ - - 2'4.1 -- - -/

k- - -.I /ii

11:1*- - -/ - - PHO/VES

POT

8"F'g. 2.-Showing how the panel is laid out and drilled. A separatedrawing of the carborundum detector will be found on the next page.

814


design being that used byhim in the Stay -Set "Crystal Receiver in theMarch issue of this Journal.The construction of thisdevice is made quite clearin the detailed drawing,and as many readers willremember the article re-ferred to, no further re-marks need be made uponthis subject.

As will be seen in thecircuit diagram, Fig. 1, aselector switch is providedin order that the change-over from. one detector toanother may he as simpleas possible. The middlestud on this switch joinsthe permanent detector incircuit, that on the leftbringing the catwhiskerdetector into operation,while the carborundumdetector is caused tofunction by moving theswitch arm to the right-hand stud. Another switch, to theright of the selector switch, Servesto break the connection from thedry cells which operate the carborun-dum crystal, when the latter is notin use, in order to prevent the cellsdischarging through the potentio-meter resistance.

The CoilIn order to give selectivity, the

aerial Circuit is aperiodically coupledto a tuned secondary circuit, the

The lid of the box has been removed in this view.

two coil's being wound on the sameformer, which is' of the X varietydesigned by G. P.- Kendall, B.Sc.

Winding, which is carried outwith 22 S.W.G. double cottoncovered wire, is commenced in oneof the slots nearest the centre ofthe coil, and the wire, for the firsttwenty turns, is wound on double.Having reached the end of thefirst slot, the wire is carried: overto the next higher slot, which willbe found to have its end on the

CATINII/S1rERDETECTOR

TO JUNCTION CF CELLS

Fig. 3.- The beginning of each winding on the X coil goes to terminalE, the end of the 20 -turn coil to A while the end of the 6o -turn coil

is joined to the loading -coil socket.

Opposite side of the former.When twenty double turnshave been wcu)-c.1 on, onewire is cut off, leavingabout 3 in. free end, andthe other wire continuesthe winding until sixtyturns have been completed,when the wire is cut andthe end secured. The twowires at the beginning ofthe coil are secured to theearth terminal, and theend of the twenty -turnwinding goes to theterminal Al, while the endof the sixty -turn windingis connected to one side ofthe loading -coil socket.The other side of thissocket connects to theterminal A, and to the arinof the selector switch Si,.as well as to the fixedvanes of the variable con-denser, the moving vanesof which are joined toearth.

TERN/NAL HEAD

Fig. 4.-Decails of the car-borundum detector.

Components RequiredIn order to make this little receive r

the' following parts are required :-One panel, 8 in. x 7 in. Thickness

may be either or 3/r6ths in. Ihave used black Radion, but anyother good brand will do.

One .0005 /IF variable condenser(Collinson's Precision Screw Co.,Ltd.), square law type.

One " Kendall X " coil former.This may be obtained from Messrs.Burne-Jones & Co., Ltd.

One good quality catwhiskertype crystal detector, with a fineadjusting screw. (Burndept Wire-less, Ltd.)

One permanent type crystal de-tector and mounting. (H.T.C. Elec-trical Co.)

One potentiometer of 300 olunsor over. (R. A. Rothermel, Ltd.)

One switch arm, knob type, threestuds and two stops.

One switch arm, lever type, twostuds and two stops.

Five larg?. terminals. (Burne-Jones.)

Quantity of No. 22 S.W.G. doublecotton covered wire for the coil.About half a pound will suffice.

A supply of spare crystal cupssuitable for the detector t'Aed shouldbe provided in order that thechange from one piece of " ite."

-4P

813

THE WIREL4SS CONSTRUCTOR

*ay, to another, shall b e as simpleIs possible.

Oue packet of Radio Presspaiiel transfers.

Some i6 S.W.G. t;ntied copperwire, of round or square section, forwiring up.

For the carborundum detectorwe shall require the following

Two complete terminals and thehead of a third.

One crystal cup.One piece of clock spring, aboutin. wide and 2.1 in. long.Some specimens of carborundum

crystal. Among other places; somegood crystals are obtainable fromthe Waterloo Tool Co.

Two small dry cells, 11 voltseach. Ever Ready cells No. U.W.iwill be found suitable.

The PanelMany firms will supply a suitable

panel ready cut to size and drilled,if the constructor so desires, pro-vided that it, is clearly stated thata panel is required for the " Com-parison " cryStal receiver. Alter-natively, of course, an undrilledpiece of ebonite of- the correct sizemay be purchased and drilled to themarkings given in Fig. 2.

If you use the parts specified,you may drill the panel exactly inaccordance with this drawing, butShould you vary the specification,make sure there is sufficient spaceand that you drill the panel in asuitable manner.

--.....rerNMEN1111

July, 1925

This view, which is taken looking down upon the back of thepanel, gives a very clear idea of the wiring. Note the connections

to the switches.

WiringThe components may then be

mounted upon the panel, and thewiring commenced. This shouldnot present any difficulty if thediagram Fig. 3 is carefully fol-lowed. The -back of panel photo -

The cells used in this view are of a convenient type, but thosementioned in the text will be quite suitable. The connection to.-54e end of the 2o -turn winding is clearly visible in the above

photograph.

graphs will also be of assistancewhen wiring up, as it will be pos-sible to see which wires are above

coil is mountedupon the panel by means of twopieces of brass strip, bent to shape,each being secured to the coilformer and to the panel.

Battery LeadsTo join the flexible leads up to

the battery proceed as follows :Take the flexible wire from thepotentiometer to one terminal (saythe positive) of one of the cells.The remaining (negative) terminalor wire of this cell is joined to thepositive of the other cell, and alsoto the flexible wire coming fromthe telephone terminal, while theremaining negative terminal of thesecond cell is joined to the flexiblewire which joins up to the " on -off"switch. The cells are now placedin the bottom of the `box, and, ifdesired, may be secured in anyconvenient manner. The panel isthen placed in position, and securedif necessary with wood screws,when the whole is ready for use.

OperationTo listen to the local short wave

station, join the aerial to terminalA1, earth to E, and place a shortingstrap across the loading coil socket.Join up the telephones, and placethe selector switch on to the middlestud, thus placing the permanentcrystal detector in circuit. Tune onthe variable condenser until the

(Concluded on p. 849.)

816

July, 1925 THE WIRELESS CONSMUCTOR

Type 610For all purposeS ofWireless Reception.Fitted with screwterminals roc detach-able Grid Leak Clips.

Type 620Similar to Type CIObut for vertical panelmounting.

Incapacities of0.0001-0-0009 told. 3/-0.001-0.009 mfd. . 3/60.01 mid.. 41.0011-0016 mid. . 4/6

(5 PHONESOR

LOuO -SPEXKLA

ti

° L7

It has always been difficult to pick out the littlethings in life that matter. It takes accountants tofind the little errors in accounts; engineers thoselittle failures in a machine that mean so much ; andexperts to tell what is really wrong with an inefficientwireless set.This last is always a troublesome affair ; a numberof very minor defects and mal-adjustments, eachinsignificant in itself, may together make a good setapparently useless.For example : condensers, which are really essential inEVERY set, can, if defective, cause rapid exhaustion of

Batteries, and in a grid circuit, they can preventthe grid from reaching its maximum efficient potential,thus weakening the signal strength.It always pays to have the best, in Wireless as ineverything else. That is why, for condensers forall purposes, it is wiser to

Specify Dubilier

DUBILIERCONDENSER CO.LTD

ADVERTISEMMIT OF THE DEDILIER CONDENSER CO., LTD.. DECOR WORKS, NORTH ACTON, LONDON, W.3. TELEPHONE: CHISWICK '441 2.3.

Ira replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.EP 3.135

817

THE WIREliESS CONSTRUCTOR 1923

WuncellDull

EmittersTypes WI, W2 & W3WI is the Detector Valve,W2 (with red top) is theH.F. amplifier speciallydesigned for long-distanceuse. W3 is the new CossorLoud Speaker Valve. Allfunction at 1.8 volts.

Types WR1 & WR2To enable users of multi -valve Sets to try outWuncells along with theirexisting bright emittervalves from a 4- or 6 -voltaccumulator, we are alsosupplying them with a re-sistance incorporated with-in the base. In all other re-spects the WR I and WR2correspond exactly to theW1 and W2. When not re-quired, the resistances canbe short-circuited and thevalves operated at theirnormal voltage of 1.8 volts.

Stations he hadnever heard before

AMONG bright emittersthere is no Valve in thecountry which ever earned

such praise for long-distancereception as the Cossor P2-the valve with the red top.Indeed, it can be said-withoutfear of contradiction-that thisValve exerted tremendous in-fluence in popularising long-distance reception. Before itsintroduction the reception ofdistant Continental BroadcastingStations was a matter of luck.If conditions were favourable-if your aerial was efficient-ifyour Set was good, then youmight reasonably hope to pickup Stations six or seven hundredmiles \away. But when theCossor P2 was placed on themarket long-distance receptionbecame a matter of habit.And now the same measure ofpopularity is being extended tothe Wuncell Dull Emitter W2 --also the valve with the red top.This valve is identical in charac-teristicS with the famous P2.Wherever you have used a P2with such excellent effect you

can replace it with the WuncellWz and get even better results.Glowing at the dulest of redheat-practically invisible duringdaylight-the Wuncell consumesonly .3 amps at 1.8 volts. WithWuncells your accumulators willlast six times as long-in lessthan three months the Wuncellswill have saved their extra costin accumulator recharging alone.Unlike many other Dull Emitters,there is nothing fragile about theWuncell. Its filament -the onlyvulnerable part of any valve-isquite as stout as that used even ina Bright Emitter. As a result theWuncell is becoming known asthe long life Dull Emitter -thevalve that should easily outlastseveral bright emitters.Before buying any more valves,think carefully how much you willsave by choosing Wuncells-yousave money on accumulatorcharging, you get a valve withalmost indefinite life, and you geta valve with a reputation for puretone, sensitiveness and volumewhich has never been equalledby any other Dull Emitter.

A. C. Cossor Ltd., Highbury Grove, N.5

- the long lifessor

ImportantReduction inPrices of allCossor Valves

Bright Emitters :Old price New price

P1 11/- 8/-P2 11/- 8/-

Wuncell Dull Emitters :W1 18/- 14/-W2 18/- 14/-WR1 20/. 16/-WR2 20/- 16/.

Loud Speaker Valve :W3 22/6 18/6

E. These pricescome into forceat once.

Gilbert Ad. 2811818 In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.


How to Connect Your High -Tension and Grid -Bias

BatteriesBy PERCY W. HARRIS, Editor

Dealing with the correct connections of separate H.T. and grid-biaterminals, this article will remove the uncertainty which at present

exists in the mind of the -beginner in this matter

4ATELY I have heard of severalcases where readers of THEWIRELESS CONSTRUCTOR

have been a little uncertain of howto join up their high-tension andgrid -bias batteries to the terminalswhich are. provided for in THEWIRELESS CONSTRUCTOR and otherRadio Press sets. To make thismatter clear to them, I am thismonth devoting a short article to theconnecting up of batteries, andeverything said in these notes canbe taken to apply to any set whichhas terminals similar to thoseshown. I hope in this way toprovide information which can belooked upon as a standard for all theRadio Press sets and to whichreaders can refer at future dates.

Fig. I.-The connections to bemade where only one positiveand one negative terminal exist.

Where the set has but one pairof high-tension terminals markedrespectively positive and negativefew people go wrong in theirbattery connections. The terminalon the set marked II.T.+ isconnected by a lead to a wander -plug which is plugged into the socketgiving the voltage it is desired to useon the H.T. battery. The terminalmarked H.T.- is connected simi-larly to a lead which goes to awander -plug plugged into thenegative socket of the high-tensionbattery. With very few exceptionsthe voltages on a high-tensionbattery are numbered from thenegative end, so that we get asocket marked negative and a

+2

+3

number of other sockets markedwith numbers such as 6, 9, 12, i8,etc., and so on up to the maximumvoltage of the battery. To apply

Fig. 2.-How a second tappingused.

is

45 volts high tension to a set, it isthus only necessary to plug in thenegative lead into the negativesocket and the positive lead intothe socket marked " 45." Mosthigh-tension batteries are numberedin sets of 3 volts.

Current from the H.T. BatteryIt is quite a mistake to imagine

that the current taken from ahigh-tension battery is negligible.The current is quite appreciable,

H.T.e +1

H.T e

H.T.9

H.T. 0-71(------

42vi

v. 60.v.

Fig. 3.-Two separate batteriesare here used, their negativesockets being both connected to

the H.T. negative terminal.

although it does not compare inquantity with that used to light thefilament of a valve. As it is not anegligible current and as every

819

valve takes a certain . currentfrom the high-tension battery, wecan soon reach a limit of currentwhich an ordinary high-tensiabattery can be expected to givesatisfactorily. Personally, I neverlike to run more than four valvesoff one ordinary -sized high-tensionbatteryLp.s if more valves than thisare run, and especkally if one or twoare power valves, the battery willbe very rapidly exhausted and maydevelop noises quite early in itslife: These noises are caused byirregularity of discharge, and set upsounds which closely resemble thosegiven by atmospherics.

Fig. 4.-In this case the twobatteries are in series, the positiveof the one on the left being joined

to the negative of the other.

The H.T. AccumulatorIf you require to take more

current from a high-tension batterythan the ordinary size will safelygive, there are three ways ofdoing it. The safest way of all isto use a high-tension accumulator,but this is a somewhat expensivepiece of apparatus and occasionallypresents difficulties in the way ofcharging, so that many people willnot care to purchase one. Thenext way is to buy a high-tensionbattery of an extra -large size.The ordinary wireless dealers rarelystock these, and they must bespecially ordeted, but the bigmakers, such as Siemens anc1


Ever Ready, will supply themthrough your dealer when askedfor them. The price is co7a-tiderably

Fig. 5. --How a grid -bias batteryis connected up.

more than that charged for theordinary size of battery, but youget excellent value for your money,

for such batteries supply tar morecurrent than the smaller sizes andwill have an appreciably longerlife. The third way, and one whichI often use personally with multi-

, valve sets, is to use several separatehigh-tension batteries. In this waythe load can be distributed, and, ifwe have, say, a six -valve set andfour separate batteries, then onebattery need never give current tomore titan two valves.

Separate H.T. BatteriesFig. 3 shows the way of connect-

ing up two or three high-tensionbatteries. In the actual illustrationtwo batteries are used. To jointhem up in this way it is necessaryto connect the two negative endsof the battery together and to takea lead from them to the commonH.T. negative terminal on the set.

This view, taken at a window of the Managing Director's roomin the offices of Radio Press, Ltd., shows Mr. John Scott -Taggartdiscussing with Mr. Percy W. Harris, details of the latter's

American trip.

8f.0

You will notice that where a sethas several H.T. positive terminals,there is only one H.T. negativeterminal.-- The reason is that this

4'1- 3 -

Fig. this case two separateG.B. terminals are provided, and

are joined up as shown:

terminal serves as a commonnegative to all the H.T. supplies.When using two or more batteries,the positives are connected towhatever voltages we require.

Batteries in SeriesFig. 4 shows how two or more

high-tension batteries can be con-nected in series, if you want to geta higher voltage than that givenby one of the high-tension batteries.In this case the negative high-tension terminal of the set isconnected to the negative of thefirst high-tension battery, thehighest positive tapping is thenconnected to the negative of thenext battery, and the positive hightension of the set is connected towhatever voltage we require in thesecond battery. In this way wemay have two separate 6o -volt H.T.batteries joined in series and mayrequire about too volts for ourset. To do this we connect, asexplained, the negative H.T. ter-minal of the set to the negative ofthe first battery and the positiveH.T.- lead -to 42 -on the secondbattery. This will give us tO2 volts(6o+42) as required. Other figuresin this article Show how to ednitecttwo or three high-tension tappingsto one battery.

" Grid-BiaSQuestions are often asked by

readers oil how to connect up grid -bias to a set where there is ,morethan one grid -bias negative% Tlieillustrations show hoiv to 'do this.In connecting your grid -bias, youshould remember that there is onegrid -bias positive only, althoughthere may be two or more grid -biasnegatives.

If you have two grid -bias negativeterminals for two separate valvesand both valves require the samenegative voltage, then there is noreason why you should not connectthe two -negative terminals togetherby a piece of wire and take one pairof leads only to the grid -bias battery,

July, 1925 WIRELESS CONSTRUCTOR

NOLOSSC 0 NJ CD S PR.

AERIAL CONDENSER.Approx. Max. Cap., 0005

Black ebonite, 27;6 (with knob and dial1 /6 extra).

Mahoganite, 30/ -ANODE CONDENSER.

Approx. Max. Cap., '0003.Black ebonite, 25/ - (with knob and dial

1/6 extra).Mahoganite, 27 /6.

Electrical and Mechanical

Pre-eminence.THE Success Noloss Condenser is the

first variable condenser of Britishmanufacture rightly designated No

Loss. Its construction departs from cus-tomary practice in skeleton outline and inskeleton end plate. Has a 4 to 1 Gear,while making a vernier unnecessary alsoremoves all hand capacity effects, sincethe body has no electrical contact withthe moving vanes. Many other superiori-ties are apparent :Rugged Construction. Fixed Vanes secured to bottomSkeleton Design. end plate only.

Dielectric losses practically tooSkeleton End Plates. small to measure.Pigtail Connection to Delightfully smooth operation.

moving vanes. No backlash. -

Copper Vanes. No vernier required.

Also ask your dealer for the SUPER SUCCESS L.F.TRANSFORMER, Frit:: 21 /-

Fully illustrated list of Success Radio Products may beobtained free upon request.

BEARD b FITCH, Ltd.34, AYLESBURY STREET, LONDON, E.C.1

Telephone: Clerkenwell 8941.19)rth of England Branch: 1, DEAN ST., PICCADILLY,

MANCH ESTER.Telephone: Central 8240

A Super Heterodyne I.F. Transformer,designed to give results.

The outstanding feature of the "Success" Superforma is the incorporation of a '0003 VariableCondenser as an integral part of the unit.

The fact that it is tunable is a consideration whichenables the experimenter to balance up the stagesfor himself, after the set is built, and to tune outinterference. That the ''Success" Superforma fr.tunable considerably increases the selectivity ofthe receiver,gi ves greater amplification and gener-ally improves the efficiency of any Super Hetero-dyne Receiver employing the type of Transformerbalanced by the manufacturer. After finallybalancing up the Superforma, by turning the smallknob, the tuning condenser may be locked inposition.

"SUCCESS" SUPERFORMA. Price 30/-.

ttarcinvs Aa.

GAMBRELL L.F.TRANSFORMERSTAGE I & STAGE II

PRICE 27(6 EACH

Ask your Dea7erfur Gambrell Products

You can achieveMAXIMUM EFFICIENCY.

Write for Folder describing the following componentswhich will put your set in the highest class.

, Efficiency" Inductance Coils, L.F. Intervalve Trans-fOrmerS, Coilholders, Switches, Stabilising Condensers.

GAMBRELL EFFICIENCY INDUCTANCE COILS

are the first choice of experiencedradio enthusiasts because of theirdemonstrated maximum strengthand minimum capacity.

You require the best and mostefficient Radio Productions

They are Designed and- Manufactured by -

GAMBRELL BROS, LTD.Leaflets can ba obtained byreturn of post from theirRADIO SALES DEPT.,

76, Victoria Street, London, S.W.1

Barclays 1202

B In replling to advertisers, please mention THE WIRELESS CONSTRUCCLak, 621


your set valvular disease?

GENERAL PURPOSE VALVES

Type R 8/- eachFilament voltage.... 4 voltsFilament current ....0.7Max. plate voltage..100 volt.

Type B 3 .. 14/- eachFilament voltage....1.8 voltsFilament current..0.35 amp.Max. plate voltage..80 volts

* Type B 5 .. 16/6 eachFilament voltage ..2.8-3 voltsFilament current..0.06 amp.Max. plate voltage -80 volts

POWER AMPLIFYING VALVES

Type B 4 .. 22/6 eachFilament voltage..5-6 voltsFilament current..0.25 amp.Max. plate voltage ..120 volts

*Type B 6 .. 22/6 eachFilament voltage.. ..3 voltsFilament current..0.12 amp.Max. plate voltage..120 volts

*Type B 7 .. 24/6 eachFilament voltage....6 voltsFilament current..0.06 amp.Max. plate voltage . .120 volts

* For use with dry cells.

The heart of your set is the valve,and in wireless a hard heart isbetterthan a soft one. " Soft', is a euphe-mism for bad vacuum. A valvewith a little air in it is liable to oxy-disation of the filament, and soonloses its efficiency. B.T.H. Valvesare very highly exhausted by a specialB.T.H. process. This ensures longlife. and maintained efficiency. B.T.H.Valves last longer and give muchbetter results than "soft" foreign(or English) valves.

FIT B.T.H. VALVES AND GIVEYOUR SET A GOOD HEARTFrom all Electricians and 3ad:b Dealers.

13.11:11.RADIOVALVES

Made in Rugby, England.

Note new reduced prices of all types.

2172 Ackertisement of The British Thomson -Houston Co. Ltd.

..=111=111111M111. .111101011M10 .1111111111.

822 In replying to advertisers: please mention Tilt WIRMESS CONSTRUCTOR.

-July, 1925 THE WIRELESS CONSTRUCTOR

OUTDOOR RADIO

Now NiQe ANO

MN-i NA°A BITE ALL

OAV !!

- \-VPY T gE

TILL tviA°You NAPPY

M.61/AVEE-11;aFAMOUS aREE WILLNOW CIIVE A TALKON "COOKING

-TNE_ PRESEMT

LORIOUS WEATHER.

WILL CONTINUE

FOR SOME-Tt N1E_ - -cc

823

NE WIRELESS CoNSTRUCTOR

Charging Accumulators at HomeBy G. P. KENDALL, B.Sc., Staff Editor

Some further notes upon a vital subject

Extent of DischargeTHE question of how far to run

down any battery in thecourse of use is an important

one from the point of view of thehealth of the accumulator, andsome definite rule should be made.A safe and convenient one is this :Obtain from the label the actualampere hour capacity of the battery,remembering that the " actual "capacity is half the " ignition "capacity, and then work out howmany hours this should run yourset, which can be done quite easilyif you know the rated filamentcurrent of each of your valves.Thus, supposing that it is a four -valve set using bright emitters,you might take it that something,a little less than 3 amperes willbe used, and if you use an accumu-lator of 3o ampere hours actualcapacity, you will then get to hoursof light. The rule should now bemade that the battery is never tobe taken right down to its lowestpossible discharge point, accord-ing to its rating, so that one shouldstop short after, say, 8 hours' use,arid recharge it. In this way itis easy to keep it in good health,without trouble from that baneof the accumulator, sulphating.As a matter of fart, of course, theexample quoted is of a battery ofthe very minimum size to run theset in question, a much larger onebeing desirable, since it is a nuisanceto have to recharge the batteryevery four or five nights of use.

Accumulators for Dull EmittersThe one exception to this method

of working occurs in the case ofvery low consumption dull emittersrunning from an accumulator,in which case it is possiblethat t:e battery would not berun down in, say, six months'use. For its health's sake, how-ever, it should be given a" re freshing " charge about oncea month.

These brief instructions will coverthe charging of accumulators bypractically any method since sofar as the battery and" its treat-

ment are concerned, the same pro-cedure is always adopted and neednot be repeated when consideringthe other methods.

Waste of PowerThe objection to the method

which we have been consideringof charging from the D.C. mainsis, as was pointed out, that con-siderable waste of power takesplace, in view of the fact that averx large series resistance has tobe used, and practically the onlyway of overcoming this in a simple

A curious aerial seen atBurnham -on -Crouch.

manner is to use a small motorgenerator, which consists of asmall -power motor driving adynamo giving a suitable outputfor the charging of batteries. Thereis such/a small motor generatorupon the market, and it is nodoubt a real economy in the longrun, once the purchase price hasbeen cleared off by the saving incharging current. This machineactually resembles a rotary con-verter in that the two functionsare combined into one machine,its appearance being that of anordinary motor, but for the fact

July, 1925

that there are commutators ateach end of the armature shaft.

The Motor -ConverterThe use of such a machine is

extremely simple : the motor endis provided with a long flexiblelead and an adaptor, which isplugged into a lamp socket in theordinary way, whereupon themachine runs as a motor. At theother end of the machine is asmall charging board carrying ananuneter and a variabl resistance,and a pair of terminals markedpositive and negative, and- fromthese terminals leads are taken tothe battery in the ordinary manner,the charging rate being suitablyadjusted by moving the slider ofthe resistance and watching theammeter. There is no need, withthis machine, to identify the pola-rity of the terminals, since this isautomatically attended to by themachine itself. The only pointsto be observed here are those con-cerned with the actual ch'argingof the accumulator, and these havealready been covered.

The House Wiring SystemA very simple makeshift which

can he used to give economicalcharging from D.C. mains withoutthe use of any expensive accessory,is illustrated in Fig.'r herewith,and consists merely in the placingof the battery whiCh is to becharged in series with the housemains, so that the current normallyflowing to light the house willcharge the battery on its way.This arrangement is not very con-venient, since one can only chargewhen the lights are in use, and thusfor only a limited number of hoursin the day, but for a small sizedbattery it is certainly the mosteconomical method. 'What has tobe done is simply to break one ofthe leads going from the mainsto the house system, and insert inseries therewith the battery, afteridentifying the negative and posi-tive leads. The best point at whichto do this will depend upon theactual house system, but it shouldbe emphasised that it should only

824


FIXED CONDENSERSARE

1. Of the permanent capacity engraved thereon.2. Instantly interchangeable.3. Of everlasting and unfailing service.

GRID LEAKS ANDANODE RESISTANCESPossess similar characteristics.

In common with all ai) Components they are of

original design, constructed by skilled workmen, of thebest materials, with but one aim and object, i.e., theHighest Efficiency to give you SuperlativeResults.

FIXED CONDENSERS0.0001 µF to 0.001 1/9 each0.002 µF to 0.01 ,uF .... 2/3

(Two clips are supplied with each condenser.)Mounted on ebonite base, with terminals, any value,0.0001 f.LF to 0.001 2/9 each0.002 µF to 0.01 fiF

GRID LEAKSGrid Leak, all values ... (040)

(Each supplied with two clips.)Mounted on ebonite base with terminals

ANODE RESISTANCESAnode Resistance, all values (041)

(Each supplied with two clips.)Mounted on ebonite base with terminals

2/- each

3/- each

2,'6 each

3/6 each

COMBINED GRID LEAKAND CONDENSER 4/- each

'Works :---WEXHAM ROAD. SLOUGH

PAone : 5Louor, 199f MICHAE LITIDD

ManuFacturers of Wireless and Scientific Apparatus7-fedcf Office:- HASTINGS HOUSE:NORFOLK STREET:STRAND:LONDON.W.C. 2. Psone: CENTRAL 8272/3TELEGRAPHIC ADDRESS: RADIETHER, ESTRAND, LONDON CABLE ADD`7ES,S : RADIETHER LONDON.

London Showrooms :-179 , STRAND W.C. 2.

Phone : CENTRAL 6988

In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.

IsBarclays Ad.

825

THE WIRELESS CONSTRUCTOR July; 1925

I.-ORMOND";

MORMON

'ORMOND

ORMOND

'ORMONDIke

.04,tÒRMOND

CC MJND

'O,MOND

Awee

'ORMOND

%or

bRMOND

'ORMOND'lestg

TWENTY-FIVE YEARS4:334N I rfi

t'O RMON D"I ©R_MORHa ° "ORMOND " 'ORM OND '

I Ttia,

MHgllERMAa ©

MANUFACTURING EXPERIENCE

11;744, ORNÒRMOND"

tiORMOND

'ldrORMOND LOW LOSS CONDENSERS iORA71ND

A NEW DE-PARTURE INBRITISHCONDENSERDESIGNGIVING THEFOLLOWINGADVANTAGES-

(1) Practically neglig-ible losses.

