24 1 UNIVERSAL SET - worldradiohistory.com

DEC.1932

C24 1 UNIVERSAL SET or

A.D..C. I pelr5lipy

REG. U.S. PAT. OFF.

The First and Only National Radio WeeklyEleventh Year 561st Consecutive Issue

Constructional Articlesand Plans

on Six -Tube Superand a Test Oscillator

The New FADA Circuit

sx*va414

A small mirror held to a fountain-pen type flashlight often enables one to look under a chassis when trouble-shooting without removing chassis from the cabinet.

RADIO WORLD December 24, 1932

Mr. SERVICEMANTake a tip! Get Rider's Volume II of the

Perpetual Trouble Shooter's Manua/. Buyit today. Don't wait until you cannot repaira receiver because you do not have the data.FREE. If :1,1!ce.ofr y...,ie arcoelt: Scodei fw

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resistors used in Atwater -Kent receivers. En-close 3c to cover postage.RADIO TREATISE CO., Inc.

1440 Broadway New York City

RADIO WORLDand "RADIO NEWS"

BOTH FORONE YEAR $7.00 Canadian

and Foreign$8.50

`You can obtain the two leading radio technical magazinesthat cater to experimenters, service men and students.the first and only national radio weekly and the leadingmonthly for one year each, at a saving of $1.50. Theregular mail subscription rate for Radio World for oneyear. a new and fascinating copy each week for 52 weeks.is $6.00. Send in $1.00 extra, get "Radio News" also,for a year -a new Issue each month far twelve months.Total. 64 issues for $7.00.RADIO WORLD, 145 West 45th Street, New York, N. Y.

AMERICAN BOSCH10 -tube Radio, $55.95

New 1933 New Essex Model Console, 10 -tubeSuperheterodyne, two speakers, the best AmericanBosch, value at $55.95.Simplex long and short-wave radio, the fastestmoving line in America, 5 -tube superheterodyne,table model cabinet, only $29.95.

We sell for cash with order, less 20% discount.Order from advertisement or write for folders.

McGuire Distributing Co., Doeville, Tenn.

SHORT-WAVE BROADCAST STATIONS -Com-plete list of those on air and ordinarily receivable;also complete list of Short -Wave CommercialStations, including Aircraft, Police and IdentifyingStations, contained in Radio World issue of Dec.3, 1932. 15c a copy. Rado World, 145 W. 45th St.,New York, N. Y.

No More Needto CalculateInductance !Correct AnswerObtained from Chartsin 1 0 Seconds!

pRECISION charts have been prepared byEdward M. Shiepe, E.E. (MassachusettsInstitute of Technology) relating inductance,

capacity and frequency, and giving the num-ber of turns of different sized wires for attain-ing inductance values for solenoid formdiameters of %, 7/8, 1, 1%, 14, 1%, 13 , 1%, 2,2%, 21%, 2% and 3".

The tri-relationship chart (inductance, capacity andfrequency plotted, so that when any two are known theunknown may be read directly in 10 seconds) is necessaryfor use of the inductance table that covers any particularwire size for all the specified form diameters.

The charts are on 9 x 1Z" photostat sheets, white lineson a black field.

The tri-relationship chart covers inductance values of0.1 to 10,000 microhenries, capacity values of 50 to 606mmfd. and frequency values of from 100 to 20,000 kc.

The tri-relationship chart is Cat. CHT-TRI, @ $1.00WHILE any one of the three quantities may be determined, the chief purpose of the tri-relationship chart is to give instant reading of the inductance needed when capacity andfrequency are known.

The turns charts (number of turns needed for specified inductance) are thirty-six in number,one for each of the following different wire sizes and insulations: Enamel Nos. 14, 16, 18, 211, 22,24, 21, 28, 30; Single Silk Covered, Nos. 14, 16, 18, 20, 22, 24, 26, 28, 30; Double Silk Covered orSingle Cotton Covered (same data apply to both), Nos. 14, 16, 18, 20, 22, 24, 26, 28, 30; DoubleCotton Covered, Nos. 14, 16, 18, 20, 22, 24, 26, 28, 30.

Each turns chart gives the number of turns for inductance ranges well in excess of commercialuses of particular wire sizes on the specified diameters. Short waves included for larger diameterwires, very long waves for finer diameter wires.

The turns charts are Cat. CHT-TNS followed by the wire size and insulation. Thus, turns chartfor No. 30 Double Cotton Covered would be Cat. CHT-TNS-30-DCC. The price is $1.00 each.

The accuracy of these charts is so high that it may be relied on in engineering practice.All charts are on a logarithmic 5x3 -cycle basis.

RADIO WORLD, 145 West 45th Street, NEW YORK, N. Y.

MODULATED OSCILLATORSBroadcast and Intermediate Frequencies

An a -c operated modulated oscillator(105-120 v., 50-60 c.), fully covering thebroadcast band (1500 to 540 kc.) and allthe commercial intermediate frequencies(115, 130, 172.5, 175, 177.5, 260, 400 and450 kc.). The vernier dial has scalecalibrated in broadcast frequencies,while the eight intermediate frequenciesare also recorded directly on the scale.No chart references necessary. Ac-curacy is 3 per cent. or better, averag-ing better than 2 per cent. Broadcastcalibration is for 5 kc. divisions at lowfrequency end, 10 kc. in the middle and20 kc. at the high frequency end.

Fundamental frequencies of oscillationwill be from 50.7 to 153 kc, so that someintermediate frequencies may be testedon the fundamental, others on the sec-ond harmonic, while the broadcast bandis taken care of by the tenth harmonic.No switching necessary despite widefrequency coverage. Sharp tuning,clear squeals in heterodyning, andstrong modulation by the 60 -cycle linefrequency. No hum except at resonance.Frequency stability is of a high order,due to stabilized grid circuit. Calibra-tion is for a 56 tube.

Cat. WOSC, @ $6.93(56 tube is 87c extra)

Same as above, except for batteryoperation, with high audio frequencymodulation, and requiring 3 -volt drybattery and 22.5 volt B battery (notfurnished). Tube required is the '30.

Cat. WOSCB,(230 tube is $1.08 extra)

The modulated oscillator has vernier dial calibrated directly infrequencies. covering, broadcasts and intermediate. The tube isinserted by removing the panel. Output post is at left, ground post

at right.

DIAMONDSUPER

Set of shielded coils, consisting of antennacoil, modulator input coil and combinationoscillator and first 175 kc intermediate coil(latter two in one shield), and separateintermediate coil with center-

3.95tapped secondary. Cat. SDCK.Combination oscillator and 175 kc only, $1.80in one shield. Cat. OSNThree -gang 0.00037 tad. condenser with trimmersbuilt in; % inch shaft, 11/8 inches long. $1.80Cat. DJA3G250,000 -ohm potentiometer with switch. .72Cat. R25SPigtail resistors, 9c each; Rola speaker, $3.83; tubeshields, 11c each; UX, UY sockets, 10c; six -pin,11c; 7 -pin, 15c.

DIRECT RADIO COMPANY143 West 45th St. N. Y. City

RIDER'S PERPETUALTROUBLE SHOOTER'S

MANUALHaving assembled 2,000 diagrams of com-mercial receivers, power amplifiers, con-

verters, etc., in 1,200 pages of Volume No.1 of his Perpetual Trouble Shooter's Manual,John F. Rider, noted radio engineer, hasprepared Volume No. 2 on an even moredetailed scale, covering all the latest re-ceivers. Volume No. 2 does not duplicatediagrams in Volume No. 1, but containsonly new, additional diagrams, and a newall-inclusive information on the circuit.covered.Volume No. 2 -Perpetual Trouble Shooter's

Manual, by John F. Rider. Shippingweight IP lbs. Order Cat. RM-VT 0 15.10

Volume No. 1 (6 lbs.). Order Cat. RM-VO$5.00

We pay postage in United States on re-ceipt of purchase price with order. Canadian,Mexican and other foreign remittances musthe in funds payable in New York.RADIO WORLD, 145 W. 45th St., N. Y. City

BLUEPRINTSg97 Five -tube tuned radio frequency,

A -C operated; covers 200 to 550meters (broadcast band), with optional ad-ditional coverage from 80 to 204 meters,for police calls, television, airplane, ama-teurs, etc. Variable mu and pentode tubes.Order BP -627 @ ZS*

628-B. Six -tube short-wave set, A -Coperated; 15 to 200 meters; no

plug-in coils. Intermediate frequency, 1,600kc. Variable mu and pentode tubes. OrderBP -628-B @ZS*

RADIO WORLD145 WEST 45TH ST., NEW YORK, N. Y.

PHONOPICKUP

Rubber -damped phono-graph pickup. elim-inating pick-up noises.Designed for full tonalrange with fidelity.Price. $4.50.

Direct Radio Co., 143 West 45th Street, New York, N. Y. Direct Radio Co., IC W. 45th St., N. Y. City

RQLAND BURKE HENNESSYEditor

HERMAN BERNARDManaging Editor

The First and Only National Radio WeeklyELEVENTH YEAR

J. E. ANDERSONTechnical Editor

J. MURRAY BARRONAdvertising Manager

Vol. XXIIPublished weekly by Hennessy Radio Publications Corporation, 145 West 45th Street, New York, N. Y.

OFFICERS: Roland BurkeHennessy, President a n dTreasurer; M. B. Hennessy,Vice -President; HermanBernard, Secretary.

DECEMBER 24th, 1932

Editorial and Executive Offices: 145 West 45th Street, New YorkTelephone: BR-yant 9-0558

Entered as second-class matter March, 1922, at the Post Office at NewYork, N. Y., under Act of March 3, 1879. Title registered in U. S.Patent Office. Printed in the United States of America. We do notassume any responsibility for unsolicited manuscripts, photographs,drawings, etc., although we are careful with them.

No. 15, -Whole No. 561

Price, 15c per Copy: $6.00 perYear by mail. $1.00 extraper year in foreign countries.Subscribers' change of addressbecomes effective two weeksafter receipt of notice.

A UNIVERSAL SETSuperheterodyne Works on A.C. or D.C.

By J. E. Anderson39 36 175 33 Y7S

MAI)

315.1.

a WATT

FiElP

FIG. 1This is the diagram of a six -tube d -c or a seven -tube a -c s uperheterodyne. It is a circuit that may be called uni-versal because it can be used on either d -c or a -c simply by throwing a switch.

S0 -CALLED universal receivers arebeing put out these days, receiversthat will work when connected to

a -c or d -c lines without making anychanges in the connections. In these re-

ceivers the filaments are connected in se-ries and a suitable ballast resistor is putin the line to drop the excess voltage.Since the voltage is the same regardlesswhether it is alternating or direct, the

same ballast will do for both cases. Now,since the a -c must be rectified and fil-tered before being applied to the platesand screens of the tubes, a tube rectifier

(Continued on next page)

CoilsTwo midget type shielded r -f tuning coils

for 350 mmfd. capacityOne midget type oscillator coil for 350

mmfd. capacity and 175 kc i-fTwo doubly tuned 175 kc i-f transformersOne power transformer capable of giving

about 250 volts rectifiedOne 30 -henry choke coil capable of carry-

ing 90 milliamperes

CondensersOne 0.25 mfd. by-pass condenser

LIST OF PARTSOne gang of three 350 mmfd. tuning con-

densersSix 0.1 mfd. by-pass condensers (eight if

BFI rectifier is used)Three 0.00025 mfd. condensersOne 0.01 mfd. condenserFour 4 mfd. by-pass condensers

ResistorsTwo 300 ohm bias resistorsOne 400 ohm bias resistor, 3 wattsTwo 50,000 ohm resistorsOne 30,000 ohm resistorTwo 0.5 megohm resistors

One 0.5 megohmOne 10,000 ohm resistorOne 7,500 ohm, 3 watt resistorOne 130 ohm, 25 watt resistorOne 315 ohm, 10 watt resistorOne 3,500 ohm, 5 watt resistorOther RequirementsOne vernier dialFive grid clipsFive UY socketsTwo six -spring socketsOne UX socketOne triple pole, double throw switchOne single pole, single throw line switch.

4 RADIO WORLD December 24, 1932

30H

§-------.287.-tigglFIELD

4-M P..

FIG. 2If a 280 type rectifier is used in the circuit diagramed in Fig. 1 the B sup-

ply circuit should be wired according to this arrangement.(Continued from preceding page)

is employed, together with a suitable filter.No power transformer is used and thisfact allows universality. Of course, thatlimits the applied voltage to the line vol-tage since there is no means of steppingit up.

