Practical Wireless, May 1914, 1914. CALLING UP THE LISTENER Published eveAb Wednesday by GEORGE NEWNES LTD. Vol. 4.- -No. 57. May 19th, 1934. .c,il,tered at the G.P.O. as a. New8PaPer. AND PRACTICAL TELEVISION EDITED BY F.J.CAMM Obtainable from all Good Dealers. In eelses of difficulty seed direct to: Sole Wholesale Distributors: BRITISH RADIO GRAMOPHONE CO. LTD. Pilot House, Church Street, Stoke Newington, London, N.16. USED EXCLUSIVELY BY MR. F. J. CAMM The metallised Baseboard that has come to stay. REFUSE SUBSTITUTES. Auoi
Transcript
Practical Wireless, May 1914, 1914.
CALLING UP THE LISTENER
Published eveAb Wednesday by
GEORGENEWNES
LTD.Vol. 4.- -No. 57.
May 19th, 1934..c,il,tered at the G.P.O. as a. New8PaPer.
AND PRACTICAL TELEVISIONEDITED BY F.J.CAMM
Obtainable fromall Good Dealers.
In eelses of difficulty seed direct to:Sole Wholesale Distributors:
BRITISH RADIO GRAMOPHONE CO. LTD.Pilot House, Church Street, Stoke Newington, London, N.16.
USED EXCLUSIVELY BY MR. F. J. CAMMThe metallised Baseboardthat has come to stay.
REFUSE SUBSTITUTES.
Auoi
II PRACTICAL WIRELESS May 19#11, 1934
MHOS OF THE MR
COSSORTs pe 210 V. P.T.
(2 Volts)i
z2
toItIs-.3atOO
44,stP 41fr
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-1 12 2
- Grid Voltz +
COSSORType 210 V.P.T.
(2 Volts)tlWO re
I2 TA/t114 AT 1.114.210r.
1.
: /...........""........-
VG 1
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COSSORTspe 210 S.P.T.
(2 Volts)
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e
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4
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3
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TWO NEW
COSSOR
VALVESTo meet the demand for valves of high impedance suitable for usein the I.F. Stages of battery super-hets and for use as H.F. Amplifiers,A. C. Cossor Ltd. introduce a Variable -Mu High Frequency Pentode,the 210 V.P.T.
Another innovation is a High Frequency Pentode, the 210 S.P.T. whichis specially suitable for use as a high gain defector or as an I.F.Amplifier in non -variable -mu super -hots.
Full details of these new valves will be gladly supplied on applicationto the Cossor Technical Service Department.
To A. C. COSSOR LTD., Technical Service Dept.Cossor House, London. N.5.
Please send me full details of newCossor Valves, types :
Name
Address
Prao. .913/34
4961 9
May 19th, 1934 PRACTICAL WIRELESS 261
EVOLUTION OF THE SUPERHET ! See Page 266
tir los
EDITOR :Vol. IV. No. 87 II F. J. CAM M II May 19th, 1934.
Technical Staff:W. J. Delaney,
H. J. Barton Chapple, Wh.Sch., B.Sc. (Hone.),Frank Preston, F.R.A.
'ROUND the WORLD of WIRELESSSummer Time
THE European countries which havenow changed over to Summer Time
include Great Britain, France, Belgium,Romania, and Portugal. Holland alters herclocks on May 15th.
Australian Empire Day BroadcastIN celebration of Empire Day, aIpro-gramme from Australia will be given onMay 24th, in the National programme, andwill be re -transmitted by the B.B.C. to otherparts of the Empire, either by means ofsimultaneous broadcast or by electricalrecording. The programme will be devisedand produced by the Australian Broad-casting Commission, and will open with thechimes of the General Post Office clock atSydney, New South Wales. A demon-stration by Kookaburra (Laughing Jackass)will follow. As an introduction to theplaying of " Australia will be there," afavourite war -time song of Australiansoldiers, a message of goodwill to theEmpire will be broadcast.
Larger Stations for AustriaTT has been decided to replace the Dorn-
birn, Salzburg, and Linz relays during1934-5 ; their power is to be increasedby several kilowatts.
Ave Minor Competition-CorrectionNVITH reference to the announcement
concerning this competition whichappeared in a recent issue, we under-stand that a slight printer's error occursin some of the folders sent out in con-nection with the competition. On page3 the last range of meter readings shouldbe 0-3 megohms, and not 0-.3.
More Musical Interval SignalsOWING to the popularity achieved by
the short musical phrase used by thePrague high -power transmitter, the Czechshave decided to adopt individual melodiesas interval signals at all their stations.Prague (2) on 249.2 metres now uses atrumpet fanfare consisting of the first fewbars of the Sokol March, and Bratislava acarillon of the folk song, HeiAt Kosice, more distinction is obtained byintroducing a native wind instrument, theFusar, and from Morayska Ostrava will beheard a short excerpt of a national song,played on a vibraphone. Brno has not yettaken a decision in the matter.
The Range of Small StationsALTHOUGH the power of Zagreb
(Jugo-Slavia) is only 750 watts, itsbroadcasts have been recently well heardin the United States. This fact provedof interest inasmuch as it was discoveredthat the aerial was slung east -west, andthus possessed excellent directional proper-ties. Most of the letters confirming goodreception were received from St. Louis(Mo.). Here you have the explanation of1....1141101/4110.114MM.0.114=1.4141MOININHNE11.0.1111.1)MINDOMIDIMENIIINIII
Have You Seen OurCompanion Journal
"THE
PRACTICALMOTORIST"
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the reason for which som 5 gst&ll Europeantransmitters are heard at e ceptionalstrength in certain parts of the UnitedKingdom.
Radio to Assist French RailwaysFOLLOWING the recent Lagny disas-
ter, the signalization on the Frenchrailways is to be completely modernizedby the use of radio short-wave transmittersand receivers. In future trains will beequipped with apparatus permitting themto maintain communication with each otheron the main lines. By this means theengine driver will be informed of the exactposition of any train he may be followingor which may be overtaking him.
Egyptian Broadcasting SystemWITH the imminent opening of the new
Cairo transmitter on 483.9 metres,the future plans of the authorities have beenofficially revealed, Egypt was granted fourchannels by Lucerne, and will make use ofthem. Work is to be started without delayon the Alexandria 5 -kilowatt broadcastingstation (267.4 metres) and later on tworelays, namely, Cairo (2) and Alexandria (2),for which the international common wavesof respectively 222.6 metres and 209.9metres will be utilized. Their power willnot exceed 2 kilowatts.
Television Transmissions
INaddition to television broadcasts
A carried out by the B.B.C. the amateurmay be interested to learn that experimentsare also being made by Germany and Italyaccording to a regular time schedule : TheDeutschlandsender (Berlin), on 1,635 metres,transmits pictures (30 lines) 12.5 per second,on Tuesdays from B.S.T. 09.05-10.00 ;Thursdays 13.45-14.45, and Saturdaysfrom 09.05-09.45. From the Berlin short-wave station on 6.98 metres (42,950 kilo-cycles) the transmissions are made on 180lines, from 09.00-11.00 and 15.00-16.00(Mondays and Wednesdays) ; 09.00-11.00and 20.30-22.00 (Tuesdays and Thurs-days), and from 09.00-11.00 on Saturdays.Rome works irregularly on 80 metres(3,750 kilocycles) with 60 lines (20 picturesper second).
Touting for TouristsDURING the summer months many
Continental States broadcast specialtalks in foreign languages with a view tobringing the attractions of their cities,watering and seaside resorts to the attentionof prospective visitors. Such transmissionsin French, German, and English may bepicked up regularly from Italy, Switzerland,and Denmark, the last-named countrycalling Europe twice weekly at 11.0 p.m.towards the end of the day's programme.
New Trondheim Transmitter TestingON 476.9 metres, a channel shared with
Radio Lisboa (Portugal) in theearly morning and late afternoon hours,tests carried out by the new 20 kW Trond-heim station may be heard on most days.When officially opened the transmitter willeventually relay the Oslo programmes.
262 PRACTICAL WIRELESS May 19th, 1934
ROUND the WORLD of WIRELESS (Continued)Improving the Swiss. StationsIT has now been decided that in view of costI entailed the power of the Beromiinsterstation alone will be increased this, yearEn addition to improvements and additionsto the existing plant the aerial masts areto be raised some 246 feet in order to assistradiation. It is also proposed to changethe wavelength of the old Berne station,now working on 218.2 m., to 500 metres,providing authority to do so can be obtained.
Wings of the MorningLANCE SIEVEKING'S new radio play,
Wings of the Morning, which isto be heard in the Regional programme onMay 24th and the Nationalprogramme on May 25th, is thestory of " a fantastic crimecommitted in the FourthDimension." As may be gathered,there is a scientific touch aboutthe play, which includes mem-bers of the Royal Society, aswell as the more commonplace
miirtions of the law," amongthe characters. The authorwill be the producer.A Broadcast Revue from Ply-
mouthON May 18th, West Regional
listeners will hear an ex-tract from the George Clarkerevue at the Palace Theatre.Plymouth. The Band of H./0.Royal Marines, PlymouthDivision, will be heard on May19th. The Director of Music isLieutenant F. J. Ricketts,R.M., and the programme willberelayed from the Abbey Hall,Plymouth. Frederick Harvey(baritone) will be the vocalist.Dance Music by Scottish Studio
OrchestraON May 19th, the dance
music period in theScottish Regional programme will beinterrupted for twenty minutes anda programme entitled Jig Time " willbe given by the Scottish Studio Orches-tra directed by Guy Daines. This willprovide a change for listeners who do notcare for jazz.
Wireless Symphony Orchestra at BelfastDR. ADRIAN BOULT will conduct the
Wireless Symphony Orchestra in theanal concert of the spring series, which willbe given in the Ulster Hall, in co-operationwith the Belfast Corporation, on May 19th.Dr. Boult paid his first visit to Belfasttwo years ago, and has become one of the,iity's favourite conductors in the interim.['he programme on this evening willinclude the Brahms Concerto, Opus 77, inwhich the solo violin part will be playedby Temianka.
" Hurdy Gurdy "ANOTHER broadcast of the popular
" Hurdy Gurdy " series will be givenn the West Regional wavelength on May2nd, when the artists will be John Rorke,114 Eaves, Brian Gaye, Mervyn Saunders,,he Revue Chorus, and the Western StudioDrchestra, Listeners all over, the worldtre delighted with the " Hurdy Gurdy "nogrammes, for they bring back memories)f other days. The programmes are notJuilt around any special theme, for the
...0.1101=1.11.11;
INTERESTING and TOPICALPARAGRAPHS
1.4)411Jusual " Hurdy Gurdy " is somewhatinconsequent in its manner of presentationand that is, of course, a part of its charm," The Boat Train "THE interesting series of talks which
are broadcast on Monday morningsunder the general title of " The BoatTrain," include any subject under the sun,from witchcraft and carpet -buying in Indiato pleasure cruising, marrying an English-man, or going on an elephant kraal. On
NOVEL COOLING APPARATUS AT H.M.V. FACTORY.
A new form of miniature railway and wind tunnel has been devised by amember of the H.M.V. staff, and installed in the condenser -making plantat Hayes. The blocks of fixed condensers, after having been filled withpitch, pass through the tunnel on rails and are automatically cooled
by air which is pumped through.
May 28th, Sir Malcolm Campbell will talkon Speeding, and on Juno 25th, Vice -Admiral Sir Charles Carpendale will talkabout Europe's wavelength problems.
513 lit THIS !PROBLEM No. 87
Tompkins built up a disc television receiver,but although he obtained splendid results hedecided that the brilliancy of the image wasnot really sufficient for his entertainmentneeds. He decided, therefore, to build a mirror -drum receiver. He purchased a completemirror -drum, motor, and grid cell, and built
I this up with his existing aeon and the necessarylens, but could obtain no results. Whatimportant point had he overlooked ? Threebooks will be awarded for the first three cor-rect solutions opened. Address your attemptsto Vhe Editor, PRACTICAL WIRELESS, Geo.Newnes, Ltd., 8-11, Southampton Street,Strand, London, W.C.2. Envelopes must bemarked Problem 'No. 87, and mast be postedto reach here not later than the first postMonday, May 21st, 1934.
1
SOLUTION TO PROBLEM No. 86The output valves of Davis's push-pull amplifier
were oscillating. A resistance in each grid lead, or asmall resistance in each anode lead would have removedthis instability and enabled good volume to be pbtained.The following three readers successfully solved ProblemNo. 85, and books have accordingly been forwardedto them :-Mr. James W. Forest, 7, Hamer Ave., Blackburn;Mr. S. W, Duncan, 24 Park Avenue, Dundee; Mr. H.
by Christine Orr, will be broadcastin the Scottish Regional programme onMay 23rd. Listeners, many of whommay remember Christine Orr's previousbroadcast plays-Walter Scott, Dunbar,and Flodden, and her historical programmeof Edinburgh, are being taken .by her onthis night to the four chief places of interestin Edinburgh, but in modern times. MissOrr has chosen Assembly Week as beinga week not only of solemn functions anddeep debate, but of junketing and jollityand the meeting of old friends. GordonGildard will produce the play and the
principal parts will be taken byMargaret Adams, Bruce Morgan,and Isabelle Pagan.
The Finnish National OrchestraIN the symphony concert by
the Finnish National Or-chestra, which will be heard byNational programme listenersin a relay from the Queen'sHall on June 4th, HelmiLuikkonen, soprano, will bethe soloist. The programmeconsists mainly of Sibeliusmusic and includes his secondand fourth symphonies. Otherof his works to be performedare Night Ride and Sunrise andLuonnotar, for soprano and or-chestra. The orchestra will alsoplay Merikanto's Pan andSwans, by Raitio. The con-ductor is Georg Schneevoigt,who is already as well knownto us, as he is to audiences inalmost every city in Europethat has an orchestra or operahouse.
" Choir and Cloister " BroadcastsON May 17th, the fifth relay
in the Midland Regional" Choir and Cloister" series will begiven from Worcester Cathedral, andWalter Pitchford, of Lamport, is againthe narrator. He will find abundantmaterial in the cathedral that looksdown on the Severn, for it has aNorman crypt, where each year there is aspecial collect said for its builder, St.Wulfstan ; it has one of the most beautifulthirteenth -century choirs in Europe ; thetomb of King John, who was brought toWorcester from Newark Castle, where hedied ; and many other interesting features.Sir Ivor Atkins will play an organ solofrom Sir Edward Elgar's second sonata,and will conduct the choir in choral music,composed by great composers of churchmusic like Dr. Byrd, Dr. Blow, Tomkins,'and Samuel Wesley-all of whom hadMidland associations.
Torquay Municipal Orchestra BroadcastTWO of the southern seaside orchestras
which can always be relied upon toprovide a first-class relay are Torquayand Bournemouth, while Hastings andEastbourne also have a large followingamong listeners. One of the increasinglyfrequent broadcasts by the Torquay Muni-cipal Orchestra will be heard on May 22ndin the National programme. The conductorwill be Ernest W. Goss, scion of a famousmusical family, and the soloist is MaryHamlin, soprano.
May 19th, 1934 PRACTICAL WIRELESS 263
CAR RADIOPOSSIBILITIES
All of the Problems of Radio in the Carthe Solutions are Here Described.
FROM time to time we have dealtwith the problem which faced thedesigner of a wireless receiver which
had to operate in the confines of amotor -car travelling along the roads underall conditions. Briefly, interference fromthe magneto, sparking plugs, etc., had to beovercome. Some form of aerial or otherefficient pick up of the wireless signalshad to be fitted so as to introduce a reallygood signal to the receiver. Constancy of
have Now Been Solved, andBy W. J. DELANEY
fully satisfies every possible requirement ofentertainment whilst driving.
Interference SuppressionSpecial resistances have been designed,
and are now manufactured on a commercialscale for fitting to the plugs and for use inconjunction with the magneto and associateddistribut6rs, which remove all interferencefrom those sources. With these fitmentsand a suitably -designed radio receiver
there are no crackles or otherextraneous noises to mar the
reproduction. Manycar manufacturers arenow fitting these sup-pressors as part of thestandard equipment,but where it is desiredto equip an existingcar with radio thesuppressors may bepurchased from anygood radio dealer.They are manufacturedby firms who have hadmuch experience inthe manufacture ofresistances, and maybe relied upon tosatisfactorily f ulf i 1their function withoutbreakdown.
This llustration shows the method of operating thecontrols from the steering column, and how the apparatus may be
enclosed in a metal case to be sunk in the floorboards.signal strength had to be obtained underall conditions. That is to say, the screeningeffects of metal bridges, high hills, etc., hadto be completely removed. The receiverhad to be disposed in the car in such a waythat it introduced no awkward boxes orother projections. The loud -speaker hadto be fitted also in an unobtrusive place,but in such a manner that it could deliverits signal to the occupier of the car. Thecontrols had to be arranged so that thedriver could turn the set on and off andcontrol the volume delivered by thespeaker. A really good voltage (of theorder of 200 or so) had to be obtainablewithout introducing too much bulk orweight. Although there are other smallerpoints, the apparently insolvable difficultieswhich have been enumerated have nowbeen overcome in a most satisfactorymanner, and the following notes will showin what an efficient manner the designershave been able to build a receiver which
Aerial EquipmentMany new cars have
an aerial built into thebody work or arrangedin the roof of the car insuch a manner that afair length of wire isaccommodated and atthe same time thereis little likelihood ofinterference beingpicked up. Where sucha fitting is not providedsome interesting typesof aerial may be ob-tained from variousfirms for fitting to the
car in an invisible manner. In most cases acopper gauze mat is employed, and this isenclosed in some dirt -proof casing and is
A complete modern car radio receiver andloud -speaker.
generally designed to fit beneath the runningboards.
A length of flexible lead is fitted and thisis of the ordinary or screened type, depend-ing upon the particular make. Fittingis only a matter of drilling one or two holes
Sparking Plug Suppressor
Rubber CeMetliSHigh Nnsion CableTo Sap,oressor.
Sparking Plug
Interference from theplugs is removed bymeans of specia!
resist ors.
and passing bolts (which are provided withthe equipment) through the running boardand locking up with wing nuts. The wholejob may be carried out in less than half anhour. As the car is running on rubbertyres it is effectively insulated from earth,but by connecting the chassis, etc., of thereceiver to the framework of the car asatisfactory earth connection is obtained.
(Continued overleaf)
This aerial fitment is intended to be mounted below the running board.
264 PRACTICAL WIRELESS May 19th, 1934
CAR RADIO POSSIBILITIES(Continued from previous page)
Constancy of Signal StrengthUntil one has experienced the testing of
a simple receiver in a car travelling atspeed over a road which passes through ahilly district and over or under metalbridges, one cannot appreciate the varia-tions in signals which can occur. This hasobviously been overcome with the simpleautomatic volume control circuit which isnow so popular, and which is carried out bymeans of the double -diode type of valve. Byemploying the superheterodyne circuitgood signal strength is obtained and themodern output pentode enables a reallyload signal to be obtained under practicallyall conditions.
Apart from the actual circuit, the disposi-tion of the receiver at one time seemed atough proposition. To facilitate its incor-poration in the car without intrusion thegeneral procedure is to build the receiverinto a small metal box so designed that itmay be sunk into the floorboards, or elseincorporated in a cabinet with a loud-speaker and designed to be fitted beneath orbehind the dash.
Special loud -speakers of the Midget typehave been designed and these may be builtinto the dash in the case of modern cars,or incorporated in a specially -built cabinetfor inclusion beneath the dash in the caseof older cars. The glove box may beextended to accommodate the speaker ifthought desirable.
The ControlsIn the design of the controls exceptional
ingenuity has been displayed. It is anessential that the driver shall have theseat his immediate reach and an indicationmust be afforded as to the tuning setting,in either wavelengths, or by means of asimple calibrated dial. In the case ofthe Lissen car radio outfit, a neat fitting isdesigned to be bolted to the steering column,and adjustment of the 'tuning knob is nomore difficult than the manipulation of thehorn control, and a neat window disclosesa numbered dial to enable the tuning -rangeto be identified. The tuning condenseris operated from this control through themedium of Bowden cables, and there is nobacklash and tuning is delightfully simple.In another case a neat dial of the clock -facetype is fitted to the steering column, andsmall knobs on the moulding enable thetuning to be carried out as well as providingfor volume and tone control. The largepointer provides an immediate indication,visible at a glance.