(2) One Bole fixing-one r diam. Bel; isneeded to fix thiscondenser to panel.

(3) Rigid construc-tion-cannot wai p;end plates of stoutaluminium, wr-fectly flat.

(4) Fixed yams sup-ported by }" eh, n-ite strips.

(5) Smooth action,spindle tension ismaintained by aspecially designedfriction washer.

(6) Moving vanes andend plates are atearth potential.

( 7) One -piece knob anddial-suppliedloose Secur.d by4 BA Set Screw.

This Condenser is fittedwith optional solderingTags, or Terminals, and canbe supplied with or withoutVernier as desired.

There is no variation inprice, the pric s being thesame as our ordinary SquareLaw Condensers.

IORM

ORM

7.7N

199-205.PENTONVILLE RD.KINGS CROSS.LONDON, N.J.

Factory:-\Whisk in'Street,Clerkenwell,E.C.1

No* SQUARE LAWSee the Inspection Labelon every Condenser

Supplied in the following sizes-Size. Price with Vernier. Price without Vernier.

.00025 6/6

.0003 7/6

.0005 8/-

.0(3r 9/-9/6

... 10/6

Write for our new (192)l'atalogue and 'trade Terms.

We specialize in turning Brassand Steel Screws and MachinedParts and Accessories of all

descriptions.

AU Cheques and Postal Orders should be crossed andmade pagable to "The Ormond Engineering Co.

;THE BEST MEANS

ed;ORt 'ORMD'i CORTD7 rORMOND7 ORMOND1r=71ge± ON

77q0E j Vgzi 60 qua' Ikag

ORMOND'

ORMOND

ON,ORMOND

ORMOND

ORMOND'

'ORMOND

AP%'ORMOND

Nog

ORMOND'

'ORMOND

ORMONDj N,Telegrams:-"ORMONDENGI.KINCRO S

!Telephone- ;'CLERKENWELL

93 f4-(31figes)..

82V In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.

%dr

ND

N

D"

July, 192

be done on the house side of themain fuses. It will usually befound that there is a simple double -pole swtteli 'which is used for turn-ing the house system on and off,and that on the house 'side of thesetwo switches will be found eithera pair of smaller fuses or leadsgoing off to some sort of fuse dis-tribution box. These provide aconvenient point to break in, andthe greatest possible care should beexercised to see that your opera-tions are entirely restricted to oneof the leads. On no account adoptany scheme which involves the useof both leads, and of course see thatthe house supply is turned offbefore you commence. In thisinstance it is not possible to adjusta charging rate very accuratelyto the .needs of the battery, butso long as it is found that the housesystem . does not take more than25 per cent. above the correctcharging rate, or 50 -per cent. belowit, fairly satisfactory results canbe obtained. An ammeter should,of course, be inserted for checkingpurposesin series with the battery.

AppliancesIt is not the' pUrPose of this

article to deal with the construc-tion or improvising Of chargingappliances for one's self, and there-fore this will be the!only instance inwhich we shall consider any actualconstruction or !wiring work. Inall the other cases we shall bedealing solely with bought appa-ratus which can be:cOnilected to themains simply and without anyparticular knowledge on the partof the operator.

Of the methods considered, itwiltherefore be seen that the mostsuitable fOr anyone who wants tokeep down; expenses to the verylimit is the last one, while forthose who, are prepared to spend acertain amount at the start andobtain economical and really satis-factory results, a rotary converteris, perhaps, .to be preferred, theother scheme being a happy mediumwhich will appeal to the greaternumber.

Charging from A.G.Charging from alternating cur-

rent mains is really; to my mind,a simpler matter even than charg-ing from the direct current variety,since there are a greater numberof convenient charging deviceswhich can simply be connected tothe various lamp sockets, wiredup to the battery, and left to carryout their work economically. Thesedevices differ from those we havebeen considering, in that they in-corporate some means of convertingthe alternating current into directcurrent.


Alternative MethodsAs before, there are a number of

different alternatives, the oneadopted usually. sdepending largelyupon the amount which it isdesired to spend upon the chargingequipment. Where lifge batteriesare to be charged, and a consider-able capital outlay is allowable,once more the rotary converter,consisting essentially of some sortof combined motor and dynamo,or commutating device, which, bya sort of rapidly revolving switch-ing arrangement, converts the alter -

SWITCH.

NAM

HOUSEJ11572 -M.

Fig. i.-The accumulator may bepIaced in series with the houselighting system as shown aboVe.

muting current into direct, is usuallyadopted. Such appliances, how-ever, do not, as a rule, appeal to theprivate user who requires to chargeonly medium sized batteries at notvery frequent intervals, and wemay, therefore, turn our attentionto some of the types more suitablefor home use. Of these there arethree principal types --namely, theelectrolytic type, the vibratory andthe " Tungar " form, in which alarge two -electrode valve performsthe desired rectification of thecurrent. The Tungar can he ob-tained in a variety of sizes, thesmallest one giving a fixed chargingrate of 2 amperes, which is suitablefor the majority of small andmedium-sized batteries.

When the Tungar is in use itgives a subdued light, a certainamount of warmth, and only amoderate amount of humming.It is, therefore, quite capable ofbeing used in the house withoutcausing annoyance.

The Vibratory TypeThe vibratory type employs some

sort of blizzer arrangement in whicha vibrating reed chops up the alter-nating current into direct, and it is_usually found that this process isaccompanied by a good deal ofnoise. There are, however, certainquiet types upon the market, andit is usually found that these arequite satisfactory in operation. Itis often objected that the vibratorytypes are likely to go out of adjust-ment, but they are usually accom-panied by a set of instructions,which makes any adjustment quitea simple matter, and some of thelater types can be depended uponto run for a very long period with-out needing any attention what-ever. It will usually be found that aquiet type, as distinguished fromone of the noisy ones, will be quitesatisfactory, needing the very mini-.alma of attention. These rectifiers,as they are called, are usuallyprovided with small ammeterswhich indicate the amount ofcurrent which is passing intothe battery, but they are not,as' a rule, fitted with anymeans of regulating that current.Should it be desired to charge atlower rates than that which isnormally given, it is a very simplematter to insert a small variableresistance in series with the battery,a large amid robust filament rheo-stat being quite suitable. Rheo-stats Which are designed to carrycurrent for a number of valves,say four, should be employed, orserious overheating will take place.

The Electrolytic RectifierThe electrolytic type consists

essentially of one or more cells con-taining some sort of electrolyte,which, of course, varies with thetype, into which two electrodes dip,the whole arrangement forming asort of non -return valve, throughwhich current can pass in only onedirection. There is not a grey'variety of these devices upon themarket, probably the best know _mone at the present time ILing, time" Balkite," sold by Messrs. liurn-dept, Ltd. This is proving to be anextremely successful device in prac-tice, the only attention requiredbeing an occasional filling up withdistilled water, and is extremelyquiet and clean in operation.

There is little to choose betweenthese three methods on the score ofcost, and the choice will dependvery largely upon the purchaser'staste. In most cases where themachine is to be used in the honk;the question of noise is a serious one.,and whatever type is chosen shouldbe heard running under sotnevoid?similar conditions if possible,

827

TEE WIRELESS CONSTRUCTOR

Handsome in appearance, this receiver will appealto readers of "The Wireless Constructor."

EQUALLY simple to constructand to operate, the finishedinstrument presents a neat

and handsome appearance, well upto the Radio Press high standard.Strangely enough, in wireless, asin many other arts or sciences, itis frequently the thing which is mostuseful- that gets overlooked for aLong period. Many thousands ofpeople own crystal sets, and thou-sands also are the proud possessorsof single valve receivers. The greatmajority of listeners probably livewithin eight or ten miles of a broad-casting station, for these have beenput up in localities where manypeople are congregated together.Except in unusual circumstances,with skilled handling and specialcircuits, a single valve will notoperate a loud speaker, and inninety-nine cases out of one hun-dred, a single valve receiver is con-structed or bought for telephoneuse. It occurred to me, therefore,that a receiver made up so that itcould be either a crystal or a singlevalve set by the mere throw of aswitch would appeal to manypeople by reason of its simplicityand economy. The receiver illus-trated will operate on any wave-length from about 25o to about3,500 metres (the upper and lowerlimits depend to some extent uponyour aerial), and is self-containedin that no exterior or separate plug-in coils are required. By the turnof the switch the set can be con-erted from a crystal set, using oneOf the new semi -permanent detec-tors, of which several good ex-amples are on the market, to 'a

July, 1925

The "Crystovalve

ti

ReceiverA NEW AND ECONOMICALRECEIVER FOR POPULAR

(ISE

By PERCY W. HARRIS,M.I.R.E., Editor

This is just the receiver many readers havebeen waiting for. Its self-contained tuningcoils obviate the necessity for purchasing acomplete series of plug-in coils to cover thewavelength band of 250 to 3,500 metres-the

scope of this instrument

direct coupled single valve receiverwith reaction.

A feature of this set is the tappedinductance coil and variable reac-tion coil made up as a single instru-ment. The use of this simplifiesthe construction considerably, aswill be seen by examining the photo-graphs which accompany thisarticle.

Components RequiredThe components required to

make this set are as follows. Inaccordance with our usual practice,the names of the manufacturers ofthe actual components illustrated

are given opposite the items, but inmany cases other good makes canbe substituted without any loss ofefficiency.

One insulating panel measuringI2 X IO X 3/16th, or a a in. (I haveused black Radion 3/16ths thick).

Suitable box for same 7 in.- deepinternally. (Cameo.)

Nine lacquered terminals withnuts.

One R.I. aerial tuning reactance.(Radio Instruments, Ltd.)

One good quality variable con-denser, square law pattern. (Atlaslow -loss. Capacity .0005 v.F.)

The wiring is wellspaced and may betraced out frompoint to point in this

view.

828

July, 1925

Things you can do with theCrystovalve ReceiverI. Handle it and receive with it just

as simply as with any othercrystal receiver.

2. Use it as a simple but efficientsingle valve receiver with re-action.

3. Change in a moment fromcrystal to valve if signalsare too weak for proper recep:ionon a crystal.

4. Switch back to the crystal in amoment when signals are suffi-ciently loud for reception inthis way.

5. Change in a moment from theshort wave broadcastingstations to Chelmsford, Radio -Paris or Eiffel Tower withoutchanging coils.

6. Compare valve and crystalreception by a mere turn ofthe switch.

7. Receive all wavelengths from250 to about 3.500 with properreaction control throughout.

8. Use either bright or dull emittervalve at will,

g..w1ervieherww1ti11ti".-6%..1V'ie. .4

One fixed condenser, 000.31...F.I have used a Dorwood one -holemounting condenser here with :-

Otte 2 megohm Dubilier grid leak.Any of the well known grid con-denser and leak combinations willdo just as well.

One fixed condenser, -ooi(Dorwood.) -

One fixed condenser, 000xL; McMichael, Ltd.

One valve holder or four separatesockets.

One filament resistance, dualpattern, for both bright and dullemitters. (Burndept Wireless, Ltd.)

One set Radio Press panel trans-fers.


Showing some of the connections to the change -over switch,and method of mounting the C.A.T. condenser.

One semi -permanent crystal de-tector with clips for mounting.There are several excellent makesnow available. That used is a" Bronel."

One four -pole double -throw" Utility " switch for panel mount-ing. Actually only three of the foursets of contacts{ are used, and athree -pole double -way switchwould do just as well. However,the four pole is always readily ob-tainable, and can be used as I havedone. It is made by Wilkins andWright, Ltd.

Furtherswitch con-nections areseen here,and, on theleft, thetelephonecondenser.

Valve and AccumulatorIn addition to the above parts

you will, of course, need a valve,which may be of any of the well-known makes, and either bright ordull emitter, according to your taste.A suitable accumulator to supplythe current will also be required.For the latter I would suggest, ifthe valve is of the o6 type, aten or twenty ampere hour batteryof four volts. If you are using abright emitter, a 20, 3o or 4o am-pere hour battery of 6 volts is re-commended. Of course, the largerthe battery the longer it will lastwithout a new charge. I do notrecommend anything less than 20ampere hours (actual) for brightemitters, but the ten ampere hourbattery is quite big enough for theo6 ampere dull emitter, which willrun for approximately 15o hourson such a battery without a newcharge. You will also require ahigh tension battery of about 6oor 72 volts, and one or more pairs oftelephones, which should be ofwhat is known as the high -resis-tance variety (2,000 or 4,000 ohms).

ConstructionThe constructional work will give

you little trouble, as the photo-graphs and diagrams show everyaspect of this proceeding. Theappearance of the set will be marredif you depart from the generallayout indicated, as the parts arearranged in line to give a sytn-

829


Reg. Des. No. 711750

THE M H H.F. REACTOR UNIT.

THE REACTOR is a patenteddevice for applying reaction to theH.F. Transformer instead of to theaerial coil, thereby largely preventingre -radiation ' and gives increasedselectivity.

OA closer control with sharpertuning is more easily obtained by thismethod. The lip Reactor circuitis undoubtedly - the most easilyapplied and flexible reaction systemever introduced to the public. Thisdevice can be applied to any highfrequency receiver embodying tr13.F. transformers by simply fixingthe two guides in place of the holdingdown screws of the engraved disc.The Vernier Carriage fits on these,being adjusted to its approximateposition by sliding, precise adjust-ment being obtained by rotating theknob. The conventional reactioncoil is then eliminated.

Two flexible leads from the VernierCarriage are taken to the conven-tional position for Reaction, theMaroon- lead -to the Anode and theblue to the other.

TWO NEW

COMPONENTSMH Reactor & MH DamperThe new devices illustrated which areauxiliaries to the oia, H.F. Transformerare here introduced to the readers of

" The Wireless Constructor." THE REA( TOR INSERTEDIN .11H H.F TRANSFORMER

Ns

ge.fitaik

The 1 I H H.F. ReactorIs supplied complete in a handsome

dustproof case with eight guide pinsand three interchangeable barrelscovering all wavelengths.

Price (as illustrated) 15/ -

Pat. No. 228834

THE 3I H H.F: DAMPERPrice -(as illustrated) 2/ -

THE DAMPER is a patented de-vice, which, when inserted in thecentral hole of the transformer hasthe property of stabilising a circuitwhich otherwise would oscillate.

(11 The simple expedient .of intro-ducing the Damper into the 11 H.F.Transformer will in nine cases outof ten, cure all oscillation troubles.

It is a device which every userof MB) H.F. Transformers shouldhave by him, since its cost islow, and its general utility remark-able.

(1 The pre-eminent position of the(ma. H.F. Transformer is not a casualhappening based on chance, but onsound technical knowledge and ex-perimental work, backed up by highgrade production.

lig The unquestionable confidencewhich the public and trade have inthe wellTknown H.F. Trans-formers will be fully reflected in thetwo new components here described.

WRITE FOR FULL DESCRIPTIVE AND EXPLANATORY LEAFLETMH H.F. TRANSFORMERS

increase the range of your set and also add to its selectivitySupplied in six ranges of wavelengths, covering 80 to 7,000 metres.

Price, 10/- each.Special C) Neutrodyne Units and Superheterodyne Couplers also supplied.

Any number of each Transformer can be sutoolied matched at NO extra charge, if requested at the time of orderirg

VorIcs .Condon Showrooms :-WEXHAM ROAD , SLOUGH,

INA m(1.-.1-4411 179. STRAND , W.C. 2.

Phone: CENTRAL 6988Phone : St.ouon 199 Manufacturers of Wireless and Scientific Apparatus,glead Office:- HASTINGS HOU SE: NORFOLK STREET: STRAND: LONDON: W.C. 2. P.Sone: CENTRAL 8272/3TELEGRAPHIC ADDRESS: RADIETHER, ESTRAND. LONDON CABLE ADDRESS: RADIETHER , LONDON.

Barclays .1.d.

630 In rep4ing to advertisers, please mention THE CONSTRUCTOR.

July, 1925

metrical design, The R.I. reactanceunit is very simply mounted byunscrewing the two grub -screws-which hold the two knobs to theirshaft, taking these latter from -theshaft, unscrewing the four screwswhich secure the ebonite disc -intothe four brass supports, and usingthe ebbnite disc as a drilling tem-plate on your panel: Small holeswill be required for the foursecuring screws and fairly large holesfor the shafts. If you have no drilllarge enough to drill these largeholes, do not worry if you `makerather a rough hole in the ebonitewith a file, or some similar device,so long as you make it larger thanthat in the ebonite disc, for thelatter which will be screwed downon top of the panel will effectivelyconceal any roughness in thislarge hole. The " Atlas " low -loss condenser, and several othercondensers, are now made with onehole fixing, which greatly facilitatesattachment to the panel, but if thecondenser you use is not of the one -hole fixing type, then you willprobably find you are supplied witha drilling template for it. If youuse four separate sockets for thevalve holders, I suggest that youuse one of the many excellentmarkinab devices sold, such as theMorris template, which will giveyou an accurate layout for the foursocket holes.

The SwitchBe particularly careful to join the

connections to the switch correctly.Notice, as I haVe remarked, thatonly three out of the four sets of


contacts are used, and that on oneside only two of the tongues areused. -For Wiring up I recommendyou to use thick square sectionedtinned copper wire, as the appear-

-

lights satisfactorily, turn the fila-ment resistance to the off positionand connect up your high-tensionbattery. Now join your telephonesto the two terminals marked, con -

tLE

0 003/u.F.II

J'ANVVV2Nri

12 a

/ .0005 44F.a

HT-®

TEL

CRYSTAL VALVE

----=--_

Fig. i.-How the switch changes over from crystal to valve.

' ance of the set is enhanced thereby,and it will be easier for you to seewhere the connections go.

Operation of the SetThe operation of this receiver is

of the simplest. tefOre COmiectingup your batteries, set the pointerof the reaction handle at zero (youwill notice it can be moved to 90 oneither side of zero), set the pointerof the inductance switch at A, putthe filament resistance at the " off "position, and plug in your valve.First of all connect up your accu-mulator, leaving the high-tensionbattery unconnected for the mo-ment. Now carefully turn on thefilament resistance, If the valve

REACT/ONC.A7:

2V

Ai4.441 AER/A

- 24/

3f,'30"

A.T.C.

5' CRYSTAL

,

--2$i- -- DETECTOR

/2'

FIL RES.

244'

r

Fig. 2.-The panel is to be drilled as this drawing shows. Full-size blueprint No. Cior7A may be obtained, price /6 post free.

0+L.T.43

nect your aerial to. the terminalmarked A, and the earth to F, andlisten. Possibly on the A positionof the switch you will hear nothingat any poSition of the condenserdial. Now turn the inductanceswitch to B and rotate the dial again.Soon you will probably hear yourlocal broadcasting station and beable to stop at the condensersetting which gives the loudestresults. Unless you are very closeto the station (within two or threemiles) yoti will find an appreciableincrease in signal strength byrotating the reaction knob in onedirection . or the other. Whichdirection is the correct one you willfind by experience. Sometimes itwill be to the right and sometimesto the left. When turning in thecorrect directir4 signal strengthwill gradually increase. Do 'notturn the knob too rapidly, but afterturning a few degrees retune onyour variable condenser. You willsoon find the position where youobtain maximum signal strengthwithout distortion. If on turningthis knob you get into such aposition that you hear a howlingor a shriek, or great distortion,turn the knob back again at once,as you will be oscillating andcausing disturbance to other people.

Constant aerial tuning may betried if -desired by connecting theaerial to the terminal CAT. insteadof to A. This form of tuningshould not be employed on thehigher wavelengths.

Radio -Paris and 5XXYou will find on experiment that

Radio -Paris and Chelmsford can beheard on this set when the induc-tance SNA itch is on the last stud butone or the one previous to that.

F31


You will tune: for . them, of course,exactly in the same way as for thelocal -broadcasting station. In goodconditions it is possible to hearseveral broadcasting stations on theshorter waves, and of course youwill hear Chelinsfoid anywhere inthe United-Kingdoni. Whether ornot you hear Radio -Paris will de-pend on your locality, size 'of aerial,etc., but I think that in the majorityof case' you will be able to hear iteasily: Eiffel Tower will be foundhi a position above Radio -Paris orChelmsford, and Nauen will beiound towards, .the end of theswitch. Both of these latterstations give time signals at thefollowing times :-

PARIS-Eiffel Tower. Call FL.Spark, 2600 metres.

Times-Greenwich British summermean time. .

a.m.9.27- 9.30

1'0.00-10.0510.38-ro.43zo.45-10.4.9

11.00-11.0511.38-11.43I 1.43-11.49

10.00-10.0510.38-10.43

p.m..00-r .05

11.38-11.4310.44-19.49 11.44-11.49NAv> s. -Call POZ. Spark, 3100

metres.Times-

G.M.T. B.S.T. .

a.m. - p.m.11.57-12.00 12.57- r.00

p.111. a.m.11.57-12.00 I2.57- I.00

Changing OverWhen you have become

thoroughly accustomed to handlingthe valve set (or indeed before thisif you so desire) try working onthe crystal side. This is done bysimply turning the switch from thepoint marked valve to the pointmarked. crystal. Of course, thesignals will be much weaker on thecrystal, but in many cases the localstation will come in quite loudenough for you on the crystal side.Remember that the reaction handle(that above the tuning switch) isnot in action when you are on thecrystal side. Your tuning will bedone merely on the variable con -

July,...

denser and on .. the inductanceswitch. If you have picked up astation on a 'valve, and it is 'oddenough to be -heard on a crystal,you will find it by:switching overto the -crystal position withOut anyretuning. Conversely, if you havepicked- Up a:station on the crystaland you' wishto receive it louder,simply turn over to the valve sideand Make a slight adjustment' of thereaction setting, With perhaps alittle retuning, to get the loudeStresuls. Finally, remembet thatthe Editor will always be delightedto hear from reader's what resultsthey. have obtained on sets.The Crystovalve is one of the Mosteconomical receivers I have. _everbuilt, for a considerable proportionof the time for listening in can beoccupied, on the 'crystal -side, whichmeans great saving of batteries andgreat simplicity of handling. Thefamily man in particular will findthe set useful, for the young canlisten in as often as they like on thecrystal side, and the valve side canbe left for more responsible membersof the family.

C4.00//2 F

H.T.

TEL

1.)C 3 0003fiF

2

R22 MO

4 NOTE.- TAGS AfARIlED3 "/- ARE AT THE TOP

DETECTOR -

MOWN6

C2 0005,1F

(:) CAT

cl-000/

fiF

Fig. 3.-1.7.-ew to wire up your panel. The tags of the switch, marled r, are furthest from thepanel, while those marked 4 are nearest it. Blueprint No. Cto17B,

832


°,9/ oal

. ,

e

Imagine an ana'yti-cal chemist withouthis scientific ba'an-ces or an engineerwithout his mcro-meter!

yo;t C(15 -not imagine yo!! r -self tuning a recei !erwith a direct (treecondenser one hav-ing experienced theaccurate tuning ofthe Col'v?rn SelectorMechanically Con.trolled Precision.Contenscr.

You can nowSEPARATE STATIONS

three metres apartThe dial divided over thefull circle provid:s 360 de- "grees value for each rotaticnof the index. This enablesBeath of a degree to be actu-ally located: AND ANY PRE-DETERMINED CALIBRATIONCAN BE RELOCATED TO TRIaACCURACY AT WILL.The Colvern Selector p:o-vides a mechanically con-trolled movement of suchconstruction that it is en-tirely free from backlashand that the relative posi-tion between the movingParts is Maintained sincethe gearing is not dep sad -able upon fyiction or simi-lar device. Incorporate theCglvern Selector into yourreceiver -then yon can sepa-rate stations 3 metres apart-a wonderful .exp srienceafter the unsatisfactory jug-gling with the direct drivecondenser.One hole fixing and cut' refreedom from hand capacityThe Calvem SelectorCapacities -0005 mfd. 21 -Capacities .0003ruM. 20 -Type F,without gearattachment .0005 mfd. 15 /-Capacities 4/003 mid. 14 /-Gear attachment

which is easily af-fixed to Typo F tocomplete the Ca-vern Selector - 7

LOW LOSS.Descriptive Folderfree up,n request.

THE sharply tuned shod wave circuit; ofSuper -Heterodyne Hee:vivo s have shownthat the direct drive condenser is an

unwieldy instrument tJally unsuitable fortuning these or any other critical circuits.In practice, definite location to ascii] s intervalis of real importance. In final timing we mustrealise that a sensitive sircuitisfinallysemiave,to a variation in capacity equal to gVh of adegree: Thus there are 3,600 vanationsof capacityeach of great importance and of greats importancethan has hitherto been deMonstrated.The C. Ivern Selector is designed with a gearratio of 20 to 1 which in the light of our owncap qimonts is suffici.nt for all requirements.Provision is made (should it be necessary) toenable the original accuracy of gearing to bemaintained.

COLLINSON PRECISION SCREW CO., LTD..Provost Works, Macdonald Rd , Walthamstow, London, E 17

Telephone : Wairliamstow 532.tsars Imanmeys1184

--

and enveloPa Inge°. much

,,,,e,red- I hulnednne lia S1Y, A T. Set nem".

Itlie.laeSreonlgrdireesitly118 a..r. 1 ,.ei'..0.1eiinThd'ecTils.

lien and thank.finer

1ayuusrptlee.ei

Ni.4irtlallettltreillne'grSaeero;1(i'mnikeTal:saanb:sileiegc:.I.

anti fathfulu .i

ell Biltish andStations, Mad,o. , Zuric.1,

"Your Amplifiesnre. tadort.

cheap, but as theleav,arti,e,

wane" are.i.oRney.they are worth the mSlane& VI.

.kIt to i.tir ti"..C..111a,m'i'soN4VIf 41/ 11

1111 11

Here's thePROOFthat-

The Curtis Constant -Tuned (Aperiodic)H.F. Amplifier reaches out !

Type A, 2M to 8:0Metres. Price 15/ --

Type B, 800 to 3,0.0Metres. Price 17/8

Type C, 2,000 to 7,000Metres. Price 18/6

Type C is especially de-signed for Super -Heterodynes.

The Curtis Constant -Tuned (Aperiodic) II. P.Amplifiers are obtain-able from all dealers. If1/, se have any dlieultyplease send direct giving11(1111C and address ofo'ealer who could notsupply.

A few old-fashioned and some very young peoplebelieve that multiplicity of tuning controls resultsin higher e fticiene: . The more knowledgeable knowthat multiplicity .cf controls increases instabilityand tendency to oscillate: thus efficiency iscorrespondingly reduced. Up -to date wirelesspractice tends entirely to eliminate every possiblesnoring control no a Receiver and aims at minimumcontrol as the ideal.Mg t) eq leney At ei iudic cc upling (i.e., ConstsntTuned s) being absolutely automaticin its action, represents the most modern Radiopractice.The Curtis Constant - Tuned H.F. (Aperiodic)Amplifier eliminates the potentiometer - thathopeless bludgeon of Radio effidiency - all thetendency to self -oscillate and guarantees absolutestability with maximum Radio efficiency.Indispensable for maximum Efficiency and...Purityof Reproduction, with all High Frequency andSuper -Helen, iyne Circuits.