One difficulty is encountered in connec-tion with the field supply for the dynamicspeaker. A -C cannot be applied directlyto the field and if part of the availablerectified voltage is used for the field com-paratively little is left for the plates andthe screens. Hence when the set is towork on a -c a magnetic or a permanentfield dynamic speaker is the logical thingto use. This, of course, can be used whenthe voltage is direct, too, so that on auniversal set one of these should be used.

On d -c a 110 volt speaker could be usedwith the field connected directly acrossthe line. with a built-in rectifier could used= -advantageously.But in neither case would the set be reallyuniversal. Only the magnetic or the per-manent field dynamic would make it that.

Use of TransformerIf we use a transformer for the a -c case

it is possible to make the set universaleven when a dynamic speaker is usedfor in that case the field could be con-nected directly across the line when thesupply voltage is direct and in series withthe plate supply when the supply voltageis alternating. To make up for the lossof voltage it would only be necessary tohave a step-up transformer giving a vol-tage that is high enough. It is a simplematter to provide a switch that will changethe set from one type to the other.

We show in Fig. 1 a diagram of a setwhich is universal to the extent that itmay be converted from one type to theother by throwing a single triple pole,double through switch. For conveniencethis switch is shown in two parts. Di-rectly under transformer T is a singlepole double throw section. When this isthrown up one side of the line is con-nected to the primary of the power trans-former. The other side of this primary ispermanently connected to the other sideof the line. This position of the switch,of course, is for the a -c case.

When the switch is thrown up thetransformer T is excited and a high vol-tage is induced in the secondary. This isrectified by the tube BH and the rectifiedcurrent is first filtered by means of two4 mfd. condensers and a 30 -henry chokecoil. The field coil of the speaker is con-nected in series with the negative lead bythe same movement of the switch. Oneside of the field is permanently connectedto the negative side of the line, negativeboth when the supply voltage is d -c andwhen it is a -c.

Additional FilteringSince the field coil is in series with

the line it acts as a choke. In order to

have a by-pass for this choke third 4 mfd.condenser is connected across the line.`

When the supply voltage is d -c theswitch Sw2 is thrown down. That throwsthe power transformer and the rectifierout of the circuit and connects the posi-tive side of the line to the positive side ofthe filter circuit, that is, to the terminalof the rectifier that would be positive.Thus the filter remains in the circuit. Thesecond part of the switch transfers thefield coil from the plate supply to the line.Then the third 4 mfd. condenser is nowthrown out of the circuit. The third sec-tion of the triple pole switch is usedfor closing the the gap in the negativeline that was made when the field coilwas taken out of it. That this is accom-plished is clear by the fact that if the sec-ond section of the switch is thrown upand the third section down, the field coilis short circuited.

The additional filtering when a -c is usedis desirable because there is much moreripple in the rectified voltage than in thevoltage on the d -c line. One 30 -henrychoke and two 4 mfd. condensers arequite sufficient on a d -c line. Indeed,practically no hum would result if the30 -henry choke were omitted and the con-densers alone were used.

Field Coil RequiredThe usual field coil on d -c has a resis-

tance of about 2500 ohms and this wouldtake a current of 46 milliamperes whenconnected to a 115 volt line. Due to theuse of a 48 tube in this set the normalplate current will be of the order of 85milliamperes, which is nearly twice thecurrent required by the 2500 ohm speakerfield. That again raises a difficulty for ifwe connect the 2500 ohm speaker in seriesand forced 85 milliamperes through it, itwould probably burn up. The best wayout of it seems to be to put a shunt acrossthe field when it is connected in seriesand adjusting this shunt so that it takesabout half the total current. The voltagedrop across the field must remain the samein the two positions. Suppose we allow afield current of 50 milliamperes when thecoil is in series. The voltage across itshould be 115 volts. This is also to be thedrop across the shunt resistor. Since thetotal current is 85 milliamperes and thefield is to take 50, the shunt will take 35milliamperes. That means that the shunt,which is marked R, should have a resis-tance of 3,300 ohms. The nearest commer-cial size of 3,500 ohms will he all right.The wattage dissipation in it will be about4 watts so that a 5 -watt or heavier resis-tor should be used. It is shorted whenthe coil is across the line so that it willnot cause any trouble.

Rectifier TubeThe rectifier tube is of the gaseous

type that requires no filament. If thepower transformer T has a 5 volt filamentwinding a 280 type rectifier can be used

just as well. The circuit for this is showsin Fig. 2.

Regardless of which type rectifier isused the secondary voltage of the powertransformer should be such that rectifiedvoltage across the second filter condenseris 230 volts. There are midget trans-formers available that will give this vol-tage at approximately the current requiredby this set. They have been designed fora 280 or an 83 rectifier so that the neces-sary 5 -volt winding is included.

All the filaments of the tubes in setproper are connected in series. The firsttube is connected to the negative side ofthe line by joining the two points marked(1). Then the connections are made asindicated by the numbers at the ends ofthe heaters. The terminal on the 48marked (6) is connected to the ballest re-sistor and also marked (6). Since the 48takes 0.4 ampere and the other tubes onlytake 0.3 ampere a 315 ohm shunt is con-nected from (5) to (1). This resistorshould be wire wound and should have arating of at least 10 watts.

Between (6) and the positive side ofthe line is inserted the filament ballastresistor. Since there are five tubes eachrequiring a voltage of 6.3 volts, and onerequiring 30 volts, the drop in the heaterswill amount to 61.5 volts. But the linevoltage is 115 volts. Hence the ballastmust drop 53.5 volts when the current is0.4 ampere, which takes nearly 130 ohms.The wattage dissipation in this circuitwill be a little over 20 watts, and the re-sistor used should have a rating higherthan this. The specified value is 25 wattsbut of course a heavier resistor would bebetter.

Grounding of CircuitNo direct ground should be used on

the circuit. On d -c one side of the line isgrounded and that grounds the circuit

directly or through thefilter condensers. On a -c the chassismight be grounded but it should only bedone through a condenser. That is, a con-denser of 0.001 mfd. or more should beconnected to the chassis and then theground connection should be made to theunused side of the condenser.

When the set is used on d -c care mustbe taken to see that the polarity is cor-rect. If it is wrong the set will not workand before the tubes have a chance towarm up the filter condensers will beruined. On a -c it makes no differencehow the line plug is inserted, providedthat the switch has been set for a -c first.

Biasing of TubesIt is necessary in a circuit of this type

to bias all the tubes by means of biasresistors. For each of the 239s a 300 ohmresistor is used between the cathode andthe chassis. Each is bypassed with a 0.1mfd. condenser. ' The bias resistor forthe 236 detector is 30,000 ohms and thisalso is shunted by a 0.1 mfd. condenser.

The 85 triode is diode biased, the biasvoltage depending on the signal. Whenno signal is coming in the bias is zero, asit is when the volume control is set at zerooutput. To prevent excessive plate cur-rent in the triode under conditions of zerobias, a 50,000 ohm resistance is used forcoupling. There is no good reason whythis resistance should not be as high as0.25 megohm.

Automatic BiasThe power tube is biased with a 400

ohm resistor. This value is a little higherthan the value obtained from the ratedbias and screen and plate current but it isall right to overbias the tube a little.However, a 350 ohm resistor could beused safely. The condenser across thebias resistor is 4 mfd. A much largervalue, say 25 mfd., could be used to ad-vantage. Condensers of this value areobtainable of the electrolytic type. Whenone of these is used the positive ter-

December 24, 1932 RADIO WORLDminal should be connected to the cathode.Automatic bias is also used on the two239 amplifiers. This is taken from thevoltage developed across the diode loadresistance through a 0.5 megohm resistor.In each grid return of the controlledtubes is a 0.1 megohm filter resistance anda 0.1 mfd. condenser across it. There is.also a 0.1 mfd. condenser connecting thecommon return to ground.

The diode load resistance is a halfmegohm potentiometer which is also usedas a manual volume control by controllingthe amount of detected audio voltage im-pressed on the grid of the triode of the85. The voltage impressed on the gridof the 85 is amplified approximately seventimes and then impressed on the grid ofthe 48 grid. The output power is around2 watts.

The six tube circuit is practically astandard superheterodyne. First there isan r -f tuner which is followed by a 39 r-famplifier. This if followed by anotherr -f tuner after which comes the 236 firstdetector, which operates on the grid biasprinciple. The oscillator is a 37 and usesa three winding coil, the tickler, the tunedwinding and the pick-up, which is put inthe cathode lead of the first detector.

The intermediate amplifier -selector con-tains two doubly tuned i-f transformersand one 239 tube. The intermediate fre-quency is 175 kc.

Padding ValuesThe tuning inductance of the oscillator

should have a value of about 196 micro -henries, if the inductance in each of ther -f circuits is 245 microhenries. Theseare all standard coils that go with 350mmfd. tuning condensers. The series pad-ding condenser Cs should have a value ofabout 900 mmfd. The best way to getthat is to use an adjustable condenser hav-ing a range from 700 to 1,000 mmfd. Thisis also a standard unit used in most 175kc superheterodynes.

The adjustment of the padding can bedone in the regular way. That is, thecircuit is first adjusted at about 1,450 kcby setting the main condenser at about 6on the dial and then tuning in the signalby means of the trimmers on the threetuning condenser sections. Then the cir-cuit is converted to a t -r -f set by movingthe grid clip from the first detector to thecap of the 85. A signal of about 600 kcis tuned in and then without touching thetuning condenser the circuit is restoredto a superheterodyne and the same 600kc signal is tuned in with the paddingconsenser Cs, and with nothing else.

PrecautionsOf course, it is first necessary to tune

the intermediate frequency circuit to 175kc. This is best done by supplying amodulated 175 kc signal from a laboratoryoscillator. In the absence of such anoscillator the tuning may be done on anysignal that can be brought in. That may

IMPROVING RESULTS

In using a short-wave dual condenserin a t -r -f circuit, if the two sections donot track after compensators have beenaccurately adjusted at the low capacityend, only inductance or resistance cancause the mismatching. Equalize the cir-cuits inductively.

A microphone used with the a -f ampli-fier of a set works better when a d -cvoltage is across it, from 1.5 to 6 voltsbeing usual. A microphone transformer,.one type for grid, another for plate cou-pling, aids, too.

If a wedge type dial is stiff, despite itsdependence on friction, a little lubricatingoil on the disc gives smoother action.

not lead to 175 kc but something near it.Warning has already been given aboutconnecting the circuit to a ground. A se-rious short-circuit might occur if it isdone. Care should also be taken to seethat the antenna used is not groundedsomewhere. The possibility of a burned -out primary in the first r -f transformer isalways present.

If the set must be grounded a 0.001 mfd.condenser may be connected between thechassis and the ground terminal of the

antenna winding. If this condenser isused there is no danger of connecting theantenna post to any antenna, nor anydanger of grounding the other end of theprimary.

It was also said that under certain con-ditions the by-pass condensers in the filtermight be damaged by voltage of re-versed polarity. That applies only if thethree 4 mfd. condensers in the filter areof the electrolytic type. If good papercondensers are used there is no danger.

In Preparation! Radio World's Holiday Illosue!

ROCIKEIFEITER CENTER NUMBER(Including RADIO CITY)

Progress and Development ofWorld's Greatest Comanercial and Amusement Achievement


TEST OSCILLATORCONSTRUCTION

OUTPUT GROUND

10"HARMONIC

COIL

The circuit diagram of the modu-lated test oscillator. The outputcoupling is obtained by the capacitybetween parallel leads, one of whichis the wire from grid of socket togrid condenser, and the other thewire that terminates at the outputbinding post. There is no conduc-tive coupling at the other end of

the output wire.

THE constructional details for build-ing a modulated test oscillator, cov-ering the broadcast band and all the

commercially used intermediate frequen-cies, are given herewith on the basis ofutmost compactness. The circuit is themodification of the Hartley oscillator asdevised by E. M. Shiepe, and a -c is usedon the plate. This of course introducesthe line frequency as modulation, ap-proximately 100 per cent. The oscillationlevel is high and the coupling is thereforeexcellent even at the lowest frequency.

The fundamental frequencies of oscilla-tion, using a 0.00037 mfd. single condenserwith compensator built in, and a "tenthharmonic" coil, will be from 152 to 50 kc,therefore the broadcast band is coveredby cipher annexation, using the tenth har-monic, and a frequency -calibrated dialwill read directly in terms of the funda-mental and indirectly (by the cipher an-nex) for the broadcast band, while twointermediate frequencies, 115 and 130 kc.,will be on the fundamental scale, another,260 kc., will be a second harmonic, andthe remaining intermediate frequenciesthird harmonics. All the popular inter-mediate frequencies are encompassed bythe following: 115, 130, 172.5, 175, 177.5,260, 400 and 450 kc.