High -Voltage GeneratorsIt is obvious that ordinary H.T. batteries
could be carried without taxing the engine,but the problem of replacement has to befaced and accessibility must at the sametime receive attention. Special smallgenerators have, however, now beendeveloped and these operate from thestarting or lighting battery and deliver agood 200 volts, thus permitting of theemployment of ordinary mains -type valveswith their resultant high efficiency.
There only remains the question oflegislation which might be introducedregarding the use of a wireless receiver in acar. Does a wireless rreceiver distractthe driver's attention from the road andincrease the risk of accidents ? Or, alter-natively, does the fitting of a wireless receiverprove so entertaining that the driver isprevented from driving dangerously ?
THE photograph and sketches show avery neat and efficient microphoneof the pedestal type, which can be
quickly constructed from simple materials.The main parts, which can be clearly
seen in the photograph, consist of a base,a tubular upright, brass swivelling ring, anda microphone -carrying disc.
The base was taken from an old Amplionhorn speaker and is ideal for the purpose,but if this is not available, a very effectivebase can be made from wood, as shown insketch.
The tubular upright is a 14in. length ofordinary steel casing, as used in electricwiring: This is flattened at one end, anddrilled to take base -bolt. If, however, thealternative wooden base is used, the endof the casing is left circular, but is turnedover with pliers to form a flange as shown.A hole is made in the centre of the topdisc, the tube passed through, and thebottom disc screwed on. A disc cut fromsheet lead and sandwiched between thetwo wooden ones will help to weight thebase. The size can be about 6in. diameter,and fairly weighty hardwood, such as oak,should be used. A short wooden peg (drilledwith a 2B.A. clearance hole) is driven intothe top of the upright. This forms a socketfor the shank of the brass swivelling ring.
The brass swivelling ring is formed froma 16iin. length of iin. diameter brass rod,bent round and having two brass lugssoldered to the ends as shown. A shortlength of 2B.A. screwed rod is passedthrough and the nuts tightened up. Thiscompletes the ring, which can then beinserted into the tubular upright.
1
BPDascaNtCP rt.rxP05,0N BRAES LUG
SOLDERED 10[ACM END OFGRASS RING
2 BA SCREWEDROO TO ;?;47,1,,r pWOOD PEG DRILLED 2. BA & DR NANiNTO TOD OF EASING TO FORMPIVOT FOR KIKROPNONE ASSEMBLY
gIIL=UJIT2L9!PT
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PEET LEAD,-ELT
The microphone -carrying disc is madefrom three-ply, 4in. diameter. The springscan either bescrewed direct onto the disc or in-serted under theset screws of thespeaker unit. Thesize of hole in thedisc will, of course,depend on the
,microphone used.In .the writer'scase, the Amplionspeaker unit wasemployed as amicrophone, andthe hole was made21in. diameter. If
using the Amplionunit, the covershould be removedby unscrewing thethree set screws,and, as these haveflush heads, a slotshould be filed ineach to facilitateremoval.
The three-plydisc is next drilledat the samecentres, adjustedover diaphragm photograph of the completeand spring washer,
microphone.and the set screwstightened up. The flex lead is connected tothe speaker terminals and held in placeby three small rubber bands against theupright.-R. L. GnAran.
---t.raLgpTO FORM 5Ye"nCIRCLE
4"
SPEAKER UNIT USED AS MICROPHONEREADY FOR HOOKING TO BRASS RING.
FRONT CASTING OF SPEAKER UNIT REMOVEDAND REPLACED DV THREE-PLY DISC.
ALTERNATIVE rzlirwrOfrofAOSII,C12.4INGSPEA
YWOOD STRIPPATH NOLECLEAR ADJ.
SCAMDNA SCR r1VED
..---BILEAKER DNA
p1.1,000 OSPAING
BOTTOM OF TUBE FLATTENED & BOLTED
TO SPEAKER BASE.
Full constructional details of the microphone and stand described in this article.
May 19th, 1934 PRACTICAL WIRELESS 265
TRIMMING GANG CONDENSERSThe Methods to be Adopted and Some Simple Tests are Described Below
ANY receiver having a gang condenserrequires a certain number of pre-
)liminary adjustments if satisfactory
results are to be obtained. These trimmingadjustments are not usually very difficultto make, but it appears that many readersare not quite sure of the procedure whichshould be followed. The first thing to bearin mind is that, if a gang condenser is tobe employed with any measure of success,it is essential that all the tuning coils uponwhich it is operative should have identicalvalues of inductance ; it is futile to attemptto use, say, two coils of similar type inconjunction with a two -gang condenserunless the coils have been bought as amatched pair. When the constructor hasone coil of a particurar type which hewishes to fit into a new receiver with gangedtuning, it is best to send the coil to themakers and ask for the other coils requiredto be exactly matched to This isespecially true in regard to iron -core coils,and there are a few manufacturers of high-class air -core coils who guarantee all theirspeeimens to be identical to within a marginof 1 per cent. or so.
Use Matched CoilsIn case it should be thought that identical
coils can be used with a gang condenserwithout the necessity for any furthermatching or trimming, it should be bornein mind that the connecting wires modifythe coils' characteristics. These leads intro-duce all kinds of stray capacities which areprobably appreciably different for each ofthe coils in use. The object of the trimmersis therefore to balance out such strays.
The actual system of setting the trimmingcondensers depends very largely upon thecircuit in use, but the first thing is to turnthe adjusting screws . to their midwaypositions. To do this, they should firstbe screwed fully in, and then unscreweduntil the springy plates upon which theywork are in the full open " position.If the number of revolutions is countedwhilst unscrewing, it is an easy matter toturn back the screws for half the totaldistance of movement.o The next step is to tune in a station onabout 240 metres. The strength of this'Should be reduced until signals are only'just audible, either by means of thevariable -mu control or by fitting an aerialvolume control; for example, a 100,000 -ohmnon -inductive potentiometer may be connec-ted between the aerial and earth terminals,and the aerial lead connected to the slider.
By varying the trimmers until signalstrength attains a maximum their correctsettings can then be found. It is not quiteso simple a matter as might be conveyedby the last sentence, however, and theprocedure should be on systematic lines.First of all, the reaction condenser shouldbe turned to its midway position betweenoscillating point and " off,' to ensure thatthe capacity in this part of the circuit isat its average value. After that thetrimmer on that section of the condenserwhich tunes the detector valve should bemoved slowly backward and forward, mean-while trying the effect of slightly varyingthe position of the tuning scale,
When this portion of the Condenser has
been trimmed properly, one should workbackwards toward the " aerial " section.It will be found that some of the trimmerscrews have to be nearly full in, and othersalmost right out. If it is found that anytrimmer requires to be set to its extremeposition, all the others should be varied.In other words, suppose, for instance, thatthe " detector " trimmer needs to be " fullout," the others should be unscrewed alittle until the first one does not requireto be in the extreme position. If this isnot done, there will be no means of checkingthat the trimming has been done correctly.
Use the Lowest Possible Trimming CapacityWhen all the trimmers have first been
set as explained, they should be examinedto see if one of them is nearly at its minimumcapacity ; if not, they should all be un-screwed a little until one of them is practi-cally " all out." The reason for this isthat the tuning range will be restricted
the adjustments should be made on astation which is not subject to fading,whilst the process is considerably simplifiedif speech is being transmitted, since thismaintains an almost uniform strength ;most music, on the other hand, variesconsiderably in sound intensity.
Coil and Condenser TestsWhilst making the trimmer adjustments
the conclusion might be reached that thecoils are not properly matched, or thatthere is some variation in capacity betweenthe different sections of the gang condenser.In such a case a further test should bemade by connecting a single tuning con-denser in place of one or other section ofthe gang component. If signal strengthis better when the separate condenser iscorrectly tuned, it will be evident thatthere is a defect in either the coils or con-denser. Very often it is possible to decidewhich item is wrong by changing over twoof the coils (when they are of similar types).Should this make no difference, it will beevident that the condenser is responsible,
The above illustration shows three common typesof gang condenser with various kinds of trimmeradjustments. The condenser on the left has " star-wheer: trimmers, the other two having
ordinary screwdriver screws.
unnecessarily if the trimming capacitiesare any greater than they need be. Thisalso explains why some constructors ofPRACTICAL WIRELESS receivers find thatthey cannot cover the tuning range forwhich the set was intended-simply becausethe trimming capacities are too high.
The above general method is applicableto all types of receiver, but the procedureis slightly different in the case of superhets.When trimming a superhet, a start shouldbe made with that section of the gangcondenser which tunes the oscillptor valve.This is the most critical turnnu circuitand must be treated rather carefully,rotating the trimmer adjustment as slowlyas possible.
After all the trimmers have been set onthe low wavelength mentioned, it is advis-able to tune to a station somewhere nearthe top of the medium wavelength rangein order to make sure that, the settings" hold " as they should. Try moving thetrimmer screws very slightly in both direc-tions, and if it is found that any appreciablevariation is called for, a third test shouldbe lade on a station at about 400 metres.It IS scarcely necessary to point out that
but if a different tuning circuit is then un-matched, the coils will have been provedto be the cause of trouble.
When the coils are at fault the onlyremedy rests with their replacement. Theonly alternative is to abandon the idea ofusing a gang condenser and to use two ormore separate ones. Sometimes, however,if the coils are only slightly " out " (whenonly two are used) it is possible to make useof a gang condenser having an externaltrimmer knob ; this must be adjusted aftermaking each tuning adjustment.
THE WIRELESS CONSTRUCTOR'SENCYCLOPAEDIA
(2nd Edition)By F. J. CAMM,
(Editor of "Practical Wireless ')'MIS invaluable encyclopaedia is written in plain1 language by one of the most accomplished
designers and writers on wireless construction. Thewhole subject is fully covered, and the volume isremarkable_, for the number of practical illus-
trations it contains..Obtainable at all Booksellers, or by Pod5/6 from Geo. Newnes, Ltd., 8.I1, South
ampton Street. Strand, London, W.C.2, 51-
266 PRACTICAL WIRELESS -May 19th, 193 4
THE EVOLUTION OFTHE SUPERHET
The Superheterodyne Receiver Offers the Best Demonstration of the
Utility of the Modern Valve. By W. J. DELANEY
THERE is a common belief in the mindsof many of the British public thatany newly -introduced invention is
brought about by a desire to obtain moneyfrom the public, without introducing anyreal advantage by that purchase. I haveheard, for instance, several suggestionsmade by wireless enthusiasts that all thenew valves are really unnecessary, and thatthey are really " manufacturers' ramps."Of course, this is not true, and I think asimple explanation of the progress of themodern superheterodyne will prove thatnot only have these new valves actuallyintroduced many benefits to the wirelesslistener, but that they have, contrary to theabove -expressed view, actually resulted ina saving of money for the purchaser.
The Original SuperhetI remember one of the really first com-mercially -produced superheterodyne re-ceivers to be introduced from America.It employed no less than eleven valves.Each of these was enclosed in a separatemetal compartment, and affixed to the endof the metal cabinetwas a socket to con-tain a frame aerialnearly two feet square.Such a receiver wouldbe laughed at to -day,yet it was the onlymethod then availablefor utilizing thevaluable superhet prin-ciple. It has alreadybeen shown in thesepages how the super-heterodyne works.Briefly, H.F. amplifi- `""mu SLV VALVE
cation has to be em-ployed to deliver a suffi-ciently powerful signal toa first detector, and thisis employed in conjunc-tion with an oscillatingvalve to change thefrequency to that em-ployed in the I.F. stages.This gave us, in the modelmentioned above, threeseparate valves. Owingto the very low amplifi-cation given by valves, itwas necessary to follow these three stagesby four I.F. stages before coming to thesecond detector. To enable a really goodoutput volume to be obtained, two L.F.stages preceded the output valve.
Modern G.P. ValvesThe normal general-purpose valve has
an amplification of 30 or 40, and is equiva-lent, at the very least, to two of the above -mentioned L.F. stages, thus enabling theover-all number to be reduced ; but it iswith the modern type of valve that I wishto deaL The heptode or pentagrid hasenabled the function of the oscillator andfirst detector to be combined, and such avalve will thus perform, in one single stage,the duties previously carried out by twovalves. But more than this, the charac-
PENTA RD
teristics of the valve are such that we candispense with the pre-H.F. stage and stillobtain louder signals. It is even possibleto employ automatic volume control withthe combined valve, and from the pointof view of expense, therefore, no one candeny that there is a definite saving in thisone stage alone. In addition to the savingin actual expense there is also the muchgreater efficiency which is obtained, andthis represents a greater advantage thanthe saving in cost. Coming to the inter-mediate -frequency stages, one of the modemvariable -mu pentodes will not only delivera greater signal than four or even five ofthe old -type triodes, but its variable -mucharacteristics will enable the automaticvolume control feature to be fully employedin maintaining a constant signal to behandled by the second detector. Thus, wehave obtained in two stages a signal whichpreviously required probably six stages,plus the advantages of the A.V.C. systemand the increased stability which comesfrom the few components which are requiredand the consequent reduction in screening.
MIAOW vgt AAU Pe4100E GODS E DCOE-PHOODE
This illustration shows the development of the superhet from 1920to the present day.
The double -diode -triode and valves of asimilar nature are now employed followingthe I.F. stage, and these combine thefunctions of second detection (one diode)and A.V.C. (second diode). The triodeportion may be used as a first L.F. stage,and thus combine in one glass bulb threeseparate stages or functions. The double -diode -pentode, however, has such remark-able characteristics that it may be em-ployed to feed a loud -speaker direct, andthis means that with only three valves thewhole of the functions of the previously -mentioned eleven -valuer may be per-formed. The genealogical tree of the super -het shows its progress from the first -mentioned receiver down to the very latesttype of apparatus in the terms of valvesonly.
A CHEAP POWER SUPPLYFOR COUNTRY LISTENERS!.
This photograph shows the complete apparatus.
AMAINS supply of electric currentwas not available, and, as powerwas needed both for various experi-
mental receivers and also for a low powertransmitter, something both efficient andpractical had to be evolved. The followinggives details of how this difficulty wasovercome at low cost.
An old disused Triumph motor -cycleengine was salved from the scrap -heap ;this was bolted to a large plank, the footrests being heated and bent at right anglesand passed through the plank, the nutsbeing screwed on from the underside.Two more bolts were passed through theplank from the back -stays, making thewhole job firm. A dynamotor was takenfrom an old car and bolted firmly to theplank behind the engine. The dynamotor,being chain driven, was driven off the gearbox, the cog being the one taken from theoriginal drive on the car and fitted to theshaft of the gear box. A fan was fittedclose to the cylinder of the engine anddriven by a belt from the engine pulley forcooling purposes. To overcome the noisefrom the exhaust a 10 -gallon oil drum wasburied in the ground, and a pipe from theengine exhaust was led into this at thebottom of the oil drum, another pipe beingled out to above ground with a fishtail on theend.
The switchboard taken from the carand comprising a cut-out, ammeter andstarter switch was mounted on the wall.A 12 -volt sixty ampere -hour car batterycompleted the outfit. The field brush onthe dynamotor was adjusted to give leamperes with the engine running smoothly,although the rate could be increased to16 amperes without any undue stress onthe engine. The dynamotor acts as amotor to start up the engine by just pressing_the starter switch. The running costs arevery moderate, and one gallon of petrolwill run the outfit for 44 hours, whilst theamount of oil consumed is very small.
The 12 -volt supply is used to supply thefilaments of the transmitter and receivers.For the H.T. supply 300 volts from H.T.accumulators is used. These are chargedfrom the 12 -volt supply, being bankedinto 10 -volt blocks for this purpose, andthe charging rate multiplied by the numberof units in naralle1.-11. J. LONO.
May 19th, 1934 PRACTICAL WIRELESS 267
CALLING UP THE LISTENERDetails of an Interesting Method by means of which Receivers can be Switched On from the Transmitting Station
THE ordinary calling -ring as used witha telephone tells the subscriber when
- he is wanted to receive a message.This simple yet essential part of the tele-phone service could, with advantage, beapplied to the needs of the broadcastlistener.
Of course it can be argued that the latteris able to consult a daily list of programmesfrom which he can " spot " any particularitem he wishes to hear, and then tune -inat the appointed hour. But this does notalways turn out to be as simple or con-venient as it looks.
One may decide, perhaps, when readingthe morning paper that such and such aniterdshould be worthlistening to ; but bythe time eveningcomes one has eitherforgotten all about itor else cannot re-member the time orstation. And so, ifthe printed pro-gramme is not handy,the occasion goesby.
But apart fromhelping the !absent-minded listener, thereis much to be saidfor the idea of beingable to broadcast a" general call " onspecial to c casionswhich would auto-matically switch -insets that had beenleft on " stand by."In this way onewould be certain ofreceiving, say, anemergency news bul-letin, or any item ofoutstanding import-ance.
Automatic calling devices operating onthese lines have already been used as a" watch -dog " for the all-important S 0 Ssignal at sea, where human lives maydepend upon the safe receipt of the message.
There is also a rapidly growing field forwireless in cotmection with police work,where, similarly, it is of the utmost import-ance that every mobile patrol carrying awireless set should be kept in constanttouch with messages sent out from head-quarters.
A Circuit ArrangementThe accompanying diagram shows a
receiving circuit which has recently beendesigned for this kind of work. The setcan be switched over to " stand-by " andleft in that condition pending a "Directly upon receipt of the signal, a bellis automatically rung-or a lamp is lit-to warn the operator, who then switchesover to " receive " and listens to themessage.
It will be seen that the output circuit ofthe low -frequency valve V2 contains twotransformers, T and T1. The first feedsa bridge detector D, whilst the second isback -coupled to the input of the firstH.F. valve V.
If the switch S is left open, the set is on
By J. X. STONE
" stand-by," and the first signal received-on the wavelength to which the circuitL.C. is tuned-will send a rectified pulseof current through the valve V2. This isfed back to the H.F. valve V through thecouplings T, Ti, and after passing throughall three valves, is fed back again, togetherwith other rectified pulses from the incomingcarrier.
The feed -back process is continued until,in a fraction of a second, the current throughthe bridge detector D becomes sufficiently
The circuit of a police patrol receiver.
strong to operate the relay R and light thewarning lamp Z, or sound a buzzer alarm.
This warns the operator, who closes theswitch S, to cut out the feed -back coil,whereupon the set receives in the ordinaryway.
Much the same kind of idea is now beingexploited in America in connection withbroadcast reception. A type of relay isused which is sufficiently selective todistinguish between different control signalsand to respond accordingly. The controlsignals are sent out in code on a frequencywell below the audible range.
Coloured Signal LampsThere are various interesting possibilities
in this direction. For instance, supposingthe set is left on " stand by," an indicationof any particular kind of programme thenon the ether is given by means of differentlycoloured flash-lamps-red, say, for dancemusic, blue for a symphony concert, yellowfor the Children's Hour, and so on. Eachlamp is energized by the same relay, whichis rotated into different positions accordingto the particular " control signal " sentout at the beginning of each performance.
For instance, a long " dash ' closes onecircuit to light up the red signal, whilstone " long " followed by.a " short " signal -
impulse brings a second contact into actionto show a blue light. And so one can ringthe changes. The owner of the set caneledt either to switch off or to listen -in,according to his mood at the moment.
A further refinement allows the listener topush a button -switch under a signal -lamp ofselected colour, so as to keep the set silentuntil the required kind of item is on theether. As soon as this happens the relayautomatically switches the set on andbrings the loud -speaker into action.
Instead of using differently colouredlamps, a buzzer or alarm bell can be ar-ranged to give audible warning to anyonein another room of what is afoot.
The use of such acalling device means,of course, that atleast one of the valvesin the set must bekept constantly inaction, so as to am-plify each controlsignal as it comes insufficiently to operatethe relay. This, how-ever, involves verylittle expenditure ofpower - particularlyin a mains -driven set-and need scarcelybe taken into con-sideration on thescore t of expense,particularly where aluxury set is con-cerned.' The calling signalmay be transmittedon a note of definitefrequency, to which apolarized relay in theoutput of a single" live " valve istuned. The receiptof the signal is suffi-
cient to throw over the relay and so closea contact which brings the remaining valvesand loud -speaker into action.
An alternative scheme, which does notrequire even one valve to be left con-stantly in circuit, is to use a clock switchto turn the set on, say, for thirty secondsevery half-hour, and then to switch it offif the programme is not to the listener'sliking. If it is, he closes another switch tokeep the set going.