BUILD YOUROWN DUODYNE

The wholly inexperienced can build this lung -range re cid ver with the.aid of ThsCurtis -Duo iyne Treatise for home Constructors, containing :-

1. Curtis diagrams for 3 and 5 valves.2, Simplified Lay -out and Wiring Charts for 3

and 5 Valves.3. Instructions fur Operation.4. Complete Schedule of all material required. 116

Sales organisation: PETER. CURTIS LTD.is toisoc'aMou with

THE FARAt4ON RUI:BER, MANUFACTURING CO., LTD., Ht:L

75, CAMDEN ROAD, N.W 17elryrttma: ' PAR ACURTEX 'Phone: NORTH 5110.

BIRMINGHAM: 76, Newhall Street. CA0111=MANCHESTER: 312, DearusgAe Central 5095

Barclay, 1154

In replying to advertisers, Please hietitiOii, 1IU WIREI,I.,'SS CONSTRUCTOR. 833

THE WTRtLESS CONSTRUCTOR July. 1 025

FURTHER REDUCTIONSin the prices of

RADIO VALVESIT was -the Co:;mos Valve which on May 1st

led .the \vav in price reduction. Thslatest reduction comes, therefore, from

the firm 'which made the first. Cosmos Valves.are -made by the Metropolitan-VickerS Elec-

/ tiicat Co., who will be remembered for theirPioneer work in..broadcasting. They havebeen pioneers, therefore, both in the scienceand in The -Selling of wireless. Having doneso much to make ' wireless ooti, they areleading the way in making it cheap. - Thelower prices of Cosmos Valves go hand inhand with an improvement in the results theygive. There are no betel- valves.

THE COSMOS D.E. 11Is an excellent "General Pur-pose" valve. It is a, remarkablyefficieift rectifier, a good high -frequency and low -frequency ampli-fier and eminently suitable forworking off a single 2 -volt accuinu-lator cell or dry batteries.Reduced from 21/- to

12/6

THE COSMOS A.45We can say with confidence it isbetter than -any other "General -Purpose " bright filament valve:In the A,45 we have the advant-ages of other H.F, and L.F.special valves combined in' thesame valve.Reduced from 11/ -.to

7/6THE COSMOS S.P. 18 SHORT -PATH VALVE 1 2/6has- also been reduced from 18/- to

Obtainable from most Wireless Dealers

METRO-VICK SUPPLIES LTD(Proprietors : Metropolitan -Vickers Electr:cal Co., Limited)

4, Central Buildings, Westminster, S.W.1

It

V90

S31 in replying to advertisers, please mention THU WIRMASS CONSTRUCTOR.


raq%%%%ffilrtqffiEffiWIEth7-,ffiMW6'5_,1-1HWSEH

Announcing the publication on' June 20th of two additions to theRadio Press Envelope Series : -

No. 10.-" How to Make the Twin= Valve Loud -Speaker Receiver."By John Scott -Taggart, Finst.P., A Price 2s. 6tl.,

Yri

ffi

ffi

ffi

Or 2S, 9d. post free.No. ii.-"An Adaptable Crystal Set and How to Build It." By

Percy TV .Harris,111.I.R.E. Price is. 6d., or is. 9d. post free.

WER5ffi it ffiMTiEffiffi%%ErlitUitS%WiffiTiTiMNTI%%%97%

Radio Press News

WHEN reflex (or "dual caliph-.fication ") circuits' firstbegin to receive attention

their novelty was no doubt one ofthe attractions which contributedto their popularity. The attractionof novelty, however, has now to agreat extent been replaced. by atrue estimate of the special usesand suitability of reflex sets, andto achieve real and lasting popa-.larity a design must possess certainvery definite merits.

' Of these, 'stability, ease of work-ing and the capability of givinggood results are no doubt the fore-most, and when it is rememberedhow completely the " Twin -Valve "receiver complies with these re-quirements there is little difficultyin understanding the great popu-la'rity this set has achieved:

Although there is to many a con-siderable attraction about a reflexreceiver in which a valve is savedby the use of a crystal, a good and

isecil51158,16.1-sa

The Twin -Valve Receiver(Envelope No. 1o).

stable design employing valve de-tection has always} a strong appealto those who wish the set to besimple to operate mid to maintainin as sensitive a condition as pos-sible. This, no doubt; is an addi-tional reason for the great- appre-ciation accorded the "Twin -Valve"receiver which employs the reflexprinciple in the first valve only, thesecond valve being the detector.

Great pains were taken in de-signing, the instrument to obtainthe maximum possible degree ofstability, together with really goodresults, and the outcome is a setwhich is notable from any point ofview, whether regarded as a receiverfor obtaining the maximum possiblevolume from two valves, or as asteady and dependable set forfamily reception which call be leftpermanently adjusted to a givenstation.

AppearanceAlthough, no doubt, the discrim-

inating constructor attaches moreimportance to the performance ofwhich a set is capable rather than thematter of the symmetry of the lay=out of the panel, and so on, believ-ing that the works -are more impor-tant than the looks, no one candeny the attractiveness of a designof really:pleasing 'appearance andgood arrangeirient, and here again

The WayType C below panel)

to Radio Efficiency(I'VE your s.t range by fitting

H.T.C. Low Capacity Valve pol-ders. The ordinary ty. e of valveID 'Icier with embedded sock -t,s ckets with large nuts and washersdangerously. c'oSe together, and so-called low capacity valve holdersparalyse your receiver,. putting &s-cant stations beyond its reach, Formounting the four -pin valve and thepopular plug-in R.F. Transformeryna can only expect The best resultsif Sou uss the H.T.C. Low CapacityValve Holders.

Type A (above panel) -Type B (Board mountieg) 1/9,Type C (below puler/ - 1 6

As used IT 11 .1. 0. Hartt in a "A Doubt:Purpose Two -Valve Receiver."

4 14

15gi* 94

3

IDEAL FOR REFLEX.For such Circuits as the S.T.100.infact, for all reflex circuits usingcryats1 rectification, the II.T.C.Fixed Detector is ideal. We find ihe"hot -spot" and test it on actualbroadcast. You simply mount it-under the nauel if you wish-and itwill do the work an no other can do.The WI .C. Fixed Detector employs aproved mineral crystal combinationwhich has held the Admiralty longdistance record (over 5,000 miles).

emember it is a peilnamnt detectorAs used liy Mr J. Ay. Barber in "AC.mparis di Crystal Sea. '

H.T.C, Fixed Detector - - 3 6C mp'eta with Ebonite Rise,

Clips and Terminals - 4 6Detector Clips only - - 3;9

Insist upon 11.1.C. Products atyour d.a!ers.

H.T.C. Electrical Co. Ltd.Telephone : Battersea 374.

2-2a, Boundaries Road,Balham, London S.W.12.

This sign cn aCondenserindicates hightuning efficiency.

SQUARE LAW'001 9 600075 9 -'0005'0003 6 9'00025 6 1

'0002 6

Vernier .. 4,6

STANDARD868 -

'001'00075'0005'0003 5 9'00023 5 3'0002 5'1001 4 9Vernier

J.B. SQUARE LAWWITH VERNIER

'0003 .. 12 6

'000'3 11 3'00023 11.3

11sSanilutill biaa

1111111l 1 Illlldolll11111110111

" What a difference !-"is the exclamation that springs spontaneously fromyou the first time you tune with .1113. Condensers. The-sincoth action, sharp toning, and freedom from back-

- lath at blice convinces you of the superiority of J.B.Condensers:

Buffo, mity of the - guaranteed rapacity and thehigh radio efficiency and special rare given tomechanical details enables J.B. C. rulensers to off et anarked improvement in the selectivity and gene alefficiency of your thine's. Furth erinore, a J.B. instru-ment will be as good aft v ears of servi c as it was uuthe day you purchased.

8. POLAND ST -OXFORD STLONDON

First Floor)

Barclays 11i5

In replying to aiiverttsers,-pleasethention THE WIRET,EsS-Co':%IsTRucToR,

gelephone:-GERRARD 7414

111=1119111111!MMIIIIIES9.1011'i 11 1 i

835


the " Twin -Valve " receiver claimsattention, as_ may be 'judged afteran inspection of, the illustration.

The popularity of the set is now ina fair way to being much enhanced,since it is being.brought_ out inRadio Press Envelope form (En-velope No. to), with all the advan-tages conferred by that method ofpublication. For example, twofull-sized blue prints are provided.in. the envelope, showing the wiringand the exact drilling of the _panel,elaborate instructions for buildingand working are given, and there is,the usual set of reproductions ofphotographs showing the instru-ment from a great variety of angles,so that not the slightest doubt canremain in the mind of the construc-tor as to its exact assembly and -wiring.

DistinctionFor a designer to produce a

crystal set of really marked distinc-tion at the present time is nosmall achievement when we re-member how very many and variedare the designs which have beenpublished. There can be no ques-tion, however, that Mr. Harrissucceeded . in producing such aset, remarkable alike from theviewpoints of simplicity of con-struction, originality of arrange-

ment and efficiency, when hedescribed in the September issueof Modern Wireless a set whichhas come to be known as the" sixteen -gauge wire receiver."

So great has been the vogue ofthis set that it is now being re-published in Radio Press Envelopeform (Envelope No. Ii), so thatall those who missed it on itsfirst appearance will now be able

The crystal set described inEnvelope No. Ir.

to Wild the . instrument with .thegreatest possible ease, and withthe aid of all the advantagesconferred by a Radio Press Enve-lope. For example, upon obtainingthe Envelope, with its attractively -coloured cover, they will find thattwo Tfull.-sized blue prints areincluded, one Showing .the dimen-sions for the drilling of the panel,and the other the wiring itself.

In addition to the customary

July, 1925

full description of the building ofthe instrument, and instructions_.for its working, there will also beblind the usual set of drawingsshowing, in this case, the circuitof the instrument and the workingpositions for the switches incor-porated in the set, with the circuitmodifications which result fromeach of these settings. .As a finalaid to the constructor, there arethree she4s of reproductions ofphotographs showing the set fromevery useful angle.

A special .feature of the set isthat there are no external coils

required for the ordinary broadcastwavelengths. A special design ofinductance devised by Mr. Harrisis incorporated inside the box,and an additional plug-in coilis only required when receiving5XX. A special circuit is in-corporated, of the auto -coupledtype, which is now receiving somuch attention, and two switchesare provided which enable suchvariations .of coupling turns, etc.,to be made that it is possible tosuit this set to practically anyconditions of aerial and earth.As an additional attraction, itwill be noted that the crystaldetector is mounted inside thebox in a convenient and accessibleposition.

SURPRISING-the difference this can make to your reception

If you are troubled withpoor results pay particularattention to the working ofthe Detector Valve. Reducethe H.T. voltage consistentwith good volume andincorporate a WATMELVariable Grid Leak.

6,u3 P.C. for 1'ctcriidiiaFel r.

6 to '5 Megolims 2 610,000 to 100,000

Ohms 3.6 All goods of one manufacture bearthismark, It is your onlyauurantee,

The WATMEL WIRELESS CO. LTD.332a, Goswell Road, LONDON, E.C.1Telephone CLERKENWELL 7990

Ixeverything it is true that theI little things count. In radio

most certainly. This we realisedwhen designing theWatinel VariableGrid Leak, with the result that thespecial attention -given to details inits construction makes it perfection.Take, for instance, the improvementillustrated.

A small but strongly shaped springfixed to the collar compressesagainst the controlling plunger. Thisspring is an exclusive feature of theWatmel, and its purpose is to ensurethat, perfect electrical contact ismaintained,even after constant use.

It's a little thing, but it makes allthe difference, and is much appre-ciated by the many Watmel users.They find it gives just the final touchneeded to bring in Broadcast that isfull of tonal quality. Its reputationamongst radio experimenters forconsistent reliability is unequalled.Therefore, if you want the hest GridLeak obtainable you must buyWatmel.

Barclays 1140

/

REG N° Me 64

OOP

Why YOU shoulduse

ENERGOPRODUCTS

A LOW FREQUENCY TRANSFORMERwith a Pedigree is the ENERGO. It gives that pureand faithful reproduction that is every experimenter'saim. Specially suited for first stage and reflex circuits,it gives maximum amplification without distortion.When next needing low loss Coils, high efficiency H.F. or L.F.Transformers, remember there are only three qualities-

GOOD--

BETTER-

These components are obtainable everywhere at most competitiveprices. If your dealer doesn't stock them, write, giving his name

and address, direct to :-

ENERGO PRODUCTS,2 OLIVER'S YARD, LONDON, E.C.I

836 In replying 'N advertisers, please me Won Tag WIRa,ESS CoNsTRucTox.


Before you buy a single componentfor your next set, consult thelatest Burndept Catalogue (sent free)

TO choose a good circuit, toconstruct with care,and to useBurndept Components; is to besure of getting good results from

your apparatus. For perlect receptionall components in your set must be,really efficient. Every BurndeptComponent i% the subject of muchresearch before it. is offered to thepublic. Many experiments areconducted in our well-equipped labor-atory to make sure that the designand materials are perfectly satisfactory.Every stage of manufacture is care-fully supervised. Finally, the finishedproduct is rigorously tested-it mustcome up to a definite standard ofefficiency-and so, because of thiscareful manufacture, we are able toguarantee our apparatus and to knowthat it will fulfil all that it is claimedto do. By using Burndept Conipon-ents, you can expect good tone, greatvolume, sharp tuning and ease : ofcontrol. Moreover, the neat appear-ance of -Burndept Components willmake your set most -attractive.

Send forthis free

Catalogue

TO -DAY

r-- CUT HERE -ToAldine

oBURNDEPT

W1RELESS, LTD,H use, Bedford2 Street,

Strand, London,I Please send me a 'free copy oft, the

latest Burndept Cata'ogue.

1

E NAME

I ADDRESS

1

The Burndept range, which includeseverything from components to com-plete installations, is fully describedin an 84 -page illustrated cataloguewhich will be sent free to any addresson receipt of the coupon below.When you are selecting the parts foryour set, consult this catalogue; thencall on the local Burndept Agent, whowill be pleased to show you the actualcomponents and give you any specialinformation you require.Hcre are two Burndept Componentsof exceptional interest to all homeconstructors-the Anti -Phonic ValveHolder and the Dual Rheostat.

Sectional view(left) shows con-structionPhonic ValveHolder. V iew be-low shows- actualappearanc:.

The Anti -Phonic Valve Holder com-pletely eliminates microphonic noisesin dull -emitter valves and will prolongthe life of any type of valve. It isparticularly suitable for use in portablesets. As the sketch shows, the valvebolder proper is supported on foursprings which absorb mechanical shocksand vibration and so protect the valve.The insertion or withdrawal of a valve

does not strain the springs. An im-portant feature is that the valvesockets are countersunk and thus therisk of short circuits is eliminated. 'Soldering tags are provided on theouter insulated shell.No. 401. Anti -Phonic Valve Holder,for panel or- base mounting, in carton,with screws, 5s.

Note thesturdy con-struction ofthe DualRheostat.

The Burndept Dual Rheostat is a mostconvenient component, as it may beused without alteration to control thefilament current of a bright or a dull -emitter valve. The first half of theelement is wound to a resistance of 25ohms and the second half to a resis-tanc2 of 5 ohms. The whole 3o ohmsresistance is used to control a dull-einitter valve ana the 5 ohms resistancea bright valve. The movement of thebrush over the Windings is practicallynoiseless owing to the special construc-tion of the former on which the wire iswound. The windings cannot be dis-placed, and they yield slightly to thebrush and so ensure good contact.No. 222. Burndept Dual Rheostat,5-30 ohms, for panel amounting, incarton, with drilling template, 7s. ed.

BURNDEPTzfr

Head Office-Aldine House, Bedford Street, Strand, London, W.C.2Telephone: Gerrard 9072 Tee rams: "Burndept, Westrand, London"

I i Branches at Manchester, Leeds, Birmingham, Newcastle, Northampton, Cardiff and Nottingham.. . _

IV freless Constructor, July1

I DATE imimmismumm

in replying to advertisers, please mention THE WIRELESS CONSTRUCTOR. 837

i ii WIRELESS CONSTRUCTOR July, 1925

-

r'74`"rff//fjr/!11111M11atVovm

On Crystal Set EfficiencyP I remember rightly," said

I John Anstruther, as we tookour seats for the next of

our enjoyable meetings, " we agreedon the last occasion that thisevening should be devoted to adiscussion upon the ways of obtain-ing real efficiency in the crystal set.Is that so ? Good. Well, now, whois going to fire the first shot atne ? "

" First of all," said Painter, " Ithink that -we ought to understandjust what is meant by efficiency-it's a word that we are alwaysKeing used in articles and bookson wireless-in any receiving set."

" That's a good idea," smiledJohn, " and as soon as I have gotsomething like efficiency -in thiswretched pipe of mine we will goon with it-. I suppose nobody's gota hairpin ? Ah, thank you, Ains-worth ; it is not everyone thatcarries a pipe cleaner."

His pipe was soon in full swing,and, puffing away, John startedhis talk on crystal set efficiency.

" What," he asked, " was 'wrongwith my pipe ? No prize is offeredfor the answer, but I will getPainter to tell me."

"Why, it was partly stopped up,of course," answered Painter ; " butI cannot see what that's got to dowith crystals."

An Analogy" Well," John went on, " I just

want to give you quite a simpleanalogy. When I pulled away atthis pipe before Ainsworth cameto the rescue with his cleaner, Iwas expending a good deal ofenergy and getting very littlereturn for it in the way of smoke.Instead of doing useful work, -myenergy -was being spent in over-coming -resistance. And that'sjust what happens in the vastmajority of crystal sets. Peoplerig -up excellent aerials and per-fectly sound earth connections ;they spend pounds in purchasing

John Anstruther'sWireless Talks

all kinds of crystals, each of whichis, of course, guaranteed to bebetter than any other; they tryevery kind of catswhisker ; in fact,they take any amount of troublein :an endeavour to secure just alittle better working in their sets.But as a rule they get hold of thewrong end of the stick, and theyallow a very large proportion ofthe energy brought in by the aerialto be wasted in doing useless work.Now, what exactlY do we want thereceiving set to do for us ? Whatdo you say, Richmond ? "

Our RequirementsRichmond thought fora moment

and 'then said : " Well, I. suppose10

28

ka -a -6" .4

41

6

0 5

1

0

/123

ie .4 .6VOLTS..

Fig. 1.-A crystal characteristic.we want it to respond well even toweak impulses and- to give -us thegreatest possible volume of soundin the receivers that can be com-bined with purity and clearness."

" I don't think we can betterthat," said John. " Richmond hasput our requirements in a nutshell.In the crystal set we are not con-cerned with distortion due to themisuse of reaction ; that is, we-shall not find our signals becomeindistinct if we work them up tothe :greatest obtainable ,strength.The whole thing comes to this :The aerial brings in impulses in theform of waves whose crests andtroughs we may regard as havingrespectively a positive and negativevalue. For a given difference involtage between the crests and the

troughs of a signal the mostefficient crystal set is the one whichdelivers the greatest amount ofrectified current to the telephonereceivers, and therefore producesthe loudest sounds. Ori to comeback to what we said before, themore efficient the receiver the lesswill be the proportion of the itt,comir°a impulses that it wastes."

" I think we all follow that,"remarked Morris ; " but I wish youwould tell us a little more aboutthe way in which the crystal dealswith these crests and troughs andturns them into rectified current."

Jolm picked up a writing padfrom the table at his elbow, and ,

was busy for a few moments with a -pencil. Then he handed round adrawing like that which you seein Fig. i.

The Characteristic Curve of -

a Crystal" That," he continued, when we

had all.had a look at the " charac-teristic," as lie called it, " is a curveshowing the behaviour of thecrystal. I know that people,especially beginners, are ratherfrightened of curves and things likethat, but there is really nothingto shy -at, and they are exceedinglyinstructive and useful things. Youwill see that I have marked off thehorizontal line into fractions of avolt, starting from 0 in -the middleand running up to 1 volt positiveon the right-hand side, and downto 1 volt negative on the left. Thevertical line through the middle ofthe - other is divided into micro-amperes, that is, millionth parts ofan ampere. We saw before thatthe crystal behaves differently topositive and negative impulses. Ifyou look carefully at the curve youwill see just what it does. NowI will get Cartwright to followout for us what happens when awave comes in whose crest andtrough have values of +4 voltand - .4 volt. Let us see first ofall what the crest does. Can you

836

July, .1925 THE WIRELESS CONSTRUCTOR

RAYMOND 2 zuDIDORTEEssms,,,Goods post free U.K. except where stated. Foreiga retail orders over 110 post free, otherwise mast send ample THESE TWO COLUMNS FORpostage, etc. Trade orders U.K. from post columns less 20 per cent, post extra. Special terms for quantities. CALLERS ONLY

ENERGO H.F. IGRANIO MILSNcr. 1 150 450 .. 3,16 1 ' -ALL POST FREE. POST ORDERS OTHER COLUMNS

150/ .. 3,11 32; 75. 5/6 ; 100, 7/-; 150,No. 3 450 1,200 . 4.3 7.10; 200, 3/8; 250, 2/-; RAYMOND300, 95 400, 10,3 ; 500,

VARIABLE CONDENSERS

SUNDRIES. -

Aerial. 7122, 100 ft 2050 ft. dittoBasket Helder and

'Plug 2 -for 2/- No. 4 400.2000.. 46

1/8

10/..Ditto, beat quality. No. 5 1,600/7,000 .. 4,9

LOUD SPEAKERS. 'Rheostat, 4,6; :,0 ohms, 7'for 2;3Ditto, spike holder

2 for 2; C.A.V. Tonpalit...... 30 -2 -way coil stands .. 219 ".A. V. Junior 55/3 -Way coil stands .... 4 6 Sterling Baby 351-

3 way nickel 4 11 'Ampli sa Junior . 27,61 Watmel3 6 Sterling Dinkie2 -way ni. kel 30/- ,Iassen 2,6

5/6 Anipl ion D. agontly - 215, I Allen26.2 -way geared1'6

12 -way Shipton cam .. 6/. A molion do. III- 20.- Br twood 3/-a -way shiptas, cam .. 7 6 A nsplion De Luxe .. 65 -

. \ mplion AR192 -way Polar cam .... 6 105,5ANODE RESIST -3 -way Polar cam ver- lilllectos . 43-

9 . Time Music Minornisr 21/-2 -way cam render- 3 6 Transformers L.F.Coil plugs, plain. 2 for 1 3Shaped wedge. ..2 fi r 1 61 Eureka (hand 30/ -

Eureka Second Stage 236De. Edison B IL 2 for -

Do. Nickel sides, 2 far 2/. Igraine Shrouded NewDo. fitted fibre, ..2 far 1/8 rained

- 21,/ -Da B B Fennel Shrouded 108Ebonite do Pot Oa- sl 12/6

Genentl Earths 83 15/-Edison Bell do. ... -10 - *spur Success (black/ 21/-Placed Condriuters :,1 ..r3 Royal 20/- TEI4EFUNKEN.Edison Bell, .

'0001 up to '0003 1 31 Terminals, complete.'002 up to '006 2- Pillar, W,O., doz., 1.:-, 1/3

Grid leak and clips .. 1/6 j's hone 1.4.0003 and grid leak.... 2/6' Nickel; 9d. doz extra:Dabilier : Vs ltmeter ..... each 5/6'0001 to '0005 ....each 2/6 Grid Leak and Clips 1/4

, '001 to '004..... each S/' Rheostat and Dial 2/32 or 3 meg Grid Leak 2/6Anode res. on stand.. 5,6 VARIOUS.130,70,80,100,000 ohms 1 6 or 30 ohms (thins) 12:11Raymond Ebonite Base: ,Resistances wound Your favourite 'phones,'0001 up to .0035 1;1 on trmer 2;6 Entirely NEW MODEL.'031 up to '006 i. . 1/3 Sterling Pot entio- Most beautifully finished

Grid leak and clips .. 1/3 meters ' 6,4 exquisite ton(4,000 ohms)'01 and '02 ......each 1:'9 Pe As ss 30 ohm Rheo-Mansbriige T:C.C. : stag, 2 62 mfd.. . 46 II ichrom Verner . : . 26 VALVES.I mfd. 310 Ormond Short Wave 8f -T5 3,8 Fixed tondens re, All makes stocked.Flush panel sockets, .00025 .003 ....each 2:- B.T.H.,Ediswan,Mullard,

will nuts doz. 1,3 Ormond Neutro :yrs° Colima . Marconi, BrightSpade terminals, doz. 1/. Condenser . . ... 2:- Emitter, Dull Emitter,Pin tennina's, ..doz. 1/- 'Raymond" L o u (1 tuul Power Valves.Spade tags. doz. 61 Speaker 1841 We hielily recommendStuds, nuts & washers !BULLARD VALVES.,,,,y. Bd. BritishyEADPHONESShert'ng plug ........ 82. 11. T. IL 20: - COSMOS VALVES.Bus Bar, 1/16th sq., Bendel' Match d 201-

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tor 6/6 genuine article and see 2 Polo c41 KnobPanel Switches.

letters N libKackstamped on 2 Pole clo 'Lever4 Me c.o Knob

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SHIPTON STRIP.7 ohm Rheostat30 or 60 ohm . 3:-1'otentiometer, 600

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With Vernier Without Vernier.001 8 6 .001 .. 7i 6

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Complete with Knob and Dial.EBONITE ENDS 1/- EXTRA.

ORMOND "AMERICAN "SQUARE LAW LOW -LOSS.'00025 - 6/6'0003 - 7/6'0005 - 8/-.001 - 9/ -

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Copper foil. foot ... 214.e I wire, 10 yards....5d.

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Twin silk flex, 6 gds, 62.Ormond Rheostat 18Raymond "' 1/3, 1/6With did 1,/8, 1,11

phones,Continental-worth4,000,muchohm

more. Callers 11'9 pair.SQUARE LAWVariable dander sera

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5:- 'PHONESCustomers buying 20/ -worth full -price goods canhave a first-class pair of'phones for 5,'-, Must betaken at time of purchase.

Fixed CondensersRaymo. 2 (ebonite base)'001, '0001 2, 3, 4, 5, 10d.

'002, 3, 4, 5, 6, 1/.rminal fittings,

REFLEX COILS."EE LUXE" Made under licence Burn -

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In replying to advertisers, please mention THE WIRELESS CONSTRUCToR. 839


EVERY LISTENERMUST READ

to be kept well-informedon all wireless matters

No other daily newspaper will give youthe same service of News, Technical

Notes and Articles

FREE SPECIMEN COPY

A Specimen Copycan be obtainedfree of chargeby filling up theappended form.

to ao a....To the Publisher,

The Times,Printing House Square, London, E.C.4

Please send me a free specimen copy ofThe Times.

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ADDRESS

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SW In replying to advertisers, please 74ention TIITti WIRELESS CONSTRUCTOR.

July, 1925 WE iMPLESS CONSTRUCTOAR

discover from the diagram ? Takea pencil and put its point on the-I positive mark ; then run up-wards till it meets the curve.Done that ? Right. Now gostraight across from that pointto the upright line. What readingdo you get in micro -amperes ? "

I made the dotted line shown inthe drawing and replied : " Justabout 1 micro -ampere."

" That's it," said John; " Sowhat 4 volt positive does is- tocause the crystal to pass 1 micro-ampere of current in a certaindirection. Now see what happenswhen the trough of the wavecomes along. Take -4 volt on thenegative side, and see what currentreading you get on the lower partof the vertical line."

The Negative SideThe space between the curve -and

the horizonthl line at the -4 voltnegative division was so small thatthere was hardly room to dot in aline, and the reading on the verticalline appeared to be about a quarterof a micro -ampere.

" That's it," said John. " Thecrest of the wave gave you a wholemicro -ampere in one directioh-tallit northwards if you like-and thetrough gives you a quarter of amicro -ampere in the opposite direc-tion. Now, if you walk a milenorthwards and then come backa quarter of a mile, where are youso far as the starting -point is con-cerned ? "

" Three-quarters of a mile to thegood," replied Ainsworth.