Sizes Given

The overall size of the wooden cabinetis 9 inches wide by 5 15/16 inches frontto back by 4% inches high, the height in-cluding the mounting feet. The panel is8.5 x 5.5 inches, and is cut out for thetraveling light full -vision dial.

The dimensions for the chassis are givenin a drawing, and also the view of thecompleted test oscillator is shown in aphotograph. When the test oscillator isin use, or even when it isn't, by virtue ofthe manner of mounting the tube the up-right position for the tube is not used,but with the new heater type tubes it isentirely practical and permissible to usehorizontal mounting, provided the heaterprongs are vertical. The tube used is oneof the new offerings, a 56, even a betteroscillator than the '27, which it otherwiseresembles in appearance and performance.

Coils

One tenth harmonic coil, tapped. Totalinductance 20 millihenries, tapped at 5millihenries

One 2.5 volt filament transformer (enamelleads are 2.5 volts)

Condensers

One 0.00037 mfd. tuning condenser, withcompensator built in ; shaft 3A -inchdiameter, PA inches long

One 0.00025 mfd. grid condenser with clips

LIST OF PARTSResistorOne 0.1 meg. pigtail resistor. Solder tails

to clips of grid condenserOther RequirementsOne UY tube socketTwo binding postsOne a -c cable and plugOne vernier dial, travelling light full -vision

type ; pilot bracket and lamp ; scalecalibrated in kilocycles, 50 to 152, withintermediate frequencies imprinted ; es-cutcheon.

One wooden cabinet, one wooden paneland one wooden chassis or base

Hardware, consisting of nuts and bolts.

It is somewhat smaller in size, however.The circuit diagram shows how simpleit is to wire up this test oscillator, sincethere are only a few connections. Thetuning coil used is of the honeycomb type,and can be wound thus within an outsidediameter of about 1 inch, even thoughthe inductance is 20 millihenries.

Ordinarily two separate honeycombcoils have been used in the past, but after

special tests it was found that a singletapped coil could be produced with an in-ductance accuracy of 2 per cent., andtherefore the tapped type is recom-mended.

The coil is so constructed that the tapis off center. There are three lugs, twofor extremes of the winding and one lugfor the tap. The tap lug is the centralone. The question then remains, which

2112"

1-1.11Q)

Vet -

4.

The dimensions of the top panel, with cutout for the dial escutcheon, aregiven at top, and the data for the wooden chassis are given below. The5/8 -inch slot is to pass the dial bracket, but even so the dial bracket mayhave to be cut down.

December 24, 1932 RADIO WORLD 7

Internal viewof the wiredoscillator. Thechassis is to beturned approx-imately halfway around,fitted onto thecabinet andscrewed ontothe pillars atthe four cor-ners. The fila-ment trans-former is heldby two boltsand nuts. Ino n e instance(upper) thebolt is the shaftof the groundbinding post.The outputbinding post(lug at upperright in photo-graph) is cou-pled by its own

capacity.

end of the winding goes to grid and whichto grid return? The larger part of theinductance is to be between grid and tap,and this is between the end of the wind-ing and the tap. The end can be seenon examination of the coil, for the leadis on the outside, being held fast bybinder and brought down to the lug. Thisgoes to grid, hence the other extreme,which may be confirmed by examinationas the beginning or inside terminal, goesto grid return. IT the coil is held be-tween forefinger and thumb, base on bot-tom resting on the thumb; tap or centrallug toward you, the grid connection isat left, tap at center and grid return atright.

High Frequency AdjustmentThe circuit will give accurate reading

at the low frequency end without adjust-ment, but the capacity of the compensat-ing condenser has to be adjusted for thehigh frequency end, and allowance hasbeen made for this.

Of course if a numerical dial (0=100 or100-0) is used, then no adjustment needbe made, since you are going to calibratethe scale yourself, and probably draw acurve, frequency against dial setting.How to do this calibration work has beendiscussed fully in previous issues, includ-ing December 17th, 1932, and October15th, 1932.

HoWever, it is assumed for the presentthat a scale pre -calibrated in kilocycleswill be used, as accurate ones are nowobtainable commercially. Then you mayselect any broadcast station whose fre-quency is at or near the high frequencyend, and adjust the compensator so thatyou pick up a beat or squeal when usingthe test oscillator with a broadcast re-ceiver. This is the only adjustment tobe made, as the coils are held to theirrequired inductance value in manufac-ture. Coils with too low inductance arediscarded, coils with too high inductanceare reduced by removal of turns.

Output CouplingThe intensity of oscillation is great

enough so that for broadcast frequenciesit is not necessary to use the coupling(output) binding post, as the radiationprovides sufficient coupling. However,any who desire to use this post may doso by connecting a wire thereto and wrap-ping the other end of the wire a fewtimes around the wire leading to antenna

post of the receiver. No conductive cou-pling to the antenna is needed, as thecapacity between the outlead wire andthe aerial is large enough.

For intermediate frequencies it is ad-visable to use the output post. Prefer-ably connect a wire to it and then hookthe bared other end of this wire to theplate spring of the modulator socket, and

the intermediate channel on thatbasis. The ear test may be used evenon receivers that have automatic volumecontrol.

The other post may be grounded, as itconnects only to the core or frame ofthe filament transformer, but this isn'tnecessary.

This test oscillator is so simple andeffective, and also costs so little, thatevery experimenter and service manshould have one, because work on super -heterodynes is almost impossible of com-plete success without a test oscillator.The accuracy will be found to be 2 percent. or better, which is entirely satis-factory, and is an improvement on thedegree of accuracy previously obtained byusing two 800 -turn honeycomb coils andadjusting the inductance by moving thecoils close together or farther apart.

Trouble -ShootingOn the score of trouble about the only

real one that need be expected is thatthe high frequency setting can not bemade properly, because the tuning doesnot go high enough. And the only rea-son for this trouble is that you havemounted the honeycomb oscillation coilwith a brass, iron or other metal screwor piece running through the core, andthis increased the inductance and de-creased the frequency. Therefore puttingany metal through the core is taboo. Thecore has a hole iii it that passes a 6/32machine screw, which may be the tempta-tion, but at the base this may be tappedfor 8/32 and a brass or other metal screwonly./ inch 'long may be used for en-gaging this tapped thread. Put the coilin a vise so that the jaws of the vise en-gage the large round base of the coilwithout touching the winding. Then taplightly and mount the coil as prescribed.This is a better method than hanging thecoil on a socket spring.

If instead of pickup squeals you simplyhear a guttural growl and the tuning con-denser does not seem to change this, thecondenser is not properly connected, that

is, either the grid end or rotor or bothare not in circuit, or the plates of thecondenser are shorted. A distinct squeal,should be picked up, clear and Thud, andon most stations zero beat can be regis-tered, which means tuning to the squealand then to that point within the squealregion on the dial for this station thatregisters no squeal. That is, there is nodifference in frequency between the testoscillator's tenth harmonic and the funda-mental of the broadcasting station.

Grid BlockingIf besides the squeals picked up there

is a steady whistle or a sound like motor -boating, the grid leak is of too high avalue. The cause is grid blocking. Theremedy is to use a smaller value of leak.Since the grid condenser is 0.00025 mfd.,it was found by experiment that the gridwould not block if the resistor were 0.1meg.

If there is a steady hum, evidently dueto vibration, then the core of the filamenttransformer is loose, and may be tight-ened by hammering a wedge between thelaminations where the opening is obvious.Sometimes simply hitting the laminationswith a hammer will so dispose them thatthe lamination rattle will disappear. Awedge, if used, need not be bulky. Astrong lug or two usually will serve thepurpose.

The specially calibrated scale has 1 kcseparation registered from 50 to 80 and2 kc registered from 80 to 152 kc, so thatfor broadcast use the equivalent separa-tion (tenth harmonic) is 10 kc from 500to 800 kc and 20 kc from 80 to 1520 kc.However, it is practical to set the dialin the center of two of the 20 kc separa-tion bars for any desired 10 kc setting,except at the very high frequency end.

The intermediate frequencies are im-printed on the scale. There is then noneed to concern one's self with whichharmonic is being used, and that is truealso of the broadcast band, by the way.For 175 kc simply set the test oscillatorat the bar registered for 175, or for 1400kc set the test oscillator at the bar regis-tered for 140.

Since the fundamental range is 50 to152 kc, any frequency within that rangemay be tested, and this includes the oldsuperheterodynes with intermediate fre-quency around 70 kc (Victoreen, Mag-naformer, etc.)

-Herman Bernard.


TEST OSCILLATORCONSTRUCTION

0.1 Mn

£0.HARMONIC

COIL

ourPur GROUND

The circuit diagram of the modu-lated test oscillator. The outputcoupling is obtained by the capacitybetween parallel leads, one of whichis the wire from grid of socket togrid condenser, and the other thewire that terminates at the outputbinding post. There is no conduc-tive coupling at the other end of

the output wire.

THE constructional details for build-ing a modulated test oscillator, cov-ering the broadcast band and all the

commercially used intermediate frequen-cies, are given herewith on the basis ofutmost compactness. The circuit is themodification of the Hartley oscillator asdevised by E. M. Shiepe, and a -c is usedon the plate. This of course introducesthe line frequency as modulation, ap-proximately 100 per cent. The oscillationlevel is high and the coupling is thereforeexcellent even at the lowest frequency.

The fundamental frequencies of oscilla-tion, using a 0.00037 mfd. single condenserwith compensator built in, and a "tenthharmonic" coil, will be from 152 to 50 kc,therefore the broadcast band is coveredby cipher annexation, using the tenth har-monic, and a frequency -calibrated dialwill read directly in terms of the funda-mental and indirectly (by the cipher an-nex) for the broadcast band, while twointermediate frequencies, 115 and 130 kc.,will be on the fundamental scale, another,260 kc., will be a second harmonic, andthe remaining intermediate frequenciesthird harmonics. All the popular inter-mediate frequencies are encompassed bythe following: 115, 130, 172.5, 175, 177.5,260, 400 and 450 kc.

Sizes Given

The overall size of the wooden cabinetis 9 inches wide by 5 15/16 inches frontto back by 474 inches high, the height in-cluding the mounting feet. The panel is8.5 x 5.5 inches, and is cut out for thetraveling light full -vision dial.

The dimensions for the chassis are givenin a drawing, and also the view of thecompleted test oscillator is shown in aphotograph. When the test oscillator isin use, or even when it isn't, by virtue ofthe manner of mounting the tube the up-right position for the tube is not used,but with the new heater type tubes it isentirely practical and permissible to usehorizontal mounting, provided the heaterprongs are vertical. The tube used is oneof the new offerings, a 56, even a betteroscillator than the '27, which it otherwiseresembles in appearance and performance.

Coils

One tenth harmonic coil, tapped. Totalinductance 20 millihenries, tapped at 5millihenries

One 2.5 volt filament transformer (enamelleads are 2.5 volts)

Condensers

One 0.00037 mfd. tuning condenser, withcompensator built in ; shaft 3A -inchdiameter, P/8 inches long

One 0.00025 mfd. grid condenser with clips

LIST OF PARTSResistorOne 0.1 meg. pigtail resistor. Solder tails

to clips of grid condenserOther RequirementsOne UY tube socketTwo binding postsOne a -c cable and plugOne vernier dial, travelling light full -vision

type ; pilot bracket and lamp ; scalecalibrated in kilocycles, 50 to 152, withintermediate frequencies imprinted; es-cutcheon.

One wooden cabinet, one wooden paneland one wooden chassis or base

Hardware, consisting of nuts and bolts.

It is somewhat smaller in size, however.The circuit diagram shows how simpleit is to wire up this test oscillator, sincethere are only a few connections. Thetuning coil used is of the honeycomb type,and can be wound thus within an outsidediameter of about 1 inch, even thoughthe inductance is 20 millihenries.

Ordinarily two separate honeycombcoils have been used in the past, but after

special tests it was found that a singletapped coil could be produced with an in-ductance accuracy of 2 per cent., andtherefore the tapped type is recom-mended.

The coil is so constructed that the tapis off center. There are three lugs, twofor extremes of the winding and one lugfor the tap. The tap lug is the centralone. The question then remains, which

0

8

4

The dimensions of the top panel, with cutout for the dial escutcheon, aregiven at top, and the data for the wooden chassis are given below. The5/8 -inch slot is to pass the dial bracket, but even so the dial bracket mayhave to be cut down.