By fitting an automatic selector, therelay can be made to switch on the remainderof the valves automatically as soon as aparticular type of programme is availableand to switch them off again on receipt ofa new control signal indicating a change inthe type of programme.
Special calling -up signals are usuallyradiated on a frequency well below theaudible range. In the first place this is apart of the frequency -band not otherwiserequired, and in the second place it doesnot interfere with or obtrude itself on anyreceiver already in operation.i«.- ..... ! Order Our Companion Journal
"THE PRACTICAL MOTORIST"To -day! 3d. Every Wednesday. es
268
PEPRACTICAL WIRELESS May 19th, 193 4
MEA tILITY TUNINGPOSSIIILITIES
An Explanation._ of the Function of Iron -Core Coils and of the Principles Underlying Permeability Tuning
THE tuning of radio receivers consists ofestablishing a resonant circuit whichis responsive to the desired pro-
gramme, the circuit accepting a relativelylow band of frequencies, and rejectingsignals outside this band. The funda-mental properties of a tuned radio circuitare capacity, inductance, and resistance,and it is an elementary principle thatvariation in tuning can be affected eitherby varying the value of the capacity, theinductance, or both.
In the early days of crystal receivers alarge coil of wire, wound on a huge former,was employed, and by sliding a suitablecontact along a brass rod, the desired num-ber of turns was selected. This varied theinductance and the idea was to change therelationship of capacity to inductance.
Practical Methods of TuningFor many years now we have used
variable condensers to tune coils of fixedvalues, and because of the mechanicalconvenience of this method it has come tobe universally adopted.
The introduction of commercially -produced iron -core coils has now brought tothe fore the possibilities of an alternativemethod of effecting gradual variations inthe relationship of inductance to capacity,and a brief explanation will suffice toindicate why such a departure should benecessary and desirable.
It is very difficult to explain the reasonsfor new methods in radio without the aidof mathematical forrnula3 or, rather, toprove the efficacy of the method withoutactual demonstration, so the reader willhave to accept certain statements whichcould be tested if this survey were to bemade more academical.
An analysis of a tuned circuit which isresponsive over a broad band of frequenciesindicates that its electrical properties arematerially changed with variations infrequency.
The decay co -efficient changes if thecapacity is varied for tuning ; this is dueto the fact that the resistance increaseswith frequency. This variation in the decayco -efficient can be side-tracked by arrangingthe tuning circuits in such a manner thatthe inductance or the relative inductanceand capacity is applied so that for everyincremental increase in inductance theresistance is correspondingly increased.
Uniform SensitivityIt has always been the aim of designers
to bring about a tuning device which willbe equally selective and sensitive at allpoints of its tunable range, and since thedecay co -efficient is a direct measure ofthe selectivity of a single tuned circuitthe necessity for maintaining this factorat a constant value will at once be apparent.
In parallel resonance circuits, selectivityand amplification adversely affect eachother, due to the fact that the tuned circuitis a direct load on the anode of the valve.The cure lies in the use of suitably -designedvalves. Modern H.F. pentodes have ahigh amplification factor and anode
resistance, consequently the damping andits resultant effect on selectivity are prac-tically negligible.
Another factor determining amplifica-tion or voltage on the aerial system is thefrequency, but this is something over whichwe, at the receiver end, have no control.
The aim of the foregoing is to show thatif inductive tuning can be arranged so as to
In this coil the variable iron core is used forcontrolling selectivity.
maintain the ratio of resistance to induc-tance or vice versa, many highly desirableresults will accrue such as
Uniform selectivity over the whole of thewave -band.
Uniform gain in H.F. amplifying stages.Favourable gain relation in a tuned aerial
circuit throughout its tuning range.Practical possibility of tuning the aerial
circuit to obtain greater input gain andthus to increase signal-to-noise ratio.
Simplification of the circuits them-selves since transformers are notrequired.
The introduction of the new typeof variable ferro-inductance has beenproduced with the intention ofobtaining the above results. The aimof the design is to produce a unit.the coil of which is arranged to havethe desired performance at thehighest frequency in the band to becovered. A magnetic core is intro-duced into the field of the coil inorder to increase the apparentinductance for tuning to lower fre-quencies. The introduction of metalinto the field of a coil would at firstsight appear to be akin to placing anL.F. transformer in the aerial circuit.
Core MaterialsThe flattening and damping of an
H.F. circuit into which iron is
introduced renders such circuits aperiodic,and since for selective tuning periodic tuningis essential, a method has had to be devised toovercome the losses which the introductionof iron would bring about. This hasresulted in the commercial productionof finely powdered or divided particles offerro-magnetic cores. These cores are madeof highly -permeable alloys so, as to com-pensate for the losses resulting from thenumerous air -gaps between the particles.
In audio -frequency amplifying work weare accustomed to insulated laminations inL.F. transformers to reduce the losses dueto eddy currents and hysterisis. However,it is found that at high frequencies thehysterisis losses are extremely small.The eddy currents introduce resistancelosses proportional to the square of thefrequency, and to the length of the circularpath around each particle.
Since the object of tuning devices is toensure constant selectivity and sensitivityover the tuning range it has been foundthat the relationship of inductance tocapacity can be varied by inserting per-meability cores into coils of special design,and achieve the desired object with coreswhich have the particles or pellets graduatedin varying intensity, that is to say, tohave these dust molecules packed looselyor tightly at different parts of the core.
Core ShapeAnother method is to shape the core in
such a manner as to bring about the sameresult. We are familiar with " shaped "vanes in the stator section of a gangedtuning condenser as used in superhetreceivers, and the principle is much thesame. The various relationships betweeninductance, capacity, and resistance can bemaintained by suitably moulding or shap-ing the core material. This brings us toanother possibility-the ganging of multi -permeability tuned circuits. In the samemanner that superhet ganged condensersfunction by virtue of the shaped statorvanes the differences in multi -circuit valuescan be adjusted by suitable compensationin the design of the cores.
Another type o; coil inwhich matching may becarried out by varying the position of a small iron core.
May 19th, 1934 PRACTICAL WIRELESS 269
With the tESIDI"SKYSCRAPERANyou get radio on long,medium and shortwave stations
from ENGLAND,
EUROPE, AMERICA,
AUSTRALIA, and AFRICA
All you need is
A SCREWDRIVER
Read whatthese enthusiastic'Skyscraper' ownerssay:From SOUTH AMERICA :"Kit used on voyage to Buenos Aireswith ho ft. aerial. On the long and med-ium bands, home and European stationsreceived at good strength. ALL EMPIREPR OGR AMMES CONSISTENTLYRECEIVED AT GOOD STRENGTH.Also received SYDNEY andMELBOURNE."
From SOUTH AFRICA :London comes through quite clearly.
The best battery set we have heard."
From INDIA :Assembled Skyscraper' Four in two
evenings. Set worked marvellously.onderfully dear. Here in Bombay, am
receiving London programme on 49.5metres as loudly' and clearly as ever Iheard it on an ordinary Receiver inEngland."
From NORWAY:Set working splendidly. Over 60
stations with inside aerial."
*Every Factory Builtand Factory -testedReceiver carries alabel to this effect.
APAIR OF PLIERS 0 andOr you can now buy it completely factory assembledand factory tested at exactly the same price.*You can assemble these Skyscraper' Kit sets in a couple of evenings, and get full -power, moving -coil reception on all wavelengths. Besides the fun of buildingyour own set you have the satisfaction of knowing before you start that the resultswill be everything you expect - because every component part of the`Skyscraper' kit has been subjected to vigorous tests under actualworking conditions.For just a few hours fascinating work, the vast range, mightypower and real economy that have made Skyscraper' radiofamous throughout the world, will be yours-to enjoy dayafter day. Act now. Post the coupon for fullinstruction chart FREE. `tip
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HOW LITTLE IT COSTS Chassis Kit, com-
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coil Speaker . . . £ 8
USE LISSEN BATTERIES-LISSEN VALVES
LISSEN ACCUMULATORS FOR YOUR SET -9-31
270 PRACTICAL WIRELESS May 19th, 1934
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SIMPLE ELECTRICAL APPARATUSAn excellent little book for those who wish to make simple anduseful electrical appliances, such as galvanometers, electricmotors, dynamos and Leyden jars.
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May 19th, 19:34 PRACTICAL WIRELESS 271
IZE.ADEIZS'\\RN ICES
Simple Drilling Jig
IToften occurs that a hole has to be
drilled a certain depth into eboniteor metal, and the following dodge enablesthe operation to be done accurately. Insert
16 Or 18 S.WG.WIRE PUSHEDDOWN BETWEENJAW OF CHUCK
A simple drilling jig.
the drill to be used in the drill chuck,take a length of No. 16 or 18 S.W.G. wire,push one end down between the jaws ofthe chuck, then proceed to wind the wireon to the drill by turning the handle ofthe brace. Take care to keep the wiretightly wound, until the length of drillprotruding from the coil of wire is the sameas the depth of the hole to be drilled.Cut off the wire not required, close to thedrill.-E. T. BOWEN (Twickenham).
Making Five- to Seven -way Battery CordsMEAT five- to seven -way battery cords1 1. can be made in the following manner.Obtain a good quality tubular boot -lace,and after cutting off the metal tags, pushthrough it a long wooden knitting needle
BOOTLACE
INSULATINGTAPE
--- LEADS.
Making multiple battery cords.
at least fin. diameter. Remove the needleand proceed to thread through five toseven strands of flex of medium thickness,afterwards cutting it to the length requiredand attaching a wander plug to each end.Unless different coloured flex is used, itwill be necessary to mark each strand witha piece of stamp edging, for indicatingpurposes, before the flex is passed throughthe lace covering.-W. V. ANDREWS(Swansea).
Remote Control On -off SwitchASMALL clock which refuses to function
may be brought into very usefulservice as a remote control switch, asfollows :-
The clock, represented by (a) in theillustration, should have the balance wheel,
I
THAT DODGE OF YOURS !Every Reader of " PRACTICAL WIRE-
LESS " must have originated some littledodge which would interest other readers.Why not pass it on to us ? We pay ,E1-10-0for the best wrinkle submitted, and for everyother item published on this page we will payhalf -a -guinea. Turn that idea of yours toaccount by sending it in to us addressedto the Editor, " PRACTICAL WIRELESS,"George Newnes, Ltd., 8-11, SouthamptonStreet, Strand, W.C.2. Put your name andaddress on every item. Please note that everynotion sent in must be original, Markenvelopes " Radio Wrinkles." Oct NOTenclose Queries with your Wrinkles.
face, and hands removed. Next, the smallpin (c) on lever (b) should be broken offand armature (d) (a small piece of tin)soldered on to the lever. The electro-magnet
BELL PUSH
A'8 %4,4*
L.T. ACCUMULATOR
d e
/411/4®,1
L.T.TERM1NALS
ON RECEIVER
A combined clockworr and electric remotecontrol switch.
(e) is easily made by windingturns of No. 32 gauge wire on abobbin with a pieceof a stout iron nailfor the core. Themagnet is energizedby a 4i -volt torchbattery operatedthrough the distantbell push. On press-ing the button thearmature is pulledtowards the magnet,thus disengaging thelever and allowingthe escapement (1)to revolve. Aweak wire spring (g)brings back the leverwhen button isreleased.
about 500cardboard
TH E
HALF-GUINEA
PAGE
Fol. the -switch proper, a piece of springybrass (h) should be soldered to the spindlewhich once carried the minute hand of theclock. The switch panel (j) is secured tothe clock frame and can easily be madefrom a piece of red fibre *in. thick intowhich sheet copper contacts (k) are inlaidso as to form a flush surface for the revolvingswitch arm. The instrument should befitted into the receiver cabinet with theclock hand adjusting knob in a suitableposition and which thus serves as a normalon -off switch in place of the existing one.
It is important that the gap between thearmature and magnet be made as small aspossible, and in order to regulate this to anicety an adjustable brass stop (1) should -be bolted to a convenient part of the clock.As this switch is very sensitive and re-quires only a feeble current to operate it,the extension leads can be made of quitefine cotton -covered wire. Its one greatadvantage over most gadgets of a similartype is that the rotary switch is operatedby the powerful force of the clock spring.and, therefore, the contacts can be madevery efficient and noiseless. The batterylasts many months, and the clock needsbut an occasional wind.-H. J. WATSON(Southampton).
Switching Arrangement of Class " B "StagePROBABLY many readers would like to
try Class " B " owing to its economy,especially if they are using batteries witha small output in milliamps. This wasmy experience, so I devised the switchingarrangement shown in the accompanyingdiagram. By using a four-way switch,which I found in the junk box, I am nowable to switch over to Class " B " or topower output, as required. On occasionswhen it is required to boost up the set, thisdodge will be found very handy, if thespeaker is of the permanent magnet type.If the speaker is not of this type wiresA and B can be taken to an ordinaryspeaker. Also, if the valve is of the Osramtype make wire C a flexible one, and takeit to the grid -bias battery (about 3 volts)instead of to L.T.-.-W. ROGERS (Dept-ford).
(Continued orerkaf)
A switching arrangementfor Class " B': stage.
272
READERS' WRINKLES(Continued from previous page)
An Easily -made Speaker ChassisTHE following description of how I
constructed a speaker chassis froman old motor -headlamp reflector and a piece
- of aluminium may interest other readers.
.41uvrta.rsiztStrip
eir*ustinQKnob
/Deflector
Alumznzurn...f'-c`rep Bent 73 -Owe
An easily -madespeaker chassis.
First of all I took the reflector and cut outfour sections with a hacksaw. The out-side rim of the reflector was then hammeredflat and four fixing holes drilled in it. Thestrip of aluminium was then taken and theunit bolted to it. The aluminium strip isfixed by bending the ends down and hold-ing the reed of the unit exactly in the centreof the hole in the apex of the reflector.When four holes were drilled in eachcorner, the strip was bolted to the chassiswith four small bolts. The cone is madeof cartridge paper and fixed to the frontedge of the chassis with adhesive tape.-R. Worth (Guernsey).
A Novel Drawer ArrangementHERE is a useful hint which may appeal
to those readers who like to have atidy workshop, and are at a loss for storagefor small parts such as terminals, wanderplugs. drills, etc. The writer purchased adozen pencil boxes with sliding lids at theprice of 2d. each. These were fixed to theunderside of a shelf in the following manner.The shelf was first removed for conveniencein working. Twelve lines were then
A neat arrangementof drawers made from
pencil boxes.
marked across the underside, the distanceapart being a little more than the widthof each box, to allow for clearance. Thelids of the boxes were removed and a centreline drawn down each. On this centreline, holes were bored to take small counter-sunk screws, and each lid was then screweddown to the shelf, as shown in the sketch,a thin brass washer being slipped overeach screw between the shelf and the lid.The shelf was then refixed to the wall, and
PRACTICAL WIRELESS
the boxes slid on to the lids. The additionof a small round -headed screw to the frontof each box, to act as knobs, completed thejob.-R. W. FARMER (Manchester).
A Simple Coil WinderIT is not an easy matter to wind coils,
chokes, and transformer coils calling formany turns of very fine wire. The simplecoil -winder shown in the accompanyingsketch will be found useful for windingtransformer coils and chokes. At one endof a wooden base, wooden blocks are fixedwith clamps to support the hand -drillhorizontally and in line with the end ofthe board.
At the other end is fastened a U-shapedpiece of sheet metal, as shown. Itsinside height is 1 in. and a hole is madeat the top, and one in the baseboard forthe spool spindle. The winding bobbinconsists of a suitable piece of wood with theshank of an old drill driven in length -wise.The wire is led from the wire spool through ascrew -eye near the edge of the boardand then to the bobbin. The numberof turns of the chuck to each turn of thecrank is then ascertained so that the bobbinturns can be tallied. The run of the wirealong the bobbin is maintained by slightfinger pressure on the wire between the
A simple coil winder.
eye and the bobbin. A thousand turnscan be wound by this little device in lessthan ten minutes.-,J. CROWSHAW (Bolton).
Tape Machine for Recording MorseTHIS machine can be made very cheaply
and assists the morse code learnerto send messages correctly. Commence bymaking four supports from tin. brass rod,one a little longer than the others to takethe ink pot. Cut a short piece of softiron rod, the length of bobbin, and drilltwo small holes at one end to take elastic.Glue the bobbin to the baseboard, and fitthe supporting rods as shown, spaced atequal distances from thebobbin. Place a woodenstop below the plungerso as to limit the size ofmarking on the tape.Next, fix the elastic tothe supports after passingit through holes made inthe soft iron rod.
For the inker, use thinsyphon wire (wire tube)supported on a small tintrough, one end beingopen for writing, while tothe other a piece of brasstube is soldered to take apiece of valve rubber forconnecting to ink tap. Forworking the apparatus, use4 to 6 volts, and for the
INK POT
May 19th, 1934
morse read the lower part of the writing. Apaper streamer can be used for the tape.-F. W. MARLow (Wembley).
A Novel Escutcheon PlateTHE accompanying sketches show how an'
escutcheon plate can be fashionedfrom a lady's belt buckle. These buckles
Cut AuutyCentre .52.140And Dri/12.!mall HilesAt each Lc -Asa
An escutcheon plate made from a buckle.
are obtainable in a variety of shapes, andthe one used for the escutcheon shown in the
sketches was chromium plated withbevelled sides. The escutcheon canbe fixed to the panel with twoscrews, as indicated.-R. L.PRESTON (Sheerness).
A Source of TroubleIF you are finding your receiver
is not giving the results withwhich it has been accustomed inthe past, try cleaning the aerialand earth switch. It will be foundon examination the copper switchpoints have oxidized and this sets
0/ up a very high resistance. Cleanthe blade and the jaws with finesandpaper so that they makegood contact. Unless the wiresconnected to the switch are
soldered in lugs, which, in turn, are clampedunder screws, remove the wires, polish themthoroughly with fine sandpaper and replace,tightening the screws as much as possible.
Drilling EboniteI HAVE always found, when preparing
a panel composed of bakelite orebonite, that it is best to use drills ofthe best high carbon steel variety. Theyshould be kept sharp, so as to avoidburrs on the face of the panel. When sawingthis kind of material do so with a hacksawhaving about twenty-four teeth to theinch.
ELASTIC
A novel tape machinerecording morse
Or
INFERSOLDERED TO
PLUNGER
DIA FLANG4/000(11r DISCROTATING FREELY
N PIN
BRASS RODTHREADEDEACH ENO
SUPPORT
aASTLC
MaY 191.4, 1934 PRACTICAL WIRELESS 273
SIMPLIFIED MAINS TRANSFORMERCONSTRUCTION
The Making of Mains Transformers Has Been Considerably Simplified by the Introduction
of New Components, which are Referred to Below.
AVERY large percentage of readersalways evince a considerableamount of, interest in the subject
of transformer construction, and, althougha number of prattical articles have previ-ously been published no apology -is con-odered necessary in presenting yet anotherone.
In the past many readers have experi-enced some little difficulty in obtaining thecomponent parts required in making
Fig. 1.-A set of parts for making a mains transformer, which, complete withwound bobbin, costs lls. 4d.
transformers, and, therefore, it will be ofespecial interest for them to learn thatcomplete kits of parts can now be boughtquite cheaply. Moreover, by using theseparts, it is an easy matter to constructeven a pretentious type of mainsformer on the dining table without the useof any other tools than a screwdriver and,perhaps, a pair of pliers and a solderingiron. Winding spools can be obtained ina variety of sizes, whilst terminal strips,core clamps, and mounting bolts can beobtained ready made and finished in aworkmanlike manner. Those who wish toavoid the rather tedious process of windingthe many hundreds of turns of wire on to thespool can buy the latter already wound tothe appropriate specification and ready tofit on to the core stampings.
A Transformer for a Type " A " RectifierA complete set of parts for a mains
transformer giving outputs of : 250-0--250volts at 60 milliamps., 2-0-2 volts at 4 amps.,and 2-0-2 volts at 1 amp. is shown in thephotograph, Fig. 1. This kit, with woundbobbin, costs only lls. 4d., and it can becompletely assembled in a quarter of anhour. If desired the same parts, but withbobbin unwound (all wire supplied), canbe bought for 9s. 4d.; the constructionin this case will occupy five or six hours,whilst the work involved will be found bothinteresting and instructive.