" Just so," smiled John. " Andwhat the crystal has done to theincoming wave is to produce anet rectified current of three-quarters of a micro -ampere. By theway, I have not drawn the exactcurve of any crystal, but actuallyyou would find that results were agood deal better than this, for the' backward step ' on the negativeside would in the case of most goodcrystals be something so smallthat we can neglect it. But nowlook at the curve again, and youwill see something that is of enor-mous importance in crystal recep-tion. You will notice that as thevoltage increases on the positiveside we get a very rapid rise incurrent, though a larger negativevoltage produces very little differ-ence. For example, if an incomingwave has crest and trough values of1 volt its positive half will cause acurrent flow of 10 micro -amperes,and its negative one in the oppositedirection of about -5 micro -ampere.The net result will be 9- micro-amperes of rectified current."

" Yes, I -follow that," said Morris," but I am wondering just what youare driving at, for I can see that-you are leading up to something."

44 Take Care of the Volts"" Just this," returned John.

" To make your crystal work effi-ciently you must apply the greatestpossible voltage changes to it. Toparaphrase an old proverb, Takecare of the volts, and the micro-amperes will take care of them-selves.' "

" And how are we to do that ? "queried Ainsworth.

John was busy for a moment -withhis pencil, and then passed roundthe diagram shown in Fig. 2.

" Take a look at that," he said." It's a simple form of crystalreceiver circuit. To tune your aerialyou have the inductance marked Land the variable condenser C1 fa

E

Fig. 2.-A simple crystal circuitwith series condenser C and

parallel condenser C1.

parallel with it. The top end of thecoil is connected to the aerial, thelower to earth. Now, what wewant to get is the greatest possibledifference in potential between thetop of the coil A and its bottom B.Also we must avoid introducinginto the circuit any undue amount ofresistance; for resistance has theeffect of deadening the sensitive-ness of the set and of flattening itstuning. The arrangement whichyou see in the drawing is not thebest one, for it is found that you donot obtain the greatest potentialdifference across an inductance ifyou place a capacity in parallelwith it. Therefore, it would appearto be better to have the condenserin series as I have shown it at C. indotted lines."

" Yes, I am always hearing that,"cried Painter. " I use a seriestuning condenser, but I do not findthat I get much better resultswith it."

" That," said John, with a smile," is probably because of the amountof parallel capacity in your cir-cuit."

" But," exclaimed Painter, I

841

-have just told you that the con-denser is in series."

" Quite so," said John. " ButI was not talking about the tuningcondenser. What sort of coil doyou use ? "

Painter told him, and John wenton to explain what he meant.

Coil Capacity" If you place two insulated

wires at different potentials side'by side there is capacity betweenthem.

Now the turns of a coil are atdifferent potentials. Suppose, forexample, that the potential differ-ence between A and B in Fig. 2is i volt, and that the coil containsro turns ; the voltage drop acrossthe coil may be perfectly regularand there May be a potential differ-ence of I volt between any twoacijuoent turns. If we wind a coil

double cotton -covered wirewhos, insulation is impregnatedwith shellac or paraffin wax, andplace the turns so that they touchone another there will be an appre-ciable amount of capacity betweenthem. We shall make mattersmuch worse if we wind the coilin two layers of five turns each,placing turn No. 6 over turn No. rand so on, for then we shall havea potential difference of .5 voltbetween -each turn of the upperlayer and the one that it coversin the lower. To use a term thatyou have all heard, the " self -capacity " of the coil will be large.You must not forget that high -frequency voltages leak away bycapacity with the greatest ease,.so that in a coil whoSe self -capacityis large we are virtually providingshort and easy paths for impulseswhich they will take, for, like therest of us, they are only too readyto escape froth doing work."

The effect is really very muchlike that which you produce byconnecting a condenser in parallelwith your coil, and you begin tosee why self -capacity is so harmful.

Dielectric Losses" How can you keep down self -

capacity ? " asked Morris.' You must wind your coil,"

John explained, " in such a waythat turns at different potentialsare as far away from one anotheras possible. Air is the best separa-tor for them, since a given thicknessOf it produces less capacity thanany other good insulator, and it isalso freer from what are calleddielectric losses.

" Will you tell us," I asked," what you think the ideal coil forthe crytsal set would be ? "

" Here's a recipe," replied John


P t o vPatentNo.2036/25

TRIPLE - CONTROL CONDENSE RS are well madethroughout and fitted withStout Circular EboniteEnd -plates guaranteed freefrom surface leakage.

Anode Ttining Model(as illustration).Price - - - - 14/6

Aerial Tuning ModelPrice - - - - 18/6

TRIPLE- CONTROLVariable Condensers

'VERY new invention and every progressive industry is marked,4 periodically by an 'important new improvement, constituting adrastic departure from previously accepted principles. Broadcastingis no exception. The Three Electrode Valve ,was the first big strideforward-others have followed, chief among them being the intro-duction of the Triple -Control Condenser. The manifold advantagesof this new Condenser are immediately obvious.

a radical departure fromt IS the usual " move all or

nothing" design.

It is Several Variable Condensersfor the price of one.It is capable of remarkable.eelectivity.

It is capable of rapid or gradualincrease of Capacity.

It is a distinct advance over theusual type of variable condenser

In the same way that no sane man would purchasea Motor -cycle without speed gears, so, in the future,no discriminating person will buy, and no keen experi-menter will construct, a Wireless Receiver withoutTriple -Control Condensers.The Condenser is made in two sizes-One for AerialTuning and.One for H.F. Tuning. The illustration isof the H.F. or Anode Turing type. Three controls aremounted on the spindle, moving respectively One, Twoor Four moving plates-from which it will he seen thatOne, Two, Three, lour, Five, Six or Seven plates can beindependently moved over the full scale reading of theInstrument.IF you are constructing a portable set, IF you desire toreceive tin se elusive distant stations obtain one of theseinstruments at once.REMEMBER - Insist on Triple -Control. There isnothing "Just as good" because there is nothingapproaching it in design on the market. If you arean advanced experimenter the advazu ages are obviousat first sight; if you are a novice ,hink it over for a fewminutes, common sense will decide.

Tf yon have any difficulty in obtaining this Condenser from yourlocal dealer send a Postal Order to the Manufacturers and Patentees,alto will despatch the condensers you require POST FREE.

The GENERAL DISTRIBUTION CO., Ltd.OAKLEY WORKS BATH ROAD SLOUGH BUCKS

Keystone Super -Heterodyne Kit:Three Intermediate Trans- One Tuned Filter complete One Oscillator Coupler - - - -- -formers carefully Matched with fixed condenser for designed to cover all , THE Iand fully tested. Each one tuning the primary winding. wave -lengths between 300contained in handsome (As all these units are care- and 600 metres. in con- I SET

!oxydised metal case. These fully matched a variable junction with a .0005 mfd. 1 I

transfOrmers have been specially condenser is unnecessary. variable condenser. _ _ _ _ _ _ _ _ _.designed to function withstandard British valves._____- - - -

Pete -Scott's WireessBook contains morethan 80 differentCircuit diagrams andmuch useful technicalinformation for be-ginners. Post free l/5d

The three Intermediate Transformers and Tuned Have you read the Pilot's Chart (sentFilter can be purchased separately by those who post free 3d.) giving illustrationsprefer to make their own Oscillator Coupler. and specifications of 30 different

Price £4 the four. Receivers for Home Construction ISend Sd. for 48 page Catalogue of Components. Invaluable for the experimenter,

PETO-SCOTT CO.,TD) sy KEYSTONE RADIO COMPONENTSSOLE AGENTS FOR

Registered Offices and Mail Order: 77, CITY ROAD, LO N DON, E.C.1Branches:- LONDON -62, High Holborn, V.C.1 WALTHAMSTOW-230, Wood Street. PLYMOUTH -4, Bank of England Place. LIVERPOOL -4, Manchester Street. CARDIFF -94, Queen Street.

The Simplest

Super - Het.in the worldand anyone can make it

EVERYWHERE wirelessenthusiasts are talking aboutSuper - Heterodynes. Their

wonderful seleCtivity and sensitive-ness have certainly - touched theimagination of the public. Withinthe sight of 2 LO's aerial, 2 LO canbe tuned out and either Cardiff orManchester received on an absolutelysilent background. Stations separa-ted by only 'three or four metres canbe eliminated with ease. The Super -Heterodyne shown here is made upfrom British -built Keystone parts andis wonderfully efficient. It uses 7valves,yet requires only a frame aerial.Its range is limited only by atmos-pheric conditions. Five Americanbroad -casting stations were loggedupon it during one night. Owing to itssimplified internal design thisKeystone Super -Het. can be built byanyone without any special wirelessknowledge and the cost will be nomore than you would pay for a ready -built 3 -valve set.Full working instructions, togetherwith an interesting article on theSuper -Heterodyne, will be forwardedto anyone sending 2 penny stampsto cover postage. Write to -day andmake up your mind to build a reallygood Set at a moderate price.

PS 2828r-amaar.esaaanaravzw.aar.rankairrannsca

S1.2 In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR

July, 1925 TIM WIRELESS CONSTRUCTOR

" which you will find pretty goodfor' broadcast purposes. Cut twodiscs of hard wood 4 in. in diameter,and with them make a kind ofsquirrel cage by fixing thin stripsof ebonite between them withscrews. In each of these stripsmake a row of very shallow notchesabout one -twelfth of an inch apart.Then wind on about 3o turns ofNo. zo or 22 bare copper wire,keeping the turns in the notches.You can attach the ends to ter-minals mounted at each endof one of the strips. This kindof coil gives 3 ou a fairly small

amount of self -capacity, and whenyou try it you will be surprisedat the results it gives even witha parallel tuning condenser. Yourresults may be even better if you,put more turns on and use a seriescondenser."

" Well, what it comes to is this,"said Ainsworth. " So long as youraerial and earth and the wiringof your set are up to the mark,efficiency in the crystal receivingset is mainly a matter of the coiland the tuning condenser."

" That's so," said John. " Andthere is one other point that I

vvvvy vv -v1, vvvvvidv-vo, -LA"Nniv Nryvv,vVvvvv liwlev),'A,,v0A0vtv't, s-tvn-rt,/

Aerial MastsUsing Trees as

ACASUAL glance at the manyaerials one sees whenpassing along, on even the

shortest train journey, goes to showthat many listeners take advantageof any conveniently high tree whichmay be in the garden, for thesupporting of the far end of the

Showing how a

A SuggestionA suggestion to users of trees as

aerial supports is given in theillustration, where a pulley issecured to the tree and the securingrope for the aerial is passed overthis pulley to be secured not bytying to a fixed anchorage, but to

--fiat/LATINS

ROPE HOLDINGPULLEY-

ROPE RUNNINGOYER PULLEY

WEIGHT

S;'

weight may be used to keep the aerial taut whenthe tree sways in the wind.

aerial. This, no doubt, has manyadvantages, chief among which isthat of expense, in that all costsfor mast erection are eliminated ;nevertheless; the aerials so erectedare rarely workmanlike -lookingjobs, the wire having a pro-nounced sag and slack appear-ance. Those readers who have usedor are now using aerials erected inthis way need little telling that theslackness is necessary in order toavoid the aerial wire breaking whenthe tree sways, thereby increasingthe tension.

a good heavy weight, the actualvalue being determined by thelength of the aerial. This weight,which should be just sufficient tohold the aerial taut, will, when thetree sways in the wind, rise or fallfrom its neutral position, whichshould be about 5 ft. from theground. With this arrangement,no matter how strongly the wind'may blow and no matter howmuch the tree may swing, theaerial wire will be always taut,and never will there be verymuch more tension put upon

84

would like to make. Don't usetelephones of too high a resistance.Lots of fellows imagine that theywill get better results by using4,000 or even 8,000 ohms phones,though really phones of from i,000to 3,000 ohms do better withalmost all the crystals that are incommon use. I want to talk, toyou about another refinement inthe crystal set, the use of thepotentiometer, but I am afraid.that I shall have to leave that tillanother evening, when we will gointo the working of this mostuseful instrument."

it than that produced by thehanging weight.

When erecting aerials in thismanner, care should be taken toensure that sufficient clearance isallowed between the aerial wireitself and the branches of the treewhich are ne'nrest to it, otherwise,when the tree is swaying in thewind; there is a possibility of thetwigs on the nearest branchessweeping across the wire and there-by interfering with reception. Inthe same way allowance should bemade for further growth of thenear -by branches.

When securing the pulley, it isas well to cover it with a good coat-inc,''' of vaseline, thereby proteetingit from the weather, and, at thesame time, ensuring that the pulleywheel will always run smoothly.

A Forlorn Maiden's Lament

to Her Wireless Lover

There was a time, dear George,when you

Would sit and gaze into my eyes,And swear that in their heavenly

blueReposed your earthly paradise.

Your fingers once for mine wouldseek,

And clasp them fondly hour byhour.

Time was we cuddled cheek tocheek

At twilight in the garden bower.

But now your alien heart desiresAmplifiers, valves and plugs,

Batteries, diaphragms, and wiresRun in and out like making rugs.

Your fingers ever twist and turnThe tuner or some other gears ;

While where my smooth cheek usedto burn

The 1-ad-phones clasp your heed-less ears. JOSEPH BURY.


MOST British wireless enthu-siasts have always takena keen interest in American

conditions, but to supply themwith really illuminating accountsof American affairs has hitherto

been a matter of extreme difficulty.Many articles from the pens ofeminent Americans have appearedin the periodicals controlled byRadio Press, and a good deal ofvaluable and interesting informa-tion has been obtained therefrom,but to show in true perspective aclear picture. of the technicalconditions in AnTrica, the, writermust be' one whb has an intimateknowledge of British condition&

The problem is one! whiCh hfThreceived much consideration frbmthe management of Radio Press,Ltd., and the outcome is alourneyof investigation which is being madeby the Editor of this Journal, Mr.Percy W. HarriS, 'for the ex-press purpose of presenting a clearaccount of American conditions.

The Editor's JourneyMr. Harris sailed for New York

on May i6 on board the " Beren-garia," and he carried with himletters of introduction 40 theprincipal authorities upon wirelessin the United States, includingmany of those actually conductingthe broadcasting organisations. Hewill have remarkable opportu-nities of making a thorough andilluminating investigation intoTransatlantic conditions, includingvisits to, such places as the laborar ,

tories of the Radio Corporation ofAmerica, The Western Electric Com-pany, The Bureau of Standards, andso propbses to give his con-.elusions in a series of articles which

In Search of First-handInformation

MR. HARRIS GOES TO AMERICA

0.0

4:4

4:4

4:4

4:4444:4

4:4

4:O

4:4404 4:44:44:4 4:.4:44:.+44:.+4:4.:":":":":":":":4+4:.4.:":":":44.:4 4:4 4:4

will appear exclusively inRadio Press publications, andthese should prove of verygreat interest.

SelecliyitySome of the investigations which

Mr. Harris will make will concernthe very vexed question of theselectivity of the average Americanreceiver, as to which Britishexperimenters have always haddoubts, although they have beenduly impressed by the very greatneed for selectivity under thecrowded conditions which appar-ently exist in many Americancentres.

In addition to obtaining generalimpressions of broadcasting condi-tions Mr. Harris will, of course,devote himself to investigationsinto the more technical matters,upon which his opinions will be sovaluable. In view of the presentincrease of interest in super -hetero-dyne receivers it is to be expected'that M will 'spend a good deal oftime in acquiring details bf thelatest American develoments .inthis field. - It has been arrangedthat he shall have opportunities ofhearing and making thorough testsupon all the leading types, includ-ing the latest modifications, whichare attracting so much attention inthe States.The American Home Constructor

An interesting sidelight shouldbe thrown by the articles ArichMr. Harris writes upon the waysand methods of the Americanhome constructor, who is to mostof us a somewhat mySteriousperson, for although the Americanmagazines give him a good dealof attention in the way of designsforsets and apparatus, they conveyvery little idea of his actualmethods and capabilities.

It is , no uncommon thing, forexample, to find a lengthy descrip-tion given of a quite_ complicatedreceiving set, without any otherassistance in wiring -up the set thana Simple circuit diagram, and one isleft to wonder whether their readers

844

are really capable of wiring upsuch a sets successfully withoutthe aid of the full wiring diagramto which we are accustomed.

ValvesOne of the lesser points to

claim his attention will be thecomparative characteristics ofBritish and American valves, andit will be particularly interestingto learn whether Mr. Harris fullyendorses the claims so often madefor the somewhat " soft " detectorvalves which have long been popu-lar in the United States.

The RouteWhen Mr. Harris leaves New

York he will make a carefully-planned tour, which will take in theimportant centres of the MiddleWest, working across to the PacificCoast, and finishing his investiga-tions in Canada.

Last moments at Waterloo. Didhis recklessness about the fasten-ing of the door result from theconsciousness that Radio Presshad insured him for the sum of

If3,000 ?

July, 1925 THE WIRELESS CONSTRUCTCS

PracticalWorkshop Hints

Starting Awkward Screws and,Nuts --Securing Vertical Panels-

Improving the Hand -drill--Shortening Screws

' Those Awkward ScrewsEVERY wireless constructor

comes across a screw placedin an awkward position,

which absolutely refuses to startwhen ordinary methods are used.The worst screw of all is thatplaced in an almost inaccessiblecorner, which has to be insertedupwards from below. One triesto balance it on the point ofthe screwdriver, and every time itfalls off just at the critical moment.If the screw has to be inserteddownwards, one can sometimesgive it the all important first turnby holding it in a pair of tweezers,but this is usually a difficult andan exasperating business. I havebeen using lately with great sticcess

A

Fig.pen

POINTS BENTSL ICHTL Y 0/Jr/YARDS..

I.-Showing how a rulingis prepared and used for

starting a screw.

a little tool specially made fordealing with screws in out of, theway corners, which will, I think,appeal to a large number of readers.It is a very simple thing to make,and the cost is only a few pence.All that you require is a cheapruling pen, which may be purchasedfrom any stationer's shop. Fig. IAshows how the tool is used whenfinished. As the points spring out-wards, they can be wedged firmlyinto the notch of the screw, whichthey hold tightly enough to allowit to be started in its threads. Thetool should not be used for drivinga screw right home if any force isrequired, as the blades of a rulingpen are made of metal which is sosoft that they will become bent

inset ationowis of the greatest importance in L.F. Transformers.Look at the G.R.C. 83. See the spacing of the terminals. Note

-the thickness of the polished erinoid top and base-and what youcan't see is the insulation of the bobbin-of the wire-between Thewindings (every layer is insulated)-the coil from case-the con-nections to leads-:and the leads to terminals.Every detail of the greatest importance in a Transformer whichmust stand up to a guaranteed service.

ONLYPROVIDES THIS GUARANTEE: -2 his Audio Ft quency Transformer has been most carefully testedbefore leaving our works, and is guaranteed for one year to !unctionefficiently if correctly used.

'MEIN EffiltAll\ft ER111101110- onwsweics FaOvsE 21 31 .5

Price 15/-

EAGIGron B40.104010,RECEIVER 00 CORI 000EIRTMEANS /WA, IT I .. TEIGIVG GIVE

COM FIVILItillf IN MM VP UMiFtwoQwwor Ammi., roatalai . a



LOUD

SPEAKER

Should you have anydifficulty in obtainingsame, write direct io

Messrs.

EDWD. E. ROSENand CO..

158-160, City RoadLondon, E.C.,

with the name of your 2716dealer.

Write for our illustrated Pamphlet,

"BREAK -NOT"BATTERY TESTER

THE IDEALHYDROMETER

FOR ALL WIRELESS

ACCUMULATORS.

716The "BREAKeNOT"HYDROMETER is therecognised standard ofquality in battery testers andshould be in the hands of

every user of an accumulator.Being packed in unbreakable car-ton the Break - Not is the onlyPractical instrument to keep in th3ool box without fear of damage.

Liberal Terms to the trade.

S. GUITERMAN & CO., LTD.35,6, Aldermanbury, London, E.C.2

Wireless Sets, Phones, Speakers,Parts, Easy Payments. Catalogue

free.WIRELESS DISTRIBUTING CO., LTD.,Wireless House, Stoke Newington Road, N.16

ELEOTRADIX RADIOSReduced Prices

"C" Valves, Air Force, low loss, 5", 6 for 24/, D.E.C. 12/-Wavemeters, 50/-, £4, £5 and £6 Morse Recorders.*6 10s. Wheatstone, *13. AltenLators, £3 103. ValveTransmitters, £3. Spark Sets, 136. R.A.F. Steel Masts,2/6 per 5 ft. run. Receivers . 2 -valve, 20, £2; 3 -valve,ilk. 4, £3; 5 -valve, £5103.; 7 valve Marconi, £8. Allprices less valves. itridges, .P.3 and £5 103. Res. Bones,multi -range standards, 1 to 2,000 ohms, 1376 to 50/-.Loud. Speakers, 19/- Ebonite Horns, A.C. Chargers,£4105. Charging Dynamos, £3. Marconi Rounds Valves-

Milliam meters, 201 and 25 -. Micro Ammeters, 651.A mp. and Voltmeters, all ranges. Ohmmeters, *10.Veiling Sets, £3 to £14. Condensers, L.T. to 10,000 v.1 to LW Call or write for new and enlarged catalogue.Post free, 4d.

LESLIE DIXON & Co., Ltd.9, Colonial Avenue, Nineties, E.1Buses pass the Door. Telephone-Avenue 4166

846

MA1 C

In reply

out of shape if strained at all.Once the screw has been given thehalf turn which usually sufficesto make it " bite " in the threads,an ordinary small screwdrivershould be used for tightening it up.To convert a ruling pen into ascrew starter proceed in the fol-lowing way : Cut off the points ofthe blades so that the ends leftare rather more than s in. in width,Trim up these ends square so thafwhen the pen rests upon them i'is quite vertical. With a smallfile flatten the curved outside ofeach blade. Now unscrew themilled nut and allow the bladesto spring away from each other.Take a small pair of flat -nosedpliers and give the end of each aslight outward bend, as seen at

Thwxact amount of bend

RC/Z.8'16 PEN

NUTFig. 2.-An awkward nut may be

started in a similar manner.

reqtkired will be found by. experi-ment. Keep on trying them in thenotch of a small screw and shapethem until they seat ;themselvesfirmly in it. Once the tool isfinished it will be found to be of thegreatest use.

A Nut StarterA second ruling pen may be

pressed into service for inaking alittle tool for starting nuts difficultto deal with in the ordinary way.It is not necessary here to cut offthe points of the' 'blades-, in factthey are better left as they are.Remove the clamping nut firstof all and let the blades spring wellapart. Then with a pair of smallflat -nosed pliers shape theni asshown in Fig. 2. A tool of thiskind made from an ordinary rulingpen will deal easily with nuts upto 4 B.A. To use the tool, insertthe nut between the blades and turndown the clamping screw until it isfirmly held. You can now intro-duce it without difficulty into themost Avkward corner and start itupon the threads of its screw, As

soon as it is started properly re-move the tool by pulling it off-it will come away quite easily-andfinish off the operation with a boxspanner or a pair of, nut pliers.The warning against using farcewith the converted ruling penapplies here also.

Fig. 3.-A very useful id:a.

Another UseYet a third use for the handy

ruling pen is shown in Fig. 3.When soldering is in progress itis often not easy to hold the wire inexactly the right position, particu-larly if it is of very fine gauge,without burning your fingers. Byclamping it between the blades ofa ruling pen, which in this caserequires no shaping or alterationwhatever, its end can be takenexactly to the place required, andit can be held without difficultyuntil the joint has been made witha small iron. I have found theruling pen employed in this wayespecially useful for one or two ofthose awkward soldering jobs whichcome one's way every now andthen. The first of these was tore -solder the lead from the " in "end of the primary winding of alow -frequency transformer to theshank of its terminal, from whichit had come adrift. Without thelittle tool the job would have beena very finnicky one, for the designof the transformer was such thatthere was no room to -use a pair ofpliers. As it was, the repair wasaccomplished in a few moments.

WOOD SCREWS

BASE BOARDFig. 4.-This forms a rigid support

for the panel.

I have used it also to the greatsaving of time and trouble for suchjobs as repairing a break in thewindings of a potentiometer andfor, re -soldering connections whichbut for its help could not havebeen done without dismantlino.''' atany rate part of the wiring of theset.

ng to advertisers, please mention ME 'WIRELESS CONSTRUCTOR.


Fixing Vertical PanelsA very large number of wireless

sets are now made on the lineswhich first originated in America,with a vertical panel carrying, as arule, only the variable condensersand the rheostats, and a horizontalbaseboardwhich supports the valves,transformers and other components.What is required is some simplemeans of fixing the panel to thebaseboard so that the two are atright angles to one another andare held firmly together. A simpleand extremely satisfactory methodof doing this is seen in Fig. 4. Herefixing is done by means of smallangle pieces such as are obtainablefrom any ironmonger for about2d. apiece. If by any chancethese are not in stock, the brackets

MECCANO STRIP.

c/SKWOOD SCREWS

BASE BOARD

Fig. 5.-A Meccano strip may beused instead of angle brackets.

used for holding stair rods willanswer quite well. With panelsup to 15 in. in length an anglepiece at each end will generally besufficient, though it is as well touse additional supports for panelsof greater length. The supports,again, may be.reinforced by drivingcountersunk wood screws front theface of the panel into the base-board at intervals of about 6 in.

Using Angle -bracketsThe best way of doing the work if

angle -brackets are used is, I think,as follows : First of all, fixthe brackets to the baseboard withwood screws, taking care to placethem so that they are parallel withthe short edges of the baSeboardand that the faces of the uprightportions are level with its front.Now place the baseboard on atable with a perfectly flat surface.Place the panel in position, gettinga friend to help you to hold it ifnecessary, and run the point of ascriber round each of the screwholes in the brackets so as toscratch small circles on the ebonite.It will be quite an easy matter tofind the approximate centres ofthese, which can be punch -markedand drilled. The panel should be

bolted on by means of countersunk4 B.A. screws and nuts. A secondway of fastening the panel and thebaseboard together is shown inFig. 5. Here the former' is firstfixed to the latter by means ofcountersunk wood screws spaced4 in. apart. The holes for theseshould be drilled or I in. from thebottom of the panel, according tothe thickness. of the baseboard.Lay the baseboard on a flat tableas before, place the panel inposition, and drive in, first, thescrews at either end. When allthe screws have been inserted, thesupports at either end can be madefrom Meccano strip suitably bent,as seen in the drawing. Eithermethod makes a very solid job,and there is very little to choosebetween them.

Improving the Hand DrillThe hand drill is a very useful

tool for wireless constructional work,but it has certain limitations. Itis not at all easy to do accuratework with it, for various reasons.Which of us, for example, using ahand. drill, can make half -a -dozenholes each absolutely at rightangles to the surface of the panel ?The usefulness of the hand drillcan be increased enormously bythe purchase of a bench attach-ment such as that seen in Fig. 6,which is by no means an expensive

addition to theworkshop out-fit. Excellentholders for thehand drill areobtainable atprices rangingfrom about15s. upwards.Besides mak-ing for accu-rate work, theuse of a benchattachmentresults in agreat saving oftime, especial-ly in caseswhere a largenumber ofholes of thesame size haveto be made inpanels. If agood drill viceis obtained atthe same time,the benchattachmentmakes it pos-

sible to drill long holes in brassor in other metals-a very difficultfeat with the hand drill unaided,since drills are so apt to bind andbreak. The hand drill used in theordinary way enables fairly good

Fig. 6.-A benchattachment for

the hand -drill.

eltACOMPONENTSProfusely illustrated sixteen -page CAT A."LOGUE just -out: If your dealer cannotgive you one send us 'a card with his nameand address to receive it direct FREE

and POST FREE.