Internal viewof the wiredoscillator. Thechassis is to beturned approx-imately halfway around,fitted onto thecabinet andscrewed ontothe pillars atthe four cor-ners. The fila-ment trans-former is heldby two boltsand nuts. Ino n e instance(upper) thebolt is the shaftof the groundbinding post.The outputbinding post(lug at upperright in photo-graph) is cou-pled by its own

capacity.

end of the winding goes to grid and whichto grid return? The larger part of theinductance is to be between grid and tap,and this is between the end of the wind-ing and the tap. The end can be seenon examination of the coil, for the leadis on the outside, being held fast bybinder and brought down to the lug. Thisgoes to grid, hence the other extreme,which may be confirmed byas the beginning or "inside terminal, goesto grid return. If the coil is held be-tween forefinger and thumb, base on bot-tom resting on the thumb; tap or centrallug toward you, the grid connection isat left, tap at center and grid return atright.

High Frequency AdjustmentThe circuit will give accurate reading

at the low frequency end without adjust-ment, but the capacity of the compensat-ing condenser has to be adjusted for thehigh frequency end, and allowance hasbeen made for this.

Of course if a numerical dial (0=100 or100-0) is used, then no adjustment needbe made, since you are going to calibratethe scale yourself, and probably draw acurve, frequency against dial setting.How to do this calibration work has beendiscussed fully in previous issues, includ-ing December 17th, 1932, and October15th, 1932.

However, it is assumed for the presentthat a scale pre -calibrated in kilocycleswill be used, as accurate ones are nowobtainable commercially. Then you mayselect any broadcast station whose fre-quency is at or near the high frequencyend, and adjust the compensator so thatyou pick up a beat or squeal when usingthe test oscillator with a broadcast re-ceiver. This is the only adjustment tobe made, as the coils are held to theirrequired inductance value in manufac-ture. Coils with too low inductance arediscarded, coils with too high inductanceare reduced by removal of turns.

Output CouplingThe intensity of oscillation is great

enough so that for broadcast frequenciesit is not necessary to use the coupling(output) binding post, as the radiationprovides sufficient coupling. However,any who desire to use this post may doso by connecting a wire thereto and wrap-ping the other end of the wire a fewtimes around the wire leading to antenna

post of the receiver. No conductive cou-pling to the antenna is needed, as thecapacity between the outlead wire andthe aerial is large enough.

For intermediate frequencies it is ad-visable to use the output post. Prefer-ably connect a wire to it and then hookthe bared other end of this wire to theplate spring of the modulator socket, andline up the intermediate channel on thatbasis. The ear test may be used evenon receivers that have automatic volumecontrol.

The other post may be grounded, as itconnects only to the core or frame ofthe filament transformer, but this isn'tnecessary.

This test oscillator is so simple andeffective, and also costs so little, thatevery experimenter and service manshould have one, because work on super -heterodynes is almost impossible of com-plete success without a test oscillator.The accuracy will be found to be 2 percent. or better, which is entirely satis-factory, and is an improvement on thedegree of accuracy previously obtained byusing two. 800 -turn honeycomb coils andadjusting the inductance by moving thecoils close together or farther apart.

Trouble -ShootingOn the score of trouble about the only

real one that need be expected is thatthe high frequency setting can not bemade properly, because the tuning doesnot go high enough. And the only rea-son for this trouble is that you havemounted the honeycomb oscillation coilwith a brass, iron or other metal screwor piece running through the core, andthis increased the inductance and de-creased the frequency. Therefore puttingany metal through the core is taboo. Thecore has a hole in it that passes a 6/32machine screw, which may be the tempta-tion, but at the base this may be tappedfor 8/32 and a brass or other metal screwonly rA. inch long may be used for en-gaging this tapped thread. Put the coilin a vise so that the jaws of the vise en-gage the large round base of the coilwithout touching the winding. Then taplightly and mount the coil as prescribed.This is a better method than hanging thecoil on a socket spring.

If instead of pickup squeals you simplyhear a guttural growl and the tuning con-denser does not seem to change this, thecondenser is not properly connected, that

is, either the grid end or rotor or bothare not in circuit, or the plates of thecondenser are shorted. A distinct squealshould be picked up, clear and roud, andon most stations zero beat can be regis-tered, which means tuning to the squealand then to that point within the squealregion on the dial for this station thatregisters no squeal. That is, there is nodifference between the testoscillator's tenth harmonic and the funda-mental of the' broadcasting station.

Grid BlockingIf besides the squeals picked up there

is a steady whistle or a sound like motor -boating, the grid leak is of too high avalue. The cause is grid blocking. Theremedy is to use a smaller value of leak.Since the grid condenser is 0.00025 mfd.,it was found by experiment that the gridwould not block if the resistor were 0.1meg.

If there is a steady hum, evidently dueto vibration, then the core of the filamenttransformer is loose, and may be tight-ened by hammering a wedge between thelaminations where the opening is obvious.Sometimes simply hitting the laminationswith a hammer will so dispose them thatthe lamination rattle will disappear. Awedge, if used, need not be bulky. Astrong lug or two usually will serve thepurpose.

The specially calibrated scale has 1 kcseparation registered from 50 to 80 and2 kc registered from 80 to 152 kc, so thatfor broadcast use the equivalent separa-tion (tenth harmonic) is 10 kc from 500to 800 kc and 20 kc from 80 to 1520 kc.However, it is practical to set the dialin the center of two of the 20 kc separa-tion bars for any desired 10 kc setting,except at the very high frequency end.

The intermediate frequencies are im-printed on the scale. There is then noneed to concern one's self with whichharmonic is being used, and that is truealso of the broadcast band, by the way.For 175 kc simply set the test oscillatorat the bar registered for 175, or for 1400kc set the test oscillator at the bar regis-tered for 140.

Since the fundamental range is 50 to152 kc, any frequency within that rangemay be tested, and this includes the oldsuperheterodynes with intermediate fre-quency around 70 kc (Victoreen, Mag-naformer, etc.)

-Herman Bernard.


THE LATEST METHODSDelayed A.V.C. and N. S. C. ExaminedRECENTLY we have had many new

devices and circuit arrangements inradio. Diode detection has returned.

We also have automatic volume control,noise suppression control, automatic volumecontrol delay, and automatic tone control.

Just what are these devices? What pur-pose do they serve? Are sets better withthem than withoul them?

Diode detection, of course, is not new,for it is older than the three -element vacu-um tube. But the application of it now isnew, especially when it is used in full -wavedetection. With diode detection the tubefunctions only as a rectifier, just the sameas the rectifier in the B supply. Detectionpartly occurs in the filter and load resistanceassociated with the rectifier. If the signalwere steady, that is, unmodulated, therewould be no detection, only rectification, asin the case of the B supply rectifier. Whenthe signal is modulated or for any otherreason varies, the rectified current varieswith the variation in the carrier, and thatvariation is the audio component. In onesense there is nothing at all new about thediode detector, for the grid leak and con-denser detector was nothing but a diode,the grid leak being the load resistance andthe grid condenser the filter. The tube alsofunctions as an amplifier. The improve-ment is due to the fact that the extra ele-ments made it possible to use a much higherplate voltage and thus to prevent distortionand overloading on strong signals.

A. V. C.Automatic volume control is not strictly

new either, for it has been used a few yearsBut the introduction of the duplex diodetriode made automatic volume control sim-pler to apply and more practical.

The function of the a.v.c., of course, isto hold the output voltage constant regard-less of the intensity of the strength of thesignal at the antenna. From the natureof the a.v.c it is not possible to hold thesignal constant absolutely for the signal mustincrease before the a.v.c can take greatereffect. But it is an automatic check on theamplification. To expect complete auto-matic volume control, that is to say, com-plete leveling of the output regardless ofthe intensity of the signal at the antennawould be the same as expecting one to lifthimself by the bootstraps. Perhaps that isnot the best analogy, but the point is thatit is not possible for the signal to hold itselfconstant.

Circuits have been suggested for makingthe effect so great that the net variation isextremely small. This is brought about byamplifying the d -c voltage used for a.v.c.before it is applied to the controlled tubes.If this voltage is amplified by a factor of10, for example, the total variation in theoutput as a result of a given variation inthe input signal is reduced in the ratio of10 to one. When this scheme is used thetriode part of the rectifier is employed as ad -c amplifier as well as an a -f amplifier.

Noise Suppression ControlIn a circuit equipped with an a.v.c. the

sensitivity rises to maximum value whenthere is no carrier impressed on the diodebecause then the a.v.c voltage is least. Thiscauses a strong rise in the amount of noisein the output of the set. Indeed, there isnothing but noise, some originating in thereceiver and some outside of it. The pres-ence of noise makes operation of a set un-pleasant, not because the set is noisy when

By Einar Andrewsa strong station is tuned in, but because itis noisy on weak stations and on no stationsat all. It is mainly noisy while tuning fromone station to another.

In order to overcome the interchannelnoise, the noise suppression device has beenintroduced. This operates so that whenthere is no carrier the audio amplifier isinoperative. The voltage developed acrossthe diode load resistance is amplified by thetriode part of the tube and the amplifiedvoltage is used to bias one audio tube, calledthe noise suppression tube. The amplifica-tion of the d -c voltage reverses the phaseof the voltage so that when the diode d-cvoltage is greatest the negative voltage onthe n.s.c. tube is least and the tube ampli-fies the audio signal, and when the dioded -c voltage is least the bias on the n.s.c.tube is greatest, and so great that the tubedoes not function at all. Thus the noise be-tween stations is cut out.

A noise suppression control could be usedon a set not provided with a.v.c., for thetwo are independent, but there would belittle object of using it without the a.v.c.

A. V. C. DelayThe a.v.c. delay is quite new. The term

delay is not a good one for it has nothing todo with time. It would be more logical to callit an a.v.c. handicap, the handicap being meas-ured in volts. We would be tempted to call ita.v.c. bias, but that would be confusing withthe a.v.c. voltage itself, which is used asbias. The "delay" voltage is really a biason the bias and therefore the term handi-cap seems appropriate. It might also betermed an a.v.c. limiting voltage.

Just what is the "delay?" Well, supposethe signal voltage at the antenna is suchthat it develops a voltage of 5 volts in thediode load resistance. If the handicap is5 volts there would be no automatic voltagecontrol for lower signal voltages on the an-tenna but there would be for all highervoltages, and in proportion to the excess.The handicap can be given any desiredvalue, and voltages as high as 50 volts havebeen recommended. That means 50 volts asreferred to the voltage developed across thediode load resistance and not 50 volts in theantenna, for a voltage of 50 volts in the an-tenna would never be encountered.

It is claimed that the degree of levelingof the volume output is more nearly com-plete the higher the handicap on the a.v.c.The idea might be carried still further bymaking the handicap infinite, or 500 volts, atany rate. That would certainly level outcompletely all voltages that exceeded thatvalue. That is a case of reductio ad absur-dum. Spoofing aside, the idea has its merits.For example, we might select such valuesthat only noise free stations would be sub-ject to a.v.c. and then put in a noise sup-pression circuit such that it would cut outall the noise, including, the signals belowthe noise level.

Another way of accomplishing about thesame thing is to build a less sensitive andless costly set, eliminating all these fancycontraptions and a good many of the tubes.or if the same number of tubes must be used,to make all of them less efficient.

Automatic Tone ControlThe automatic tone control, which may

also be called an automatic selectivity con-trol, seems to have some merits in fact. Theidea of it is so to arrange the circuit thatthe selectivity of the set becomes low onstrong local signals and high on weak, dis-

tant signals. Thus the quality would beexcellent on the local stations and no worsethan absolutely necessary on the distantones. That is surely as it should be.

But no set worthy of all these new de-vices would be complete without a manualtone control. There must be something bywhich the operator may spoil the excellentsignals from the local stations. It wouldnot do to shackle his freedom of choice ofquality. In a free country it is unreason-able to put any constraint of this nature onan individual. And we may be sure that hewill not abuse his privilege. The man whoprefers nothing but the bass notes will notenter the other man's drawing room andtamper with his set, and if he himself prefersall bass and no treble, that is his concern.Moreover, there are times when bassy sig-nals are really preferable. They have asoothing quality not possessed by signalsthat contain all the sparkle inherent in theoriginal.

Of What Use?Well, are these new contrivances worth

while in a receiver? Some of them are allthe time. All of them are some of the time.Diode detection is decidely worth whilewhere quality of reproduction is one of themain objects of the receiver. Automatic vol-ume control is certainly essential in an auto-mobile, or any mobile, receiver. It is alsohighly desirable in any receiver that is regu-larly used in receiving stations in the fad-ing zone, or any distant stations. Even insome cases of local reception there is a fluc-tuation in the signals that would be reme-died by an automatic volume control.