As mentioned above, the kit includes thecore stampings -6 dozen size No. 4 stalloy-winding spool to fit, three bobbinscontaining the required wire, and the
special shroud clamp fitted with a neatpaxolin terminal plate and terminals.For those who prefer it, however, fourIngle clamps, the necessary clamping bolts,and two terminal strips (shown in Fig. 2)can be obtained in place of the shroudclamp, the total price of the kit in this casebeing 1 ls. 4d. with the unwound bobbin,or 13s. 6d. ready -wound.
Constructional DetailsThe method of construction is practically
the same no matter which set of parts isused, and a very satisfactory instrument issure to result in either case. First of allthe bobbin must be wound, the primarybeing put on first. For the type of trans-former previously referred to the primaryconsists of a total of 1,920 turns of 32 -gaugeenamelled wire, tappings being taken afterwinding 1,600 and 1,760 turns. By
making con-nection to the" beginning "end of thewinding andthe 1,600 -turntapping thetransformer issuitable f o ruse on 200 -volt A.C.mains havinga frequencybetween 40and 60 cyclesper second; for
220 or 240 -volt mains connection must bemade to the 1,760 -turn tapping and theend of the winding respectively. Forintermediate voltages it is in order to usethe nearest tapping point.
Before the winding make asmall hole in one end -cheek of the spooland pass a short length of flex through this.Solder the end of the 32 -gauge wire to theflex and cover the joint with a strip ofinsulation tape. The appropriate numberof turns can then be wound on either byhand, or by mounting the spool in a lathe orin the chuck of a hand -drill, this tool beingheld in a vice. So as to guard againstbreakdownthe wind-ing shouldbe put onas nearly aspossible inlayers, anda sheet ofoiled silkshould beused toseparatethewindingapproxi-mately into Fig. 2.-Another set of parts for a mains transformer including angle clampstwo halves.Tappings clamping bolts, and terminal strips.are made by baring the wire for a shortdistance, making a loop, and solderingshort lengths of flex. The flexible leads canbe brought out through the end cheeks.
The Secondary WindingsAfter the primary has been completed
it should be covered with a layer of oiledsilk before commencing to wind the second-aries. It is desirable to screen the primarysince this reduces the possibility of mainshum. The screen may consist of a sheet ofcopper foil wound nearly round the bobbin,or the 4 -volt, 4 -amp, low-tension windingmight itself be employed as a screen. If
of a Number
By FRANK PRESTON
the copper foil method is employed it isvery important that the foil should notcompletely encircle the bobbin, because, ifit does, it will act as a short-circuited turnand cause the transformer to overheat,besides reducing the output almost to zero.A flexible lead should be soldered to thescreen and this will later be clamped urin contact with the core. (Incidentally,it might be mentioned that a screen isprovided on the ready -wound bobbinspreviously referred to.)
Another layer of oiled silk must be usedto cover the metal screen. If the L.T.secondary is to be used as a screen it shouldsimply be wound on top of the primary inthe form of a single layer comprising 32turns of 18 -gauge d.c.c. wire. A tappingshould be taken after winding on 16 turns,and this will be made exactly as explainedin respect of the primary. In order toavoid any confusion later on it is advisableto mark all the leads by means of papertags, or otherwise to pass them throughsystoflex sleeving of various colours foreasy identification.
Cover the L.T. secondary with a strii,of oiled silk, and then put on the 4 -volt,1 -amp. winding ; this will consist of 32turns of 20 -gauge d.c.c. wire, a tappingbeing taken after winding 16 turns. Againinsulate and finally wind on the high-tension secondary. This will consist ofa total of 4,000 turns of 38 -gauge enamelledwire, a tapping being taken after the2,000th turn. Wind on this wire as evenly-as possible and insulate after about every1,000 turns, taking care that no later turnsslip past the insulation.
The set of No. 4 stalloy stampings com-prises 6 dozen pairs, and there will be twoor three left over. The stampings are
inserted alternately from one end of thespool and then from the other, and arefitted in the following order ; first insert a" T " and then a " U " from one end ;then repeat from the other. This order imaintained until the bobbin is quite full,the last few stampings being lightly driveninto place to ensure that the core will be atight -fit and therefore free from vibration.
All the parts referred to above, andillustrated, can be obtained from Messrs.McDaniel and Co., Eastern Road, Rom -ford, Essex, whilst this firm will be pleasedto quote for any kind of transformermaterials.
274 PRACTICAL WIRELESS May 19th, 1934
TWO TNT F,S1 1 INGUNIV Hi 1p SAL AMP LIFIEThe Universal Amplifiers Described Below are Supplied by the High -Voltage Rad o
as Kits of Parts or Completely Assembled and Tested
UNIVERSAL valves, which can beoperated equally well from eitheran A.C. or D.C. supply, have rapidly
increased in popularity during the lasttwelve months and are now recognised tobe as efficient as their ordinary A.C.counterparts. We have described fromtime to time a number of circuits in whichthis type of valve can be employed, andwe therefore found it particularly in-teresting to try out in our laboratories twopowerful low -frequency amplifiers in whichthe universal valves have been successfullyemployed. The amplifiers in question havebeen designed and made by The UniversalHigh -Voltage Radio Co., whoare well known as suppliers ofOstar-Ganz universal valves.
The 3-4 Watt UnitThe smaller amplifier has a
maximum undistorted outputof some 3.5 watts and is builtaround a comparativelystraightforward circuit com-prising a special screen -gridinput stage, resistance coupledto a type K 3560 triode out-put valve. A type EG 100Ostar-Ganz half -wave rectifieris used in the H.T. circuit andis followed by a Ferrantismoothing choke and two8-mfd. Dubilier electrolyticcondensers. An output trans-former is fitted, and this willgive correct matching withmost types of loud -speakers,including small ones for home use and largeauditorium models. The amplifier can beobtained ready-made and tested for £6 6s.,or as a complete kit of parts with wiringplan and full instructions, for £5 5s. British -made components are used throughout, andthe unit is assembled upon a very stoutsteel chassis.
It can readily be connected to almostany type of receiver without any modifica-tion to the standard wiring being necessary.On test, the amplifier proved to be ex-ceedingly efficient, and gave great volumeand particularly pleasing quality. Therewas an almost complete absence of humboth on A.C. and D.C. supplies, and thissays much for the rectifier and smoothingequipment which are provided'.
A Larger AmplifierThe larger amplifier has the same input
circuit, but the first valve feeds into adouble amplifier using a modified duophasecircuit arrangement. There are two triodevalves (Ostar Ganz type K3560) and thetwo ends of the primary winding on theoutput transformer are connected betweentheir anodes, a centre tapping going toH.T. positive. The grid of the second valveis fed from the anode of the first through a.01 rad. condenser and a 1 megohm gridleak, a .5 megohm leak also being con-nected between the grid and H.T. negative.Both valves receive their correct bias dueto the voltage -drop across a 500 -ohm
resistance, which is by-passed by an 8-mfd.electrolytic condenser.
A Double RectifierThe power -supply system is very in-
teresting and includes a " double " half -wave rectifier-an Ostar-Ganz type NG100.This is again followed by a large smoothingchoke and two 8-mfd. electrolytic smoothingcondensers. Very ample decoupling isused throughout, with a result that mainshum and signs of L.F instability are entirelyabsent. The undistorted output is justabout twice that provided by the smallerunit, or, in other words, between 6 and
The larger amplifier described on this page.
8 watts. It is thus more than sufficient for" home " use, and certainly adequate formany forms of public address work andfor use in small halls.
Like the 3.5 watt amplifier, the largerone can be bought either completely as-sembled or as a kit of British -made parts ;the prices are £8 8s. and £10 10s. respec-tively.
Both amplifiers are sure to prove verypopular, and it' need scarcely be mentionedthat the prices are distinctly reasonablein view of the excellent quality. Eitherunit can strongly be recommended to anyreader who is in search of a really first-class amplifier for use on any mains supply.When ordering it is best to state whatmains .voltage the amplifier will generallybe operated from, since the valves (whose
The above photograph gives a general impression of the 3-4 wattamplifier and shows the underside of the 7-8 watt chassis.
Co., and can be Bought
heaters are fed directly from the mains)are supplied in different working voltages.Advantage of Universal Valves
It need not be stressed that universal(A.C. or D.C.) mains working is an extremelyvaluable feature in an amplifier, and isgenerally of greater importance than it isin a wireless receiver. This virtue is verypronounced in cases where an amplifier isused by a dealer or tradesman for demon-strating purposes, although it is by nomeans insignificant from the amateur'spoint of view, since it enables him to testout quickly any type of set with the ampli-fier in circuit. Those readers who at presenthave a D.C. mains supply which will in allprobability be changed to A.C. in the verynear future (as soon as the grid scheme iscompleted), will readily appreciate theadvantages of a universal receiver or ampli-fier which can be used just as well afterthe supply change -over as it can now, andwithout the slightest modification beingnecessary.
Special RectifierThe special mains -voltage
rectifying valve has a heaterwhich is fed directly fromthe mains supply, in thesame way as are theheaters of the receivingvalves. This rectifier func-tions in the normal mannerwhen the amplifier is fedfrom A.C. mains, but behavespurely as a series resistancewhen D.C. mains are
employed. The resistance is, of course, quitelow and therefore does not reduce the H.T.voltage to any appreciable extent. Incident-ally it might here be mentioned that thespecial " double " half -wave rectifier used inthe larger amplifier is an entirely new depar-ture. It is also wired in an unusual way sothat one section supplies the necessary D.C.current for the field windings of a normalmains -energized moving -coil speaker, whilstthe other hal f feeds the anodes of the valvesin the usual manner. By following thissystem the advantages of the energized
speaker can bemade use ofwithout the in-troduction ofany attendant
voltage-drop,suchas occurswith the
generally -adopted methodof speaker enerrgization.
Altogether,the amplifiersunder reviewhave been welland carefullyde-signed, with theresult that they
are just as good intheory as in practice.
May 19th, 1934 PRACTICAL TELEVISION
z-15
it ulOkaMAY 19th,19th, 1934. Vol. 1. No. 20.
SUPPLEMENT TOPRACTICAL WIRELESS
Amu_ iii
ILL ES1100NOTES OF THE WEEK
By H. J. BARTON CHAPPLE, Wh.Sch.; B.Sc., A.M.I.E.E:Additional Power for Television
MANY readers using simple discreceivers have found that theirradio set used in conjunction with
it just lacks sufficient power adequately tomodulate the neon lamp or give a strongenough synchronizing signal to hold theimage steady. In such eases one of theeasiest solutions to the problem is to makeup an amplifier adaptor to connect betweenthe radio and television receivers.
Although many circuits can be furnishedto cover such a scheme as this, that shown
pair of input terminals of the unit,thereby inserting in, circuit an effici-ent constant -inductance low-freqUency choke L.F.Cf. The inputpotentiometer, which should have aresistance of 100,000 to 250,000 ohms,serves as an efficient volume control.
In the anode circuit of V are twoswitches, Si being a triple -pole double -throw type and S, a double -poledouble -throw type. The object of S2 is tochange a negative image into a positiveone merely by reversing the primary
I.,FC. .G.13.-
in Fig. 1 is of quite a representative anefficient type. It converts the outpvalve of the radio receiver intoa choke -capacity stage coupledto an additional super -powervalve. The open " anode cir-cuit of the receiver's outputvalve is connected across the
St
Fig. 1 -A suitable circuit for an amplifieradaptor to use in conjunction with a disc typetelevision receiver. Suitable values for C1 and
C2 are 0.1 mfd. and 2 mfds. respectively.
circuit connections of the ',output trans-former T.
Regarding the switch Si, when this isd in its bottom position the unit is connected
ut to the television apparatus via the
Fig. 3.-Modifying the output connections to a choke -capacitytransformer feed.
Fig. 2.-The transformerconnection to the television
receiver.
transformer T alone, as shown in Fig. 2,which remtsents a simplified diagram ofFig. 1 with S1 switch blades down, S2omitted (this only is for positive and nega-tive pictures) and the jack J ignored. Thevoltage applied to H. T. -I-1 must suit thevalve employed-a valve such as theCossor 620T is admirable for a unit of thischaracter-and since the neon lamp (andsynchronizing coils if included) are joinedacross the output terminals the voltage forH.T. + 2 should be 200/250 and drawnfrom a source capable of furnishing the fullpolarizing neon lamp current.
With the switch blades of Si in the topposition the circuit connections are changedto a choke -capacity transformer link withthe television apparatus as indicated in thesimplified diagram of Fig. 3. The high -impedance choke L.F.C.2 is now inserteddirectly in the anode circuit of V, thetransformer primary of T being linked toL.F.C.2 by C2.
If switch S1 is left in this top positionand a loud -speaker plug inserted into jackJ, then the transformer and televisionappafratus are cut out of circuit, Fig. 4showing the simplified arrangement. Theunit then functions as an additional poweramplifier for ordinary sound reception.
Polarized LightThe original Kerr cell, which was later
L.F. C.2H.T.
Fig. 4.-Introducing a loud-speaker for tuning purposes.
Z?b.11 PRACTICAL TELEVISION May 19th, 193 4
developed by Dr. Karolus ,fot televisionpurposes, has played an important part inthe science of television. It enables abright source of light to be modulated inintensity and, as far as Iow definitiontelevision reception is concerned, it givesthe brightest and largest image.
The complete unit operates on theprinciple of polarized light, of which thefollowing is a simple explanation. Lightitself is an electro-magnetic manifestation,and a beam of light consists Oftransverse vibrations in all direc-tions at right angles to the directionof propagation. Many years ago itwas discovered that light could bepolarized, or limited to a singleplane of oscillation or vibration.Later 'it was found that a crystalof Iceland spar, cut along its axisand 'with a segment removed;could be rejoined in such a mannerthat it would transmit advancinglight in one plane only.
Two of these crystals in seriesFig. 2.-Wave motion is stopped at the second diaphragm.and with their axes crossed at
right angl6s would entirely prevent LIGHTSOURCE
PRISMSthe passage of light. In otherwords, the action of a Nicol prism(this is a particular form of 'V.Iceland spar crystal) is to selectthe component of all the trans- Fig. 3.-verse vibrations (our light beam)in the direction of a given line fixed withrespect to the prism.
It is difficult to show this effect in ascientifically correct manner, but a referenceto the accompanying diagrams will nodoubt help to convince readers. Supposea rope or string is drawn through twodiaphragms, as shown in Fig. 1, in such amanner that one end is fixed and the otherfree to be moved by the hand. Moving thestring rapidly up and down will result inthe travel of a wave along the cord passingthrough both diaphragms, provided theyare in the same direction.
Fig. 1.-Allowing the s ring to vibrate.
impression that they are stationary.By adjusting the motor speed to thiscondition, therefore, before the tele-vision transmission commences, the imagewill appear stationary, right at thebeginning, and time is therefore not wasted.
But what can be done by those readerswith D.C. mains, or alternatively use H.T.batteries and a.-6-volt.motor to feed thetelevision receiver P. If the ordinary neonlamp is connected in series with a D.C.
voltage through' a resistance (thiso is usually included in =the lamp's
base for normal domestic illumina-tions purposes) with a condenserof any capacity joined in parallel- with the neon lamp, the previoussteady direct current supply will beconverted into a regular pulsatingcurrent. With a large capacity
" condenser the pulsations will beseen as light flashes which can becounted. The period of the neonflashes or current pulsations bearsa definite relationship to theresistance and condenser includedin the circuit. Referring to thediagram, the period of the currentpulses is given by the simpleequation P =kCR, where k is aconstant and C and R represent
passes. the capacity in farads andresistance in ohms respectively.
With C or R constant and R or Cvaried, a linear law exists between thefrequency of the flashes and the variablequantity, and this holds good over verywide limits.
Here, then, is a very simple method forbuilding up a stroboscopic neon " flasher "with either D.C. mains or a 200 -volt H.T.battery joined across the voltage sourceterminals shown in the diagram. Exactvalues for C and R cannot be furnished,as the pulsations will obviously vary witheach form of assembly, but as a roughguide it can be stated that with a 2-megohmresistance for R and a .01 mfd. capacitycondenser for C, an ordinary beehive neonlamp will pulsate with approximately 50flashes per second. If this condition is used,then only four spokes will be required inthe scanning -component, but if the resist-ance is halved (or the capacity halved)then we shall have 100 flashes per second,and eight spokes are necessary.
Connect up the apparatus as in thediagram, using the values just mentioned,but arrange a semi -variable compression -type condenser (or an ordinary tuningcondenser if preferred) of about .0005 mfd.maximum capacity in parallel with thefixed condenser. Close the switch S duringthe course of one television transmission, andadjust the motor speed to its correct valueso that there is no image drift. Now adjust
the compressiontype condenseruntil the neonflashes are of thecorrect number togive the station.ary spoke con-dition.
If now the second diaphragm is turnedthrough a right angle, as in Fig. 2, so thatthe slots are as indicated, the wave motionwill stop at this second diaphragm. Ineffect this is analogous to the operationof the two Nicol prisms with their axescrossed. Light passing through a Nicolprism is said to be plane polarized sinceit exists in one plane of oscillation only.(Strictly speaking, when there are twoprisms the first is called the polarizer andthe second the analyzer.) Thus, if two suchprisms are set up as in Fig:3, no lightpasses, but if it was possible to rotate thefirst prism a gradually increasing passageof light would be secured as the axes of thetwo prisms approached the parallel state.
It is not possible for television purposesto effect this actual rotation rapidlyenough by mechanical means to make thisproperty of any value, but by means of theKerr cell, it is possible to utilize the polari-zation effect. The simplest type of Kerrcell consists of a pair of plates suspended orimmersed in a medium of nitro -benzine,carbon bisulphide, or other highly refractivedielectric fluid. If this device is placedbetween the two Nicols it has the effectof distorting the line of vibration passingthrough the first prism into an ellipse ofeccentricity progressively changing as thevoltage between the plates is increased,passing through a circle and eventuallybecoming a line of vibration at right anglesto the initial direction. Accordingly, aprogressively increasing component is avail-able for passage through the second prism.
As the light -voltage characteristic curve
of a cell of this nature is not a completestraight line (it resembles somewhat astatic characteristic curve of a thermionicvalve) it is necessary, in order to avoiddistortion, to apply an initial D.C. biasingvoltage just the same as we do to a L.F.amplifying valve. Whereas for a valve thebias is negative, however, that for a Kerrcell is positive and of much greater mag-nitude (up to 400 volts) and under theseconditions the light variation with voltage
I
z
When the prisms are set up in this manner, no light
variation is linear over quite a large rangeof signal voltage.
If the received and amplified televisionsignals are fed to the Kerr- cell it is possibleto secure an amount of light passing out ofthe second or analyzer prism, which isproportional to the light activating thephoto -electric cells at the transmittingden. The addition of a scanning mechanism,preferably of the mirror -drum type, com-pletes the television receiver, as was thecase of the Mirrorvisor described recentlyin this journal.
A TELEVISION STROBOSCOPEFOR D.C. MAINS
ATELEVISION receiver is only capableof giving images which can bewatched satisfactorily when the
speed of the rotating scanning member,(disc, mirror drum, mirror wheel, etc.) isidentical with that employed at the trans-mitting end. For the standard B.B.C.transmissions this is 750 revolutions perminute, but without some means of check-ing or measuring, the experimenter canvery easily waste a considerable time ingetting his speed correct. Those readerswith 50 -cycle A.C. mains installed have aready means of checking to hand by usinga flashing neon lamp. When this is con-nected across the 50 -cycle mains its lightis interrupted or is extinguished 100 timesper second (one for each half -wave of volt-age). As the scanning mechanism rotatesthrough 4,500 degrees per second (121 x 360)the number of degreespassed through inone second is 45. If,therefore, there are .4:.eight spokes or marksspaced at equal anglesof 45 degrees round rs k,the disc or drum at ,.,;:t
the correct isochro-nous speed of 750revolutions per minutethe regular flashingneon lamp illuminationthrown on to thesespokes will give the
1:1C VOLTAGE PLIED HERE
The complete circuit for a D.C. television stroboscope.
May 19th, 1934 PRACTICAL WIRELESS 277
THETHE EASY ROAD TO RADIO
BEGINNER'S
FADING -ITS CAUSE ANDPREVENTION
A Simple Explanation of a Summer Topic.