EFFICIENCY AT A MODERATEPRICE WITH

goath DUPLEXCOILS

Compare our prices, arrd as! yourDealer to show you samples.

25, 1/6; 50, 2/0 ;100, 2/9 ; 175, 3/6 ;35, 1/9 ; 75, 2/3 ; 150, 3/0; :100, 3/9.

Postage 3d. each. Set post free,

LINK ACTIONBACK OF PANEL COIL

HOLDERMinimum capacity, all parts, evenscrew, of ebonite, best finish,

Price, 5/. each, -)ost 3d.If your dealer has not got them we send pos,free if you mention his nanfe and address

GOSWEL LENGINEERING Co., LTD12a. Pentonville Rd., Lonz!on, N.1Liberal Trade Terms. 'Phone: North 3051.

In replying to advertisers, please mention Tar WIRM.Itcs COWSTRTICTOR. 847

THE WIRELTZS CONSTRUCTOR July, 1925

THE MICROSTATFilament ResistanceGives that perfect filament control,which is so essential for the efficientworking of the receiver, with an infinitegraduation of resistance ranging fromzero to 100 ohms. A silky silent actionenables you to detect the faintestwhisper while adjusting. Experts areloud in their praises of the Microstat,and users are continually sending usletters which prove its efficiency in allessentials.

One Hole 'Fast Lock'Fixing email under -panel space. NoSoldering necessary.Cannot PackPRICE ONLYWhen purchasing, be sure to look for the PatentNo. 218523 clearly stamped cn each Microstat.

2/9

--CONTINEN-A' EL -LOW -LOSS

4eV74-E-E

THE superior features-a- of the CONTI-NENTAL Low -Loss areso pronounced that theexperienced operatorcan comprehend themat a glance. First, thegeneral design of theinstrument ensures me-chanical strength, rig,-ditY, extreme accuracyand long life. Mechan-ical perfection in theCONTINENTAL Low -Loss was attained onlyby the use of qualitymaterials, expert work-manship, and manyrigid inspections.

FROM a radio technician's viewpoint, the CONTI-NENTAL Low -Loss has all the advantages

necessary for use in high -frequency sets. Specialattention is called to the way in which losses were

reduced to a minimum. A pig-tail attachment ensures positivecontinuity in en tire rotor circuit.

'00025 23/6d. each00025 24/9d. each't005 26/6d. each'001.. . 31/3d. each'00025 with inde-pendent vernier 28/6d. each'00035 do. 30/- each'0005 do. 31/9d. each'001.. do. 36/9d. each

Midget Vernier, Ifsupplied separately

'000022 7/6d. each.

R. A. ROTHERMEL, LTD.24, 26:0 STREET,

NDON,D"

Burcleys 1208

MASTER OF

EVERY NOTE

LISTEN

-000tavor

$.

LISTEN TO REAL MUSICTO CLEAR UNDISTORTEDTO DO THIS-USE ONLY

LOEWE AUDION VALVESBRIGHT

EMITTER7 /- ON YOUR WIRELESS SET

VOICES

(The Valve with the Orange Ring) DULLEMITTER

12 /8

Ask your dealer for folder describing LoeweAUDION Long Distance Valves.

Every Loewe AUDION Valve Is guaranteed by the

AUDION RADIO CO., 52, Dorset Street, W.1(R. E. STICHLING, LTD.)

These Two Components Ensure Efficiencyand Save You Money

Fit this Interchangeable Fixed CondenserTHE "K" TUBULAR FIXED CONDENSER

BROS., LTD.

Embodies a new method of fixing. Only the clipsscrew to the panel, and capacities can be changedin 3 seconds without the use of tools, whichoften slip and damage your wiring. Nosoldering required-small underpanelspace and accurate capacity, un-affected by changing atmosphere.

0.001, 0.002, 0.003, 0.006,2 / - each.

0.0001, 0.0002, 0.0003, 0.0005,1/9 each.

Before purchasing any more components, send for ourILLUSTRATED FREE CATALOGUE.

It features many specialities designed to ensure efficient reliable working, andsave you money To quote a few-

B'. " Square Law Variable Condenser. Brass Parts for all purposes.Ideal Glass Accumulators. Pyramid High Tension Batteries.

Supra Transformers.Wales' products are sold by all discriminating Radio Dealers, who will willinglydemonstrate. We can supply carriage paid, but your Dealer's name must be

enclosed with order.

HEAD OFFICE:

12, 13 it 14, GT. QUEEN STREET, KINGSWAY, W.C.2'Phone : Gerrard 575-578. 'Grams: " Zywatesead, Westeent."

WORKS : LONDON, BIRMINGHAM & WEITCLIFF.

84S In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.

July, 1925 Tim WIRELESS CONSTRUCTOR

work to be done in ebonite up toin. in thickness. For thicker

ebonite or for brass a benchattachment is almost essential.Many hand drills, by the way, arefitted with chucks which will nottake drills larger than 4- in. Noteveryone knows that bigger chuckscan be purchased to fit many types.These are not expensive and theymuch increase the usefulness of thedrill since, when making up areceiving set or a piece of apparatus,one is frequently called upon todrill ff in. holes in order to mountrheostats, variable condensers,selector switches, and so on. Whena new drill is being purchased, careshould always be taken to see thatits chuck will take in. drills.

Shortening Screws

It often happens when one isengaged in constructional work thatit becomes necessary to shorten oneor more screws. You may, forinstance, wish to mount a low -frequency transformer or a fixedcondenser to the underside of thepanel by means of screws. If

in. ebonite is being used, i in.screws will be rather too long for thejob, for obviously their points tolook neat must be flhsh with thesurface of the panel. In theordinary way, to shorten onescrew by exactly the right amountand then to cut the others to jestthe same length is not an easy

o The " Comparison "o Crystal Receiver4.

(Concluded fronz page 816)

station is heard at theloudest. You may nowchange over to either of theother detectors, and com-pare the results obtained.It is best to adjust the con-denser after changing over.The pressure on the car-borundum crystal is ad-justed by raising or lower-ing the head of the forwardterminal, thus altering thepressure of the clock springon the crystal. Whenusing the carborundumdetector, the batteryswitch should be in the" on " position-thaton the left-hand stud-and the potentiometer ad-justed for best results.

To listen to the high -power station, at presentsituated at Chelmsford,

business. trequentiy, when rue.job is done, one or. two screwsprotrude a little from the panel,whilst others do not quite reachits surface. A further difficulty isthat, when the end of a screw iscut off with a hacksaw, the threadsare always slightly damaged, sothat it shows some reluctance tostart in the hole prepared for it.

HACKSAW cur

&AIDINGSCREW

SCREW TO BESHORTENED

JAWS OFVICE

Fig. 7. Showing the use of theblock for shortening screws.

For some time now I have beenusing a very handy little gadget.when screw -shortening becomesnecessary. This is seen in Fig. 7,and consists of a piece of brass ormild steel in. in thickness andabout in. in width by 2 in. inlength. About in. down from thetop of it a 4 B.A. hole is drilled andtapped. Quite close to the topanother 4 B.A. tapped hole is

the aerial lead is transferred tothe terminal A, the shortingstrap across the loading coil socketis removed, and a No. 15o coil in-serted. On rotating the variablecondenser the station will soon be

Showing the mounting of the coil andmanent detector.

the per -

made at right angles to the first,right through from edge to edge,to take the binding screwseen in the drawing. A hacksawcut is now made as shown, andthe thread cleared from the lefthand half of the binding -screw hole.The binding screw is inserted andthe tool is ready for use. Toshorten a screw, determine, first ofall, by measurement, the amountthat has to be cut off. Then drivethe screw into the metal untilthat amount protrudes. Lock it in

-position by means of the bindingscrew ; place the gadget in the jawsof the vide, and cut off the unwantedportion of the screw with the hack-saw. Trim up the end if necessarywith a fine file, slack off thebinding screw a little and removethe shortened screw. Any damagethat has been done to the threadswill be automatically set rightduring its withdrawal, and when ithas been slightly pointed with afine file it will start 'easily in thethreads prepared for it. By theuse of this little gadget screws canbe shortened accurately and quickly,and there is no difficulty at all ingetting as many as you may require,since this is the size used in ninety-nine cases out of a hundred inwireless work. If, however, youoccasionally use another size andrequire to shorten them, a similartapped hole, hacksaw cut andbinding screw may be made in theopposite end of the piece of metal.

1:1

picked up, provided, of course,that you are within crystal range.

On the short wave stations, withaperiodic aerial coupling, which isincorporated by joining the aerialto A1, and earth to E, the set will

be found to be very selec-tive, and therefore will be ofspecial interest to thosewho live in areas wherespark and other inter-ference is troublesome.'

As regards results, Lon-don at roughly 5 milesconies in at very goodstrength, be4ng audible in aquiet room about 2 ft.from the phones.

Chelmsford is also re-ceived at good strength,and there is no interferencewhatever from the shortwave station.

This receiver shouldprove very, useful to theman,who wishes -to find thebest in crystals, at the sametime having a receiver onhand by means of whichboth the long and shortwave stations may beheard with good selectivity.

C In replying, to advertisers,- please -mention THE WIRELESS, CONSTRUCTOR. 81a


Very little ebonite is used inthe construction

THE writer does not wish tosay that the present set isthe latest thing in

crysta: set design, but simplythat it works very well, and testedside by side against a well-knowncommercial receiver, beat thatmodel hands down. The receiveralso works much better than oneusing ordinary plug-in coils. Com-parisons were made by changingover the tuning systems of eachreceiver by means of a change-over switch, the same crystal andtelephones being used.

There is nothing new in thecircuit used, but the style ofconstruction differs from the usual.The set may, of course, be mountedin a cabinet of suitable design,the writer leaving this to thewants and inclinations of theconstructor.

The CoilsThe main features of the set

are, of course, the inductances.These are single -layer coils of

Fig. r.-The aerial coil is "tuned".by the slider.

fairly thick wire, spaced and wellinsulated. There are two coils,one within the other. The outsidecoil has fewer turns than the innercoil, and is used as a semi-aperiodicaerial inductance. When the re-ceiver was first built, this aerialcoil consisted of only fifteen turns,and it was -intended that this

A Low -LossCrystal Set

By W. H. FULLER

A description of a type ofcrystal receiver new to readers

of " The Wireless Constructor';

should not be altered, but ontest better signals were obtainedby tuning it-or rather, semi -tuning it-and it was then decidedto make the necessary alterationsto accomplish this conveniently.

Fig. r shows the circuit diagram,which may intetest the moreadvanced constructors. L1 is the

. toms ft/ ONE STR/P ONLY

58 Jars OtAPARTFri

ItlIJI11111111(4,-

1,7

8"11:11111,11,111111Cl

COUNTERJUNdr712 CLEAR WIRE

Fig. 2.- Showing how the ebonitestrips are cut.

aerial tuning coil, consisting of anumber of turns of thick wire,coupled to L2, also wound withthick wire. Across the latter- coilis placed the crystal and telephonesin the orthodox manner. No tele-phone condenser is used, as thiswas considered unnecessary, notthe slightest difference being noticed

__either in signal strength with'phones, or in current flow with amicro -ammeter in circuit.

ConstructionThe building of the receiver

should offer no difficulties to theconstructor of average ability ;the only point which may requireexplanation is the winding of thecoils, which should be built first.

Three discs of wood 3f in. indiameter are first required, andthese may be cut from a suitablepiece of wood about f in. thickwith a fretsaw.

Next cut four strips of ebonite8 in. long by j in. wide and f in.thick. On one of the narrowsides of each of these strips 58small slots are cut with a three -

850

Showing the position ofvariable condenser

the ,.%

cornered file. These grooves areto hold the wires in position whenplaced on the completed former.The ends of the strips are fileddown as shown in Fig. 2, so thatwood screws may secure the stripsto the wooden discs. In oue ofthe strips two holes are drilledin the side to which the ends ofthe wire are fixed.

The strips are then secured tothe wooden discs, one of the latterat each end and one in the middle,with wood screws. 1 -in. No. 4 brassscrews will be found suitable forthis joh.

Winding the CoilThe wire is first wound on a

temporary former, and the coilthen transferred to the properformer. The first coil is woundon a 33 -in. cardboard tube, afterthe wire has been made perfectlystraight. This may be done bydrawing the wire through a numberof holes drilled in a piece of wood.The wire should be wound on theformer as tightly as possible, and

PANEL

112

FORMER nASCS

7K2

Fig. 3.-Details of the framework.

evenly. There is no necessity tospace the wire. When 70 turnshave been wound on, cut thewire and slowly let it untwistitself, and slide it off the former.Carefully transfer it to the properformer, lifting each turn over

. the, grooves without straining thewire: Should the wire become

July, 1925

SUPER -HETERODYNE VII.Now on DemonstrationIs not a slavish copy of American

practice adapted to American con-ditions AND 'American VALVES, BUTIS exclusive in design, of maximumselectivity and power and includesthe following exclusive features :

1. Single control.2. All way -25 to 3,000 metres.3. Non -radiating.4. May be used as a"3 -valve"

regenerative for local work.

24 Curtis Super -Heterodyne VII.'s arebeing distributedamong 24 prominentRetail Distributorsfor demonstrationpurposes of CurtisSuper -HeterodyneComponents.

N.B.-Home constructors are warnedagainst the purchase of Americancomponents and others of hasty design,alleged to be suitable to British condi-tions. Your only safeguard is to witnessan actual demonstration of the com-ponents in a Receiver before purchase.

PETER CURTIS, Ltd.75, CAMDEN ROADLONDON, N.W. 1Telephone North 3112

NOTICE and WARNINGT has come to the knowledge of BurndeptI

Wireless Limited that working drawingsrelating to certain of their Patents have

been unlawfully produced in facsimile andare being sold to the public. The distinctivenumbers of such drawings are 335/4, 335/5and 335 /6.

Burndept Wireless Limited hceby givenotice that any person using any suchdrawings or any extract therefrom will renderthemselves liable to proceedings for infringe-ment of Copyright.

£100 REWARDBurndept Wireless Limited will pay a

Reward of £100 to the first person who givesinformation leading to the identification andconviction of the person or persons respon-sible for the abstraction of the originaldrawings and the reproduction and distribu-tion or sale of the facsimile copies,

May 19'h, 1925

LE3URNDEPTHead Office : Aldine House, BedEad Street, Strand, London, W.C2.


seT scamCIXING 5crcEw

PANEL-

DISTANCE PIECES

1111401111

,goottit11419bri NINVEMERNSI

NEET.--.0

Allj=1 UMCOO PLATE

ER,PROOTO FORF.XED

I STANCE PI etZ

-.=.

ToLESFVH news:H-... ".-------_______._:g

BOAR HYC-aaFARING--,. ----1

--r

I

T M i ...JAL. L USD0

4.40EC-, i-ocn NO FOR C1.11.4.0SKAF NO CVSH CO.T.1,aiN, SPIRAL

SPFH4D

3% 4-1 NC'

CR EWIre.EAR N

Study its Constructionand you will realise that its " straight-line "tuning and low loss claim cannot "be otherthan upheld by its performance. The IgranicSquare Law Variable Condenser is a deviceOf instrument precision embodying unusualrefinements. Compare these points withthose of your present condensers :1 Stout sheet brass plates specially

shaped for "straight-line" tuning.2 Negligible losses resulting from

perfect insulation in mountingof fixed plates.

3 Earthed rotor - positive earthobtained by connecting movingplates to frame by means of en- 6 Capacity range fromclosed hair - spring connection 55 micro-microfaradsthus eliminating tuning noises, to .0003 mf.

Ask your dealer to show you oneIGRANIC RADIO DEVICES INCLUDEHoneycomb Duolateral Coils, Variable Condensers,Fixed Condensers, Filament Rheostats, IntervalveTransformers, Variable Grid -Leaks, Variometers,Vario couplers, Coil Holders, Battery Potentio.met2rs, Vernier Tuning Devices, Sxitches, etc., etc.

All carry the 1GRANIC guaranteeWrite for List Z565

4 Ball bearing shaftgiving ease of move-ment and minuteadjustment.

5 Aluminium end-pl at es eliminatinghand capacity effects.

IG RAN ICELECTRIC

V411149, Queen Victoria Street

LONDONWORKS: BEDFORD

BIRMINGHAM: 73-74, GLASGOW:50, Welling- MANCHESTER: 30Exchange Buildings ton Street Cross Street

CARDIFF: Western LEEDS: Standard Build- NEWCASTLE: 90, Pil-Mail Chambers ings, City Square grim Street


THE WIREISS CONSTRUCTOR

TWO -TEN a TWO -ELEVENTransformers are producedunder new and advancedmanufacturng processes withsuch great uniformity thatthey can be supplied withindividual an,plificationcharts indicating exactlywhat may be expecte.l ofthem in actual operation.

raterfriegixe c sr TransformersTWO -TEN and TWO ELEVEN Transformers may be Type 40Ib. Transformer Unit, heretofore supplied foru ed In front one to four stages for operation at appioxi- :operation at 50 kilocycles, is now supplied to work atmutely 60 kilocycles with any standard tubes.the it -design 60 kilocycles, and employs two TWO -TEN and onebeing such than vitt int i011.1 in inte: -elect, ode cc/parity TWO -ELEVEN transformers, sealed in ae,aall,romi actof to rebut; tubes tont not offset the pus forniones of bias, container. Its eleetical characteristics are the/hi', system. The frequency of 60 kilocycles or 5,000 met, es nine as those of the individual transformers, but itsis ideal for in te niediate ampli ficati on in super -heterodyne mechanical construction Is much more compact. Suppliedcircuits, for it combines the extreme selectivity of short- in a brass ease, finished in black lacrider, with eachwave amplifiers with the high anipitieatlon and sensi- tramfornier indiv iduallyshielded. Site Viin.x2Rin.x-ifiin.tivity obtained at the longer waves. Price/CZ: 1: 9 each. Tyte b. Transformer Unit. Price Z 3 : 12:6

THE PORTABLE SUPER -II ET ERODYN E, by McMurdo Silver, Ass"' I.R.E.This bock, by a recognised authority on Soper -Heterodyne Receiving System., explains in detailthe Poriable and Laboratory Models of the S.M. Sneer -Heterodyne Receiver, Price 2/..

Ty pt. 40!1, R. A.ROTHERMEL9 .1 LONDONLtd 24/26, Maddox

-StreetW.1.,-

July, 1925

101a OSCILLATOR COUPLER.Sloth stator and rotor coils arewound with double green silkcovered wire upon genuine Bake-lite tubing. Will cover a wave-length range of 150 to 550 metreswhen both coils are shunted witha 0005 ofd. condenser.Price, with mounting lugsattached, 13/6.

Altrz #\Wlagialusic fioni the fkies

the GI I= PAY brings itout mall its Purity drone

READ THIS Royal College of ScienceDear Sirs-It may interest you to know that I have recently scientifically tested

your "GIL-RAY crystal. Its performance was truly extraordinary when testedboth electrically and on a Crystal Set. Prom its characteristic curves it would appearto be particularly useful in Reflex Circuits. Yours truly, L.C D.LC., A.I.C., etc.OUR GUARANTEE : We will gladly replace any crystal free of

charge that does not.eve entire satisfaction.Price 1 /6 each If unobtainable, please send 1f6 and name of

dealer to:-

1:RELESSCRYSTAL

it CRYSTALucnomsrscLosto1,,,.,.........-

GIL-RAY TRADING CORPORATION,SICILIAN HOUSE, SICILIAN AVENUE, LONDON, W.C.1

Tel.: Museum 3206 TRADE IMO:FRIES SOLICITED

en, dif

icientThe C A.V. TRANSFORHERwas designed by one who hashad great experience of high-fregnency currents. Mostcareful attention has been givento the impedence and capacityof windings, wits the result thatit makes possible the reproduc-tion of speech and music freefrom distortion.

Write for further parttruturs.

cayanderVell &Oar)ACTON VALE. LONDON W. 3.

Asti

First Stage (Blue seal)Second Stage (Red seal)

FAMAR DUTCH VALVES.REDUCTION IN PRICE.

FAMAR DUTCH VALVES are GUARANTEED to be theCHEAPEST, MOST RELIABLE AND MOST EFFICIENT

VALVES on the MARKET.Fil.

Type- Volts.AnodeVolts. Amps,Price.New

0.0 i DE 1-8 to 2-5 20 to.100 06) 10/9Power 3.5 to 4.0 100 to 200 0.5 4/6Detector 3-5 to 4-0 20 to 60 0.5 4/6

AmplifierR " 3-5 to -4-0 30 to 100 0.5 4/6

LIBERAL TRADE DISCOUNTS.Don't delay. Witte to -day. Buy from the actual Importers.Keenest Quotations to the Trade for all Wireless Components.

Write for Price List.H. D. ZEELLANDER, & CO..

St. John's House,126.127, Olnories, 1,011111141111, E.1'Phone : Avenue

ALVES repaired WenEACHPOSTFREE

441111M.18.101M111.111

We are actual makers of valves, therefore eve can repair and exhaust thevalve to give the necessary high vacuum. In fact we do this job so wellthat we guarantee:-Same Amplification. Same Radiation. Not to consume more current.Space won't permit of full price list here, but we'll gladly send you BOOKLETpost free on request. Here are prices for the most popular types of valves.Bright Emitters 5/- Dull Emitters, 2 and 3 volt types, 7/6 post free.

.1f your dealer is not alert enough to collect valves for RADIONrepair. send straight off to us with remittance and obtain real

prompt bervice.

RADIONS Ltd., BOLLINGTON, Near Macclesfield

5,,DULL EMITTERS 7 /62 & 3 Volt Type

Yost Free.

FREE 7100KL ET entitled " H wI long should my accumulator elm leI last ?" gives this information and

4,1.°w°. curves of RADION valves- high in6111111611611.116163111161111161111111111111111111111 I perform.nce, low in cost. Send Now !

252 replying to cuLertisers, please mention THE WIRELESS CONSTRUCTOR,

July, 1925

taut, give the, free end of the coilhalf a turn, which will release thewire. When all the turns are onthe former, (they, will look ratherhopeless for the moment), passone end of/ 'the 7 Wire through oneof the holes in the prepared strip,and bend the end round so thatthe wire will not pull through.With the fingers, lay the wire inthe grooves, taking up as muchslack as possible. When all theslots have wires in them, cut offthe excess and push the end ofthe wire through the other holein the strip. Now return to thebeginning of the coil and take upall the slack, working it towardsthe end of the coil. The excessshould be cut off and the end bentround to prevent the wire loosen-ing. This completes the secondarycoil. The aerial coil may now beproceeded with.

The Aerial CoilFour strips are cut and slotted

as were the first four, but these areonly 3i- in. long, and are slottedon both sides. Thirty slots oneach side are needed. Holes forfastening the wire are drilled inone of 'the' 'strips; similar to thosedrilled in the previouS strip.

These strips are 7.secured to thesecondary:: coil by sealing wax,which is sufficient to hold thestrips While the wire is beingwound. The strips should eachbe equ1/4distant from the ends of


the coil and immediately over' and the construction is now per -the lower strips. Only the smallest fectly straightforward. The coilsamount of wax should be used, and the panel a e mounted onand it should be applied as hot wooden strips in. by in., which

8"

Fig. 5. This view, shows how the ebonite panel ismounted on the wooden framework.

as possible, which will ensure agood fixing.

Forty turns of wire are nowwound on a 4i -in. former (thewriter used a custard tin), andthis is transferred to the former,in the same manner as the firstcoil The ends of the wire arepassed through the holes and allthe slack taken up and the endssecured.

This completes the inductances,Pt rot

NOTE - BACH OF PANELSHOWN IN r/0.5 POSITIONFOR CLEARNESS

Fig. 4.-A plan view of the set, with the front panel showndropped down in order that the wiring may easily be followed.

853

drilled and

may be either nailed or screwedtogether. Figs. ,3 and 4 show theframework. The panel is 2 in.by 8 in. by in. thick, and isdrilled as in Fig.. 5... -The panelshould be of ebonite guaranteedfree from leakage. The condenserused in the receiver is one of thenew low -loss condensers recentlyput on the market. by Messrs.Ormond. Engineering Co., and hasa maximum capacity of 0005nF,The model has a vernier fitted,which, though not essential, isuseful when a very small portionof the aerial coil is in use.

When all the components, etc.,have beta fitted to the panel itmay be secured to the frame bywood screws.

The Aerial SliderThe aerial slider contact is made

from a piece of springy brass strip3- in. wide. The end of this stripis.?; curved so that only one turnneed be touched. Two A. in.holes are drilled in the strip asshown in Fig. 6 (a) . The 'one inthe end is to pivot the strip, andthe other to hold a small eboniteknob. The writer used a " Clix "insulator. This is secured to thestrip with a in. 4 B.A.: screw.The strip is then bent to, the shapeshown at (b), and secured to thepanel by a 1- in. 4 B.A. screw tapped'into the edge. Should the con-structor not possess a tap to dethe job. with, a slightly smallerhole than the diameter of the screwMay be drilled in the ebonite andthe screw gradually worked intcthe hole.

WiringTo avoid any mistake being made

in the wiring, the following 'scheme


should be followed. Looking atthe front of the receiver, theaerial terminal A is connected tothe slider with a piece of thickflexible wire. The right-hand sideof the aerial inductance is con-nected to E, the earth terminal.The left-hand side of the secondaryinductance is joined to one sideof the crystal detector, and alsoto the fixed vanes of the variablecondenser; The other side of thecrystal detector is wired to the topterminal for the telephones. Thebottom telephone terminal is con-nected to the moving vanes, andthe right-hand side of the secondarycoil.

Using the ReceiverConnect the aerial to the aerial

terminal and the earth to theearth terminal. Join up the tele-phones to the telephone terminals.Place the aerial slider on the lefthand side of the coil, see that thecatwhisker is making contact withthe crystal, and turn the condenserdial. As soon as signals are heard,re -adjust the crystal and re -tunethe condenser. The aerial slider

should now be adjusted. Moving_this slider will alter the tuningslightly, and the condenser shouldbe adjusted each time the slideris moved. Signals may be ob-tained when only one turn of theaerial inductance is used. Theadjustment of the variable con -

a 0/X

-4" "of

6"

Fig. 6.-ow the sliding contactis made.

denser in this position is verycritical.

ResultsOn the writer's aerial the best

signals are obtained when fourteenturns of the aerial coil are used.The set has been tried on severalother aerials of different sizes, andgood results are usually obtained

between the twelfth and theeighteenth turn. On the higherwavelengths-5IT, etc.-the wholeof the aerial coil may have to beused.

List of Parts .

A list of parts and materialswhich are required to build thereceiver is here appended foi thebenefit of those amateurs who maywant to try. this type of crystalreceiver, and the writer feels surethat they will be amply repaid forthe time and trouble taken to build" Yet another Crystal Set ! "

One 0005a.F low -loss square -lawcondenser with vernier (OrmondEngineering Co., Ltd.).

Crystal detector (Burndept, Ltd.).Four 4 BA terminals.Two lbs. bare or tinned copper

wire, 16 S.W.G.9 inches of in. wide brass strip.Odd pieces of wood.One small knob.The 2 lbs. of wire specified is

rather in excess of the actualquantity needed, but the con-structor will, no doubt, find ause for the lengths that remain.

o Dry Cells forDull Emitters

(;)

x.OPOP00.O0PP000G.?00.0 00000000000000000xNOW that the warmer days

are coming round oncemore a good many con-

structors will be turning theirattention to making up portablesets both for outdoor use and fortaking away on holidays. Forthese sets the bright emitter valveis quite out of the question, sincethe accumulator necessary is soheavy and so liable to accidents.Fortunately we have in the dullemitter a valve which will enableus to do all that we want with thedry cell, which is comparativelylight in weight and contains noliquid electrolyte liable to damageclothes, carpets or furniture.