A noise suppression control is a desirablefeature in a receiver that is to be usedregularly in receiving weak distant stations,when that receiver is equipped with an auto-matic volume control, but not in a receiverwithout an a.v.c. What is most needed isnot a noise suppression control but a noiseremover, a device that removes noise com-pletely on all stations. And it should notcost more than five cents. While we are'waiting for that key to the DX Utopia letus stick to the automatic noise suppressioncontrol when it is really needed.

An automatic volume control "delay"seems to be a denial of the need of a.v.c. Ifthe "delay" is limited so that it will pre-vent the a.v.c. from taking effect on theweakest signals it may be all right, for itwould tend to make the receiver more sen-sitive on those stations. This might be anadvantage when the noise level is extremelylow. And if it levels the output more thor-oughly than the "undelayed" a.v.c. it mightalso help out considerably on all fading sig-nals.

If the automatic tone control works, itmight be a desirable addition to a- fancyreceiver, especially in view of the fact thatit costs practically nothing to add it to theset. This device works on the principlethat the selectivity of a tuned circuit is lessthe lower the resistance of the plate to whichit is connected. This is true whether theprimary connected to the plate is tuned oruntuned, just so one or both the windingsare tuned. The resistance in the plate cir-cuit is varied by varying the suppressorvoltage on the tube. The more negativethis is the less the plate resistance. The lessthe plate resistance, the better the high fre-quency audio notes come through.

It would seem that the simplest way toapply automatic tone control would be toconnect the suppressor grid to the a.v.c.voltage, for the voltage on the suppressorgrid would then vary in the right direction.


MICROPHONE INPUT

It is convenient to have a micro-phone jack on the side of the con-sole, in case you want to use anyof the currently popular low-pricedmicrophones in conjunction withthe audio amplifier of your receiver.The jack also can work a pilot lamp,which is fed from the 2.5 volts a. c.of the receiver, so the lamp glowswhen the microphone is in circuit.The microphone transformer would

be inside the console.

SMALL SET IN EMPIRE STATE CABINET

A few parts such as these were puttogether to constitute a small bat-tery -operated receiver, housed, in acabinet that followed the lines ofthe Empire State Building, the tall-est building in the world. This cab-inet was made of wood by an ex-perimenter as a Christmas presentto his little son. The view shownis that of the wired set removed

from cabinet shown at right.

LAYOUT FOR INDUCTANCE OR RESISTOR SLIDER

Front view of the cabinet modelledafter the Empire State Building.At top an indicator pendant wasplaced, upside down, as it were, sothat the blimp anchorage of thebuilding was simulated, and also sothat the radium coating of the in-dicator would cause the top to glowin a dark room. A pilot lamp of theusual type was inside, and whenthe set was turned on caused thepaper windows of the building to

light up.

If one desires to make a loading coil or a variable resistance he may do it,using parts as shown. A moving arm travels over the wire. In the caseof the inductance coil about 50 feet of No. 30 enamel wire would be used,and to provide contact the enamel insulation would be scraped off alongthe arc of the arm's travel. For a resistance the wire might be nichromeand hence uninsulated, but the turns should be far enough apart to prevent

them from touching adjacent ones.

FLEXIBILITY OF CONDENSER MOUNTINGSometimes one runs across a drilled chassis that has holes that do not coincideexactly with those required by a given gang condenser one has on hand. Ifsmall right-anglei brackets are used they may be so pointed, toward the frontor rear, as to pick 'up two or more of the holes, usually. The anchorage atfront is firm enough due to the dial being bracketed to the chassis and engag-

ing the condenser shaft. See illustration at right.

10 RADIO WORLD. December 24, 1932

THE NEWEST FADARA Circuit as Used in Different Consoles

THIS Fada nine -tube superheterodyneis of the type now generally referredto as de luxe. In other words, it is

a regular set and not a midget. Thereare several devices in this circuit notfound in the ordinary. First let us ex-amine the automatic volume control. Inthe first place not all of the output of thediode is used, either for a. v. c. or foraudio ouput. However, about 85 per cent.is used.

Again;- the full a. v. c. is not appliedto the i-f amplifier but only about one-third of the a. v. c. voltage that is appliedto the other tubes is applied to the i-famplifier. Thus the intermediate tube ispermitted to operate with a lower biason the high signals than the other con-trolled tubes.

Another feature is the oscillator. Thegrid leak, which has a value of 50,000ohms, is put across the series paddingcondenser rather than across the tuningcondenser, which is the usual place.There is an advantage, for the series con-denser does not change during the tuningwhereas the other condenser does. There-fore the grid leak is always across thesame impedance. When a resistor isconnected across a condenser the capacityof that condenser is effectively increasedby 1/R2Cw2 farads, in which R is the re-sistance, C the capacity, and w is 2n timesthe frequency. The minimum capacity inthe circuit may be 50 mmfd. when the fre-quency is 1,675 kc. The capacity changefor 50,000 ohms would be about 0.145 percent. When the same resistor is con-nected across a 900 mmfd. condenser thechange is only about 1/300 as great andthat at a place where even a large changemakes little difference.

Another fact about the oscillator is thata very high voltage is used on the plate.A very wide voltage swing is possible. Ahigh resistance in the plate circuit pre-vents high plate current and hence dis-tortion of the wave shape.

A special feature of Fada sets is theflashograph, a visual aid in tuning to exactresonance. A column of neon light overthe dial lengthens and shortens accord-ing to the strength of the signal. Whenthe column is longest the tuning is exact.This takes the place of the usual tuningmeter.

Compensating Instructions for RAReceiver, Models 74, 76, 83, 87, 88,

89, 97-25 or 60 CycleIn order to accurately adjust the va-

rious trimmer condensers of the receiverin accordance with the following instruc-tions it is essential to use a shielded signalgenerator capable of giving a modulatedcarrier frequency which can be accuratelyattenuated at 175 kc, 600 kc and 1400 kc.

This receiver is equipped with an auto-matic volume control which necessitatessetting the manual volume control of thereceiver to its maximum position, to as-sure accuracy in alignment. To controlthe signal output of the receiver it will benecessary to use the attenuator of thesignal generator.

Adjustment of I -F CondensersThe four I -F condensers are located in

the rear and side of the chassis itself, asindicated in the sketch.

1st-Disconnect the outside antenna sys-tem from the receiver.

2nd-Connect a lead wire from thedummy antenna system of the signal gen-erator to the control grid of the first de -

OFFICIAL DATA FOR SERVICE MEN

Continuity and Voltage Readings on RA Receiver-Models 74, 76, 83, 87,88, 89, 97 (60 Cycle)

Line Voltage 115 A.C.-Wattage 95No signals-Ant. and Ground leads tied together

Typeof

TubePositionof Tube

PlateVolts

Plate(MA)

CurrentControl

Grid VoltsScreen

Grid VoltsF-58 R. F. & I. F. 180 7.0 42 110F-58 1st Detector 173 1.1 11.0 103F-56 Oscillator 70 4.0F-56 2nd DetectorF-56 1st Audio 164 io 10:6F-247 P. P. Audio 248 34.0 15.0 262F-280 Rectifier 112 total

Noes :-Bias readings are to be taken across each respective bias resistor. Correct read-ings cannot be obtained at control grids due to use of series resistors.

VOLTAGES ACROSS VOLTAGE DIVIDER AND BLEEDER RESISTORSVoltage across 280 ohm AF filter choke (1933-X) 31 voltsVoltage across 800 ohm Speaker field (3 -1266 -Ms) 95 voltsVoltage across 7,000 ohm Resistor (3 -1264 -Ms) 92 voltsVoltage across 25,000 ohm Resistor (3 -1450 -Ms) 161 voltsVoltage across 30,000 ohm Neon control (3 -1440 -Ms) 115 voltsVoltage across 200 ohm Bias resistor (3 -1283 -Ms) 15 voltsVoltage across 300 ohm Bias resistor (3 -1444 -Ms) 4.2 voltsVoltage across 5,000 ohm Bias resistor (3 -1445 -Ms) 10 volts

VOLTAGES ACROSS ELECTROLYTIC CONDENSERSlst-402 2nd -371 3rd -276

D -C RESISTANCE VALUESPrimary Secondary

1927-X1929-X1939-X1924-X1925-X

Antenna coilR. F. CoilOscillator coilI. F. transformerI. F. transformer

. ohms71 ohms

.8 ohms97 ohms97 ohms

3.5 ohms' 3.5 ohms

3.5 ohms97 ohms97 ohms

2-2036-Y Suppressor coil 15.5 ohms 1.47 ohms1926-X Input AF transformer 2,933 ohms 9,600 ohms1934-X Output AF transformer 745 ohms .75 ohms1933-X Choke 280 ohms2413-Y R. F. choke 134 ohms3 -1266 -Ms 12-E speaker field 800 ohms

The foregoing voltage and current read-ings were taken beneath the chassis withthe meters available in an ordinary setanalyzer with the idea in mind of ap-proximating the conditions the average

service man has to contend with. Per-missible variations in tube characteristicsas well as commercial tolerance allowablein portable test equipment may result ina deviation from the above readings.

tector tube. Do not disconnect the con-trol grid connector from the tube, nor re-move the tube shield. Connect the ground(slate) lead of the receiver to the groundpost of the signal generator. In the eventthat the signal generator being used doesnot have a dummy antenna system, con-nect a 250 mmfd condenser in series withthe lead wire.

3rd-Remove the F-56 oscillator tubefrom the receiver socket.

4th-Place an output meter across thesecondary of the receiver output trans-former (which is mounted on the speaker)so that the variations in signal output canbe noted. Output meters with a multi -range scale are generally supplied withgood quality commercial signal generators.

5th-Place the signal generator inoperation and adjust the frequency outputto 175 kc. Regulate the attenuator con-trol so that the output signal is lowenough to insure accuracy in adjustingthe I -F condensers of the receiver.

6th-With the aid of a No. 4 socketwrench, adjust the four I -F condensersto resonance as indicated by the greatestswing on the output meter.

Adjustment of the Ganged VariableCondenser Compensators

The compensators are located at thetop of their respective tuning condensers,and can be adjusted with the aid of ascrewdriver. There are three holes (seesketch) in the overall condenser shieldhousing, which permit the insertion of ascrewdriver for compensating purposes.

1st-Remove the lead wire which is con-nected to both the control grid of the firstdetector tube and to the dummy antennasystem of the signal generator.

2nd-Connect the antenna (red) wire ofthe receiver to the dummy antenna sys-tem of the signal generator. The ground(slate) wire should remain connected tothe ground post of the signal generator.

3rd-Adjust the carrier frequency out-put of the signal generator to 1400 kc.

4th-Set the calibrated dial -of the re-ceiver to read 1400 kc.

5th-Starting with the compensatornearest the rear of the receiver, adjusteach compensator in turn for maximumsignal output as indicated on the output

(Continued on next page)


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The circuit diagram of the Fada LR.

of the console of thereceiver. The chassisis the RA.

(Conlin/iced from Preceding page)meter. Do not disturb the setting of thegang condenser during these operations.Leave the volume control on full and reg-ulate the signal output with the attenuatorcontrol of the signal generator.

Adjustment of Oscillator SeriesCondensers

The oscillator series condensers can beadjusted through the hole in the rear righthand corner of chassis (see sketch).

1st-Adjust the carrier frequency out-put of the signal generator to 600 kc.

2nd-Set the calibrated dial of the re-ceiver to read 600 kc.

3rd-With the aid of a No. 4 socketwrench adjust the oscillator series con-denser until a maximum output signal isindicated on the output meter. To insureperfect adjustment it is necessary to"rock" the gang variable condenser inorder to follow the maximum signal out-put.

4th-After the oscillator series con-denser is properly adjusted, turn the' cali-brated dial of the receiver to 1400 kc andadjust the signal generator to the samefrequency, then readjust all variable con-denser compensators as outlined in theforegoing instructions.

Phonograph Pick -UpThere is a provision for a phonograph

pick-up in the grid circuit of the firstaudio tube. One side of the phonographpick-up is connected to the grid and theother is grounded. There is also a pro-vision for short-circuiting the effectiveportion of the manual volume controlpotentiometer so that no radio signals cancome through to interfere with the phono-graph music. The silencing switch, as itis called, is located in the tone controlswitch.

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The tone control is located in the gridcircuit of the push-pull output stage. Itgives a choice of three different toneranges. In one position of the switchthere is no shunt across the secondaryand the highest audio notes can comethrough. In the second position thereis a condenser -resistor combinationacross the secondary, and this gives, amedium tone range. In the third posi-tion only the condenser is across thesecondary, and in this the high audionotes are cut out the most.

The circuit uses the nine tubes to fulladvantage and shows every evidence ofthe highest type of engineering.