THOSE readers whose interest inwireless dates only from lastwinter may have been surprised
/ and rather perturbed of late to find thatI the reception afforded by their receivers! is now considerably worse than it was,I say, a month ago. The longer periods of
daylight are largely responsible, so thereis no need to start to dismantle the set
i with the idea that it hassuddenly developed a fault.There is, in fact, very littlethat can be done except toadd an H.F. amplifying
! stage or to erect a newand more efficient aerial,
I but both of these pointsshould be considered.
The reason for the falling -off in strength of the moredistant stations is very
Isimilar to that which ee-1 counts for fading, a phe-
nomenon which is oftenmore pronounced in winterthan in summer. To
Iunderstand the cause offading and reduced signalstrength in summer it is necessary toconsider how wireless signals actuallytravel from the transmitting to thereceiving aerial. Although we speak
I rather loosely of wireless waves, there arereally two sets of waves, one of whichtravels parallel to the surface of the
! earth-called the ground wave-and onewhich is sent upwards into space. Thelatter is called the reflected wave, forreasons which will be explained.
The Reflected WaveIt is known that the upward set of
waves is reflected back to earth againin the manner represented diagrammatic-
? ally in Fig. 1, and reflection takes place at1 what has come to be called the Heaviside
Layer. This is a layer of gas situatedsome sixty miles above the surface of theearth, the condition of which depends
! upon the strength of the sun's rays uponI it. When the rays are strong the Heavi-
side Layer is a very poor reflector, and itI absorbs the greater portion of the wireless
waves which strike it. When it is indarkness, however, this layer of ionizedgas acts as a very good reflecting surface,and so " returns " the waves to earth.
Reflection and WavelengthNot only does the effect of the Heavi-
I side Layer vary with the amount ofI sunlight falling upon it, but also with the
wavelength of the high -frequency wirelesswaves which strike it. The conditions of
Pp
reflection stated above apply mostaccurately to medium -wave broadcastsignals, for waves shorter than 100 metresor so are reflected very little by the Heavi-side Layer, and pass through it. The": transparency " of the Layer increasesrapidly as the wavelength is reduced, sothat wavelengths of 20 metres or lesspass through it almost without hindrance.
ows-HEA vaDe zap.,
"Fo
Fo
4".
Fig. 1.-This drawing shows how theground and reflected waves are sentfrom the transmitting to the receiving
aerial.
The shorter waves, however, are reflectedback to earth, but from a much greaterheight-that of the so-called AppletonLayer, which is thought to be nearly160 miles above the earth's surface.
How Fading ArisesIt is now possible to understand
exactly how fading takes place. Considerfor the moment a medium -wave trans-mission and assume that the ground andreflected waves are approximately equalin intensity. During darkness the receiv-ing aerial will pick up both sets of waves,although the ground waves become veryweak after travelling for a comparatively
Fig. 2.-When the ground and re-flected waves are in correct phase, asshown above, signal strength is at
maximum.
short distance, due'to the fact that theyare fairly readily " absorbed " by metallicobjects, hills and buildings. The reflectedwaves, however, are strong, and thereforeproduce good signals. If the surface ofthe Heaviside Layer remained perfectlystill, signals would be received at uniformstrength so long as darkness prevailed.But it is considered (no one has yetproduced a definite proof) that the layeris in constant movement, with a resultthat the degree of reflection varies fromone moment to the next. At one momentthe signals from any particular stationmight be directed right at the receivingaerial, but shortly afterwards the angleof reflection would have changed so thatthe signals were not received so well.
Phase DifferenceThere is another point to consider, which
is in relation to the " phase " of theground and reflected rays. Supposingthat both waves were in the same" phase," as shown in Fig. 2, thenthey would be added together, the signalstrength being equivalent to the com-bined effect of the two. On the other
hand, if the two were ofopposite " phase " (see Fig. !I3), the effect upon the re-ceiving aerial would onlybe equivalent to the differ-ence in strength between Ithem.
It his not difficult to It
imagine what would be the Icombined effect of changes
'4 in the reflective angle and IIalso the changes of phase ! INor is it difficult to under-stand why signals fromany particular (distant) I,
station may vary from fullstrength to inaudibility ina few minutes.
IF.
Fading d'h Long and Short WavesBefore considering methods of prevent-
ing fading we must see what happens onwavelengths other than those generallyreferred to as " medium " and beingbetween 200 and 600 metres. On longwaves, for instance, fading is almostentirely absent. This is because thetransmission is almost entirely confined tothe ground waves ; any upward wavesthat there might be would be completelyabsorbed by the Heaviside Layer. It isalso worthy of note that there is less !
absorption of the ground wave, andtherefore the distance over which the Isignals can be sent without any trace of .1
I
I
Fig. 3.-This drawing shows conditionof minimum signal strength, theground and reflected waves being out
of phase.
I
. I, a.14111.1 -141111101 }IMII4 '4111=4 11111101}0.1...
THE BEGINNER'S SUPPLEMENT(Continued from precious page)
fading and with a given power is greateron long than on medium waves.
It has been explained that short wavesI are reflected from the Appleton Layer,
and the effect is very similar to the reflec-tion of medium waves from the Heavi-side Layer. The principal difference isthat on the shorter wavelengths theground wave is almost non-existent, due
9 to the fact that it is so rapidly absorbedby metallic objects. Thus, the reflectedwaive gives somewhat more steady recep-
i tion because there is no question of phasedifference. It is also very important to
I note that the Appleton Layer is not sogreatly affected by daylight and darkness ;
I in fact, wavelengths in the region of120 metres can generally be received better in daylight than after dark.
Beam TransmissionOne method of overcoming fading is to
i direct the transmission along a narrowbeam, and although this has proved a
t very effective method it has the greatdisadvantage that the signals can only bepicked up by aerials situated in the lineof that beam. The only other method ofpreventing the effects of fading is to fit
! an automatic volume control device toI the receiver itself. There is no need to
describe here the method of doing thissince the subject has been very fully
.4. treated in these columns before. At theI same time a warning should be given that
constructors should not expect too muchI of A.V.C. It is possible to design aI receiver the output volume of which will
remain constant for signal ratios of 1,000to 1, but such results cannot be expectedfrom a simple set modified to incorporatean A.V.C. arrangement. The averagemodified receiver of the type having acouple of H.F. stages and fitted with anAX.C. unit can scarcely be expected to
I provide a uniform output for signal ratiosin excess of 50 to 1 or so on the mediumwaves. In other words, if the signal
! voltages applied to the aerial exceed avalue which is fifty times greater or fiftytimes less than the average value, the
output volume will be affected. With agood superheterodyne having two I.F.stages it is possible to compensate forsignal variations up to about 300 to 1 byfairly simple means. When consideringa very simple type of set such as thatdescribed in PRACTICAL WinELEss datedNov. 4, 1933, the A.V.C. action cannot beexpected to be complete on any signalswhose aerial -voltage ratio exceeds about15 to 1, but even this apparently smalldegree of compensation is extremelyuseful.
There is just one other point whichshould be made clear in connection withA.V.C. This is that the control does not-cannot, in fact-increase the strength of
I fading signals ; it can only reduce thestrength when the signal voltages becomegreater than some particular value. Itis therefore useless to expect A.V.C. tobe of any appreciable value in a com-paratively insensitive receiver.
The only other solution to the fadingdifficulty rests with the wider use ofshort waves, and those readers who areD.X. (long-distance) " fans " would dowell to build a short-wave receiver forreception during the summer months.
THE IMPORTANCE OFVOLTAGE MEASUREMENTSIT is small wonder that in many sets
valves have a tendency to fail intheir emission or suddenly fade outaltogether. It is a common practicewith set operators to feed the valves in aset with a high-tension potential whichaccording to their reasoning is correct.The method usually adopted is to increasethe H.T. until the reproduction in thespeaker is what they consider it ought tobe. This adjustment by ear, whether high-tension batteries or eliminators are used,is a very bad policy, for it almost invari-ably results in the use of excessive platevoltage, and is frequently responsible fordissatisfaction on the part of the listener atthe service life of the valve. This pointis particularly true in the case of powervalves, with which the reception, whenjudged by the ear, improves as the valveis overloaded as regards plate voltage. Ifthe best life is to be expected from a valve, acareful survey and study should be made of
the complete [specifications and operatingcharacteristics regarding the proper usewhich valve manufacturers supply withthe valve, and is usually to be found inthe carton. The information regardingthe proper filament voltage, plate voltage,and grid bias to use and the best applica-tion of the valve in a circuit should bestudied carefully, so that full advantagecan be taken of the knowledge gained bythe manufacturers in the experimentaland development work which has beendone with the valve. It is very essential,after having done this, to measure thevoltages applied correctly. As theseeliminators and the conditions underwhich they are used vary greatly,, it isalmost impossible to determine the correctsettings merely by listening to there production of the receiver and adjustingthe supply until reception sounds allright. The variable adjustments on theseunits should be set accurately to thereceiver with which they are used, and ahigh -resistance voltmeter employed forthe purpose.-C.D.K.
AERIALS -4
ALTERNATIVE METHODS OF FIXING AERIALAND EARTH LEADS
TN LID OR METAL COVER
GroovesPREVENT
WIRESL/P.FiNG.Down,
CORRECTMETHOD
INCORRECTMETHOD
ATTACHING INSULATORS
A SHORTSAFETY WIRESUPPORTS AERIALIF JOINT 'X'SIVES WAY
DOWNAO
CLAMP
SWITCH
LEAD -INTUBE
A CLAMPHOLD/VG DOWNLEAD To WALLRELIEVES STRAP,/ON AERIALSWITCH.
SLACKSAFETY
W/RE
DOWNLEAD
/NCORRECT
CORRECT
A SLOPINGDOWN- LEAD& ADVISABLE.
PIECE OF TIN
SWITCHFROM THEWEATHER
AERIALSWITCH
To EARTH
WIRE
PULLEY
WIRE SHOULD BE USEDFOR ATTACHING PULLEYTO MAST. THE PULLEY SHOULDBE WELL GREASED.
EARTH LEAD
PIPE I
THE EARTH LEAD MOST Y AOFTEN BREAKS AT THEPO/NT WHERE IT ENTERS
V
THE GROUND UNLESS PRorecrE/Mil
I
May 19th, 1934 PRACTICAL WIRELESS 279
cuttiont
By the Editor.
Broadcast Reorganization in SwitzerlandIT is reported that Marconi's Wireless
Telegraph Company, Limited, havereceived an order from the Swiss TelegraphAdministration to increase the power of theexisting Marconi station at Beromiinsterfrom 60 to 100 kilowatts. At the sametime, a number of modifications will beeffected which will make the station one ofthe most up to date in existence.
One of the most interesting of thesemodifications is the incorporation of the" floating -carrier " system, which auto-matically controls the carrier wave radiatedby the station. In this sytem both thecarrier power and the input power are smallin the absence of modulation, or when alow degree of modulation is present.Deeper modulation automatically increasesthe carrier power, and, consequently, theinput power, so that higher modulatedvoltages can be correctly reproduced. Bythis means a large saving of power iseffected. The transmitter will be stillfurther improved by the introduction of theMarconi " series modulation " system,similar to that incorporated in the designof the new Droitwich station and that atMotala in Sweden. This feature representsthe latest development in broadcastingtransmitters, ensuring the highest possiblequality of reproduction and, at the sametime, a marked simplification of design andconstruction.
Lucerne Wavelength PlanUNDER the re -allocation of wavelengths
recently decided upon at Lucerne,the question of stability of the trans-mitted frequencieshas becomeof the greatestimportance, a n dmost existingbroadcasting sta-tions are now beingre -equipped withdrives of a fargreater precisionthan those in usepreviously. T omeet these newconditions, Bero-minister will beprovided with ahigh -precision crys-tal drive havinga frequencythat will complywith the moststringent inter-national frequencystabilization re-quirements.
The increase ofpower from 60 to100 kilowatts willbe effected by re-
placing the existing poweramplifier at Beromiinster,which consists of twoaluminium and glass units,by a new stage of a similarconstruction containing twoMarconi CAT. 14 valves, thelargest water-cooled valves oftheir type in existence.Droitwich, Motala, and otherhigh -power stations n o w
under consideration are being fitted with thesame type of valve. The appearance ofthe other units of the Beromiinster trans-mitter will not be changed, but the technicalalterations projected will naturally requireconsiderable modification to the internallayout of the circuits. The newequipment necessary is being manu-factured at the Marconi Works, Chelms-ford, and it is expected to be ready forfitting at Beromiinster in the autumn ofthis year.
Wembley's New Amplifying ApparatusTHE Empire Stadium, Wembley, after
using various types of amplifyingequipment since its opening, is now equippedwith a permanent installation. Probablythe biggest of its kind in Europe, since theStadium holds nearly 100,000 people, theapparatus is the work of Philips, the lampand radio manufacturers.
Formerly, a stand carrying the ampli-fying gear used to be placed in the middle ofthe grass and dragged off after the musichad finished, just before the beginning ofplay. But spectators at the England -Scotland International and the Cup Finalwill have noticed the shining new aluminiumpainted loud -speakers on their polesencircling the ground. The apparatusincludes a 600w. amplifier, giving 130w.undistorted output, a double turntablegramophone cabinet for two microphones,fourteen super -power loud -speakers, andtwo high -capacity rectifiers for loud -speakerfield excitation. The amplifier valve is aPhilips type MA. 4/600, operating at ananode potential of 4,000 volts, and dis-sipating approximately 600w. There aretwo rectifier valves, type 1762. Theamplifier is housed in an earthed metalcasing so constructed that all power isautomatically cut off on the opening of tilt,inspection gate.
AN " EKCO " OF THE CUP FINAL
Manchester. City football team, who recently won the F.A. Cup atWembley, enjoying a little relaxation with their Ekco model 74 receiver.
Early Morning BroadcastsTHE British listener who rises at an
early hour is now given many oppor-tunities of hearing musical broadcasts whilstenjoying his breakfast. Hamburg is alreadyon the air at B.S.T. 6.20 a.m. and theconcert is taken by a number of Germantransmitters ; Cologne (Langenberg) followsat 7.0 a.m., with Stuttgart a close third atabout the same time. The Dutch stationsare usually heard working from about7.40 a.m., and Poste Parisien, Radio-Normandie and Radio -Paris also offerrecitals of gramophone records almost dailyfrom 7.0 a.m." Intimate " Stagecraft
AN entirely new type of stagecraft per-formance has been designed by
Marconiphone Publicity. Previous showsembodying the stagecraft principle wereput over to audiences of from fifty to 2,000people and, as is by now well known, weredistinctly successful and fulfilled theirobject. The new entertainment, whilstembodying the above -mentioned stagecraftprinciple, differs materially from its pre-decessors. More attention has been devotedto continuity of the entertainment as wellas to subject matter. The show is designedfor presentation to audiences of not morethan fifty people and, when put overproperly, gives the listener the impressionthat he or she is seated at home listeningto broadcasts in normal home surroundings.
Marconiphone have taken as the basisof their operations two B.B.C. plays,namely, Flags on the Matterhorn and Chopin.Both of these have been very successful onthe air, and have been recorded on ordinarygramophone records.
Those entrusted with the task of pre-senting this entertainment have a veryimportant psychological factor to bear inmind, to which every attention will begiven. These recorded plays will be putover on a single instrument, which will beplaced to one side of an ordinary domesticfireplace. The show will take place in avery dim light in order to lend that in-timacy to the occasion which home listeningdemands." Tom Thumb " ValvesTHE introduction of a " Tom Thumb "
Osram valve may mean that in thenear future the police throughout thecountry will be equipped with miniaturewireless receiving sets in which thesevalves are incorporated. As these valvesare only about two inches long, with acircumference not much larger than thatof a shilling, it is obvious that they can beinstalled in a set of very small dimensions,particularly as they can be associated withthe more compact coils and condensersof a highly efficient character, which arenow available.An Interesting Lecture
THE last lecture of the present sessionto be delivered before members of
the British Radio Institution, members ofthe International Faculty of Sciences andvisitors will be given at King's College,Strand, W.C.2, on Thursday, May 24th,at 7.0 p.m., by Professor A. M. Low, D.Sc.The subject will be " Sound and Noise."Readers of PRACTICAL WIRELESS areespecially invited. Admission is, of course,free, although invitation cards may beobtained, if desired, from the Secretary, 36,Gordon Square, W.C.1. This lecture con-cludes a very successful session before largeaudiences and has the strong support ofboth the Faculty of Sciences and of King'sCollege.
280 PRACTICAL WIRELESS May 19th, 1934
Sha t aveSection
ELIMINATING NOISES IN A.C. MAINS -DRIVEN SHORT-WAVE RECEIVERS
By A. W. MANNsome Useful Hints on Tracking Noises Which Apply
to Both Broadcast and Short-wave Receivers
THE elimination of parasitic noises,should they develop in A.C. mains -operated short-wave receivers, is
not a difficult undertaking, but one whichrequires systematic methods of procedureand common-sense reasoning. The purposeof this article is to enable technically -minded readers, who may look upon thechassis of an A.C. short-wave receiver as amass of complications which is a littlebeyond them, to tackle the elimination ofminor troubles without difficulty.
Do not get into a panic and jump to theconclusion that the source of the trouble isinside the receiver. It may be external-and, above all, do not guess or take any-thing for granted when trouble tracking.File this article for future reference in caseof doubt, should hum, crackling, buzzing,and ticking noises be super -imposed uponthe programme matter emitted by the loud-speaker, and proceed to trace and eliminatethem as follows
HumIn order to trace the cause, examine all
external leads. Aerial, earth, or speaker
leads may run too close to a wall in whichmains wiring is embedded. Remove eachlead in turn from the wall. If this procedurecauses hum to cease, direct inductive pick-up by the respective lead which, whenmoved, cured the hum, was responsiblefor it in the first place.
The possibilities of sound -wave emissionfrom the speaker causing vibrations of theinternal valve elements, should not beoverlooked. Move the speaker away fromthe receiver, and note the effect.Microphonlcs
Tap valves in turn (set working), inorder to test for microphonics, and if anyparticular valve causes a howl to build upin the speaker when tapped, replace witha new valve.
Examine all electrically -operated domes-tic appliances, fans, vacuum cleaners, etc.Appliances of this nature, even thoughlocated some distance from the receiver,may cause interference.Crackling
Remove aerial and earth leads, switch onreceiver (as in case of hum). If crackle
stops, examine all lighting and powerswitches, operate them, and note ifcrackling is heard in speaker when doingso. Examine and operate all domesticappliances. Examine fuse and junctionboxes.An Obscure Fault
The writer recently traced two causes ofcrackling in a mains receiver ; another,however, remained, and tests as describedabove showed, O.K. It was noted that whensomeone overhead crossed the landing.crackling was heard in the speaker. Ex-amination showed a slack connection in ajunction 'box of the house wiring underfloorboards. One of the latter, when walkedupon, pressed down on to mains lead,causing sparking between the bare endsand junction box terminals, which, beingin effect a miniature transmitter, causedcrackling in the speaker, due to pick-upby aerial system. This was cured by switch-ing off mains and tightening junction boxterminals.Common Sources
Do not forget, that unless suppressiondevices are fitted, electric neon signs, robottraffic signals, trolley systems, and carignition systems are all sources of cracklingand interference.
Rock each valve in its associated socket(set operating). Increased crackling denotesfaulty contact between valve pins andsockets respectively. Hum, if heard,denotes open circuit between valve pinsand socket. Adjust sockets or valve pins.
Clean between -Wiling and other variablecondenser vanes with a pipe cleaner.Before using the cleaner compress it be-tween two pieces of board, so that it willpass between vanes without forcing.
39 TYPES IN THE DARGOOD VALVES THAT SAVE Y
Get our list and study the table which shows the DARIO altefor all popular valves. Note the prices and you will see thatDARIO means a worth -while saving of money-something like £the case of a mains 5-valver.More than that, the DARIO range is so complete that whateverhave or contemplate, there's a highly efficient DARIO exactlyfor every valve -holder.Few low-priced valves can show you anything like so comprehensirange and no valve at anyprice can give you more up-to-date design or more con-sistently accurate manufacture
than DARIO I
VALVESIMPEX ELECTRICAL LTD., 47, VICTORIA STREET, WESTMINSTER, LONDON, S.W.I
May 19th, 1934' PRACTICAL WIRELESS 281
A "SAFETY FIRST"SWIIB'CH
Constructional Details for a Simple and Novel Switch, for Disconnectingthe H.T. Supply when the Lid of the Set is Opened
IMMEDIATELY the lid of the receiver isopened more than an inch the set isswitched off and remains so until the
lid is almost closed again, the switchoperating on the initial opening movementand the final closing movement.