The Most Suitable Types"The two most suitable kinds of dull

emitter are the Wecovalve (or itsstandard 4 -pin equivalents) and the".o6s." The first require an E.M.F.of 1 volt or a little over, and havea consumption of .25 ampere. Sofar as the voltage is concerned, theyWare therefore within the powers ofa single dry cell. It should, how-ever, be remembered that a cur-rent of .25 ampere delivered con-

tinuously for any length of timethrows too great a strain upon acell of the size used ordinarily forworking electric bells. For even asingle valve set it is advisable toprovide a large dry cell, and if it isdesired to use two or three valves,each of them should have its ownfilament supply. This means thatthe dry cells required will mount upconsiderably in weight.

The 06 TypeFor anything bigger than a

single valve set it is, therefore,better to use the ":o6 " type.These require an E.M.F. of fromv5 to 3 volts, and are, therefore,within the compass in this respectof two new cells in series. As theircurrent consumption is only 6omilliamperes, even a pair of bellcells will heat the filaments of twoof them for some little time. Atwo -valve set can therefore be pro-vided with a couple of bell cells, oneof them being replaced by a newone as soon as the drop in voltagebecomes too great for properworking. For three -valve sets witha total filament consumption of

18 ampere it is best to use cells ofrather larger size, though bell cells,if of good make, will supply thisamount of current for some, littletime. R. W. H.

94

QU

A Reader's Resultswith V

the " A.A. Six" v

SIR, -I am writing to tell youthe results I have had on my" Anglo-American Six," designedby Mr. Percy W. Hatris. London,too yds. away on L.S. Birming-ham, about the satire. Glasgow,4o ft. away on L.S. Bournemouth,5o ft away on L.S. Cardiff, 5O It.away .on L.S.

I have also had Munster, Ham-burg, Leipzig at good L.S. strength.Koenigswftsterhausen comes inloud. Radio -Paris is also loud.I had all these stations on January18th and 19th. I also had Londonand Birmingham on 3 H.F. Det.with ro ft. of 16 gauge squarewire lying on the floor. I find theset very easy to tune. I use aBrown (large) L.S. I will writeagain shortly and tell you moreresults that I get.

Wishing you every success withyour publications in the future,

Yours truly,.'Oxford. R. G. 11. NASD.

854

July, 1925

" UTILITY"1.1th.

Wu"124

SWITCHESFor use in high frequency circuits. switchesmust have negligible self -capacity. 011re:-wise ssrious losses will result. The UtilityNO -CAPACITY hwit-h is suitable for allH. F. switching. Further, the contacts ares 'If -cleaning. Supplied either with leveror knob and pointer.

PRICESLEVER PATTERN

acit Pole CO. ..

C.O. .. .. 7 6

KNOB PATTERN. each2 Pole C.O. .

C.O. . . .. 6,-

WIR ELESSSPECIALITIES

CONDENSERSThe variable condenser illustrated is ofthe same type as that tested by theN.P.L., which gave the remarkable read-ing of .04 ohms resistance at 400 metres.The Utility Condenser is more than aLOW -LOSS instrument, it is practicallya NO -LOSS one. The use of a lever forthe vernier control gives afar finer adjust-ment than the more usual small eboniteknob. For accuracy anal efficiency, thecondenser you will eventually buy, sowhy not get one NOWT

PRICESSQUARE LAW OR ORDINARY

PATTERNCapacity each

.001 19/6.0005 10/6.0005 8/9

Vernier 2/6 extra.Fitted with Radian Dials.

Black Bronzed.Lever type nickel plated 6d. each extra.

Get a complete list of "Utility" compo-nents and prices by writing to day toWILKINS & WRIGHT

Utility WorksKENYON ST., BIRMINGHAMTel.: Central 2334 Tel Ad.: Utility, B'gliam." Utility " for Efficiency

l;arvdtasI 1.

The Aristociral o Loud. SpeakersACTUAL users cf the AMPLION, often after many disappointments

with other makes, assert most emphatically that no Loud Speakercompares with an AMPLION for tonal quality, clarity, and freedomfrom objectionable resonance cr distortion. The AMPLION is theoutcome of many years' striving for perfection by the originators ofthe Loud Speaker.

The

S

World' s

PLIONW ireless

Loud

Speaker

FOR " BETTER RADIO REPRODUCTION."p,oenreeR and ALFRE-) GRAHAM & COMPANY (E. A. GRAHAM)/l1,,,,,for;,,r,,r,: St. Andrew's Works, Crofton Park, London. S.E.4racemes.

THE WIRELESS CAN

PRICE:'0031 mfd. to '0015 mfd.

1/3 each.

'002 mfd. to '006 mfd.2/- each.

EQUAL COCALIBRATEDAPPARATUS

Faraday Houseprove this condenser efficient

How many components in the radio market to -daycould pass through stringent laboratory tests andemerge with a high percentage of efficiency?The THERLA Fixed Condenser is a radio componentthat has a definite 'guarantee of efficiency by labora-tory tests. In this respect, it is the first fixedcondenser to be offered to the radio public that isbacked by such a guarantee.Every THERLA Fixed Condenser is individuallytested by the laboratory of Faraday House and isguaranteed to be within very accurate limits of thestated capacity. This uniform capacity and thesuperior construction of the THERLA improves re-ception and renders it markedly free from noise.Therefore, when you need a Fixed Condenser, askfor the THERLA.

OBTAINABLE FROM YOUR DEALER.

igiito=E"t? /VP 4570.42

so'e SEL-EZI WIRELESS SUPPLY CO., LTD. Telephone:Distributors: 6, Creek St., London, W.I. & 2e, Old Haymarket, Liverpool Regent 1140.

Ii..73arclays11 8

NOW YOU CAN MAKETHE WONDER SET OF THE YEAR

Any amateur can build athome the most selectivewireless receiver ever in-vented ; a receiver that willbring in- most English andContinental Stations on aFrame Aerial. It is a Seven -Valve Instrument, simplycontrolled by only twoknobs, yet the reports ofthose who have made itshow - that it gives resultsequal to those obtained withsome nine -valve instruments

The Bowyer -Lowe Super -Heterodyne is the mostfascinating receiver yet in-vented. Six months' re-search .and simplificationare behind it, and as youturn a knob and hear stationafter station coming inclearly with pure volume,you feel as one of our

customers felt who said," Its power is only limitedby atmospherics." Startbuilding this wonder setfrom our new instructions.It is simply written so thatany amateur can wider -stand it. It contains FullSize Blueprints of Paneland Wiring, TheoreticalDiagram, Complete Instruc-tions with ProgressiveWiring Photographs, Hintson Soldering and LocatingFaults, Operating Hints,Specimen Log of Stationsand Log Chart. Indeedeverything that will helpyou to work successfully.

Moreover the FREE helpand personal advice of ourexperts is available to allwho start making the setaccording to instructions.

INSTRUCTIONS FOR BUILDING

THE BOWYER-LOWESEVEN -VALVE ALL BRITISH

SUPER -HETERODYNE 216Obtainable direct by post 2, 9 from

1 THE BOWYER-LOWE CO., LTD., LETCHWORTH

In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR: S55

k

THE WIRELESS COIN7E.iTRUCTOR

Summer eveningswith a town

UN a lead from your Set into the garden,and enjoy your Zrown Loud Speaker in thecool of the evening. Its mellow tone-free fromthe slightest trace of harshness or distortion-is adelight to everyone. Music and song are renderedin a manner which reflects even the personalitiesof the artistes thomselves.No other Loud Speaker can approach the 313rownfor truthful reproduction because none other canutilize its famous tuned reed principles which areprotected by patents throughout the world. Justas the famous 38COW11 A -type Headphones areadjudged the standard by which all others aremeasured, so 313r0W11 Loud Speakers are chosen bycritics as being the nearest approach to perfectionthat science and modern engineering practice haveyet evolved.The masterly combination of the tuned reed inconjunction with an aluminium diaphragm ofexceptional thinness results in a sensitiveness andtonal purity which have definitely placed theVW= Loud Speaker in a class by itself.

AVAILABLHI. 21 in. high120 ohms £5:5:0

2000 ohms £5:8:04000 ohms £5:10:0

E I N T HType Q

As illustrated£15:15:0

in all resistances

EE SIZES:11.2. 12 in. high120 ohms £2:5:0

2000 ohms £2:8:04000 ohms £2:10:0

S. G. BROWN, LTD., Victoria Road, N. Acton, W.3Showrooms:

19 MORTIMER ST.,LONDON,W.I15 MOORFIELDS, LIVERPOOL67 HIGH ST., SOUTHAMPTON

Headphones and Loud Speakers

Gilbert Ad. 2817

to advertisers, please menlion Tn WraELIPSS

July, 1925

MAKE YOUR OWN CABINETSWe supply timber cut to size and ready for

assembling to make wireless cabinets. Theparts flt accurately and make a well -finishedcabinet.

Any size and type of cabinet can he supplieq.Write and let us know what you require and we

shall be pleased to quote you.Only best timber used.Money back if not satisfied.

PRICES:' Cabinets made,Size. Parts. poi ished.6X8 1/9 3;-9 x 8 3/6 7,-

10x9 4/3 8/-12x10 /- 9/ -

Postage lid. extra. Only best oak or mahogany used.Sloping cabinets sOr, on Ol.se hriceS.

seas f.r illustrated bit.F. & J. FLETCHER, °relish Timber Yard,

Water Lane, Halifax, Yorks.

POSITIVE -GRIPPLUG AND SOCKET

Pat Applied fir #9248.51.25.ELECTRICALLY MECHANICALLY

PERFECT PERFECTRETAIL 67 PRICE

PLUG & SOCKET COMPLETE,

THE PERFECT TERMINAL

the accompanying il-lustration (enlarged) it willbe realised that we haveevolved a plug of unique

and distinctive design, elimina-ting the use of all small finikingcrews , and one that can be assem-bled in as little time as it hastaken to read this. The strandsof wire are turned back overthe cone section, which is insert-ed into the recess of the p'u tand clamped down by the inns-larcd sleeve, which holds it witha vice.lil:e grip. By this meansa positive connection it assured,and one that it is impossible tobreak. Designed to take thesmallest flex up to 5 m/m cable.Obtainable of your local dealer,or direct, from the Sole Manu-facturers and Patentees,

The LISENIN WIRELESS Co.la, EDGWARE ROAD, LONDON, W.2

Liberal Trade Discount

11111111111MIIIIMI

MORRIS SOLIDOAK STANDARDCABINET WITH

LOCKS,to lock up any setand batteries withpanel up to 36" X 18

Sent an approvalTrade supplied

Price carriage paidand packing free:

22" wide inside 24 152e £5 0

18 1.)

MAKERIMPYT GO.Wept. 25)

50a, Lord Street,LIV ERPOOL

858 In re frlying CONSTRUCTOR.,

July, 1925 THE WiRty,r,ss CONSTRUCTOR

SY,'i9yi Ali

Great New Radio. Press Laboratoriesffi

ffi

AN IMPORTANT ANNOUNCEMENT

ffi

rT

ffimisninENimffiFesimffiwifiwa_m%wmgaiyesmcm6F,FVERY reader of THE WIRE -

4 LESS CO:.:'STRITCTOR must bynow have realised that the

policy of Radio Press _Ltd. (pro-prietors of this Journal and ofModern Wireless and 'Wireless117eekly) is one marked by an ever-increasing .endeavour to secure-for readers the best in circuits andin set designs, the best and sound-eSt advice, and the best and mostup-to-date -information upon everybranch of the subject which providesso fascinating a hobby.

DependabilityOne of the characteristics of the

work of Radio Press Ltd. which hasplaced them in their unrivalledposition in -the world of wirelesspublishing, is undoubtedly thatfeature which may be expressedin the one word " dependability - :every _article, from a description ofan ambitions multi -valveset to one giving instruc-tions for making a simplecrystal set for the beginner,represents the outcome ofthe same painstaking pre-liminary design work, thesame striving after full andlucid description, and thesame care and accuracy inpreparing the article forpublication.

One of the recent stepstaken by Radio Press Ltd.to maintaivand still furtherincrease that feeling of confidencewhich every reader should have inhis journal and the sets describedtherein, was the establiShment of avery completely organised 'ServiceDepartment.

These are "some of the thingswhich have won Radio Tress 'Ltd.luindreds Of thousands of -supporters.The joint net circulations of theirthree journals approximate 400,000copies, and the sales of their non -periodical publications are of theorder of 500,000 per annum.

,Played, as they already are, in aunique position, Radio Press Ltd.are now taking advantage of thatposition to embark upon .an 'in-teresting new enterprise. To de-velop and consolidate their position

still further and to iherease theirprestige amongst the wireless publicof this -country and amongst themembers of the industry, they aresetting up laboratories at Elstreewhere .research -and developmentwork will be carried out for theexpress purpose of supplyingreaders of Radio Press periodicals,books, etc., with the best possibleinformation, the most recentdevelopments and the most effectiveset designs.

The scheme under which theselaboratories will be worked -will bethe:most ambitious which has everbeen undertaken by any -technicalpublishing house.

A recent portrait of Mr. ScoA-Taggart, taken inthe New Offices in Bush House.

Measurement and TestingIn addition to research and

development work, there will bedepartments for standardisationand measurement, for the testingand repairing of readers' sets (on alarger scale than hitherto), and

-for affording to the industry itselfsuch assistance as it may, of itsown accord, desire.

One of the -fundamental differ-ences between these laboratoriesand those of the commercial com-panies and the Government depart-ments will be that the organisationat. Elstree will exist chiefly for thepublication of the results of itswork. The Radio Press labora-tories are being established for the

express purpose of giving refidersthe full benefit of their investiga-tions, not, obviously, as a gratuitouspresentation to the public, hut asa very great inducement for thatpublic to purchase the publicationsof Radio Press Ltd.

Chief EngineerThe new organisation will, of

course, demand a large staff, 'andthe position of chief engineer willhave been observed to form thesubject of an announcement inthe advertisement pages of ModernWireless and -of Wireless TVeekly.This position, involving a totalremuneration in the neighbourhoodof -44,00o per annum, will be oneof the most responsible and highlypaid in British technical radio. Anumber of lower -grade vacanciesalso exist.

So far as can be judged in the earlystages of such an enterprise, the com-pletion of the main scheme of build-

ings will take three years.The work is beginning im-mediately, however, and -itis being planned so thatcertain sections will befinished speedily, and thelaboratories will begin theiroperations at a very earlydate. An almost -ideallocation at about twelvemiles from London hasbeen chosen, and the free-hold of seven acres of land

has-been acquired, in order that freedevelopment may -be assured inyears to come. The locality isreadily accessible, and it is proposedthat when the laboratories areworking fully they -shall be opento inspection by both readers andthe industry.

A great enterprise has beenlaunched, and will have a con-siderable effect on the whole trendof experimental work in thiscountry, and the Managing andTechnical Director of Radio Press

' Ltd. (Mr. John Scott -Taggart,F.Inst.P., A.M.I.E.E.) believes thatthe great expense (a sum of 420,000is allocated for preliminary ex-penses) will more than justifyitself in public support.

857

,THE WIRELESS CONSTRUCTOR July, 1925

.

111111111 11 111111 1 1 1, 1 I 1 41111111 111111111 1111 1 1 1111011111111N11

1

E

1

1

,

1

1

1

__ ---.--- ------------11 1

THE 1` STAY -SET" CRYSTALRECEIVER.

:-,-I feel I ought to dropyou a line in praise of one of yoursets. I refer to the " Stay -setCrystal R6ceiver," describedin your Mardi' CONSTRUCTOR' byMr. D. J. S."1-Iartt, B.S.:. It reallyis the best thing I have yet struck,and I have tried some dozens atleast. I made this set a month ago,and the adjustment of the crrundum detector still holds good.I find it as loud as many one -valvesets I have heard, and, as I -havesaid, it certainly gives more volumethan any crystal set I have comeacross, while its quality of receptionis beyond reproach.

The unique part about this setis, I think, its remarkable " stay -set " capabilitieS, and the followingincident made me decide to writeto you. One day I was using theChelmsford part of this Set, when'heard another band' (it turned 'outto be Radiola), and I wanted 'afriend to hear this, so I turned awayto get another pair of 'phones, for-getting I was already wearing apair: This pulled the set off mytable, and the whole contraptionfell a distance' of over three feet onto the floor with 'a crash. I wasmore annoyed because my panel isscrewed down, and I expected tohave to take it to pieces and re-make, but on connecting up againthe whole thing was exactly asbefore, except for a slight adjust-ment of the condenser. liven thisbang had not disturbed the detec-tor. I think all will agree this bearsout your claim for " Stay -set."

Yours thankfully,.H. McD °NAM).

Brockley,

A STRANGE AERIAL.SIR,-In the March WIRELESS

CONSTRUCTOR you ask for par-ticulars of a strange aerial. So farI haVe not seen a description ofone similar to my own, though nodoubt there may be many similarones already in use.

The P.O. telephone (desk type)is installed, and Shortly after 5XXcommenced I discovered that goodresults 'were Obtained by placing

a spring washer, to which a ,shortlength of flex was soldered, in theslot of the 'pin tarrying the Swivelmouthpiece of the 'phone, andconnecting the other end 'of theflex to. the aerial terminal of a'varibmeter 'crystal set.results were obtained by taking alead to the -aerial terminal from allypart of '-the metal casing 'of thephone, but the spring washermethod was adopted for con-venience.

Latterly I tried placing the'phone on a metal plate which wasscrewed down on a piece of teak,and having a wood screw terminalmaking contact with the plate.This terminal was used as an alter-native connection, but _ more in-ductance had to be added to bringsignal strength up to normal. Asthe bottom of the 'phone has arubber band projecting about -1, in.all round the circumference belowthe metal, the decrease in wave-length was no doubt due to theseries condenser effect in the aeriallead. This method is seldom used,as there is not quite sufficientinductance in the above set to give

results up to the first method, butthis could no doubt be 'remediedif need be.

In passing, I may add thatresults are all one could wish for. ona crystal set.

Hoping this may prove, of in-terest,

Yours truly, -

D. F. 'MCINTYRE.Glasgow-.

THE LOW -LOSS CRYSTALRECEIVER.

SIR,-Just a line to say I havemade the "Low -Loss" Crystal Setdescribed by Mr. Percy W. Harrisin your February issue, and findit gives much better results thanthe set we purchased, and becauseof the superior results we haveobtained, a few others have beeninduced to purchase the Journaland make up the set with equallysatisfactory results. We are sixmiles from the Dundee station.

Yours truly, '

P. KILCOUR.Moinfieth,

Forfarshire.

This " Twin -Valve " receiver was made by M:. Louis J. Collinswhilst in hospital. When visiting the hospital the Queen com-

plimented Mr. Collins on his excellent workmanship.


Nearly every Mail brings

LETTERS OFAPPRECIATION

and

REPEAT ORDERSAn indication of the best service one can

clf,r to their customers

YOUR CABINETHand made selected well -seasonedwood in Polished Mahogany, Oak, orWaxed Teak by highly skil ed crafts-men to your own particular design or

requirements

YOUR PANELHighest grade Ebonite only fully guaran-teed, free from surface leakage, cut to

your desired dimensions

INSURE PERFECT CONNECTIONSwith

RAN I AsAws I SOLDERResin -Cored

Galenite 2 -or Bow,: 1/3 pest free.CLEAN TO HANDLE. NON-CORROSITE

tINIVERSALLY USED

W. H. AGARManufacturer of Telephone & Radio Apparatus,

'19, Whitecross Place, Wilson Street, E.C.2Tel.: London Wall 3305 Est. 1912

rM AY

write Now ter FREE copy44,.. of the "Reliability Wire-pew- less Guide." complete Ref -

Crease Book. Trate

HTAY LOR 6 CO7 RADO HOuSEACAUL STI HUDDERSFIELD

Ii WIRELESS 0_CONSTRUCTORS

MEAN MELLOW MUSIC.The Power Equipment co Ird The thide,,Hendon.N.W.9.

Just out of reach -Because your hone leads are too short.A PHONEREEL

will allow you to move freely about the roomandtake your seat wherever ismostpleasant,no matter where the set is placed.

If yo a, possess a Loudspeaker this is aconvenient method of transporting it intothe garden or any room in the how e thatyou desire, the wire being rim out as youwalk along, free from knots and tangles.

Each Fhottercel carries Tour pairs of ter-minals and twelve yards of good quality

flexible twin wire.Price complete 15/- :Trade enquiries sol:cited"Fit a Phonereel

and listen inComfort"

J.MERRETT& Co.Trowbridge, Wilts.

COUPONQuestions &Answers

This coupon 'mat be ac-companied with a 2/6 P.O. andstamwd addressed envelope.

,6 WIRELESS CONSTRUCTOR"July, 1925.

Advertisement of Portable Utilities Co., Ltd., Fisher Street, London, IV' .C.1In replying to advertisers, please mention THE IVIRF,LESS CONSTRUCTOR,

Tiu WIRELESS CONSTRUCTOR July, 1925

Tools for the HomeConstructor

By JOHN UNDERDOWN

A group of useful tools for wirelesswork. A pair of round - nosed

pliers is seen on the right

THE choice of suitable toolsfor the home constructionof receiving and transmitting

sets is one of vital importance toall amateurs, and a. few words onthis subject will got come amiss.Reviewing the question generally,it will be seen that such tools fallinto' two groups -7 -namely, thosefor constructional work, and thosefor wiring.

Cpnstructional WorkDealing with the first group-

that is, tools used in construction-the first essential is some type ofhand -drill, and these are generallyobtainable at a reasonable price'somewhere in the nature of 7s. 6d.A suitable type is one taking drills -from the smallest up to about

or in. Used in con-junction with this, theminimum 'number of drillsI would advise any con-struetor to purchase con-sists of one each of No. 2,4 and 6 B.A. clearancedrills. These will be foundsuitable for the majorityof holes for terminals, etc.,whilst for the larger holes -such as for condensers,valve windows, etc., a con-venient method is to usea carpenter's brace, andeither the ordinary wooddrills ranging from I to

in., or in conjunction withthe brace a Clark's Expan-sive Bit, or some such de-vice, which will drill holesup to I in. in, diameter.Generally', however, forsuch holes as valve win-.doves a bit up to i in. is

- suitable, and an ordinary car-penter's type will do admirablyhere. It is merely necessary_ whendrilling boles with this type of bitto first drill a centre hole with a4 or 6.B.A. drill, and using this hole

A chat about the implements necessary to those who construct

their own wireless sets

as the centre, drill half through fromone side of the panel and finish fromthe reverse side.

ScribersWhere a blue print of the panel

for a set is not available for setting -out purposes, an ordinary car-penter's 6 in. square will be foundextremely useful. Used in con-junction with this for setting -outpurposes, I would recommend somefairly stout form of scriber, suchas that shown in the photograph,as with this the centres for thevarious holes may readily be made,thus eliminating the_ necessity fora centrepunch, the -use of whichgives rise to a certain amount ofnoise, often bringing disfavour onthe home constructor if the workis carried put in the evening. For

will be extremely useful. Thesemay be obtained in various typesand for very modest prices, andtheir accuracy and utility amplyrepay the small outlay.

Screwdrivers.Usually the only other really

necessary tools used duringassembly consist of a pair of fairlyheavy pliers and a long. screw-driver. It is well worth while toObtain a really good screwdriver,with a properly ground edge and acomfortable handle.

Tools for WiringUnder the heading of " Too:s

for Wiring " come a .pair ofsidecutting pliers such as seenin the Photograph, a long

pair of tin flat -nosedpliers, also seen in the

The Clark Expansive Bit is seen on the left, lyingacross the chuck of the hand -drill. In the fore-

ground are a scriber and a steel rule.

measuring the correct distancesbetween centres a 6 in. or i ft.steel rule should be used. Whereit is intended to use valve socketsand not some moulded type ofvalve holder, a drilling template

photograph, and a smallsmooth file. This latter isextremely useful in filingterminal shanks, &a., togive a really clean surfacefor soldering. If a type ofthree -cornered file, such asis used by carpenters forsharpening saws, is pur-chased, this will also befound extremely handy inslightly enlarging holes forcomponents of the onehole fixing type. A smallbrush is also extremelyhandy for brushing awaythe filings made, and forthis purpose a smallpainter's brush is useful,and one of the type shownin the photograph shouldbe obtained. Where anumber of wires are to be

taken under screws, such as. of, -con-densers, some types of rheostats',and: under transformer terminals, apair of round -nosed type pliers isuseful. These latter are, however,by no means essential.

660


GREAT

FREEGIFT(Value 20,'-)

To advertise the

(ALL BRITISH FRODUCTION)

Consumption, '06amp. at 3 volts.

The new '06 DEXTRAUDION VALVE is the bestdull emitter in the world to -day, and we want everyoneto know it. 'Po every purchaser of 3 Dextraudion Valveswho sends or brings this advertisement to us we will presenta pair of BROWN'S FEATHERWEIGHT 'phones,brand new, in sealed bcxes, value 20/-. Each valve is

carefully tested and we guarantee safe delivery.

ORYou can purchase through y sir local dealerand We trill arrange an- h hint accordingly.

ECONOMIC 'ELECTRIC, Ltd., 10, Fitzroy SquarePatentees and Manufacturers LONDON, W.1

Showrooms: 303, EUSTON ROAD, N.WA

TAPPED COILSThe imsking of a tapped coil is a difficult task for themost enthusiastic amateur, and it is well to purchasecomplete units, such as the Efesca series of tapped coils.In these the ideal has been attained in every respect -the winding is particularly accurate, each tapping -issoldered up to its corresponding stud, and the wholeunit is arranged for the Standard Efesca One:HoleMounting to the panel. The unit incorporates aswitch as an integral part and the tappings are so ar-ranged that there are no dead ends.

Ask your Wireless Dealer feT show you Efesca components,orwrite to us for Catalogue 522/11 describing Efesca Products.

EFE8 CA TUNED ANODE.An alternative method to H.F.-Trans,former Coupling.. Must be usedeiinjnnetion with a variable conden-iesof 0003- to :0005 mfd. Wave-lenzi lirange, 150 to -2,600 metres.with self-contained split switch, ku,,I,pointer sad scale, one -hole fiAng, 21

each.

Sold by all Wireless

Dealers and Electricians.

Wholesale only

FALK, STADELMANN & Co., LtdEfesca Electrical Works.

83-87, Farringdon Rd., LONDON, E.C.1VIA

NEIL

Aud at Blanchester, Glasgow and Birmingham

4%

-4a

EVERYTHING RIGHT

-won't have one unsoldered joint in the whole circuit.cany the good resolution out.Ask your Ironmonger or Hardware Dealer

FLUXITEIt is perfectly simple to use, and willlast for years in coastant use. Itcontains a special "small space"Soldering Iron with non -heatingmetal handle, a Pocket Blow -lamp,FLUME, solder, etc., and fullinstructions. Price 7/6. Write tous should you be unable to obtain it.

FLUXITESIMPLIFIES SOLDERINGAll Hardware and Ironmongery Stores sellFLUXITE in tins, price 801,1/4 &

Buy a Tin To -day!FLUXITE, LTD. Welt'. -3301.1WeAtil.nne'Works. Hotherhillie,N;E.Di

With FLIdh:11-1.. it is aneasy job to solder thewiring .of your home-made set.

'Soldered joints cannotgo, Wrong; they makeyour circuit one unbrokenpiece of wiring which younever need worry about.

Let FLUXITE helpyou to make a thoroughlygood job ,of your set. ItSI_MPL IFIESOLUERIAG - makes

it a job yon like to dobecause you're sure ofsuccess.