* * *

[ See striking views of chassison following two pages. ]

12' RADIO WORLD December 24, 1932

STRIKING VIEWS OF

Ruggedness and balancecharacterize the chassis

A notable example of construction excellence is evident from these remarkable views of the new Fadchassis. Every precaution for best results is taken and the parts so selected that even after several host

of operation the power transformer, resistors, etc., do not get hot.

4 -Tube SetsPopular, Both

T -R -F and SuperThree tubes have been tried for an

a -c receiver, but not with much suc-cess. When it comes to four tubesthe t -r -f set, as diagramed, is simplest.Only because of the output pentode'shigh amplification is it possible to getreal speaker volume on such a smallset. Much satisfaction is being afford-ed to thousands of persons by smallsets of this type, and also four -tubesupers, which however are more dif-ficult to construct. The small set is byfar the biggest seller in the presentmarket.

Driving a Screw in anOften when one is building a radio set

he desires to hold a screw in an inaccess-ible place so that it can be started by ascrewdriver.

One way to do this of course is to havethe screwdriver magnetized, but thatwon't help if the screw is brass. A methodused by some is to put some "stickem" onthe screwdriver, and then the screw willadhere long enough to render the desiredservice. This "stickem" may be any formof stiff lubricating rease. Still another

Unhandy Placeway to achieve the end is to use a screw-driver that has a gripping extension.

A simple solution that requires nothingspecial is to put a thin piece of wirearound the screw, tightly enough to holdthe screw but not so tightly that the wirecan not be pulled off readily, once thescrew has been started. Then bend thewire at the screw, so that screw and wirelook like an awkwardly scrawled Z. Thescrew may be held in the desired position,and started on its course, when the wire

is simply pulled free. This little kink oftensaves a great deal of fuSsing about anotherwise difficult job. Two good thingsabout this method is that it doesn't costanything and that also the wire may bepulled away no mater if there is no roomto put anything in the place selected ex-cept the screwdriver tip and screw itself.The stunt has been worked successfullyin positions so narrow and confined thatthe total diameter of clearance of every-thing was less than one-half inch.


NEW FADA CHASSIS

Fullest precautions in shield-ing are taken for stability.

Suppressor Grid Circuit Novelties

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is is the circuit diagram of a six -tube set that uses suppressors in an unusual manner. The first tube's suppressorthe oscillation input, while signal is delivered to the control grid as usual. Cs is the padding condenser. Thisoe is therefore an autodyne, or combination modulator-oscillator. The 55 is used both as single -sided detector and:omatic selectivity control. The suppressor voltage on the preceding 58 is determined by the current through the0.5 meg. resistor on the upper anode circuit of the 55. The output tubes are Class A push-pull.


Construction and Adjustment of

THE SUPER DIAMOND, 58

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A circuit that accomplishes much on only six tubes. It has automatic volume control.Direct coupled first audio is fed from the full -wave diode detector.

THE Super Diamond, a six -tube super-heterodyne, is built on a chassis 13%x x 3 inches. The circuit is given

herewith, also a diagram for the chassis.While the chassis will accommodate eighttubes, only six are used in the present cir-cuit. The chassis is meant to be generallyuseful for a variety of circuits, and has,besides the eight socket holes on top, an-other socket hole at rear for speaker plug,but if a circuit of fewer than eight tubes isbuilt, then one of the right-hand rear socketis used for speaker plug and one socket holeis blanked on top, as well as the one atrear.

The layout is as follows :Extreme left front, radio frequency am-

plifying tube; to the right of it the antennacoil. Just behind these two the autodynetube is at left, the input radio frequencycoil for the autodyne control grid circuit tothe right. In the next row, left to right,are the first intermediate tube and the com-bination oscillator -first intermediate coilsystem. The two inductance systems are inone shield, but are not isolated from eachother, the green lead emerging from the topof this shield being for the cap of the firstintermediate tube.

Speaker Socket ConnectionsAt extreme left rear is the second inter-

mediate coil, and to the right of it is the de-tector -amplifier 55 tube. Since the triodeunit of the 55 is the first audio stage, all theapparatus to the left of the centered tuningcondenser accounts for the complete radiofrequency and intermediate frequency chan-nels, as well as one audio stage. So onlytwo sockets at right are needed for tubes,one for the 59 output, the other for the '80rectifier.

The two 3/4 -inch diameter holes at right arefor the electrolytic condensers, one of which

is to have its case insulated. For this pur-pose two insulating washers are suppliedwith the condensers, and also a special lugthat goes between the under -chassis insulat-ing washer and the fastening nut. This lugconnects to B minus on the power trans-'former and also to one terminal of thespeaker socket. This is usually the terminalthat would be for cathode, if a tube '27 or56 tube were to go into that socket. Thecircuit diagram gives the code for the speakersocket connections to agree with the virtual-ly standard connection of popular types ofspeakers. However, you should check upthe resistance of the field coil, and betweentap and both extremes, to be sure that the300 -ohm section goes between tap andground, tap being the equivalent grid springof speaker socket, ground being the equiva-lent plate spring, and B minus of powertransformer, the other extreme of fieldwinding, being equivalent cathode.

The parts are so arranged that the circuitprogresses naturally, and leads are short,except for the coupling between triode unitof the 55 and output tube, but as audio fre-quencies alone are concerned, the length ofthat lead does not matter.

Keeping Out the I -FUnless the intermediate frequency is fairly

well kept out of the audio channel therewill be oscillation, whereby a squeal is pro-duced every time a carrier is picked up bythe tuner, but the filtration will be sufficientif the three 0.00025 mfd. condensers areused where shown. It is important to in-clude the condenser between slider of thevolume control potentiometer and groundedcathode, otherwise at center position on thepotentiometer a high resistance is in serieswith the lowest 0.00025 mfd. condenser, andwould negate the intended bypassing by thatcondenser across the total of the potentio-

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meter, looking from the grid of the 55 tube.The necessity of including the extra by-

pass condenser between moving arm andground was determined only after severalexperiments directed at the solution of os-cillation trouble at the intermediate level.Aside from this fact, the oscillation wasnever present, yet the advice holds true thatif any does develop, it may be eliminated byincreasing the value of the fixed biasingresistor, marked 350 ohms, to whatevervalue is necessary to effectuate the cure.This recommendation applies also to anyoscillation that maye arise in the t -r -f stage,where another 350 -ohm biasing resistor isshown, and this should be made largeenough to afford the desired results.

Circuit Simple As PossibleThe circuit is purposely shown with con-

stants for creating an operating conditionjust below the point of oscillation at theintermediate level, and also at the 1520kc frequency in the t -r -f section. The cir-cuit will tune that high, yet will strike thelowest broadcast frequency, 540 kc, at 98 onthe dial.

While the circuit is a superheterodyne,and as such affords constructional and ad-justment problems not present in t -r -f re-ceveirs, it has been made as simple as pos-sible, so that even those not very familiarwith radio technique can make a successof building this selective and sensitive DXreceiver.

The chief difficulty, of course, is in pad-ding. It is assumed that the intermediateamplifier is lined up at 175 kc, for whichpurpose a test oscillator has its output leadconnected to plate of the autodyne tube, atsocket spring. Then all capacities are incircuit, and the tubes are working, too. Thetest oscillator is set at 175 kc and the inter-


LIST OF PARTSCoils

Two shielded radio frequency transform-ers for 0.00037 mfd. condensers.

One combination oscillator and 175 kcfirst intermediate transformer, in a singlehigh shield.

One 175 kc intermediate transformer, withcenter -tapped secondary.

(The intermediate frequency coils haveboth primary and secondary tuned.]

One power transformer, primary, 105-120volts, 50-60 cycles ; secondaries, 5 volts, 2amperes; 700 volts center -tapped, 60 ma; 2.5volts, 7 amperes.

One dynamic speaker, with 1,800 ohmfield tapped at 300 ohms, and with outputtransformer for 59 tube used as pentodebuilt in; equipped with 18 -inch cable andUY plug.

CondensersOne three -gang 0.00037 mfd. tuning co --

denser with trimmers built in; hshaft PA inches long, mounting spa,esbuilt in on the short side.

Two 0.002 mfd, fixed condensers mica.One 700-1,000 mmfd. padding condenser.One 20-100 mmfd. equalizing condenser,

to be used as a vernier on for the paddingcondenser.

One shielded block containing three 0.1mfd. condensers.

Three 0.00025 mfd. fixed mica condensers.One 0.01 mfd. fixed mica condenser.Two 8 mfd. wet electrolytic condensers,

inverted mounting type; two insulatingwashers and extra lug for one of them; nutsfor both of them; peak voltage rating 435volts d -c.

ResistorsTwo 350 -ohm pigtail resistors.One 3,500 -ohm pigtail resistor.Two 0.05 meg. (50000 -ohm) pigtail re-

sistors.One 2 meg. (2000000 -ohm) pigtail re-

sistor.One 5 meg. (5000000 -ohm) pigtail re-

sistor.One 20 -potentiometer.One 250000 -ohm potentiometer, insulated

shaft type.

Other RequirementsSeven socket insulating wafers and seven

sockets as follows: four six -spring ; oneseven -spring; one four -spring; one five -spring; (U.Y). The UY socket is forspeaker plug.

One vernier dial, travelling, light type,equipped with pilot bracket, lamp and es-cutcheon. One drilled chassis. Four tubeshields. One a -c shaft type switch. Threeknobs.

mediate channel is lined up by adjusting thefour set -screw condensers, two on each coil,for primary and secondary are tuned in eachinstance. One may determine resonance bymaximum response by ear alone, as the au-tomatic volume control is not so effectiveas to defeat this method of line-up. If onehas an output meter of course he will usethat, especially if the test oscillator is ofthe modulated type.

As for the padding, while much generaladvice has been given on this subject, thepresent instructions have to do with thisreceiver alone, and dial settings will betaken as examples.

Padding Reduced to Practice

Assuming specified coils and condensers,the trimmers on the r -f and modulator in-put coils should be at minimum, while thetrimmer on the oscillator tuning condensershould be about half way in, or a littlemore. You may screw down the oscillatortrimmer all the way, then turn back onecomplete revolution.

Turn the dial to 98 and feed a test oscil-

lator frequency of 540 kc into the antennapost, or, if that isn't within scope, tune into receive a station at 540 kc. The stationmay be not be heard, for the padding con-denser, Cp, has not been adjusted. Now,using an insulated screwdriver, start fromnearly minimum capacity and keep on turn-ing the padding condenser to higher capacityuntil the station is heard, which will benear maximum capacity of the usual 700-1,000 mmfd. padders. If the volume beginsto increase, but does not come up sufficient-ly by the time maximum capacity of thepadding condenser is in circuit, then put asmaller trimmer (20-100 mmfd.) across thepadding condenser, turn out the paddingcondenser one turn, and then adjust thistrimmer. The circuit diagram shows thistrimmer across the padding condenser Cp.

600 and 1450 kc Points

Now a start has been made. The circuithas been tentatively padded for the lowestfrequency end, for at this end the paddingcondenser is most effective, the trimmingcondensers least effective, whereas at thehigh frequency end the padding condenseris least effective and the trimming condens-ers most effective.

The tie -down points are a function of theoscillator's tuned inductance, and these points(limiting them to three) are 600, 990 and1,450 kc. So now set the test oscillator at600 kc and tune in the modulation to maxi-mum strength, using the receiver dial. Makeany readjustment of the padding condenserthat circumstances require. This readjust-ment will be slight.

Now turn to 11 on the set dial and ad-just the test oscillator to 1,450 kc. Thesensitivity may be low, denoted by responsemuch weaker than at the other extreme,but the circuit at this end has not been linedup. Adjust the trimmer on the oscillatoruntil the signal comes in loudest. It maybe necessary to turn down the oscillatortrimmer nearly all the way.

Next adjust the trimmer across the firstsection only of the condenser, front to back.The oscillator section is at rear. No radiofrequency level oscillation need be expected.

Stop at 1520 kc

Now turn the dial to less capacity, andby checking with the test oscillator, deter-mine how high in frequency the circuit tunes.There are some police stations between 1,710and 1,560 kc, and you may be able totune to one or two police channels at thelow extreme of their span, possibly tuningto 1,580 kc. This is one reason why r -fsquealing may set in, say, above 1,500 kc,but the 'oscillator circuit should be trimmedso that 1520 kc is not exceeded.

If the circuit is padded for police calls.the oscillator and r -f sections probably arenot tracking, and this would be confirmedby squealing in the high frequency tuning,associated only with carriers tuned in.

High frequencies at relatively high numer-ical settings of the dial need not causealarm. They are due to the very smallchange in capacity from 11 to zero on thedial.