The actual method of operation of theswitch is clearly shown in Fig. 1. With thelid open the switch knob is in the " Off "position. On closing the lid the sliding armslides down the knob until the spring catchand the knob are in contact. By this time
Method OfMthifbta9,._roltch
The CompletedUtOMCZZIZC 07Z -
Off 814itCh
AlrMethod Offittmo 144th
Zower,510,4ch
Fig. 1.-A view of the finishedswitch, and constructional details.
the lid is almost closed, and in the finalmovement the knob is pressed down (and" On ") by the spring catch, and then,having reached the end of its movement,allows the spring arm to be clipped over it.On opening, the strength of the springcatch is sufficient to operate the switch, thelatter then remaining in the up (or " Off ")position while the spring catch slides overthe knob and the lid is fully opened.
When Using a Rotary SwitchIf a rotary type of switch is used the
method of connection is shown, inset Fig. 1,the lower inset showing how the lever typeis utilized. An arm will be necessary withthe former type, but it can easily be madefrom a piece of aluminium or, preferably,brass. If the latter material is used the nutin the lower parts of the " U " can besoldered in position. A screw is insertedinto this nut and turned until it grips thespindle, holding the arm in any desiredposition.
A round -headed screw is inserted in a nutsoldered on the end of the arm, a furtherlock -nut securing it in position, the head ofthis screw taking the place of the knob ofthe lever type. A less workmanlike, butquite efficient arm, is illustrated in Fig. 2,the inset showing the arm before bending.
The switch is supported in a brass oraluminium bracket of the type shown. Thisbracket should be large enough to clear the
connections to the switch, and to preventthese connections being touched by handwithout removing the bracket from theside Of the cabinet. The actual connectionsshould be made with heavy flex leads beforethe bracket is fixed in position.
The Sliding ArmThe sliding arm is made from a lid stay,
the part which is usually fixed to the sideof the cabinet being removed. This can beaccomplished by filing away the top or
cutting the arm at the bottom andresoldering after removal. Thislatter operation will definitely benecessary if a lever switch is used,because the slot must be narrowerthan the diameter of the switchknob, otherwise it will slip through.With the rotary switch this is notnecessary, because the screw can befitted through the slot. Thissoldered cut will be seen in Fig. 1.
The spring catch is clearly illus-trated in Fig. 1, and is made fromspringy brass. Do not make thearm too short, otherwise the move-ment may be somewhat erratic
when it is in use ; it shouldbe securely fixed to the slidingarm with a nut and bolt.
To simplify the fitting of theswitch, make the two distances(marked X) equal, it will thenbe found that as the stay isupright when the lid is closed,one or two dimensions willsuffice to ensure that the switchis in the right position. Theideal to aim at is-when the
lid is closed the spring catch has justslipped over the knob (or screw -head), thelatter being, of course, in the down (or" On ") position by this time.
The distances X should also be chosenso that in the maximum open position thelid just goes over the top dead centre.
The switch is additional to the usual On -Off switch. The mains lead should be takendirect to this new switch and from there tothe present mains -input terminals.
Fig. 2.-An alternative form ofccnnecting arm.
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282 PRACTICAL WIRELESS May 19th, 1934
Before You Go For Your Holidays!Some Timely Hints On Leaving Your Radio Behind. By A RADIO ENGINEER
THOSE who are about to depart forany . holiday will assuredly not
1,, forget to turn off the gas and thewater, to Hick and bolt all the doors andwindows, and, put the cat or dog out toboard. Will they, however, expend anequal amount of care upon the radio equip-ment which has served them so wellmonth in and month out ? Probablynot, but here are a few suggestions whichare worth considering if you intend to beaway from home for any time.
Let us start at the very beginning ofthings-the front and back door of ourradio, so to speak. I mean the aerial andearth. The risk of an aerial being struckby lightning is very remote in any case,but certain periods usually bring one ortwo severe thunderstorms, so it will beas well before leaving home to disconnectthe' aerial and earth leads from the setand connect them together, thus earthingthe aerial.
One listener I know goes further thanthis. He actually lowers his aerial (notthe pole but only the wire) and coils it upfor storage in his garage. His explanationis that it is as well to be on the safe side,and besides, if he takes the aerial down itgives him an automatic reminder to cleanor renew the insulators when he comesback, and to examine and, if necessary,repair the halliards. Quite an excellentscheme, this. If you decide to leave youraerial up, and to earth it, I think I shouldgive the ground near the earth tube a goodsoaking before... I went away. This willensure a reasonably good earth connection-lightning has been known to seek abetter path than that afforded by a poorearth.
AccumulatorsThe next thing to consider is the set itself.
If it is a mains operated receiver, you will,of course, see that it is switched off, andpull out the plug if it is normally suppliedvia a wall socket. Beyond this, no furtherprecautions are necessary in the case of amains set.
With a battery -operated receiver, how-ever, one has to consider what to do withthe batteries. A few years ago, listenerswere warned that if they intended to leavetheir radio for as long as two weeks it wasessential to empty out the acid and leavethe low-tension battery filled with distilledwater. To -day, however, batteries havebeen so improved that this precaution is no
longer necessary. It is, however, veryunwise to leave a low-tension accumulatorfor any considerable period in a run-downor even partly run-down condition.
The best plan is to take your accumulatorto the charging station a couple of daysbefore you go away, and have it properlycharged. Then you may leave it at homefor two or even three weeks without riskof it becoming sulphated. This, of course,is assuming the battery is in reasonablygood Condition. If, however, you suspectthat your battery is in poor health-if,that is to say, it has not been retaining itscharge well-why not give it an overhaulas well ? Hand it over to the care of areally reliable charging station, asking theproprietor to examine it thoroughly andhave it properly charged and ready for youby the time you return.
The cost will not be great, and you willhave the satisfaction of knowing that yourbattery will return to you with a new leaseof life. If you are leaving your batteryin the house, it will be wise to remove it tothe kitchen or scullery, or somewhere elsewhere there is a stone floor so that, shouldany acid leak out, no damage will be doneto carpets or furniture.
As for the high-tension battery, I thinkI should disconnect it in order to removethe slight possibility of its running down ifthe insulation of the circuit is not perfect,or the unlikely risk of damage shouldchemicals leak out. I have known instanceswhere some defect in one or more cells hasresulted in the formation of a sticky messof chemicals which could damage neighbour-ing components and at all events causeunsightly stains..
If your high-tension battery does notlive in the radio cabinet, see that it isnot placed where it will be exposed to anyform of heat. Neither should it be storedin a very (lamp place. Provided thesesimple precautions are taken, no harmis likely to occur to your high-tensionbattery.
Now let us see if there are any otherpoints which require attention before youlock up the house. The set itself-thatwill come to no harm if left in its normalposition. As for the remainder of yourequipment, speakers, extensions leads, andso forth, they will come to no harmwhatsoever if you leave them as they are.
OverhaulsBut the fact that you are going away
gives you an opportunity of having anyoverhauls or repairs done which you mayhave been inclined to put off previouslybecause of the inconvenience of beingwithout the radio. Perhaps you have a" sticky " condenser, or an unreliableswitch ; or possibly you know there is abad connection which causes cracklingnoises at odd intervals. If you are not oneof the amateurs who build their ownreceivers and do their own runnintrepairs,now is the time, while you are on holiday,to hand your set over to your local dealerwith instructions for repairs and renewal.
Or possibly you have long intended tohave your set modernized, or even con-verted for mains operation. This is a jobwhich your dealer will be glad to tacklewhile you are away. Perhaps it would notbe a bad plan if I suggested a few of theimprovements which could be carried out onvarious types of set at very moderate cost.
Suppose you are now running a two -valveor three -valve battery set of the detectorand low -frequency type. A screen -gridvalve in front of the detector will makeall the difference to the range and selectivityof your set, and the cost, including the priceof the screen -grid valve, should not exceedabout thirty shillings.
If your set already incorporates a screen -grid high -frequency stage, you may thinkit worth while to substitute one of thelatest variable -mu valves, and thus obtainsmooth and efficient volume -control bythe use of a simple potentiometer across thegrid -bias battery. This is a very cheapreconstruction. Beyond the price of thevariable -mu valve, there is only two or threeshillings for the potentiometer.
Conversion to mains operation is, ofcourse, a rather more costly job, becausethere are new valves to buy as well as apower unit. If you are now using a mainseliminator, this can also be used for thehigh-tension part of the power pack, whenthe only new apparatus beyond the mainsvalves will be the filament transformer.There will, of course, be the cost of thework of conversion, and a shilling or so forfive-pinholders.
Another job which might be done whileyou are on holiday is the overhaul ofyour moving -coil speaker, should it needadjustment. It is something of a ticklishjob to re -centre a moving coil, and it isbetter, unless you are really handy at thissort of thing, to return the speaker to themakers for servicing.
wirrearAwrorairk kar
UNIVERSAL HIGH VOLTAGE MAINS VALVESThe full range is available for me by any manufacturer, kitmaker or constructor. Work on either A.C. or D.C. withoutany alteration. Marvellous results already achieved by Britishmanufacturers with these famous valves.
THE VALVES USED IN THEUNIVERSAL THREE-VALVER
and Universal Super described in recent issues of "Practice!Wireless " are the latest types of the famous °star -Gana High.voltage Valves with which No Barretters, No Mains Trans-formers or Cut -down Resistances are used, because they workstraight off any mains.Free Circuit with each set of valves. KITS of parts to enablehome -constructors to build Universal Sets with the minimumof simplicity and cost, also supplied.
Details Free on request.Phone : TEMPLE BAR 8603.EUGEN J. FORGAT,
28-29, Southampton St., London, W.C.2
The First and Finest entirelyself-contained
UNIVERSAL A.C. - D.C.
SHORT-WAVE ADAPTORCan be used on either A.C. or D.C. without anyalteration and also on any mains from 100-250 volts.Simple to connect. Just plug the unit into themains, connect the aerial to adaptor and takeanother lead from top of adaptor to aerial terminalof receiver.Suitable for all wavelengths between 12 and 85metres.
PRICE £6 6s. Od.Complete. Fitted with the famous Ostar-Ganz High -voltage Valves. Adaptable to any Mains Receiver.UNIVERSAL HIGH -VOLTAGE RADIO LTD., 28-29, SOUTHAMPTON STREET, STRAND, LONDON, W.C.2.
UNIVERSALA.C. D.C.
AMPLIFIERSEmploying the famous Ostar-GanzUniversal High Voltage Mains Valves.
4 to 10 WATTS UNDISTORTED OUTPUTRead the "test" report on page 274 of this issue
SINGLE OUTPUT DOUBLE OUTPUTAssembled AssembledComplete £6.6.0 Complete f10.10.0KIT with Valves 25.5.0. KIT with Valves 28.8.0.
Complete Public Address Unit 22 Got.District Agents Wanted. 'Phone Temple Bar 4985.
PRACTICAL WIRELESS 283May 19th, 1934
RADIO CLUBSAND SOCIETIES
Club Reports should not exceed 200 words in lengthand should be received First Post each Mondaytnovning for publication in the following week's issue.
INTERNATIONAL SHORT-WAVE CLUB (MAN-CHESTER CHAPTER)The seventh meeting of the above Chapter was held
on May 1st, at 8 p.m.,!at the Clarion Café, 50A, MarketStreet, Manchester, at which there was a good attend-ance of radio enthusiasts.
Arrangements were considered for visits to BartonAirport and the North Regional transmitters atMoorside Edge , also a proposed " Field Day " inJuly or August was discussed. At this meeting alecture was given by Mr. G. V. Colle, of Ward andGoldstone Ltd., entitled " Practical Consideration ofShort-wave Reception, including Interference Prob-lems." Reference was made in this lecture to theuse of A.V.C., Q.A.V.C. and superhets on short waves.
The next meeting will be held on Tuesday, June 5th,at the Clarion Café, 50A, Market Street, Manchester,at 8 p.m. Any PRACTICAL WIRELESS reader desiringfurther information should write to the secretary,R. Lawton, 10, Dalton Avenue, Thatch Leach Lane,Whitefleld, near Manchester.
ANGLO-AMERICAN RADIO AND TELEVISIONSOCIETYMr. K. T. Cawse demonstrated his transmitter at
the last meeting of the Uxbridge District Branch ofthe above society. Among the experiments carriedout were the exploding of gunpowder by means ofinduction. To do this, gunpowder was placed acrossa one -turn coil, and when this coil was placed nearthe tuning coil of the transmitter the gunpowderwent up.
Mr. William Johnston was appointed honorarysecretary.
There are no charges for attending meetings of thebranch, and everyone is welcome. Full particularsfrom Leslie W. Orton, " Kingsthorpe," Willowbank,Uxbridge.
INTERNATIONAL SHORT-WAVE CLUB (LONDON)At a meeting of the London Chapter, held on Friday,
May 4th, Mr. J. A. Wilen, B.Sc., described anddemonstrated the new Scott all -wave fifteen -valvesuperhet on both radio and record. The receiver tunedfrom 13 to 550 metres, good reception being obtainedfrom W8XK, WIXAZ, RW59, CT1AA, EAQ, etc.Records of reception of the Empire Station and theGerman short-wave station as received in Americawere then reproduced. All readers of PRACTICALWIRELESS are welcome at these meetings, and thenext one will be held on Friday, May 18th, at 8 p.m. -Secretary, Arthur E. Bear, 10, St. Mary's Place,Rotherhithe, London, S.E.16.
SLADE RADIOAnother lecture by Dr. Ratcliffe was given at the
last meeting of this society, and for the benefit ofmembers who were not present on the previous occasion,he repeated the details of the early experiments byCarl Hertz, Clarke Maxwell, Sir Oliver Lodge, andSenator Marconi, etc. In the course of his lecture hedescribed how the propagation, transmission, anddetection of wireless waves were discovered.. -Hon.Sec., 110, Hillaries Road, Gravelly Hill, Binhingharn.
I EDITOR'S NOTE: Querists must limit theirqueries to three per letter.
L. PM11,11..11.111.1.04111141.11moes
H. RUSSELL (Leeds) : EAQ : P.O. Box 951, Madrid,Spain ; W8XK, Westinghouse Electric and Manu-facturing Co. ; studios at William Penn Hotel,Pittsburgh (Pa.) ; 12110 ; E.I.A.R., ria Asiago N.10,Rome, Italy. ONE-VALVER (Forest Hill): W8CPC,B. T. Simpson, M.D., 108, Homer Avenue, Buffalo,New York; VK2WB, W. Bullivant, West Wyelong,N.S.W. ; K4SA, It. Bartholomew, Barrio de SabanaHoyos, Garrochales, Porto Rico. E. WALKER(Sheffield) : F8RR, E. Bonamy, Les Pieux (Manche),France ; G6LL, J. Matthews, 178, Evering Road,Clapton, E.5, G6LI, A. Livesey, Stourton Hall,Horncastle, Lincs. SNORT -WAVER (Greenock) : SUR,Abou Zabal (Egypt), 44.25 m. (6,780 kc/s) ; ORD,Ruysselede (Belgium), 22.19 m. (13,520 kc/s) ; RKL,Khabarovsk (Siberia), 17.26 m. (17,380 kc/s), 27.97 m.(10,723 kc/s) and 45 m. (6,666 kc/s). ADAPTOR(S.W.26) OK1BC, J. Chmel, Libusina 6, Plzen-Loehotin, Czecho-Slovakia ; EA5BE, Santos Yebenes,Juan de Austria 17, Valencia, Spain ; VE1BZ, F. W.Hyndman, Box 249, Charlottetown, Prince EdwardIsland. D. C. PARKER (Witham): W1BES, L. Bellem,Jnr., 143, Eastwood Avenue, Providence, RhodeIsland ; W2GAQ, S. T. LeRoy, 103, 5th Avenue,Watervliet, New York ; W2TT, G. W. McCauley,220, Front Street, Mineola, New York. BRS1330(r. R.E.S.) LR5. Radio Excelsior, Buenos Aires, on361.4 m;
viAA 4, is
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11
A TREATTO LISTEN
NOW" with theA nightmare of "crackles" and "buzzes" hasended for this Southampton listener whofitted a T.C.C. Anti -Interference Unit. Neonsigns, motors and generators do not exist forhim as far as his radio is concerned. Don'tlet your listening be marred by such "man-made static "-this T.C.C. Unit will cut it out.Ask your Dealer to -day.
The Telegraph Condenser Co., Ltd.,Wales Farm Road, N. Acton, W..3
PRICEcomplete
withinstructions
CONDENSERANTI - INTERFERENCE6UNIT
10 4909
284 PRACTICAL WIRELESS May 19th, 1934
faistsf4TutesComponent$ d in our Laboratorq
BY THE PRACTICAL WIRELESSA USEFUL KITALTHOUGH, probably appealing more to the
Service man than the average experimenter,the interesting kit of spare parts which is here illus-trated should find a place on every experimenter'sworkbench. Often it is found necessary to fit a newfuse or a plug for some temporary connection, andalthough many of these parts may be found lyingon the bench or in some drawer, it is very convenientto have them all together in one spot as in this kit.Elastic bands firmly grip each individual part, and inaddition to the standard types of plug, there are tencartridge fuses and 2 screw -type fuses. The priceof the individual parts is 10s. 7d., so that the makersof the kit, Messrs. Belling and Lee, give you 1 Twintapplug valued at id., in addition to the box and packingfree. It is a very handy kit.
A neat 1,it of spares which should find a place on everyexperimenter's bench.
NEW BULGIN CONTROLATONEA _NI: \ V version of the Controlatone has been re-
ed from Messrs. A. D. Bulgin, and this isknown as a De Luxe model. There are several interest-ing features about this particular component, one ofthe first being the interesting type of dial which issupplied. The principle of the Controlatone is, ofcourse. to give a variation in tone from deep bass tohigh treble, and to give some indication of the responseof the device at various settings the dial is engravedwith a tapered line, wide at the position of good low -note response, and thin at the position of high -noteresponse. The central position, which providespractically even amplification at all frequencies, ismarIced " normal," and a small catch may be felt as theknob is rotated so that this setting may easily be
The newly -designed Controlatone, showing the graduateddial.
TECHNICAL STAFFreproduced when desired. Unlike the previous modelsof this type, it is conductive to D.C., and it is thereforeadvised that the potential difference across the terminalsof the Controlatone should not exceed 12 volts .D.C.As the device is intended for connection across theoutput load of a receiver (or across the primary of anL.F. transformer in an L.F. stage) it is unlikely thatthis condition will be exceeded when used in the correctmanner. The list number of this device is C.T.Oand the price is 7s. 6d.
A NEW ANTI -FADING BATTERY VALVETHE use of double -diode -triode valves for volume
control purposes with mains receivers is now wellknown, and battery users will be interested to knowthat a very efficient valve of similar type is nowavailable to them. This is the Osram 111)21. Thisvalve is unique in that it consists of two entirelyseparate electrode systems within the one bulb --moreor less similar to the principle adopted in Class " B "valves. The filament system is divided into two halveswithin the bulb ; one half encloses the two small diodesnecessary for detection and A.V:C., and the otherfilament encloses the' triode system necessary foramplification. Owing to this method of constructionthe diode system can be enclosed within an earthedscreen which provides a very effective electrostaticshielding within the valve. In addition, the whole ofthe filament on the second system is available to providethe necessary electron emission for the triode.
The main points, therefore, of interest in the Osram11D21 valve are as folows
1. Two diodes provide linear detection and delayedaction A.V.C. combined with the triode for high -efficiency amplification.
2. Extremely effi-cient shieldingbetween the diodeand triode ele-ments avoidsdistortion and im-proves the actionof the valve.
3, The full charac-teristics of thetriode element, inthis case similar tothose of an OsramIlL2 valve, arerealised, givinggreat sensitivityon weak signals.
The Osram 11D21is fitted with a filamenttaking 0.2 amp. at 2volts, and gives thefollowing triodecharacteristics: ampli.fi ea ti on factor 27,impedance 18,000ohms, mutual con-ductance 1.5 ma/volt.
The valve is suppliedin a 7 -pin base withmetallised or clear bulb, and in this valve the controlgrid is taken to a small metal cap 'on the top of the bulb.This metal cap takes the place of the screw terminal,and is a convenience in making a quick and firm con-nection by means of a metal clip.
The price of the Osram HD21 valve is Os.