Reseliis now that vonFLUXITE will lielp you

to show you the neat little

SOLDERINGSET

Price 716

ANOTHER USE FOR .FLUXITEHardening Tools & Case Hardening

AS5 FOR LEAFLET cm i,,,prorect 7riCt hod;

" BETTER RECEPTION 71

is the unan mous opinion of Thousands of Satisfied Usersof the

"LOTUS" Cut GearedVernier COIL HOLDER

Vernier Movement,actuated by Three Sets

of Encased 'Precision'Cut Gears, representing,alteduction of 8 to 1.

Moving Block Cannot Fall."LOTUS" COIL. HOLDERS

are made frontBAKELITE MOULDINGS, with

Nickel -Plated Brass Parts.

Retail Two-way, 7,'-Se/lingPrice Three-way, 10 -6

Garnett, Whiteley & Co., Ltd.Lotus Works, Broadgreen Road, Liverpool

411

In replying to advertisers, please mention TIII; WIRELESS CONSTRUCTOR. -- 861


The Soldering IronPerhaps, however, the most essen-

tial tool for wiring is the solderingiron, to which very little attentionis usually paid. The most efficienttype the author has ever used isshown in the photograph. Thisconsists of a 3/ in. length of / in.round copper rod which is fixed toa 4 or 5 in. length of in. mildsteel and inserted in the usualwooden handle. The method offixing the round copper bar to thesteel rcd is by drilling and tappingthe former to take a 2 B.A. threadwhich is cut on the mild -steel rod.A 2 B.A. nut put on before thetopper bar and then tightenedback effectively holds the former inposition. ,The tapping of the copperbar is by no means an easy opera-tion for the amateur, as a lathe isaccessary. Where one is not avail-

able it will be well worth while tohave such an iron made by a pro-fessional.

The Tinned SurfaceThe most important part of the iron

is the surface, which is tinned. Thisis cut off at roughly an angle of6o deg., as shown, giving an ovalend. This should be thoroughlywell cleaned, and then covered withflux and the iron heated in the gas.The point should not be inserted in.the flame, but left clear andtouched with flux occasionally tokeep it from oxidising. When theiron has reached a sufficient heat,it touched with a stick of solder,with a certain amount of flux onthe end, this will run evenly overthe iron and give a wellItinnedsurface. An iron of this type willbe found extremely useful, and; by

The latest liner of the P. and 0. Company, the s.s. "Ranpura,".is well equipped with wireless gear. This photograph shows theinterior of the wireless cabin. The operator is seen adjusting

a waverneter.

having a long length of coppersuch as is used here, it will keep hotlunch longer than the usual typew ith. a short piece of copper andpointed, and will be found to give abeautifully rounded

. joint in' allcases. With this arrangement theiron need never have its tinnedsurface inserted in the gas flathe.

Taps and DiesThe previously mentioned tools

are all that are really essential ifthe constructor is to build. his setof bought' units: If, Imweyer, it.is desired to make ,certain gadgetsWhich., cannot be purchased, othertoolS will he necessary. In thislatter case I would advise that ahaekSaw taking .'blades .from 8 in.

' upwards, a vice with jaWs from2'in. to 4, in.; a. pair of shears for ,--cutting sheet metal, and. a numberof taps and dies .be purchased.

The most useful sizes for wireless,-work will be found to be 2, 4 and-6 B.A. for both the taps and dies.

253,180A striking testimony to the

appreciation accorded by the_ public. to the policy of Radio. Press, Ltd.,

is provided by the remarkablefigures q. oted above. The averagenet sales of THE WIRELESS CON-STRUCTOR for the six issues of aperiod ending on the 14th of Apr:Ihave been certified to be 253,180copies per issue, after deductingall free or returned copies.

It is evident that so great a circu-lation can only be based upon, asound foundation of se ice anddependability, and these figurestruly reflect that confidence whichis the natural outcome of theincreasing effort of the Radio Pressto provide always that which issoundest and best in information,in advice, and in -reliable set designs.

It requires little imagination tosee that the proprietors of a journalwhich equals the joint circulationof all the technical and semi -tech-nical publications of other firmsput together are in a position togive their readers advantages whichwould be impossible to any otherpublisher. The establishment of aService Department is a recentexample of the way in which thereaders of Radio Press publicationsbenefit by the strong positionachieved by the firm, and the latest

-development of the great labora-tories at Elstree is another proofthat Radio Press, Ltd., realise theirresponsibilities.

862


FROM ALL WIRELESS DEALERS.SOLE DISTRIBUTORS, United Kingdom:

THE WHOLESALE WIRELESS CO.,103, FARR1NGDON ROAD, LONDON, E.C.

Colonies and Dominions :

A. VANDAM, WESTMINSTOU ER,S LONDON, S.W.CAXTON HE,

A New " TURRET " 3 Teles:opic Aerial Mas'.10 ft. lloiste 1 as a Soft., with moving top se, tinColuntbian timber. All fittings. Ccmple.e, £2 18 9

Phone : Gerrard 2650.

SIMPSON & BLYTHE, 8-9, Sherwood St., Piccadilly,W

Dorwood Precision CondensersOTECTED.

..rd by Mr, PERCY W. It ARRI4, M.I.R.E., a.sistant Edit r ,o \v.;Maypage 423, ay 1925 and June 1925, also ' Wi: .sti , I

THE ONLY GRID CONDENSERHAVING 3 -POINT CONNECTIONFOR SERIES OR PARALLEL

COUPLING.No extra unit needed for this purpose.ILX PRICES,

11111 Capacities .000 ME. with or without Gard Leak Clip.00t to .106above .006 to .01

2G

46Please note .01 can be supplied with G.L. Clip if desired without,

extra charge. Other Capacities on applicat oa,

To be obtained through usual Wholesalers and Retailers,. r direct fiom theSole Manufacturers Post Free at List Prices,

hERBERT B WYE I & Co., la, Railey Mews, Leverton St., London, N.W.5

Through the Magnifying GlassA SILENT BACKGROUNDis essential ii long dis-tar ce reception is desired.'the use of a grid leakcontaining carbon isbound to produce a noisybackground. In a vari-able grid leak. especially.the resistance materialused must be constantin use.Ouch a variable grid leakC. the"BRETWOOD"GRID LEAKSu oessfully used and r,-c,nuncinital evengsc L: re.

SPECIALITIESare obtainablefrom mostWireless Dealers

TI the inexperienced eye a -variable gild leak isjust that and no more. Examine one througha powerful magnifying glass 11 wever and weSod tut vital facts.

Th.: cabon- pellet, impregnated paper or pencil Markgrid leak looks like so much coarse sand paper, andwhen current pates a minute arcing effect is noticed.This is s small as to be invisible except ruder thehighest nrgni fication. But as constant dripping wearsaway state so this arcing may ultimately consumeconsiderable portions of the leak material, renderingit inconstant in action and fina ly worthless. The useof such a leak produces a faint hissing noise thatspoils the, reception of weak signals.By fitting a "Bretwood" variable grid leak youeliminate all such possible disadvantages. The materialused is such that current flow is perfectly smooth anduninterrupted although it offs: s a high steady resistant, e.

Pric'e 3;-. Postage 3d.

BRETWOOD LIMITED12-18; LONDON MEWS. MAPLESTREET - - LONDON, W.

Barclays 1199

The New kM11:1-AccumulatorSpecially designed for Wireless

GUARANTEED TWELVE MONTHS.If you I e too far away to call and see theBatter] Mill your Order to us for thesise Son W0.11 t. We willingly retina

your money if you are disappointed.

6A031!PS8.0 11/0

VOLT .. 7 6 I 9 6 11 /61 14,-4 VOLT 15 - 18 6 22;- 25/66 VOLT .. 22 6 27 - 32/6 37/6

Packing 1/- extra Per battery.,1'.B. -Repairs to any make of

Battery in 24 hoursMAXEL ELECTRICAL 'Co. 28, Clipatone Street, Great

Portland Street, W. ITelephone: 111/s I,G Nf

OrOr

or

RADIO

Send fo.ue

PirmENIS

BUILD WITH

e " TANGENT " FITMENTSand get perf ct results.

They include: -" TANGENT " TUNING COILS" TANGENT " LOUD SPEAKERS" TANGENT " L.F. TRANSFORMERS" ILSCOL" B.F. TRANSFORM ES

GENT &Co ,Ltd., Works, Leicester

In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR,

......................................

.5

" Tangent" L.F Transformer.price 12 6; if with "tangent "

terminals 14 6

0 0863

41


SAVE 25 0'0

Get REAL EBONITE Coil Plugs for5,- per doz. (4/- gross lots.)Made of best tested materialsthroughout, theie Plugs offer theadvantages of nickel -plated sideplate contacts, baving- patent lip

lid ad. cctra for poataar ou sami.7,.

CECIL RIDLEY35 & 37 DUNDAS MEWSMIDDLESBROUGH

.

illim rhilri

4s141-aiii ,,imie ..' ,,'rillb- MIIIIIIIIII!IL-'1

%moo...,...,_,1

All.0,

-......6.-- 2.111166'....st.......Z5 ii,S.,_-.......n

4...,..,.......Pe.,, .9.= '

'...."-."- ....

Inn Pi .

CONTINUOUS RECEPTION3 in any p sit t it ;it all times. owl wg to tl 0,000 i Ni 116,4111of both m si and cu I swhisker, beiligalwais it 0,.nta..t.GUARANTEED TONE-VOLUME-PURITY.

1,166051. Nickel -plated, detachable, dust -proof cover.2. Special Harlie " supersensitive crystal.3. Ebonite wheel for rotating crystal. No fumbling

4 about adjusting, just turn the wheel-simplicityitself.

4. Catswhisker on slider for covering whole surfaceof crystal. Shockproof.

5. Nickel -plated sockets for panel mounting.Obtainable from all dealers or lire,' t. from Patenteeànd manufact urers. PRICE COMPLETE 3,6

in WI- tickle: the eryx'ut-It e

,.isional Palest 3371,1.53G ne rows T1...1. Terms. Tacplione Clissolil 5061.

HARLIE BROS., 36, WILTON ROAD,DALSTON, LONDON, E.8

SEND feudyosii sam maim sass =NM siase cam - sass

20s. today, together with your order for tie' Tony -phone,'and tills wonderful set, which receives all R. B.C. stations, willhedelittaredeomplete, including all accessories. You pay a fur.'they El each month afterwards. The total cost is only £15 so.,or, if you firefer. RI I is cash.

"TONTNIONE " Super 2 -ValvesComplete with ACeilMhi.t.'.It 7? llottorp, Aorthil, f pair4,000 ansalleadphottes, andCoo rcilmis-otte digit Ire.gummy and see bteC6106.All Rop,glticy paid.

Send today and enjoy broadcasting NOW

BRITISH ENGINEERING PRODUCTS CO.(Battery OW.) WINDSOR HOUSE VICTORIASTREET LONDON,S.W..al

wiew swam law so iiisso - MINIM MIMI sr. MOM

-00.g.4.0g_q0000000000.0000.0000-65-0.0.0.00.0.72- mm A Word to Advertisersmr4 Every reader of " Modern Wireless," " Wireless P4m Weekly" and "The Wireless Constructor" is a F2M Mpresent or potential buyer of wireless products.M A convincing advertisement in all or even one of mM these journals(which fully cover the radio public, m

beginner and expert aiike) will result in anm increased sale of your products. gim For rates and other particulars write, nM The AdVertisems.nt Manager, M

MM Barclays Advertising, Ltd. Ki

F2' Bush House, Strand, London, W.C.2 61Ki0 ES.11100000000000EZZIEZIORZ10000000000

THE PANELDE LUXE

r_OOD news travels apace-and it is not-.7- surprising, therefore, to find that wire-less enthusiasts are gladly paying the fewshillings extra for Radion Panels. Alreddythey have realised that at a Very small extracost they can insure azainst surface leakage andall the deadly ills to which cheap ebonite is prone.

Radian is available in 2X different sizes inblack and inahoganite. Radian can also besupplied in any special size. Black ad. persquare inch,mahoganite ald,per squareinch:

DION TradeMark

American Hard Rubber Company (Britain) Ltd.Head OAT ; 13a Fore Street, Depots: rzo Wellington Street, Glasgow.

116 Snow Hill, Birmingham.London, E.C. z Irish Agents: 8 Corporation Street, Belfast

G.A. 2834

DIAL INDICATORSAs used on 'Radio

Press SetsPRICE 9d. PAIR

RHEOSTA;71for Portable Sets

New design made to take up littleSpace Separate control tor each valve.Numbered indications. Black finish.

I way size, 1 r X 3"....Price 3/6 each2 way 11' X 3'.... 7/-3 way 2" x3".... 1 0 / 6

Resistance 25 ohms each.Fro -m all Dealers, or if,.noble to supply. urile to

AULGiAl 4 Go2-ii.cuaSiVaa ST

ITEL HOLBORN 2072. CIMMCfililY WINE 101I. ,,

---111111"1411101111"1"....ri-

EFFICIENCY without EXPENSE!Low -Loss Square -Law ,Condensers, which Cost No More

than the ordinary mouels.'Inc fact word in design, Wqrkinanship an,d rffieioncy. A,

illustrated or With Ebonite End -Plates as dewred,Prises. (including Dials and Knobs);

Maximum Capacity. Without Vernier. With VernierOXON nit ,. 7/8 11/90.0005 mf. .. .. 5'8 10;3C.0003 inf. .. .. 4/9 9'30.0002 mf. .. .. .. 365 -plate Vernier .. .. .. 3/-3 -plate Vernier .. .. .. 2/3

Poslage, 0'C, lid. cam.. ONE -HOLE FIRING COMPONENTS. --

. (Prices include D al and.linob.)Filament Rheostat, 5 ohms. 119; Millistat," 50 ohins,for Dull Emitters, 2/-; Potentiometer, 350 olunS, 26;variable Grid Leak, '5 to 6 megolams, Ifs; Variable

Anode Resistance, 50,000 to 100,000 Ohl., 21-.Pos:ag, extra on above, 3d.

Above components cannot pack., as no carbon discs, granules or555.468 fluids are used in their construction.

SCIENTIFIC SLIPPY -AV' STORES80, Newington Causeway, London, SZ. 1 'Phone: flop 4177. .

Branches -126, Newington Causeway, S.E.1; 7, St. Georges Circus, S.E.1 : 16, Nanette StreakCharing Cross Road. W1; `:07, Edgware Read, W.2; Si, Church Read, tipper Norwood. S,E,25.

a -

861 In rep/y/1/g to ackertisers, please mention Tun WIRM,F,SS CONSTRI,CTOR;

lea

July, 192:5

per 10 ft. coil

reduction in theprice of 10 it. coils

GL TITE,,jThe price of GLAZITE in 10 ft. (1/18 S.W.G.)

coils has been reduced from 1/6 to 1/2 per coil.Already recognised as an important improvementin circuit wirir,g,GLAZ IT E is now actually cheaperthan the old method employing insulating sleeving.

Wireless constructo:s everywhe-e quickly realisedthe superiority of " Glazite," resulting in a hugedemand. Increased output has resulted in se;duction in cost of manufacture, and wirelessconstructo -s everywhere now have the benefit-.

"Glazite" cons'sts of tinned copper wire firstcove.ed with cotton and then with a film of heavyinsulating material. Flame -proof and damp-proof," Glaz:te cannot deteriorate in use. It is alsoflexible and has a high d'electr:c strength.

"GLAZITE' NOW PACKED IN 2 FEET LENGTHS(1 /16 S.W.G.) for the convenience of amateurs constructingone- or two -valve sets, four lengths in an envelope (onelength of each red, blue, yellow and black). Price 1 /- per packet

Our mark is a guarantee of quality

The LONDON ELECTRIC WIRE CO.AND SMITHS LTD.

(Makers of Electric Wire for over forty years)

Piayhouse Yard, Golden Lane, London, E.C.1Telegrams : t lectric, London. Telephone : Clerkenwel, 1383, 1389, 1390, 1391

011111011%.11141101111111.11111111.1111111011111°D

TI -12 WIRELESS CONSTRUCTOR

Don't letHAND

CAPACITYSpoil your Reception

You can stop that squealing and howling by fittinga " Fulstop " Variable Condenser. A "Fulstop "condenser is positively guaranteed to cut out allhand capacity noises and your money will bereturned in full if it does not do this and give youevery satisfaction. A " Fulstop " is not merelya square law condenser, but has many distinctimprovements worthy of note. The dial isgraduated over the complete circumference andis geared at two to one in relation to the movingplates, thereby allowing great accuracy of tuningto be obtained and being specially suitable foroperating on critical circuits. Every day we arehearing from " Fulstop " users claiming won-derful improvements in reception. Have youfitted a " Fulstop " yet ?

Protected throughout the World001 ... 13/6 0003 ... 10/3'0005 ... 11/3 '0002 ... 9/6Stocked by most Wireless Dealers, hut if you have any

difficulty in obtaining write to:

J. H. NAYLOR, LTD., WIGAN

VARIABLE CONDENSER

In replying to advertisers, please mention TIM WIRaESS CONSTRUCTott. 865

bow


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COMPONENTS tor PERMANENT RE -LIABILITYFinston Fixed and Variable Square Law condensers and Variometers

TI,e Finston Fixea Condenser was the Seat' one hole -fixing condenser put...on themarket and itis guaranteed within 5 p.c.of stated capacity; no wax is used, therefore climatic conditions haveno ill effects ituonit. Buy one. Test one. It will prove our statement& and thoroughly satisfy you,CAPACITIES: .0001 to .0O2 .. price 2/- etch. Aim to .006 ., price 2.6 each.

If Your dealer cannot supply Finston Components, send -yourorder to us together with his name and address, please /

LIGHTING SUPPLIES CO., 2, Finsbury Avenue, London, E.G. 2.

Barclays in -is

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Post Office i. one of them

HAVE YOUR BATTERY REBUILTWe guarantee it for 6 months on Money Back 're: me

EXAMPLEof cost ofre -plating'with n wPOSSTIVE, 4 volts 9/ -and I or newNEGATIVEPLATESthroughout,separators,case repairs,terminals, etc.

A MP-i10

12/ 14/6

6 volts 13 15;'6 18/6

Carriage Paid HorneDELIVERY THREE DAYS

Ai' will giveyo ii -crap leadallowance 'onBattories -Taitefficient repair

Nof?.-Pricesshown areMaximum.Lego eqn ice -mutts at apptox-twat,. y less rates

SERVICEBATTERY COOT,trpoPRPERILAMNADRSYTLREEBEOTNELSONTRDEOENT,w

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All the year round-from January to Deeemlwr,we are supplying every known radio component bopost trial a 24 HOUR SERVICEUse the Order Form in this issue-and besure you will get A SQUARE DEALYour Satisfaction is our Recommendation.

THE BRIGHTON RADIO STORES163, Western Road, Brighton

1925-6 New 90 page Catalogue jusi, reinly-pot free. WANT ONE?

July, 1925

BOOKSThe choice of your radio literature is important. AllRadio Press publications are written by Wireless

Experts.Price. Post

Free.1 Wireless for All '9d. 11d.

By John Scott -Taggart, F.Inst.P., A.M.I.E.E.2 Simplified -Wireless 1;-- 1 2

By John Scott -Taggart, F.Inst.P., A .M.1.E.E.3 How to Make Your Own Broadcast Receiver - 1 '6 1,'8

By John ,Scott -Taggart, l'.1 nst.P., A.M.I.E.E.4 How to Erect Your Wireless Aerial .. 1,- 1,2

By B. 3littell, A.M.I.E. E.5 The Construction of Wireless Receiving Apparatus 1,6 1,8

By P. D. fryers.6 The Construction of Crystal Receivers .. 1;6 1;8

By Alan L, M. Doaglas.7 How to Make a " Unit " Wireless Receiver 2,6 2,8

By E. Redpath.8 Pictorial Wireless Circuits 1'6 1,'8

By Oswald J. Rankin.9 Wireless Valves S imply Explained .. 26 2'3

By John Scott -Taggart, F.Inst.P., A.31.I.E.E,10 Practical Wireless Valve Circuits .. 2:6 28

By John ,Scott -Taggart, E.Inst.P., A.M.1.E.E.12 Radio Valves and How to Use Them 26 2,'8

By John. Scott -Taggart, A.M.I.E.E.13 500 Wireless Questions Answered 26 2,8

By 0. P. Kendall, B.Sc., and E. Redpath.14 Twelve Tested Wireless Sets .. 26 28

By Percy W. Harris, M.I.R.E.15 More Practical Valve Circuits.. 3/10

By John Scott -Taggart, F.Inst.P., A.M.I.E.E.16 Home -Built Wireless Components .. 26 2'817 Wireless Sets for Home Constructors.. 2,6 2,8

By E. Redyath,18 Tuning Coils and How to Wind Them 1,6 18

By G. P. Kendall, B.Sc.21 Six Simple Sets- .. 1'6 1 8

By Stanley 0. Rattee, M.I.R.E.22 Switches in Wireless Circuits.. 16 1,8

By Oswald J. Rankin.24 Wireless Faults and -How to Find Them 1,'6 1,8

By R. 11". Hallows, M.A.Elementary Text -Book on Wireless Vacuum Tubes 10j - 10,6

By John Scott -Taggart, F.Inst.P., A.M.I.E.E.

RADIO PRESS ENVELOPES Price.1 How to Build an ST100 Receiver..

By John Scott-7'aggart, A.M.I.E.E.2 How to Build a 4 -Valve Receiver 2,6

By Percy W. Harris, M.I.R.E.3 How to Build the " Simplicity " 3 -Valve Set .. 2 5

By G. P. Kendall, B.Sc.4 How to Build the" All -Concert de Luxe" Receiver 26

By Percy W. Harris, 31 I.R.E.

PostFre?.1/9

2/9

2'9

2:9

5 How to Build the " Omni'' ReceiverBy John ,Scott -Taggart, F.Inst. P. ,A.M.I ,E.E'.

2.6 2, 9

6 How to Build the ABC Wave TrapBy 0. P. Kendall, B,S'e.

1/6 1/9

7 How to Build a 2 -Valve Amplifier de LuxeBy Herbert K. Simpson.

1/6 1/9

8 How to Make a 1 -Valve Reflex Receiver-By Herbert K. Simpson.

1/6 1,9

9 How to Build an Efficient Single -Valve SetBy Herbert K. Simpson.

1/6 1;9

All the above Boaks and Envelopes are obtainable fromall Bookstalls, Newsagents and Wireless Dealers, or direct

from Dept. W, Radio Press, Ltd.

1Ra0i0 11)re6.43, Vb.BUSH HOUSE, STRAND, LONDON, W.C.2

Barclays

866 lit replying to adi'ertisers, Please mention THE VIRELESS CONSTRUCTOR.


1 11 1 1 1111111111 1 11 1 1111 8 1 1111111111111 11

.11

1 1111 I

ROOF?111

r-

The " ATLAS " SQUARE LAW LOW LOSSVARIABLE CONDENSER is the latest additionto a distinguished range of first-rate components.It has been months " on the way," but now it isavailable it is the lowest of low loss " square laws"-a masterpiece of skilled craftsmanship anddesign.

Proof of the remarkable performance under severetest conditions is given in the report of the National'Physical Laboratory. Here are a few of the out-standing features of Clarke's " ATLAS SquareLaw Low Loss Condenser.

As the fixed vanes are insulated from the. movingones by means of ebonite tubes of small crosssectional area, placed outside the electrostaticfield, the lowest dielectric losses result. Lossesare further reduced by the end plaques, which,instead of being Z' full," are " cut -away." Its Zerocapacity is negligible. High -frequency resistanceis reduced to a minimum. It has a low phaseangle difference and power factor. The rotor, beinggrounded to the frame, gives freedom from hand -capacity effects. It gives straight-line tuning-( f course.

PRICES :

ooi 13 /6 0003, 11 1-

-0002-5 12 /3 -00025 10 ,'9

0005 11/6 -0002. 10,6

H. CLARKE & CO. (MAO LTD.Radio Engineers, ATLAS WORKS,OLD TRAFFORD, MANCHESTER.

REPORT.

Variable Air Condenser. (marked Vests, Atlas).

MeSare.11. Clarke 6 Co.. (tanobeete:) Ilmited.

The effective series reeistance of the condense:....

...tree at a frequency of I COO kilocycles per easeae stet R.

condenser 4C7 at its earls.= capacity.

The effective eyries resistance sae 'o -w4 Ss Es lees

ttar. 0.1 Obas.

Aral

Type AProv. PatentNo. 5030j25

Q{Lyini=1V0 99

TletikRadio Specialities

In replying to aciceriisers, please inenlio;z THE: WIRELESS CONSTRUCTOR. 867


A Reflex Loud Speaker Setin which no crystal is employedThe undermentioned are a few of the striking features of the" Twin Valve " Loud Speaker Receiver, full constructionaldetails of which are given in the latest Radio Press Envelope.

i. Will operate a Loud Speaker at distances up to 25 Milesfrom the local station, with an aer;a1 system of averageefficiency.

2. Only two valves are utilised. Either Bright Emittersor Dull Emitters cm be used.

3. No crystal is employed. The set, therefore, willmaintain a given adjustment indefinitely.

With the assistance of Radio Press Envelope No. to you willfind it an easy matter to construct this wonderful receiver:The Envelope contains, -as usual, every possible detail.It contains :--

Two full-size blue prints.Three sheets of reproductions of photographs on

art paper.Three sheets of working drawings.Five sheets of instructions.

You cannot go wrong, even if you have never built a set before,so explicit and full are the instructions, and so helpftil are thespecial progressive wiring diagrams. ..

The "Twin -Valve" Loud Speaker Receiver has been designedby John Scott -Taggart, M.C., F.Iust.P., Editor of" WirelesS Weekly " and of " Modern ireless," originator of -the renowned S.T.ioo circuit, and author of many technical''best sellei-s."

RADIO PRESS ENVELOPE No. 10You can order this envelope from all Bookstalls, Newsagents,and Wireless Dealers. Price 2'6. Or 2/9 post free, directfrom Dept. W, Radio Press, Ltd. To be published June 20th.

Radio Press, Ltd.,Bush House, Strand, London, W.C.2.

July, 1925


July, 1925 THE WIRELESS CONSrRUCTOR

CABINETS CABINETS

WRITE AT ONCE feuirdnuertsii,luosrtrraatglissettsof 1LiOcOluvgirnigetiiensanovf

described in "MODERN WIRELESS," "WIRELESS WEEKLY,"and " WIRELESS CONSTRUCTOR," etc., or 'phone Clerkenwell 6903

NAME

(ADDRESS

writein

BlockLettersPlease

sit along here and post in unsealed envelope bearing ld. stamp.TRADE ENQUIRIES ESPECIALLY INVITED.

CARRINGTON MANUFACTURING CO., LTD.18 20, nicrmans Buildings, Mitchell St., Central St., E.C.1

The BRONEL PERMANENT DETECTOR¶THE BRONEL PERMANENT 'THERE IS NOTHING

DETECTOR IS ABSOLUTELY TO AD JUST AND IT& DEFINITELY PERMANENT IS ALWAYS SET

FITTEDwith adjustable

screw whi h gives I'extension, thus allowing

it to ba fitted too xistiag

5 YEARS SOLIDGUARANTEE

From all Wireless Dealersor post free from --Wm. R. BOWMAN

LTD.47, MARK LANELONDON, E.0 3

Barclays 1190

AusilesseWHY SPEND MONEYON EXPENSIVE COILSwhen yoi can wind them yourself on the

WESTMINSTER"

..... .

adjustable coil winder and cavepounds ? You can make coils ofany size or weave on this machine.