So that the above directions shall holdtrue, the dial should be affixed to the con-denser with the 100th division representingmaximum capacity, whereupon minimum ca-pacity setting may result in slightly lessthan 0 dial reading. The dial should not beset at first with condenser minimum repre-senting zero, although by the other and rec-ommended procedure it may turn out to bezero nevertheless.

Final Setting

Now the third tie -down point may beused as checkup. This is 990 kc, which

Directions forWinding the Coils

The two radio frequency coils have sec-ondaries of 245 microhenries inductance, buthave diffrent primaries. The primary on theantenna coil is larger, and this acts auto-matically as a corrective of squealing atthe r -f level. In the same direction thesmaller primary for the interstage coil,joining r -f tube to autodyne, has fewer turns.In general, the fewer the primary turns thegreater the selectivity, and as more turnswere used on the antenna coupler fewerare used on the next coil without reducingthe selectivity.

Different PrimariesTherefore the antenna primary consists of

30 turns and the interstage primary of 15turns.

The secondaries have 127 turns of No.32 enamel wire in the commercial coils, ona diameter of 1 inch, while the primariesconsist of any fine wire, and are woundover the secondaries, with insulating fabricbetween. The primaries are nearer the bot-tom of the coil and are wound in the samedirection as the secondaries, but the sec-ondaries have the grid connection from thetop, while the primaries have the plate (orantenna) connections from the bottom.

Those who can not obtain No. 32 enamelwire for the secondaries may wind instead140 turns of No. 30 enamel wire.

The Oscillator CoilThe oscillator coil has an inductance of

190 microhenries, consisting of 115 turnsof No. 30 enamel wire. This presupposesa padding condenser adjustable from 700 to1,000 mmfd. and also that an intermediatefrequency of 175 kc is used. The diameterof the tubing is again 1 inch.

The pickup winding of the oscillator, theone connected in the cathode circuit, has40 turns of No. 30 enamel wire wound overthe secondary, and insulated therefrom aspreviously. One end of this winding is tiedto one end of the tuned winding, to con-stitute the outlead marked "black" on thecircuit diagram.

The oscillator coil is in the same highshield as contains the first intermediatetransformer, and is placed below it, with nomagnetic shield between. It is not deemedpractical to attempt to make this transform-er, nevertheless the directions are given forthe benefit of those who may desire to try.

Intermediate CoilsThe intermediate transformers can not

well be built at home, either, but they mayconsist of 800 -turn honeycomb coils, 1 -inchoverall diameter, for primary and second-ary, centers 1 inch apart, and tuned by 20-100 mmfd. equalizers. These are not ex-actly the constants used in the commercialcoils, but will register the same frequencyat near maximum of the available capacity.

All coils are shielded, and the shieldsshould be no less than 2 inches in diameterand no less than 2.5 inches high, while thecombination coil system is in a shield about4.5 inches high.

should come in at 45 on the dial. If it comesin somewhat lower in numerical dial read-ing, the capacity in the oscillator circuit istoo high ; if it comes in higher in numeri-cal dial reading, the capacity in the oscilla-tor is too low. This will be your key inthe final checkup, because since trimmershave been readjusted the padding has beenthrown off a little, and the padding con-denser should be reset at 600 kc, on thebasis of the 990 kc disclosure. When thisreadjustment is made the padding is com-pleted.

If the intermediate channel is accurately(Continued on next page)


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This differs slightly from a commercially obtainable chassis.(Continued from preceding page)

set, the oscillation frequencies themselvesmay be read indirectly, by adding 175 kc tothe test oscillator frequencies. Thus, at540 kc the test oscillator frequency fed tothe set, replacing aerial, the oscillator fre-quency is 615 kc, at 990 kc test oscillatorfrequency the set oscillator's frequency is1,165 kc, while at 600 kc test oscillator fre-quency the set oscillator frequency is 775kc.

Once the intermediate frequency amplifieris lined up, the second intermediate fre-quency coil should not be readjusted, be-cause resonance will not change there, dueto any parallel or series padding. However,realignments made at the r -f level, eithert -r -f stage or input to autodyne controlgrid, will affect the tuning of the first in-termediate transformer, the plate circuitparticularly. While normally the platecircuit setting is not controlling, in that theintermediate grid tuning has the predomin-ating effect, in this combination coil systemthe opposite is true. Therefore we have oneintermediate coil in which the plate tuningleads in importance and another where thegrid tuning leads.

Option of Grounded CpSo we shall be prepared, after the set is

lined up, to try a small readjustment of theplate condenser across that has one side toprimary of the first intermediate. We knowwhich one this is. It is the condenser thathas caused sparks when the adjusting screw-

driver slipped against the shield during ad-justment. If we didn't have that smallshorting accident, we know the circuit fromthe grid circuit because the plate circuit is"hot" and subject to body capacity effects.

Whenever such effects are present it willbe found that in any adjustment when re-sponse becomes maximum, if we remove ourhand the response falls. That means wemust add more capacity, a bit at a time, andretest by ear or meter until the maximumis registeher with hand off.

The same effect rules in the padding con-denser, because it is not grounded. Thecoil code given is for anon -grounded type.But it would be practical to ground thepadding condenser by putting it betweenground the return of the oscillator second-ary, using the moving plate lug connectionfor ground. The commercial combinationcoils do not provide for this, but efforts arebeing made to obtain such a coil (forgrounded padding condenser) so that anywho prefer that system may have it. Thecircuit would have to be changed to thepreviously stated - extent of relocating thepadding condenser, and the total number ofcombination coil outlets would have to beeight. The color code would still hold, ex-cept that the return for the oscillator's tunedsecondary would be the extra outlead, of acolor not covered by the seven others.

The Manual ControlThe radio -frequency section has been cov-

ered. The input to the diode detector is from

the center -tapped secondary of the secondintermediate transformer. Center tap goesto one side of the load resistor of the diode.The potentiometer is the load. Thus wehave direct coupled audio. To have a goodmanual control we connect the grip cap ofthe triode section of the 55 to the slider ofthe potentiometer, and then the volume isgoverned by taking off all the voltage dropto none of the voltage drop, and if the po-tentiometer's minimum is zero, then the sig-nal doesn't go through at grounded positionof the control.

The bias on the triode unit depends on thesignal, and it is the same as the amount ofbias contributed by the automatic volumecontrol to the intermediate amplifier tube.Bias on the 55 triode really never is zero.because so long as there is a signal, it willbe necessary to include some resistance ofthe potentiometer in circuit to hear thatsignal, and the bias voltage is proportionalto the resistance. Also, any strong passagesimmediately elevate the bias, so that thebias is diode -controlled, and the audio tubeis a diode -biased triode.

PerformanceNot only has the circuit been built, but

rebuilt and improved. It has been tested onthe air and in the laboratory. It has proveditself well worthy of construction, havingexcellent tone, selectivity and sensitivity.What the sensitivity will be depends on theaccuracy of the adjustments, and on theselection of loads and voltages, but as shown


the sensitivity will come close to the maxi-mum allowable. When a set is too sensitiveit is too noisy, and if ever you want to re-duce the sensitivity you may increase the'value of either of the biasing resistorsmarked 350 ohms. The general sum of suchreceivers is gaited to a sensitivity of 10microvolts per meter, which is high enough,but the circuit as shown goes beyond thata little, and can be built, by most carefuladjustment to just below the point of oscil-lation in the intermediate amplifier, so thatthe sensitivity is around 2 microvolts permeter at the high frequency end.

Hum is very low, but if you build theset and find that the hum is too high, re-verse the connections to the primary of thespeaker's output transformer, check up onthe resistance of the field coil, especially asto the disposition of its 300 and 1,500 -ohmsections, and see that a resistance measure-ment between cases of the electrolytic con-densers gives a reading equal to the tap -to -ground resistance of the field coil (300ohms).

Phonograph ConnectionThe circuit provides for a phonograph

pickup in an original position. As the man-ual volume control of the receiver is turnedtoward ground the signal is reduced, untila few hundred ohms before zero resistanceis reached even loud signals are eliminated.Therefore to keep out the signal, turn thepotentiometer to ground. The phonographpickup's own volume control should be usedfor control, although the set's control willfunction somewhat, provided the set is turn-ed to no signal. Since there were signalson 80 out of the 96 channels in one even-ing's test, maybe you'll have the same troublein finding a quiet spot.

If no pickup is to be used, short thephonograph pickup terminals, as designatedby the bracket under the word "Phono" inthe circuit diagram.

Results ObtainableWith Super Diamond

If the padding has been done properly,the voltages are correct and the wiringlikewise, the Super Diamond should affordexcellent distance reception in nearly alllocalities. The limitation is placed on thestatement because of occasional semi -deadspots, as encountered in some previous ex-periences (including Reading, Pa., whereresidents wanted to hear New York sta-tions direct).

The circuit has been worked for aboutthree weeks in New York City, and therewas not the slightest difficulty in regard toselectivity, for WOR, the strongest localat this point, could be tuned out completely,and WLW, a distant station 10 kc removed,tuned in. At the low extreme of the dial,the Canadian station on 540 kc (sharingwith Detroit interests) could be tuned inwithout interference from a Buffalo stationon 550 kc, as likewise could a Philadelphiastation without WMCA, 570 kc, 10 kc re-moved, causing any interference. Thesetests confirmed the condition at the lowradio frequency end, while the selectivitywas greater at the high frequency end dueto the regenerative effects beginning to takeplace in the r -f stage. These effects, asexplained, should not rise to the point ofsquealing, and if they do (which is evi-denced by unholy racket), the 350 -ohm r -fbiasing resistor should be increased. Thisalso will increase the selectivity. Do notput a resistor in parallel with the antennacoil to eradicate squealing, for while thiswill do the trick the value will have to beso low that selectivity suffers.

Use An Outdoor AerialThe stations at the high frequency end,

on t -r -f sets in general, are subject to moreinterference, but on this set to less inter-ference, for the selectivity derived fromthe intermediate level is constant, and the

frequency increase in the r -f section causesthe increase in small values of feedback tovery helpful proportions. Thus, a stronglocal on 1,450 kc could be tuned out and aweak distant station on 1,460 kc could bereceived without interference.

Use Outdoor AerialIn using this receiver no hesitancy need

be felt about using an outdoor aerial. It ishoped that short indoor stretches of wirewill not be used, as in any receiver that issensitive (as this one is) the very shortaerial, while providing results, relies toomuch on the amplifier ahead of the audioand here does not give the a -v -c enough ofan opportunity. Thus the signal -to -staticratio is decreased, while an outdoor aerialincreases the signal in relation to the staticlevel. The static here referred to is thenoise arising from various causes along theroute from the sending station to the re-ceiver, and not to the local static attendanton storms or local meteorological conditionsas found in warm climates on the broadcastband.

A good ground is helpful, and it shouldbe preferably to a cold water pipe ratherthan to a radiator. The length of the aerialis not specified, as it is not crucial, but anywell -constructed outdoor aerial will be foundin general superior to an indoor one, forDX work, particularly as with many in-door aerials the ground will prove a "better"aerial than the short antenna, therefore thedesirability of a better antenna is obvious.The aerial should be at a higher radio fre-quency potential than the ground lead, whichisn't true when the ground as aerial givesmuch more input than does the orthodoxconnection.

Keen Response Over DialAt almost every division on the dial there

should be a station or a sign of one, ifthe padding is done well, and the point ofreception is good. If there is little responseat the high frequency end, the trimmershave not been set properly. If there is goodresponse at the high radio frequencies butpoor response at the low frequencies thenthe series padding is at fault, while if thereceiver is insensitive throughout the dialspread, both the trimmers and series paddingcondenser are improperly adjusted.

Directions forMounting of Parts

It is preferable to solder 6 -inch leads toeach of the stator lugs on the condenserat the side opposite to the one where thetrimmers are. The reason is that once thecondenser is mounted on the chassis theselugs are not readily accessible to a solderingiron, although they can be reached thatway. However, if the sockets and the tubeshield bases are mounted the difficulty ofreaching the lugs becomes too great. Onlya small -tip soldering iron would afford ac-cess. So put on the leads before the con-denser is mounted. Then pass the leadsthrough chassis holes to the under side ofthe chassis and fasten the condenser and dialin place.

The circuit requires only one unit forcombination manual volume control and a -cswitch, and therefore this should be mountedat center. There are three holes, so thatany who desire to mount the switch inde-through chassis holes to the under side ofat right and the volume control at left. Thecenter hole then would not be used. Dueto cabinets available with the two holes ateither side of the condenser hole, the sepa-rate method is followed by the author.The commercial chassis has the two sideholes, none at center.