WEARITE " NUCLEON " COILS-A CORRECTIONIN our issue of April 28th we illustrated one of the
Nucleon coils and described this as being the sameas is used in Leader series of receivers. The coils inthe Leader receivers do not, of course, employ iron -cores, and we regret that we wrongly described these.
N EW ERIE VOLUME CONTROLTHE makers of the well-known Erie composition
resistors have now introduced a very neat variableresistor which is of the three terminal, or potentiometertype. Of very small dimensions, the element andmoving arm are protected by an insulated cover andthe actual essential parts are mounted on a very thininsulated (bakelite) disc. The resistance element is ofthe composition type, and the ends are riveted tosoldering tags for connection purposes, the heads ofthe rivets acting as stops at the ends of travel in eitherdirection. The moving contact is of the light spring
type and contact with the resistance element ismade by means of a small graphite stud. Thisprovides a very smooth movement practicallyfrictionless, and at the sametime removes the possibilityof noises due to erraticcontact. The connection forthe moving arm, and thearm itself are well insulatedfrom the control spindle, sothat the component may bemounted direct on a bracketin contact with a metalchassis if desired. The com_ponent is very well madeand should prove highlysatisfactory in use. It isobtainable In five ranges,from .5 megohms down to25,000 ohms, and the priceis 3s. 6d.
MAGNUM MIDGETSCREENED COILS
ALTHOUGH we are nowaccustomed to seeing
tuning coils of very smalldimensions, due to the intro-duction of the iron -core, thenew Magnum coils are veryinteresting in view of thefact that they are of theordinary air -core type. Theillustration shows three ofthese coils from which fulldetails of their constructionmay be gathered. The coilformer is lin. in diameter and21ins. long. The windingsare rigidly held in positionby means of some compoundwhich keeps the self -capacitylow, and the ends of thewindings are soldered to tagseyeletted to the lower endof the tube. The ends of these tags are leftsufficiently long to project through the holes in themetal base and thus permit of the receiver wiringto be easily attached. A circular indent at the top ofthe screening can holds the coil former rigidly centralin the screen and the base of the screen is similarlyindented to ensure that the coil will not move andintroduce short-circuits. The base and screen areheld together by means of registered punch -holes,and they should not be separated as there will be adanger of the coil moving when they are reassembled
The new Osram "K"type valves referred tolast week. The valvebase is of standard size.and the smallness of thebulb may therefore bejudged. The prices forthese valves are the sameas for the standard
types.
This view of the Magnum Midget coils shows the complete method of construction.
with the consequent risk of short-circuits betweenscreen and connecting tags. A very complete rangeof these coils is obtainable, including super -het. coilsand I.F. transformers, and the price of the coils isOs. each and 8s. for the I.F. transformers. All coilsare accurately matched on both wavelengths and thefinish is in grey cellulose. A folder is issued by Messrs.Borne Jones and Co., Ltd., of Magnum House, 296,Borough High Street, S.E.1, describing these coils andthe recently -described multi -contact switches, andreaders who are interested should write for a copy.
THEPRACTICAL MOTORIST
3d. every Wednesday.Published by George Newnes, Ltd.,
! 8.11, Southampton Street, Strand,W.C.2.
May 19th, 1934 PRACTICAL WIRELESS 285
11111111111111iit,:i....
REVIEWS OF THE ;LATEST RECORDS
ON TaiANUMBER of fine records are intro-
duced this month by the BritishHomophone Company, of special
note being a number of popular dancetunes by Teddy Joyce and his Band, whoare now playing at the Kit -Cat Restaurant,and are recording exclusively on Sternorecords. His records include such favouritesas In Town To -night, composed by EricCoates, and Go to Sleep on Sterno 1384,In a Little Rocky Valley and 0/,' Poppyon Sterno 1383, and Spin a Little Web ofDreams and Because it's Lave on Sterno1385. The Casani Club Dance Band, ablydirected by Charlie Kunz, also supply anumber of up-to-the-minute numbers inWho's Gonna Take You Home To -nightand Gosh ! I Must be Falling in, Love,Sterno 1376, Doggone I've Done It, with,xylophone effects by Tommy Blades, andHells Bells, Sterno 1377, and It's Time toSay Good -night and Oceans of Time onSterno 1378. Each of the above six tuneshave vocal refrains ably sung by DawnDavies and Harry Bently, the well-knownvocalists of Charlie Kunz's band.
Light MusicMantovani and his Tipica Orchestra,
who 'have made a number of very finerecords for the above company, make yetanother fine record, which you shouldcertainly hear. This introduces twofascinating tunes from the film PrincessCharming, these being Near and Yet SoFar and Brave Hearts, Sterno 1399. Thevocal chorus of each is sung by ParryJones, the well-known tenor, who is oftenheard on the " air." That versatile com-poser Haydn Wood personally conductsJoseph Lewis's Orchestra in two of hisown compositions-namely, Prelude andThe Unforgotten Melody, on Sterno 1405.Andre Astan and his Orchestra give a finerecording of " Footlight Parade," which isa selection from the film of that name,introducing such popular tunes as Sittingon a Backyard Fence, Shanghai Lil, By aWaterfall, The Moon is Here, and Honey-moon Hotel. On the other side of thisrecord is Moulin Rouge, which is also aselection from the film of this name, in-troducing Boulevard of Broken Dreams,Song of Surrender, and Coffee in the Morn-ing. This record, which is 'Remo 5015,is a long playing record, the playing timeof which equals two 10in. discs.
Vocal RecordsIf you want to enjoy a good laugh you
should certainly hear Leonard Henry, thewell-known comedian, singing The TurkishBath and S'Painful on Sterno 1379, andHarry Hemsley, the popular child im-personator, in his rendering of the Drawingon the Slate and The Picture Book on Sterno1381. Kitty Masters, who styles herself as
ByT. Onearm
the mask singer, records two popularnumbers in What is There to Get Its Placeand Masquerading in the Name of Loveon Stem) 1403. Dan Donovan, the lightbaritone, who has made a number of finerecords for the above company, gives aclever rendering of In the Hills of Coloradoand Am I Ever Remembered in Erin onSterno 1380. Other fine vocal records areOld River Road and Wagon Wheels, sungby The Singing Minstrel on Sterno 1482,and Little White Church -on the Hill and Ina Shelter from a Shower on Sterno 1404.
Pariophone RecordsThose clever harmonists the Modern-
iques indulge in some amazing vocalimpersonations of musical instruments onParlophone R1802, the tunes on thisrecord being Your O.K. and After You'veGone. Harry Roy and his Band, who areheard quite frequently over the radio,make a fine record in Keep Young andBeautiful and Build a Little Home, whichare two numbers from the film RomanScandals, on Parlophone R1795. For thosewho like pianoforte solos, Ivor Moretonand Dave Kay, the two pianists playing inHarry Roy's Band, give a good renderingon two pianos of Kitten on the Keys andNola ; Polly on Parlophone 81797. Alsoworth hearing is Allotria and Lucy's Lips,played by the Harmonica Dance Orchestraon Parlophone R1798.
Homochord RecordsBest and Best, the two popular duettists
who have made a number of very finerecords for the British Homophone Com-pany, make yet another big success onHomochord H.R.93. They sing on thisrecord My Mother's favourite hymn andSpringtime is here-you should certainlyhear this as it is a fine piece of recordingby these artists. They also appear onHomochord H.R.94 singing You're justunfair, and .,on the other side. is So Sky,sung by Syd Kennedy (baritone). If youlike dance music then I suggest WagonWheels and It's time to say good -night,played by Dick Rose and his Band onHomochord H.R.86, I have had to change thewards and Swaller-tail coat, played by thesame band on Homochord H.R.87, How canI believe in you I and After to -night on Homo -chord H.R.89, and Jimmy had a Nickeland Annie doesn't live here any more onHomochord H.R.90, these last two recordsbeing played by Al Gold and his Band.All these tunes are equally good and willcertainly appeal to readers.
50 Tested Wireless CircuitsEdited by F. J. CAMM
2/9 from Geo. Newnes, Ltd., 8-11, South. 216Obtainable at all Booksellers, or la post
ampton Street, Strand, London, W.C.2.
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Ask pour nearest radio dealerfor full particulars and FreeEntry Forms, or if you haveany difficulty, write direct.
THE AUTOMATIC COIL WINDER &ELECTRICAL EQUIPMENT Co. Ltd.Winder House, Douglas Street, London, S.W.1
286 PRACTICAL WIRELESS May. 19th, 1934
PRACTICAL MHZ fROMftEADERS
The Editor does not necessarily agree with opinions expressed by his correspondents.All letters must be accompanied by the name and address of the sender (not necessarily
for publication).
Schedule of Interesting Foreign Trans-missionsSIB,-The following information may be
of interest to readers of PRACTICAL WIRE-LESS :-
YVIBC, Broadcasting Caracas, Apartado290, Caracas, Venezuela, works on 312.3 m.,960 kc/s, 5 kW., and on 49.08 m. (6,112ke/s) and 25.65 m. (11,695 kc/s), 200 watts,daily, 11.0 a.m. to 1.30 p.m., Caracas time.On Sundays, 9-11 a.m., 2-6.30 p.m.,7.30-8.30 p.m., and 8.30-10.30 p.m.,Caracas time.
YV3BC, Radiodifusora Venezuela,Caracas, works on 1,200 kc/s, 6,150 kc/s.,and. occasionally, on 9,510 kc/s.
VE9GW, Canadian Radio Commission,Bowmanville, Ontario, works on 6,095 kc/s
PR A3 (via PSK), Radio Club do Brazil,Rio de Janeiro, is S.B. on 860 kc/s and8,185 kc/s.
W8NAL, Crosley Radio Corporation,Cineinatti, Ohio, works on 49.5 m., 6.060ice/s. with 10 kW. poWer, and chiefly relaysWLW' and WSAI from 11.30 a.m. to10.45 p.m., and from 3.0-5.30 a.m.,G.M.T. (temporary schedule). They statethat W8X0 operates on 700 kc/s with500 kW. The transmitter is at Mason,Ohio. and the aerial is vertical and rises 831ft.
ZSB, Transmitting Station, Klipheuvel,C.P., S. Africa, operates on 33.7 m., 18,660kc/s-used for C.W. and occasional 'phone-and also on 8,900 kc/s, used at night forC.W. and occasional 'phone ; power 10 kW.This is the beam transmitter to Bridge.water, Som., ZSB (both waves). It is indaily use. They also use :-
ZSR, 9,180 kc/s, for telephony (notoften). ZSI, 9,305 kc/s and ZSL, 18,290 kc/s,for facsimile (fairly frequently but not atpresent). ZSS, 18,890 kc/s, for commercialtelephony to London (daily).
HAS, Research Labs. for ElectricalCommunication of the R. Hungarian Post,Gyali Str. 22, Budapest : Located atSzekesfehevvar, 30 m. S.W. of Budapest.Wavelength, 43.86 m., quartz -controlled.Power, 5 kW. Aerial directed West.Schedule. 05.45 to 23.00, G.M.T., " if any."They also use HAT, 21.92 m., 13,685 kc/s,5 kW.
The above information comes direct fromthe stations, and is, presumably, accurate.-BRS 1330 (Misterton, Somerset).
A Wallasey Reader's SuggestionsSIR,-Having been a reader since No. 1,
I feel I am now in a position to write you aletter offering what I think are somegood suggestions for improvements in yourpages. To begin, I suggest that pictorialdiagrams of circuits, unless they be in theform of a particular layout, be discontinued.From a beginners' point of view they areuneducational and, from that of one moreexperienced, meaningless. Further, unlessthe components are " ghosted " connectionsare difficult to follow, and, especially in
coils and transformers, the disposition ofterminals varies with different makes.
Also, could not the space occupied bysuch meaningless illustrations as, " Areceiver in which the valves are not squarepegs in round holes " or, " A power packwhich makes no pretence of being nig-gardly with the volts " be occupied bysomething more useful and interesting, suchas additional " Topical Technicalities " or" Do You Know " ?
After these little criticisms, here is abouquet ! The inauguration of a Tele-vision Supplement is purely a master-stroke, and another instance of PRACTICALWIRELESS being first in the field.-W. N. H.JARVIS (Wallasey).An Australian Reader's Appreciation
SIR,-I have taken PRACTICAL WIRELESSever since the first copy appeared here, andthe bound volumes are a great help in timeof trouble! I have abandoned three othermagazines in favour of PRACTICAL WIRE-LESS, which gives me all I want in the wayof up-to-date information, understandablywritten.
It is a pity that American valves havesuch a strong hold here. It seems thatour local set manufacturers are so wellserved with circuits, sample chassis, andtechnical service by American agents thatevery new set has American sockets asstandard, and American or replica valvesas first equipment. What are Englishmanufacturers doing about it ?-N. K.STRACK (Sydney, Australia).
[English radio manufacturers, pleasenote.-ED.]
CUT THIS OUT EACH WEEK.
-THAT an indirectly -heated rectifying valveremoves the necessity for fitting a thermal -delayswitch.-THAT images in natural colours have beensuccessfully televised.-THAT hum may often be cured by providingan artificial centre -tap to a mains -heaterwinding.-THAT when fitting a mains -aerial condenserboth leads to the mains should be tried in orderto select the quietest lead.-THAT when fitting wave -change switchesto short-wave receivers high capacity betweenadjacent contacts should be guarded against.-THAT a vertical aerial often proves moreefficient than a low short horizontal wire.-THAT the capacity of the anode by-passcondenser in the detector stage will affect thereproduction of high notes.
The Editor will be pleased to consider articles of apractical nature suitable for publication in PRACTICALWIRELESS. Such articles should be written on one aideof the paper only, and should contain the name andaddress of the sender. Whilst the Editor does not holdhimself responsible for manuscripts, every effort will bemade to return them if a stamped and addressed envelopeis enclosed. .411 correspondence intended for the Editorshould be addressed : The Editor, PRACTICAL WIRELESS,Geo. Newnes, Ltd., 8-11, Southampton Street, Strand,W.C.2.
Owing to the rapid progress in the design of wirelessapparatus and to our efforts to keep our readers in touchwith the latest developments, we give no warranty Matapparatus described in our columns is not the subjectof letters patent.
A Lamp Unit for TelevisionSIR, -In an article on the use of ordinary
neon lamps for television purposes whichappeared in the April 21st issue, I noticedthat the writer recommended readers touse a " beehive " lamp.
Now the area of the neon disc is small,and the fact that the lamp must be placedat an angle is a great drawback. Therefore,I would like to point out that I use aPhillips neon lamp with the wires woundin cylindrical form. These lamps work onfrom 100 to 130 volts, so that by using200 volts high tension in the output stageof the receiver it is possible to obtain agood degree of light from the lamp. Anotheradvantage is that it can be used uprightand quite close to the scanning disc, andalso that the light area is approximatelysquare in shape.-J. W. HOBLEY (Welling-borough).
ATALOGUESRECEIVED
To save readers trouble, we undertake to send oncatalogues of any of our advertisers. Merely state, ona postcard, the names of the firms from whom yourequire catalogues, and address it to " Catalogue,"PRACTICAL WIRELESS, Geo. Newnes Ltd., 13111.Southampton St., Strand, London, 'W.C.2. Whereadvertisers make a charge, or require postage, thisshould be enclosed with applications for catalogues. Noother correspondence whatsoever should be enclosed.LUMEN RECEIVERS
AFINE range of Lissen receivers, including thepopular " Skyscraper " series, is displayed in an
.attractive folder issued by Lissen Limited. There aresets to suit varying tastes and purses, and from whichthe most discerning listener should have no difficultyin choosing a receiver tosuithisrequirements. Thereismodel 8060, a high-class six -valve all -mains superhet.Equipped with A.V.C.,band-pass tuning, and an electro-dynamic loud -speaker, this high-class instrument ispriced at £14 14s. Other models include A.C. andD.C. models with moving -coil speakers, and battery -operated portable and table sets, all housed in hand-some cabinets of modern design, and at prices rangingfrom £4 4s. to £12 12s. Full particulars of all thereceivers are given in the folder, copies of which canbe obtained on application to Lissen Limited, LisseniumWorks, Worple Road, Isleworth, Middlesex.CHARGING FOR PROFITAUSEFUL handbook by H. W. Gambrell and T. W.
Price, bearing the above title, has just beenissued to the trade by the Edison Swan Electric Co.,Ltd. The purpose of the book is to give practicalsuggestions and advice on the questions of layout ofbattery charging stations, and the choice and operationof suitable equipment.COSSOR BOOKLET ON CLAMS B AMPLIFICATIONLISTENERS who are users of battery receivers will
find Messrs. A. C. Cossor's book B.21 on Class Bamplification of special interest, as it explains how toincorporate a Class B valve in a receiver to obtain anoutput comparable with that of a mains receiver.Several circuits are given, together with advice onhow this latest form of output may be most success-fully used and added to suitable existing receivers.
Certain precautions may have to be taken andrefinements added to ensure satisfactory results, andthis book clearly explains what these additions areand how they are best utilized. A copy of the bookletis available free to readers of PRACTICAL WIRELESS onapplication to Messrs. A. C. Cossor,Ltd., Highbury, N.5." LE8DI X " MICROPHONESVARIOUS types of microphones, from pocket
voice amplifiers to stand instruments, arelisted in a folder issued by Electradix Radios. In-cluded in the comprehensive range are microphonesfor home recording, band repeating, and publicaddress work. Also included in the folder is a range ofmicrophone transformers, telephones, and microphoneparts. Copies of the folder can be obtained from 218,Upper Thames Street, London, E.C.4, by enclosingstamp for postage.HIVAC VALVESFULL particulars with characteristic curves of the
full range of Hivac valves is given in a booklet ofdata strips. These valves are the result of severalyears of intensive research work, and no pains havebeen spared to produce a high-class valve at a reason-able price. They embody the latest and most advancedmethods of construction, and great care has beentaken to ensure that individual valves are up tocharacteristics. Comparative tables of equivalentvalves, from which can be seen at a glance titscharacteristics and prices of Hivac valves in com-parison with similar valves of other makes, is given ina neat folder, copies of which can be obtained onapplication to the High Vacuum Valve Coy., Ltd., 113-117, Fariingdon Road, London, E.C.1.
ell
May 19th, 1934 PRACTICAL WIRELESS 287
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SPECIAL NOTE.We wish to draw the reader's attention to thefact that the Queries Service is Intended onlyfor the solution of problems or difficultiesarising from the construction of receiversdescribed in our pages, from articles appearingin our pages, or on general wireless matters.We regret that we cannot, for obvious reasons -
(1) Supply circuit diagrams of completemulti -valve receivers.
(2) Suggest alterations or modifications ofreceivers described in our contem-poraries.
(3) Suggest alterations or modifications tocommercial receivers.
(4) Answer queries over the telephone.Please note also, that all sketches and drawingswhich are sent to us should bear the nameand address of the sender.
MODIFICATION NOT POSSIBLE" I enclose a sheet showing details of two coils
which I have got. I also have two separate .0005 mfd.condensers, and should like to incorporate these partsin the " Leader." Can you show me the connections ? "-J. H. B (Limerick).
We regret that your coils would be unsuitable for usein this circuit. Further, as pointed out on manyoccasions, departure from the specified parts andarrangements will not enable us to guarantee theperformance of a receiver, and you can, therefore,only make the change at your own discretion.
A MATCHING PROBLEM" A 3 -valve set has been brought to me, viz., S.G.,
det., and pentode. The receiver is quite intact, butthe speaker was originallymeant for Class B or Q.P.P.,and requires approximately 3 watts. The pentode valvehas an output of 1 watt. Will a 3 to 1 step-up L.F.transformer be necessary in the output to match thevalve and speaker? "-8. A. K. (Bridgend).
The question of matching is not concerned with thestrength of the input signal, but with the impedance.The fact that the speaker will handle 3 watts simplymeans that a signal greater than that value shouldnot be passed to it. The pentode, which only delivers1 watt, may be coupled to it (through a suitable im-pedance matching device) and will work satisfactorily.You will probably find that by using the two outsideterminals on the speaker, and connecting these directin the anode circuit of your pentode valve, the matchingwill be approximately correct, as the usual load ofa Class B stage is in the neighbourhood of 8,000 to12,000 ohms, and this is also the normal load of apentode. You should, therefore, ignore the centreterminal on the speaker and use it in the ordinaryway.