PRICE 4/- FreePost

THEWESTMINSTER

VALVE HOLDERFOR

Under Panel MountingSafeguards your valves fromaccidental shorting of fila-merits with H.T. Neat inappearance, efficient inworking. Capacity effectsreduced to a minimum.Price 9d. post free

If your local retailer cannot supply you, orderdirect and send his name and address toWATSON, JONES & Co.

6, ST. STEPHEN'S HOUSEVictoria Embankment, London, S.W.1Wholesale only-Liberal discounts to trade. 'Phone : VICTORIA 7571

LThe L.E.S.EARTHTUBE

SIZE

Length 2' 6Diameter I"

441sonnmmammll.

ICESObtain oblefrom all dealers

PRICE/ 7/6Post Free 8:'6

THE L.E.S. EARTH TUBE ismade of thick copper, with ascrew casting at one end to facili-

tate driving it into the ground. Ithas heavy brass screw and washer formaking perfect contact with earthwire.Tne funnel top and holes drilled inthe tube enable one to keep the -

earth moist and so secure efficientreception at all times.

pi!! DON STREET, HAYMARKET, SAVALONDON ELECTRIC STORES, LTD., . Regent 5.505 and 55013

ff,f,-Pivs 1200

THE " SECURITY " VALVE HOLDER(Pron. Pat. No. 2187,25).

ANTI -CAPACITYPROTECTS THE VALVE

METAL DRILLINGTEMPLATE Included.

OBTAINABLEFROM ALLRETAILERS & FACTORS.

MP,

Advert. ofWilliams, Ellis & Co.. London.

ea.,,ecar..2;

.501.0.11'2

SOLDERED JOINTS SUPERSEDED !You can easily connect tin the most complicated setentirely without use of solder, ssilh the PATENT

"KRISCROS"CONNECTORS

Kriscros Co., 5O, Gray's Inn

Strong and perfectjoints. Used by Mr.Percy W. Harris andother leadingexperts.A "Kriscros"forevery standardthread. No Solder.Prices :1/610 r. per dos.

Seed for List.

Road, W.C.1

In replyEng to adverfisers, please mention THE WIRELESS CoNsTRucToR, s.C,)

TIM WIRRLESS CONSTRUCTOR

A

July, 1921

New Radio Press Envelope

Radio PressEnvelope No. 11.

" AnAdaptable

CrystalSet"

Price 1/6Post Free 1 /9

1

To be publishedJUNE 20th.

You must buildthis wonderfulCrystal Set

A special feature of the " Adaptable Crystal Set "by Percy -W. -Barris; M.I.R.E., Editor 'of ' TheWireless Constructor," is the adaptability tovarying earth and aerial conditions.By means of a specially tapped efficient inductanceplaeed inside the cabinet it is possible to makethe set match with any aerial in a few moments.In the case of the auto -coupled circuit used inthis set, this results in appreciably louder signalsand the set :is,capable of receiving 5XX, with theaid of a loading coil, within reasonable range, inaddition to your local station; provided your aerialand earth systems are of average efficiency.

Full instructions for the building of this uniquereceiver are contained in Radio Press EnvelopeNo. 11.

Radio Press Envelope No. 11 contains the fullestinstructions for building -the set, with blue printsof the wiring and panel layout, reproductions ofphotographs and working drawings:

You can order Radio Press Envelope No. 11 from all newsagents,Booksellers, your local wireless dealer or direct from Dept. W,

'Pablo tress,BUSH HOUSE, STRAND, LONDON, W.C.2.

d.arclays



CRACKLING?Do you get crackling inyour radio reception ?Refuse to have this dis-turbance any longer. TheRadiotester willfind the troubleimmediately !

NO MOREWIRELESS

PERPLEXITIES

PRICECOMPLETE

6/9POSTFREE

Is every junction perfect in your wiring ? Is every sectionof your H.T. giving full voltage ? Has your grid condenserthe necessary insulation to isolate the grid from H.T.?

Are your transformer windings perfect?These and hundreds of other questions are answered by

THE RaDIOTESTERAsk your dealer or write 4 CI

The British & Colonial Industries Association, Ltd.Southampton House, 317, High Holborn, LONDON, W.C.1

t Opposite Chancery Lane Tube Station)

Radio PressPublicity

The publicity enjoyed by" ModernWireless," " Wireless Weekly,"and " The Wireless Constructor,"has proved its great worth to thoseenterprising radio manufacturerswho use their advertising pages.The enormous confidence the radiopublic have in Radio Press publi-cations is reflected to advertisers,resulting in a heavy demand forthose products which are adver-tised in the above journals.It is difficult to see how a moreideal field could be found for theconducting of your advertisingcampaign.

FOR RATES ANDOTHER PARTICULARSWRITE THE ADVER-TISEMENT MANAGERS

BARCLAYS ADVERTISING LTD.BUSH HOUSE STRAND LONDON W.C2.

.4t,," r;,,a.',";1/,g; , -4,iat,,41"

In replying to advertisers,

211111111111111111111111111111111111I11111111111 11111111911111111111111111111111111111V

"ELLA:BATTERY CHARGERS

g Se wort liarn a Zrm kicizr

A.C. Model.Output 6 amps . 9 volts.Complete with Pole In-dicating Ammeter andall connecting leads andadapter. To standardvoltages & frequenciesup to 220 volts. £6 6 0

D.C. Model.Output 5 amps. 9 volts.Machine only £5 12s. 6d.With Switchboard and PoleIndicating Ammeter andRegulating Resistance asillustrated - - £6 15 0

ANOTHER ADDITIONA FAMOUS LINE

THE ELLA" SUPER CHARGERCharges 2v., 4v., 6v. and 8v. Low TensionAccumulators, and 20v. to 120v. High

Tension Batteries.

For further particulars write to:

LIONEL ROBINSON & CO.,3c, STAPLE INN,

-Z-

LONDON, W.C.1

= Telephone: -=- HOLBORN 6323 (two lines)= ,

please mention THE WIRELESS CONSTRUCTOR. 671

THE WIRELESS Co] ST1117C101: July, 1925

Worth Keeping!

I,...Worth BuyingEvery Wednesday 1

II PRICE

I

I

II

I

I Buy or order a I

Copy from your I

Newsagent or 1

11 any Bookstall

smaxmo, stem vispe, sasrama GM if IN nasmi

EVERY copy of " Wireless Weekly you buy is worth keeping.The information it contains is invaluable both for present

and future use.

The articles are written by experts, men whose abilities in radiotechnique make them the finest of all to guide and advise theamateur.

" Wireless Weekly" is edited by John Scott -Taggart, M.C.,F.Inst.P., A.M.I.E.E., whose name and reputation are universallyrenowned.

Experimenters 'and those possessing transmitting licences areamong its staunchest readers. This itself is further proof of thereputation Radio Press, Ltd., has for producing the best inradio literature.

Wireles kIyADVERTISEMENT OF RADIO PRESS LTD., BUSH HOUSE, STRAND, LONDON, W.C. 2.

Barclays Ath,l.

872 In replying to advertisers, please mention THE WIRELESS CoxsTRUCTOR

July, 1925

The CRYSTAL which isEverlasting on Reflex CircuitsA natural mineral Hurd as a diamond

Unaffected by heat Crystal can be set insolder

Every Crystal Tested on Broadcasting and GuaranteedThis crystal is a natural product and not a compound.Being as hard as a diamond it will never wear out andthus avoids the constant trouble of turning in order to geta good point. There are other cheaper crystals to be ob-tained, but the cheapest is the one that gives best servicefor the money. Every user of a crystal set should send forone to -day. PRIcE:

If your local dealer does not stock write direct to

MIKRO LTD*, LONDON C32c CRAVEN STRWEET.2,

DON'T BE PUT OFF WITH A CHEAPIMITATION- YOU ARE THE USER

NOW READY Price 5s. 6d.A Textbook ofWIRELESS

Telegraphy and TelephonyBy W. GREENWOOD, .Sc.B (Eng.), A.M.I.E.E.,A.0.0.1.,

Wireless Engineer, His Majesty's Signal School, Portsmouth.In this book the subject of wireless telegraphy and telephony has beendealt with simply and concisely, yet scientifically and adequately. Theinstruments, apparatus and circuits in amateur sets, in radio -stations,in aeroplanes, and on ships receive full treatment, and at the sametime the essential theory underlying the whole subject is thoroughly

investigated and explained.A Descriptive Frospectus of the above and CompleteCatalogue of Educational Books post free on application

UNIVERSITY TUTORIAL PRESS, LD.,25, High Street, New Oxford Street, London, W.C.2

Pray. Pat. Na.11016/14.

EVERYBODY NEEDSthe RADIO DEAD

Every radio enthusiast is troubled by the twist-ing and kinking of the flee leads of his head-phones, loudspeaker, or batteries, and theconsequent damage resulting in, interior recep-tion. But now there is a remedy-

THE, RADIO BEADlea simple accessory which clamps qn to your flex leads(no disconnecting necessary) and e mattes you to instantlyremove kinks and prevent their recurrence.Light in weight and email in cost, it prevents thatfrequent and often unknown cause of loss of signalstrength which is so difficult to trace.Approved by leading radio expert. Satisfaction guaranteed

ESSENTIAL TO TOM GET ONE NOW.Obtainable front all dealers. ft rade enquiries invited.WIN PATENTS, Hridgewar House, Hammersmith,London, W.6. Tel. Riverside 3553.

.3.1rc/ay.i .41. Mortlake Road, Kew.In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR,


20 lears agoTWENTY years spent in the manufacture and

development of one particular product is a longtime. Yet this is just how long we have been makingT.C.C. Condensers. Obviously we must have grownexceedingly wise in this business of condenser manu-facturing-in fact, there are not many difficultiesthat we have not come up against and successfullysurmounted.

Even a simple little component like a wirelesscondenser plays a most important part in the workingof your Set. It may be badly insulated-itsvalue may be incorrectly stated-it may not standup to high voltages-these are but three of themany requirements. If you choose a T.C.C. Con-denser.). ou'll know tbat it will have passed a completeseries of the most rigorous tests that it is possibleto devise. You'll know, too, that it is as nearperfection as any fixed condenser can be. So nexttime you want a genuine Mansbridge Condenser besure to ask for a T.C.C. in a green metal case.

None genuine without rir rithe mark

Sole Manufacturers :Telegraph Condenser Co., T

Suvlied in all valiteiitem .coax mfds. to

a revds.

Sold by allWirelessDealers.

6.4.:593

873


Selection from Contents ofJUNE ISSUE

PORTABLE SETS AND THEIR USES.By Percy W. Harris. M.I.R.E.

HOW TO MAKE A FOUR - VALVETRI-COIL RECEIVER.

By C. P. Allinson.

A TWO - VALVE PORTABLE SET.By A, S. Clark.

A SINGLE VALVE SET WITH REINARTZCOUPLING.

By Stanley G. Rattee, M.I.R.E.

A ONE -VALVE RESISTANCEAMPLIFIER

By J. Undeidoten.

A SPADE - TUNED CRYSTAL SET.By E. J. Mairiort.

A NINE -VALVE SUPERSONIC HETER-ODYNE RECEIVER (Contd.)

By John Scott -Taggart, F.Inst.P., A.M.I.E.E.

ADAPTING YOUR RECEIVERKDKA.

Ey G. P. Kendall, B.Sc.

FOR

FAULT FINDING. AERIAL SWITCHING.

Buy or Order

July, 1925

When you goaway

on your holidaysthere is no necessity to depriveyourself of the joys of Broad-casting.A portable set will give you music whereveryou are. Get ready now. June " ModernWireless " contains an interesting article on" Portable Sets and Their Uses," by PercyW. Harris, M . I . R. E.You are shown just how you can get themost out of a portable set under all conditions." A Two - Valve Portable Set," illustratedabove, is described by A, S. Clark. Fullconstructional details are given showing ex-plicitly how the enthusiast can build thiscompact and useful receiver.John Scott - Taggart, M .C. , F. Inst. P. ,

A.M.I.E.E., the Editor, continues his veryinteresting article on " A Nine -Valve Super-sonic Heterodyne Receiver."Those interested in multi -valve set constructionwill find the article on " How to Make aFour -Valve Tri-coil .Receiver," by C. P.Allinson, of special interest, describing fully,as it does, the building of a novel and efficientfour -valve receiver.The June issue of " Modern Wireless " alsocontains, as usual, numerous hints and tipsof great value to all radio enthusiasts.

ON SALE EVERYWHERE

Your Copy To -day.

MoCern WireiessEdited by John Scott -Taggart, F.Inst.P., A.M.I.E.E.

Barclays Advt.

811' In replying to advertisers, please mention THE WIRELESS CONSTRUCTOR.


MOOEiR30.3000000012E20/2000EIDS:3000EliZ3012

RADIO PRESS ENVELOPE No. 9

A SINGLE -VALVE RECEIVER

"It's a beauty !" I've had all the B.B.C. Stations andmany continental ones. The best ofit is, I have never built a set before.My first venture in Radio, and allthanks arc due to Radio Press Ltd.,for my success."

RADIO PRESS ENVELOPENo. 9

By I I ER BERT K. SIMPSON

Contains all the instructions necessaryfor the building of this really efficientSingle -Valve Set.It includes full and elaborate sheets ofinstructions for making the Set, twofull-size blue "prints, three sheets ofreproductions of photographs on artpaper, and one sheet of workingdrawings.The Set will receive 5 X X anywhere inGreat Britain, and forms a perfectstarting point for the novice whodesires to construct a set.

Radio Press Envelope No. 9 is obtainable from allBookstalls, Newsagents, and your local WirelessDealer, Price 1 /6. Or for 1 /9 Post Free direct from

(Dept. W.)

RADIO PRESS LTD.Bush House, Strand, London, W.C.2

12

F2

12

P2

12

12

12

F2

El

12

F2

F2

F2

E2

E2

12

P2

53

F2

12

P2

F2

P2

P2

12

F2

F2

E2

F2

F2

12

12

f2 12

RIO F2 69 RI El 63 RI RI 61 RI F23 tZBar:lays .3d.

. . an Absolute Necessity66

MICROHM " VERNIER CONDENSERDear Sirs, 5:3/23. Southport, Lanes.

A few weeks ago 'obtained from you one smallVernier Condenser. I should be pleased it you will for-ward'me anotne r at your =best convenience, as I cannotobtain one locally.

The one I am using -now, enables me to get thelast ounce out of my set. I Consider that they are an ab-solute necessity to any serious experimenter and relegatethe antiquated vernier plate to a dini position in thebackground. Wishing you all kinds of good things.

Dear Sirs, 3e3/25, Bradgate, Rotherham.I shall be extremely obliged if you

would fof-ward tOo.naore of your VernierCondensers. More than satisfied with them.

24 turns of tinting adjustment.Single t(in.ho'e foong Maximumcapacity .000015 nib" Minimunecapacity Negligible.

For use in parallel with aerialand anode tuning condensers.

Indispensable for"Neutrodynes." Postage 3d.

It is a recognised fact that signals weaken as the hours of darknessdecrease. With a "MICROHM" Vernier in your set, you are assuredof sharp tuning at all times. You will have infinite accuracy of tuningwith the greatest ease of adjustment. If you have the space of a three-penny piece on your panel, you can fit a "M ICROH :\,1 Vernier-ANDSTILL HAVE ROOM TO SPARE.THINK-you can improve your reception wonderfully for a vary smalloutlay : why not bring your set up-to-date ?

MAKE A NEIGHBOUR OF TH.4T DISTANT STATION ,

MICROHM ENGINEERING CO.VARSITY WORKS, COLLEGE ST., LONDON, E.9

'Phone - . - - Clissold 2887Scottiqt Agents: KEITH & IRWIN, 35, Robertson Street, Glasgow, C.2

/hi re fa es iu 7 5

Telephone-Victoria 3171.

Telegrams-Itentfones, Pad."

1111111111111111111111111

is tlLSasso

-"Noutii MA7FX..

ifillimeAl

NEW TYPE STRIP RHEOSTATS.THE MOST PERFECT RHEOSTAT YET INTRODUCED.A specially de igned spindle gives one -hole fixing and in-corporates a tension spring which ensures perfect electri-cal contact at all times terminal connections are

provided.The 7 -ohm Mod- 1 is fitted with a replaceable fuse. whichlittle device may save youths cost of an expensive valveIn operation they are noise free. One -ho e axing.SHIPTON New SHIPTON NOV SHIPTON NewType STRIP Type STRIP Type STRIPRHEOSTAT g) / RHEOSTAT 0RHEOSTAT /.

7 ohm. UI 30 ohm, 01 to ohm. U(with fns)

E. SHIPTON & CO., LTD. AlsoOTHL STREET, WESTMINSTER. S.W 1.at 14, KING ST., COVENT GARVEN, W.C.0.

Build that Super Het,-NOWThe foundations of this system are the

Bareenlis

RADIAl.Filter Circuit.Osci llator and Coupling, andthe Intermediate Frequency Transformers. RIPARtlikrosiWe have now produced sets ofthese components which simplifythe building of a Super Het. Set,and with the splendid diagram,list, of valves and general infor-mationwhich we supply cut out alldoubts and difficulties in con-struction, These components areof the highest possible quality asregards finish, accuracy of calibra-tion, insulation, etc.

RADIAX Ltd

5 Valve Outfit, comprising: -1 Oscillator, 1 Oscillator vari-able coupler, 1 Intermediatefrequency filter, 2 Intermediatefrequency transformers (30kilocycles), circuit diagram,etc. No. 813 52s. 6d.

6 Valve Outfit No. S14 64s. 6d.

7 Valve Outfit No. 815 77s. 6d.

44, Radio House, Percy Street, Tottenham Court Road, London, W.1.


Barclays 11a9


Index to AdvertisersPAGE

Aget (W. W.) .. 859American Hard Rubber Co. 864

Gambrell BrosGarnett, Whiteley and Co.

PAGE

821861

PACE

Peto-Scott Co. ... .- 842Portable Utilities Co., Ltd. 859

Audion Radio Co. ... 848 General Distribution Co. ... 842 Power Equipment Co., Ltd 859Autoveyors, Ltd. ...Beard and Fitch, Ltd.Bobin (M.) ... Bowman (Win.), Ltd.

813821876869

General Radio Co....-Gent and Co.Gil. Ray Radio Co.... ...Goswell Engineering Co. ...

845863852847

Radiax, Ltd. ... 6.. ... 875Radib Instruments, I,td. Cover ivRadians, Ltd. ... 852

Bowyei and CI. 863 Graham (A.) and Co. 855 Raymond (K.) .. 839Bowyer -Lowe Co. ... 855 Guiterman (S.) and Co. 846 Ridley (Cecil) 864Brandes, Ltd. ...Bretwood, Ltd. ...Brighton Radio StoresBritish and Colonial Industries

80.6863866

Harlie Bros.... ...Herrett, J. ...H. T. C. Electrical Co.Igranic Electric Co.

864859835851

Ripaults 793Robinson (Lionel) and Co. 871Rosen (Ed.) and Co. 846

Assn., Ltd. "... 871 Jackson Brothers '... 835 Rothermel (R. A.) ... 852British Engineering Products Co. 864 Kriscros Co.... ... 869 Scientific Supply Stores 864B.T.-H. Co., Ltel. 822 Laker (J. and J.) Co. 876 " Sel-Ezi " Wireless Co. 855Brown (S. G.), Ltd. ... 856 Lighting Supplies Co. 866 Service Battery Co. 866Bulgin (A. F.) and Co. 864 Lisenin Wireless Co. 856 Shipton (E.) and Co., Ltd. . ... 875Burndept, Ltd. ... 837, 851 Lissen, Ltd. 805 Simpson and Blythe ... 863Burn -Jones and Co. 876 London Elec. Stores 869 Stirling Telephone and Elec. Co., Ltd. 794Carrington Mfg. Co. London Elec. Wire Co. ... 865 Taylor (j. "H.) and Co. ... ... 859Clarke (H.) and Co. ... 867 McMichael (L.), Ltd. 825, 830 Telegraph Condenser Co. ... ... 873Collinson's Precision rev,- Co., Ltd. 833 Makerimport Co. ... .... 856 The Times ... 840Cossor (A. C.), Ltd. 818 Maxel Electrical Co. ... 863 University Tutorial Press, Ltd. ... 873

'Curtis (Peter), Ltd. ... 813, 833, 851 Merrett ,(J.) 859 Vandam (H.) 863Dixon (L.) and Co.... ... 846 Metro -Vick Supplies 834 Vandervell (C. A.) and Co. 852Dubilier Condenser Co I,td. ... 817. Michrom Engineering Co.... 875 Wates Bros.:.. 848Economic Elec., Ltd. ... 861 - Mikro Co. ... 873 \Vatmel Wireless Co. 836Edison Swan Elec. Co., Ltd. ... 809 M. 0. Valve Co. ... 810 Watson, Jones and Co. ... 869Energo Products ... ... ..: 836 .MullardRadio Valve Co., Ltd. Cover ii Wilkins and Wright, Ltd. 855Falk, Stadelmann and Co., Ltd.... 861 Naylor (J. H.), Ltd. 865 Williams, Ellis and Co. ... 869Fletcher (F. and J.) 856 Neii, London Electron Works 876 Win Patents 873Fluxite ... 861 Oldham Accumulators ... 866 Wireless Distributing Co.... 846Yormo Co. ... ... 813 Ormond Engineering Co. ... 826 Zealander (H. D.) ... 852

STEEL! A rb TENNISMASTS Lcri GnPO STSWell known throughout the world.Send for either WIRELESS MAST or

TENNIS POST Catalogue.JOHN and JAMES LAKER Co., ENGINEERS,

cont,,rtors to IT.M. Gore 1.717110tf.457, Romford Road, London, E.7.

Take tjourWirelessinto the Garden with300WEE'rSt.'

CAT A.,.OViWYWPrERE

///,4Ixtenji6n:E AU WARE.

7he New London Electron Kbths LtdLondon, E.6

L.F. TransformerAR (SHROUDED)

RATIO 5 to 1. 15/ -OF ALL DEALERS OR

M. ROBIN, 21 Warwick Lane, London, E. C,Telephone : Central 4372.

Do you realise that theefficiency of your nigh....

Frequency Stages dependsupon the intervalve coupling device?Magnum B.F. Transformershave been designed fogivemaximum . amplificationwith distortioniess results.Magnum Transformers arewound with__the 'highestgrade Double Silk CoveredWire on Solid Ebonite,machine' cut former, lurvingan air core, the windingsbeing completely protected.Each unit is subjected torigorous tests for, insula,tion and wavelength rangeand guaranteed to be con.MICE 71- EACH

Guaranteed correctly rectly matched when suppli-matched 14,.- per pair. ed forMulti II. F. Coupling.

MAGNUM B.F. TRANSFORMERS With ProtectedWindings.

The most efficient 11.1'. Transformer obtainable. (See reportn " Wireless Weekly,'' 7. each. Postage ad. Guaranteedsorrectly matched 14/per pair. (Postage ad.)

No. 0 .. 150.300 No. E .. 650.1200iNo. OA . 2E0,525 No. 3 .. 1100-3000No. 1 .. 300-0-O ,No. 4 .. 2E00.7000

*Specially recommended for super heterodyne circuits.ISpeciid winding for Anglo-American Six referred to as

Nentrodyne Units. Per set of 3, 21/. tpost free,.

SPECIALISTS in SUPERSONIC -HETERODYNESWe are now specialiging in Supersonic-Idetero-dyne Circuits and as a result of patientresearch- have produced a circuit which wehave named the MAGNADYNE.This circuit employs our MAGNAFORMERSwhich we haee-pleasUre in offering as follows :-3 Matched Tuned Magnaformers 18/-

Modern developments, more especially withreference, to Supersonic -Heterodyne and

2 Aperiodic Magnaforrners , qr.18fr- Short wave reception make it essential that' 1 Magnum Oscillator (Broadcast range) @ 115/ -The above outfit including Instructions andwiring diagram £5- 0 0

all 'Stray eaphcities be reduCed to an absoluteminimum. The Magnum Anti -Capacity...

(sent on 7 days approval agaipst cash,), Valve -Helder has been specially designed toNote:-Magnum Oscillator units are inter-changeable and available from 50 metresupwards.

meet these requirements and is undoubtedlythe Most suitable for present day radiopractice. Made from Solid Ebonite,

specially channelled.BURNE = JONES CO., LTD., PRICE 2/6; Packed in neat carton.Magnum House,288, 298, BOROUGH HIGH ST., LOhoon , 8.E.1;Telephone, Hop 6257. Telegrams, BURJONAG;Sediet, London. Cables, BURJOMAG, LONDON.

Carriage and Packing FREE on Retail Ordersvalue 22 and over.

Mail Order Dept., 288, Borough High Street,London, S.E.1.

Send stamp for illustrated list and set ofleaflets dealing with Radio Press Circuits.

Trade Enquiries Invited

676 Ii. replying to advertisers, please mention THE WIRELESS CONSTRUCTOR,

July, "1925 THE WIRELESS CONSTRUCTOR

The right way to enter the field of radio is theRadio Press way. The words " Radio Press "are the " open sesame" to wireless proficiency.

The reputation for being " sound people" hasbeen increased still further by the announcementof the great new radio laboratories to be erectedat Elstree and the immediate appointment of aChief Engineer at a basic salary of £2,500(exclusive of further fees which will raise theremuneration to approximately £4,000 perannum).

As wireless engineers devoting their effortssolely for their readers, the Radio Press haveacquired an international reputation, as isevident by the numerous foreign letterspublished.

The industry and the general public havenaturally come to look upon the Radio Press asthe obvious source of literature catering fortheir respective needs.

In short, a Radio Press publication is a RadioPress success.

Ida,e aye Ad.


40,111,111IIIIIII

II

11,--.,...--.., "s - - 1i1_,-.,.; im v6iirpialma

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IL II 1%0

Price 39/6Write for leaflet W.C.

free on application.

R.I. adds yet another successto its list of wireless com-ponents for the perfection ofwireless reception.

Here we have a sectional view of the new R.I. AerialTuning Inductance with variable Aerial Re-action designed for panel mounting and covering a wave-length range of from 175-4,000 metres.The unit is better and in addition is cheaperthan a complete set of coils.It comprises a cylinder of paxolin on which is wound a number of turns ofsilk -covered wire, with eight tapping points leading to a special dead endswitch fitted in a panel, which is secured to one end of the cylinder.The aerial reaction is operated from the front of the panel by means ofa fine bevelled gearing which gives a beautiful smooth action, allowingadjustment to the finest degree. A large black ebonite dial, suitablyengraved with two scales, one indicating the tapping points and the otherdegrees of reaction, is supplied with each instrument and can be usedas a drilling gauge for fixing the unit to the panel of the receiving set.This R.I. component ensures correct and efficient aerialreaction over the entire range of wavelengths in a manneralmost impossible with plug-in coils.The special dead end switch entirely eliminates all energy loss, andwhen used in conjunction with a variable condenser it practically formsa complete receiving circuit.

Contractors to Me Admiralty and all Government Departments

Pr, Lieu tar tae Proprietor.. KADIO oi Dash mouse, 6.0 -an°, Dy PLriETWAY eRE33, LIMIThU, 51y, Lane street, and published by the Pro-prietors, Radio Press, Limited, at Bush House, Strand, W.C.2, on the 15th of each month. Address for Subscriptions and Editorial communications:-Bush House,Strand, W.C.Z. Advertisement Managers:-BARCLAYS ADVERTISING. LIMITED, Bush House, Strand, W.C.2. 'Phone, City 9911. Registered as a Magazine for true/ -mission by Canadian Magazine Post. Subscription Rates: 816 per annum, 4/3 for six months, post free. Sole Agents for Australia: Goapou & Garcx (Aurreataa)

LTD. Sole Agents for South Africa : CENTRAL NEWS AGENCY, LTD.

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