CINEMA INTERFERENCE" I have a three -valve straight three, but when I
tune -in to the local station I get a terrible noise, some-thing like falling bricks. I have got all good com-ponents, but the house is situated fifty yards from themain road and three cinemas are close by. Can thesebe responsible for the trouble ? "-J. H. (Oldham).
It is quite possible that either apparatus in thecinemas, or electric signs fitted to these places areresponsible for the noise. This could be verified byremoving the aerial from the aerial terminal. If the
LET OUR TECHNICAL STAFF SOLVEYOUR PROBLEMS
uERIES and ; page must be attached, to every query- ;
The coupon on this
If a postal reply is ENQUIRIESdesired, at stamped ad--
query and drawingbe enclosed. Every hy Our Technical Staffdressed envelope must
which is sent must bearthe name and address of the sender. Sendyour queries to the Editor, PRACTICALWIRELESS. Ceo. Newnes, Ltd., 8-11,Southampton St.. Strand. London. W.C.2.
noise is reduced or entirely removed, then you shouldfit a screened aerial lead, or endeavour to obtainsatisfactory results with a small indoor aerial arrangedin such a direction that the interference is reducedto a minimum.
A WET RECTIFIER"Can you supply me with details of a wet rectifier
for use in a trickle charger to use in place of a metalrectifier? I should like to know the nature of theelectrolyte, ratio of the ingredients and the plates." -E. V. T. (Tottenham, N.)
A wet rectifier for your requirements could be builtup by using a solution of ammonium phosphate inwhich plates of lead and aluminium are immersed.The strength of the solution is approximately 2ilbs.of salt to the gallon of water, and it is preferable touse a rod of aluminium with a plate of lead cut to fitround the inside of a half -gallon jar. Full details willbe found in "Accumulators, Charging, Maintenanceand Care," published by this house and obtainablefrom any bookstall or newsagent, price Is.
DATA SKEET No. 79I Cut this out each week and paste it in a noteboa k i
GRAMOPHONE RECORDCLASSIFICATION
!t
t 4
SIZE I LABEL TYPE No. PRICE NAME
10in. Black - 2a. 113d. Bromwich12in. Blue - 24. ed. Pana-10in.
Tin.BlueOrange
'-AS
IL ed.L. (Id.
).chord
10in. Plum B Be. ed.12in. Plum C 4s. Cd.10in. Black B 45. Od.12in. Black D es. Od.10in. Red DA 4s. Od. His12M. Red DB (is. Od. Master's10in. HMI Si 75. Od. voice12in. Hoff DH 103. Od.12in. Pale Green DK 11s. Oil.12in. Pale Blue DO las. Oil12in. White DQ Hs. 011.10in. Red E Ils. ed.10in. Blue R 251. Bd. ).Parlophone12in. Dark Blue E 41. ed.
(1000 series) -Nal Red & While - U. Od. Broadcast10in. Red - L. ed. Broadcast
SoperTwelve
10in. Red - L. 114. BroadcastFourTune
10in. Blue - 21.04. BroadcastTwelve
THE MAINS UNIT?'I have recently built a three -valve receiver exactly
to specification, but I can only get a loud buzzing noise.am working from the mains with a good mains unit.
Aerial, earth, and unit are in good order, as they workwith my old set." -F. L. (Mitcham).
In all cases where a mains unit is employed and theset proves unstable it is worth while trying a drybattery in place of the unit, in drder to check that thewiring and components of the receiver are in order.If results are then satisfactory and instability is in-troduced when the mains unit is connected, it provesthat the unit is unsuitable. The reason may be thatthe unit will not deliver sufficient current for the set
and is seriously overloaded, or it may be necessaryto employ separate voltage supply leads for each valve.In some cases it may be necessary to incorporateextensive decoupling in the receiver. The exact curewill depend both on the receiver circuit and themains unit wiring.
TELEVISION AND A 4-VALVER" My set is a four -valve S.G., del, power, and pentode,
and it is used with an A.C. mains unit. Could I worktelevision from this ? I am very keen to try out someexperiments in television." -W. M. (Ashington).
We see no reason why you should not be able toobtain good results from your receiver, provided youcan obtain a really good loud signal from the LondonNational station, which transmits the televisionsignals. If this station provides you with a signalwhirls is very comfortably audible, you could buildup a disc receiver and obtain quite good results.If, however, the signal from that station is weak,you would probably need a further H.F. stage togive you sufficient strength to obtain a well -modulatedpicture.A CLASS B ELIMINATOR
" I am thinking of building an eliminator for mypresent set, which is an ordinary S.G., detector, and powercircuit. Later I am going to add Class B. Will it besatisfactory to build a Class B unit now, or will thisnot work with my present set? S. (No address).
It would be preferable to build the unit as it will berequired for the Class B conversion. It will workquite satisfactorily with the straight circuit and willnot then require alteration when you modify your set.SPARK FROM SPEAKER LEADS
" My set is working wonderfully, but I am puzzledby having noticed a spark when the set is workingand I make -and -break the negative loud -speaker lead.The set is working from the mains through an eliminatorand has a choke output. Is it in order, and am I safein taking the negative of loud -speaker to earth at somedistant point? "-A. J. R. (Roche).
It is quite in order to connect the speaker to anyearthed point, but you should not disconnect thiswhilst the receiver is switched on. You break theanode -load when you disconnect the speaker and thiscauses a surge which gives the spark as the connectionis made and broken. It does no harm in itself, but maydamage the valve or even cause a breakdown of thefilter condenser due to the surge.THE FURY FOUR
Could you let me have particulars for obtainingwiring details of the set known as the Fury Four(battery -operated.? I have seen the circuit in a Valvemanufacturer's booklet, and it is described as anefficient and selective set." -P. M. (Dublin).
The circuit you referred to was described in 1933in PRACTICAL WIRELESS Nos. 19 to 21. This receiverhas, however, been modified and brought entirelyup to date, using iron -core coils and variable -muvalves and the battery version was described inPRACTICAL WIRELESS Nos. 71 and 72. Copies of theseissues are obtainable from our Back Number Depart-ment, price 4d. post free.
1.411M(114.=1.4
FREE ADVICE BUREAU.COUPON
This coupon is available until May 26th,1934, and must be attached to all letters con-
taining queries.PRACTICAL WIRELESS, 19/5/34.
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/WITHHANDY
HOLDER. . . . 2/6
INCREASE THE SELECTIVITY OF YOUR SET!OVER 1,500,000 LISTENERS USE A
to separate those stations that overlap each other. Get rid of thatannoying minziro ss that spoils local reception. Just FIX A PIXin your aerial lead. You will be surprised how sharply your set tunes,and delighted at the number of new stations you can hear clearly. Tryone to -day. Send us 2/-. If you are not completely satisfied, return itto us within 7 clays for full refund.
BRITISH FIX CO., Ltd., LONDON. S
288 PRACTICAL WIRELESS May 19th, 193 4
Miscellaneous AdvertisementsAdvertisements are accepted for thesecolumns at the rate of 3d. per wordprepaid - minimum charge 3/- perparagraph -and must reach this officenot later than Tuesday for the followingweek's issue. All communications shouldbe addressed to the AdvertisementManager, `Practical Wireless," 8 South-
ampton Street, Strand, London.
PREMIER SUPPLY STORESoffer the following Set Manufacturers' Surplus NewGoods at a fraction of the original cost; all goodsguaranteed perfect; carriage paid over 5/-, under5/- postage 6d. extra (Ireland, carriage forward).
PREMIERSUPPLY STORES announce the
purchase of the entire stock of a world-famousContinental valve manufacturer. Ali the followingtypes of standard mains valves at 4/6 each. H. HL.L. Power. Directly heated 6 -watt Pentode. Directly -heated 9 -watt Pentode, High magnification Screen -grid, low magnification Screen -grid. Variable -MuScreen -grid. 250 volt 60 milliamp, full -wave rectifiers.
THE following type 5/6 each. Indirectly heatedPentode, 350 volt 120 milliamp, full -wave Recti-
fier. 500v. 120 ditto, 6/6. Dario Battery Valves 4v.filament, Set of 3, consisting of Screen -Grid, Detectorand Power or Super -Power, 6/6 the lot. Power orSuper -Power, 2/6.
ELIMINATOR Kits, including Transformer, choke,Westinghouse metal rectifier, Dubilier condensers,
resistances and diagram, 120v, 20 ma., 20/- ; tricklecharger 8/- extra; 150v. 30 milliamps, with 4v.2-4 amps. C.T. L.T., 25/-, trickle charger 6/6 extra ;250v. 60 milliamps, with 4v., 3-5 amps. C.T. L.T.,30/-; 300v. 60 m.a., with 4 volts 3-5 amps. C.T. L.T.,37/6 150 volts 50 milliamps, 27/6.
AMERICAN Triple Gang 0.0005 Condensers, withtrimmers, 4/11 Premier chokes, 25 milliamps.
HARLEY Pick-up, complete with arm and volumecontrol, 12/6.
BRITISH RADIOPHONE Wire Wound Potentio-meters, with mains switch incorporated, 10,000
ohms, 3/6.PREMIER British -made Meters, moving -iron, flush
mounting, accurate, 0-10, 0-15, 0-50, 0-100,0-250 ma., 0-1, 0-3, 0-5 amps. ; all at 6/..SPECIAL offer of Mains Transformers, manu-
factured by Phillips, input 100-120v. or 200-250v.output 180-0-180 volts 40 ma., 4 v. I amp., 4 v. 3 amp.,4/6. 200-0-200v., 4v. la., 4v. 3a., 4/6.A L L Premier Guaranteed Mains Transformers have
/+-, Engraved Terminal Strips with terminal con-nections, input 200-250v. 40-100 cycles, all windingspaper interleaved.
PREMIER H.T.B. Transformers, 250v. 60 m.a.,rectified with 4v. 3-5a. and 4v. la. C.T. L.T., screen
D.T.H. Truespeed Induction Type (A.C. only) Elec-D trio Gramophone . Motors, 100-250v., 30/- ;complete. Type YR 100/250v. A.C. or D.C., 42/-.Q PECIAL Offer of Wire Wound Resistances, 4 watts,p.,./ any value up to 10,000 ohms, 1/- ; 8 watts, anyvalue up to 15,000 ohms, 1/6 ; 15 watts, any value upto 50,000 ohms., 2/- ; 25 watts, any value up to50,000 ohms, 2/6.riYLDON Capacitors (Double Trimmer), 1/-. Utility
.0065 2 -gang Bakelite Condensers, concentricUniknob Trimming and Disc Drive, complete, 3/6. .rDISON BELL Double Spring Gramophone Motors,
complete with turntable and all fittings, a reallysound job, 15/-.
ORMOND Brass Variable Condenser, .0005 com-plete with knob -dial 2/-.
HMS''Block Condensers, 400v. working ; 4 x 4 x 1
xlx 1 x 1 x 0.1 x0.1 x 0.1, 6/-; 4x 2x lx1 x 1 x 0.5, 4/6.
DUBILIERCondensers, 2 mf. 1,200v. working, 4/-;
8 mfd. dry electrolytic, 450v. working, 3/-.MBE Following Lines 6d. each or 5/- per1
dozen -Chassis valve holders, 5 or 6 pin, screened
screen -grid leads, any value 1 -watt wire end resistances,wire end condensers, 0.0001 to 0.1, trimming condensers,T.C.C. 6 mfd. 50 v. electrolytics.
PLEASE mention PRACTICAL WIRELESS whenordering.
PREMIER SUPPLY STORES20-22, High Street, Clapham, S.W.4, MACaulay 2188.Close 1 o'clock Wednesdays ; open to 9 o'clockSaturdays. Nearest Station, Clapham North Under-ground.
THE following unused Set Manufacturers' Surplus ;allgoods guaranteed perfect ; immediate delivery.
FERROCART coils, Gl, 02, G3, or Gil, G2, GSwith switch, 27/6. G11, G12, 013, G14, with
switch, 34/-. Colverdynes (Ferrocart), 7/6.nITBILIER or Erie resistors, 1 watt type 7d.,
2 watt type 1/2, Marconi K19 pick-ups 22/6.Radiophone IF transformers, 110KC or 117.5KC, 6/6.
M.R.D. Co., offer following guaranteed surplus.Carriage paid or call. Dubiller 8 mfd. electro-
lytics. 450v. working, 3/6. Tubular 800v. testcondensers, .01. .02, .05, .1 mfd., 6d. T.C.C. .1 x .1buffer condensers, 450v. working, 1/4. Formo dualrange aerial coils, new and boxed, screened, withganged switch and -circuit, list 7/8. 3/3. VoltronH.F. chokes, high inductance, 9d. -Mains RadioDevelopment Company, 4-6, Muswell Hill Road,N.6, London. Tudor 4048. ,
ALL I ASK OF YOUis to look into this Revolutionary Announcement:All I ask of every individual Pr.W.' reader is to look
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It is only through a combination of three of the mostadvantageous bulk purchases I have yet made that thisbargain became possible. These -'were (1) UltraPanther' Console cabinets -the - most beautiful
cabinets I have seen. (2) British Radiophone 6 -stagesuper -het chassis with A.V.C. (3) A loud -speaker asgood as any made -the W. B. Permanent Magnet.
That three lines such as these which are almost' made to fit together' should have become availableat the same time is a piece of 'good fortune, which cannever reasonably be expected to repeat itself.
They are now offered to Use home constructor at aridiculous price as a complete outfit which is easily'and quickly assembled into a Radio receiver whichcan have few or no superiors.
The obtaining and presenting of this bargain hascalled for opportunism on our part. It now calls foropportugism on your part to secure It while thegoing is good, and test it without any obligation Inyour own home.
Youkvill be helping yourself and helping us.Thank you.
G. DE C. TAYLOR (General Manager, L.E.C. TradingCo.)
THE BARGAIN OF THE AGEA 22 On, Super -het with A.V.C. for 86.19.6 or 15/ -down. .
ON FREE APPROVALTHE CHASSIS BY BRITISH RADIOPHONE.
A six stage super -heterodyne with Class B out-put and Automatic Volume Control, for use withbatteries or with a suitable eliminator (see below)off A C. or D.C. mains.
THEVALVES BY MULLARD. A complete set of
Mullard valves are supplied with the chassis.THE SPEAKER BY " W.B," a permanent magnet
1 speaker of the highest class with universalmatching transformer. List price 35/-.
THE CABINET AN ULTRA "PANTHER." Atable model polished walnut cabinet of superb
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FOR BATTERY, A.C. or D.C. USERS. Completeset of high capacity batteries, price extra 15/ -
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THIS WEEK'S SPECIALS !Supplementary to the May' RADIO GOLD -MINE.'/ EACH, LOTUS DIFFERENTIALS, also
2/2 ; Lucerne Coils, Aerial or Grid, 2/4.1 /8 EACH. AMLION CONE SPEAKER UNITS
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2/6 IRON CORED DUAL RANGE COILS.Dubilier 8 Mfd. Electrolytics, 2/10.
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3/6 IsGwlittgAM4RON CORED COILS, with8/6 SHORT WAVEWnsAinVEsea.takePaTtoOnsR KITS, with full
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qd, EACH, FIXED CONDENSERS, 1 watt.)re-sistances and Grid Leaks. ALL valves. EdisonBell 4pt. jacks and switches (list 4/-) 9d. H.F. Chokes9d. Mansbridge condensers 1 mfd. Dd., 2 mfd. 1/4,4 mfd. 2/8.THERE ARE HUNDREDS UPON HUNDRED(
of equally attractive bargains in the new Maiissue of the ' Radio Gold -Mine,' the most comprehensive surplus radio lists published in Great Britain.You CANNOT afford to be without them.
LONDON EAST CENTRAL TRADING COMPANY(Dept. M.112), 23, Bartholomew Close, London,
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For Everything Surplus In Modern RadioTHE `GOLD -MINE STORES'
.T.400 Kits, all specified proprietary components;S £2/19/6 list £4/17/6).GRANIC Coils, let of four (1 osc., 2 I.F. with
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.P.F., 4/- (list 12/-) ; all brand new in originalcartons.
thing you need for radio we can supply. Valves,stc. Lists free.DAND-PASS superhet 6 -valve A .D.C. mains,101 Lucerne wavelengths, stations named, £9!12/6.
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AULLARD Valves, complete, ready to switch on, WI and guaranteed.
VAUXHALL UTILITIES, 163a, Strand, W.C.2.
PRACTICAL WIRELESS
PEARL & PEARL190, Bishopsgate, London, E.C.2. All bargainsguaranteed new goods. Cash or C.O.D. Carriage
Paid.POLAR 2 -ganged Screened Condensers, with trim -
mere, pilot lamp holder, calibrated scale andescutcheon ; list 27/6, our price Sill. Several of ourbargains as advertised in previous issues, still available.FREE. Send postcard for Pearl & Pearl BargainList " B."
WOBURN RADIO offer following new and Bank-rupt stock:-
WESTINGHOUSE Rectifiers : ILT.7, 8, and 9, 9/- ;H.T.10, 9/6'. L.T.2 and 5, 10/6.
ERICSSON 3/1 L.F. Transformers. List price17/6.New and guaranteed. Our price 2/3 post free
U.K.VARLEY Constant Square Peak Band Pass Coils,
Type B.P.S. Complete with switch, brand newin makers original carton. With full instructions anddiagrams. List price 15/-, our price 3/9 post free U.K.
POLAR3 -gang Star Minor Condenser with Trimmer.
Brand new. List price 18/9. Our price 7/6each post free U.K.
Mains Transformers, quoted for. Any kind of screwsmade or small metal repairs done. Trade discount.Clerk. 9069.-Mason, 44, East Rd., City Rd., N.1.
YOUNG men trained for all branches of WirelessProfession. Britain's leading College, situated
on sea -front. Boarders accepted. Training fee pay-able after appointment. Prospectus free. The
WIRELESS COLLEGE, COLWYN BAY.
iii
EVERYTHING to make your own Coils, Trans-formers and Chokes.-Lumen Electric Coy.,
9, Searkbrick Avenue, Litheriand, Liverpool, 21.EPAIRS--REWINRING-OVERHAULS. NewR cones. and centres fitted any make hfic chassis,
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WANTED good Modern Wireless Parts, Sets,Eliminators, Meters, Valves, Speakers, etc.
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MAKE your own Aluminhini Coil Screens withbase. Size 31" high, 24"diaineter. Price 1/ -
each. "MPR " Ltd., Roinford, Essex.
LONG RANGE &LONG SERVICE362 will bring in those di.tantforeigners, now only whispers.Their te,hniutl ercelleme as-sures this, also Ivng life. No
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THE 382 RADIO VALVE CO., LTD,(Dept. W.), Stoneham Road, London, E.5.
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Electradix Radios offer 1000 bargains at sacrificeprices in radio components, meters, dynamos,microphones, switches, chargers, valves, etc.Send for Sale List" N." It will save you pounds.
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iv PRACTICAL WIRELESS May 19th, 193 4
THE NEW WEEKLYFOR. EVERY MOTORIST
If you run a car' get acopy of the new motoringpaper, "PracticalMotorist," to -day - thepaper for which hundredsof thousands of owner -drivers have been waiting,It costs pennies, but willsave pounds in upkeep andrunning costs, and willshow how to get the bestout of your car. In fact,it is the paper foreconomical, efficient and
trouble -free motoring.
Published by
GEORGENEWNES
LTD.
PRACTICAL110110TORIST WEEKLY
P.W. Gift Stamp No. 20
Geo:Newncs, Ltd.
Printed in Limit Britain 1.y NEWNES to: PEARSON PRINTING CO., LTD., Exmoor Street., Ladbroke Grove, W.10, andpublished by I GEORGE NEWNES, LTD., ,4-11, Southampton Street, Strand, W.C.2. Sole Agents for Australia and .NewZealand: GORDON & °OTOS, LTD. South Africa: CENTRAL NEWS AGENCY, LTD. Practical Wireless can be sent to anypart of the world, post free, for 17/1 per annum ; six motif hs, 8/8. Registered at the General Post Office for Transmission
![The true Democrat (Bayou Sara, LA) 1914-09-19 [p ]chroniclingamerica.loc.gov/lccn/sn88064339/1914-09-19/ed-1/seq-3.pdf · young people, and, in fact, every way4 maintained a reputation](https://static.documents.pub/doc/80x56/5aad2aa27f8b9a59658df26c/the-true-democrat-bayou-sara-la-1914-09-19-p-people-and-in-fact-every-way4.jpg)