Dial Bracket DetailIt often happens that the bracket of the

dial hangs down too far to clear the volumecontrol when that control is at center,

whereupon it is necessary to saw off theexcess of the dial bracket. The fasteninghole, through which a screw is put frompanel front, is as high as practical, to re-quire deletion of a smaller excess.

Depending on the type of condenser usea,and the length of the -condenser shaft, thedial may have to be mounted farther back.This may be done by putting a bushing ofthe desired length between the rear of thefront flap of the chassis and the pointwhere the dial is affixed. A screw throughthe front flap hole then passes through thebushing and then through the slot in thedial bracket, being fastened at rear by meansof a nut.

The ElectrolyticsOne of the 8 mfd. condensers has tobe insulated. This is accomplished by using

two insulating washers as follows : the onewith extruded collar goes on top of thechassis, with collar pointing downward, andthe condenser's threaded bolt is put throughthe hole. On the under side the flat insulat-ing washer is next put on, so it is againstthe chassis, then the special lug is slippedover the threaded bolt of the 8 mfd. con-denser and the nut finally is tighteneddown. The lug is wired so that it connectswith B minus of the power transformer(thin black lead).

Padding CondenserIf the padding condenser is to be mount-

ed underneath the chassis at some pointthat requires that at least one of the twoholes be under the tuning condenser, thenit is necessary to mount the padding con-denser before the tuning condenser ismounted, or at least as to the one hole af-fected by the tuning condenser. The screwfor this padding condenser hole should beinserted so that its head is on top of thechassis, otherwise the screw, if the excessis too great, would stick upward, and mightinterfere with the tuning condenser.

STANDARD RESISTOR CODEOhms Megohms Body End Dot350 .. Orairge Green Brown3,500 Orange Green Red50,000 0.05 Green Black Orange5000,000 2.0

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A THOUGHT FOR THE WEEKCC n1 SMISSED!"-and Louis Vichio

1-1 walked out of Judge Feinberg'sCourt in Chicago. Louis had been on trialon a charge of robbery. His alibi restedon the claim that he had been listening in onstation WJJD. The Court asked the prisonerwhat was on the air at that particular timewhen he was supposed to have been rob-bing somebody. Louis replied: "I heardFrankie 'Half -Pint' Jaxon and his band,your honor." Judge Feinberg had a courtattache phone to WJJD, found that theprogram on that night had been broadcastat the time Louis indicated, examined wit-nesses who appeared for the defendant andfreed the prisoner.

And now radio has one more use -it fur-nishes a perfect alibi at a crucial moment.


Radio UniversityA QUESTION and Answer Department. Only questions from Radio Uni-

versity members are answered. Such membership is obtained bysending subscription order direct to RADIO WORLD for one year (52 banes)at $6, without any other premium.

RADIO WORLD, 145 WEST 45th STREET, NEW YORK, N. Y.

Getting the LowsCOULD the low frequency response

be improved by tuning the output trans-former to the lowest audio frequency thatis desired, say 30 or 25 cycles per second?-G. J. M., Paterson, N. J.

It can, provided that the tuning is donecorrectly. The tuning condenser cannot beconnected across the output transformer pri-mary or secondary for that would kill every-thing but the low tones to which the tuningis adjusted. But it may be connected inseries with the primary provided a chokeis used to supply the plate with power. Tun-ing the primary in this manner would makethe primary current much greater at andnear the resonant frequency and thereforemore power would be put into the second-ary. This method of tuning would not ap-

. preciably alter the performance on the high-er frequencies.

* * *

Padding a Trap CircuitSOME time ago you published an article

on padding a wave trap so that it wouldtrack with the r -f tuner and always be tunedto the image frequency. In this you actuallypadded the r -f and the oscillator circuits.Would it not be possible to use a largertuning condenser for the trap and then padthat circuit so that it would not be necessaryto tamper with the r -f circuit at all?-S. G. A., Springfield, Mass.

The padding under these conditions hasnot been worked out but it seems possible.It will not work with the same size con-denser; for the results from the computationsare negative values for both the inductanceand the series capacity. In fact, the mini-mum capacity also turns out to be negative.While a negative minimum capacity is pos-sible under certain conditions, since it onlymeans a certain amount less than the capac-ity iii the r -f circuit, a negative inductanceand a negative series capacity have no di-rect physical significance. Such values onlyshow that some other circuit arrangementis required.

* * *

Selection of IntermediateWHAT is the highest intermediate fre-

quency that can be used in a broadcast setif the second harmonic of the intermediatefrequency is to lie below the broadcastband?-S. H. W., Racine, Wis.

The lowest broadcast frequency is now540 kc, since Canada put a station on thischannel. The intermediate frequency mustbe less than half this. One-half is 270 kc,so this is the limit. However, in order toget this station clearly it is necessary tomake the intermedite frequency at least 5kc less than this limit. That is, the lowestpossible frequency would be 265 kc. In anycase, divide the lowest frequency to be re-ceived clearly by two and select a frequencyat least 5 kc less than this one-half.

* * *

Connecting Condensers in SeriesAN electrolytic condenser is usually not

rated higher than 500 volts. But in somecircuits the voltage is much higher. Wouldit be possible to connect such condensers inseries to get the required voltage rating? Ifso, are there any precautions to be observed?-D. B. McK, Peoria, Ill.

They can be connected in series providedthat the polarity is observed and that theone on the high voltage side is properly in-

sulated. The can of one should be connectedto the central cathode of the other. Or, thepositive of one should be connected to thenegative of the other.

* * *

Padding Short Wave TunersI AM about to build a short-wave super-

heterodyne and I wish to use ganged con-densers to simplify tuning. Is that practicalin short wave sets? In other words, is itpossible to pad a short wave tuner so thatit will always track as well as a broadcastsuper does ?-J. A. E., Salt Lake City, Utah.

For any one band of short waves it is notdifficult to pad so that the tracking will beclose enough. If the receiver is to coversuch a wide band that several coils are need-ed, either of the plug-in or the tapped type,it is necessary to pad each one independent-ly, and the padding must be associated withthe coil and not with the oscillator con-denser, unless the condenser padding ischanged for each band. There is' one thingin favor of padding, and that is that verylittle is needed for the shorter waves. Theintermediate frequency, though itself high,is relatively small for the higher signal fre-quencies. Most of the padding can be ac-complished simply by making the oscillatorcoil slightly Smaller than the correspondingr -f coil. If the radio frequency coil is veryselective it becomes difficult to make thecircuits track accurately and a small man-ual trimmer on the oscillator is desirable.

* * *

Mistaken SelectivityMY RECEIVER is too selective on the

shorter waves and it is impossible to logstations. Several stations come in inside thesame division and it is not possible to tellwhich is which until the announcement ismade. Can you suggest a method of makingit less selective?-G. S., St. Louis, Mo.

The set is not too selective but the dialis too small or the plates of the tuningcondensers are not cut right. If you wantto spread out the stations on the high fre-quency end you should get a much largerdial or else a condenser with plates cut sothat the capacity change is slower at thehigh frequency end. Better still is both toget a larger dial and a straight line frequen-cy condenser.

* * *

Use of Small CoilsMANY years ago it was considered ne-

cessary to have the very best coils in radiosPfq. Much stress was laid on low loss.Now all that seems to be disregarded entire-ly. Were they wrong at that time or arethey wrong now?-E. W., Chicago, Ill.

There has been a great change since theday of the single tube set and low powerbroadcast stations. Tubes especially havebeen improved to give a greater amplifica-tion. More tubes are used in every set.To get selectivity now many tuners areused.

* * *

Padding Long Wave SetsIN BUILDING a superheterodyne that

will receive both long and broadcast wavesis it possible to pad the oscillator for bothbands? If so, about how close will thetracking be? Is it practical to use the sametuning condenser for both the long and thebroadcast tuners ?-A. B. A., Newark, N. J.It is quite easy to pad the oscillator forboth bands and the closeness of the tracking

is about one per cent. of the intermediatefrequency. That applies to the broadcastband and to the other band as well, pro-vided that the ratio of the highest to thelowest frequency is the same as the corres-ponding ratio in the broadcast band. If theratio in the long -wave band is lower thetracking can be made still better. If it werenot practical to use the same tuning con,densers for both bands it would hardly bepractical to have a dual range circuit. Theintermediate frequency in the dual rangecircuit should not be higher than about 115kc, and 95 kc would be better.

* * *

Two -Volt Tubes on Six VoltsA RECEIVER I have has been designed

for use on 3 volts, all the tubes being of the2 -volt type. Please tell me what changesare necessary to adapt it to 6 . volts, as Iwant to use a storage battery of this volt-age.-H. W. J., Rockford, Ill.

The easiest way is to put in a ballast re-sistor to drop the excess voltage. Since thetubes are of the 2 -volt type and the set hasbeen designed for three volts there is al-ready a ballast resistor in the circuit. In-crease its resistance or put another resistorin series with it. Since you gave no inklingof how many tubes or what kind of two volttubes are in the set, it is not possible to givethe value of the extra resistor needed. How-ever, you must drop the difference betweenthe storage battery voltage and 3 volts. Ifthe normal voltage of the battery is 6 voltsyou must drop 3 volts in the extra resistor.Add up all the filament currents drawn bythe set and divide 3 by this current in am-peres. The result is the value of the extraresistance in ohms.

* * *

Changing VoltageA TRANSFORMER I have gives a sec-

ondary voltage of 7.5 volts when connectedto a 115 volt line. I want to drop thisvoltage to 5 volts. What resistor do I need?-R. V. C., San Antonio, Tex.

It all depends on the current you draw,first because the transformer winding hasresistance and second because there is nodrop in any resistance unless current flows,and the drop is directly proportional to cur-rent. Decide what current you are going todraw from the 7.5 volt winding and thendivide 2.5 by this current, expressed inamperes. The result is the number of ohmsthat you must use.

* * *

Shorting TurnsMANY dual range receivers change the

wave range by shorting the long wave coils.Does not this introduce serious losses anddetuning in the broadcast coils?-E. F. Z.,Milwaukee, Wis.

If the long wave coils are not inductivelycoupled to the broadcast coils there will beno appreciable loss or detuning. Even ifthe coils are inductively coupled the effectsare small because the shorted coils are somuch larger than the broadcast coil. De -tuning would not matter, since the circuitis not tuned until after the change has beenmade.

* * *

Diode Bias AmplifierIS IT all right to use the diode -biased am-

plifier with a 55 tube? When there is nosignal there is no bias and it would seemthat the plate current in the triode of the55 would be extremely high when no signalis coming in. Also, is there not dangerof not having insufficient bias on the triodegrid when a strong signal is coming? Is itpossible that the triode would become over-biased?-J. L. B., Philadelphia, Pa.

Sure, it is all right to use the diode biasedamplifier. It has been used for about tenyears in millions of sets, only that we usedto call it grid leak detection. The dangerof a heavy current in the plate circuit whenno signal is coming in is real, but it maybe prevented by using a high resistance load,say not less than 20,000 ohms. There is nodanger of having insufficient bias, for thebias is determined by the carrier, which isalways greater than the modulation on that

19December 24, 1932 RADIO WORLD

400KC 239 400KC 239 unrwav

+90 4-155

MOTECONTROLseuxer

237

N.8. TF A vorrs POSITIYECONNECT X TO + AND yro Tr ANff ZSmEctAnvf conarrx TO

-AND yro+.

89 50017(sorrom raw)

03 Gl

Nf

If an automobile set is wired according to this diagram it can be used on any type of ;ar, provided the X andY terminals are connected properly for each type.

carrier. It is quite possible that the tubemight become overbiased, but that wouldmean that the tube was overloaded. Thereshould be a volume control to take care ofthis. The bias on the tube is always fluctu-ating, but if the carrier remains constant thisfluctuation constitutes the audio signal.

* * *

Determining InductancePLEASE explain a method of measuring

the inductance of an intermediate frequencycoil by means of a laboratory oscillator. Iunderstand that this is possible. I have avery good oscillator that is calibrated to the

frequency band.-F. C. E.,Boise, Idaho.

Measure the natural frequency of the coiland any condenser whatsoever across it.Then measure the natural frequency aftera condenser of capacity C has been added tothe capacity previously across the coil. Thenthe inductance of the coil can be computedfrom the formula L= (Fo-F) (Fo-l-F)/472F2F2C. Since a frequency difference oc-curs it is well to make the two frequenciesquite different by choosing a large value forC, or a very small original capacity. Pos-sibly the self capacity of the coil would bebest as the original capacity. Naturally, Cmust be accurately known. Let us selectvalues for the various factors occurring inthe formula by way of illustration. Let thefirst natural frequency, F0 be 450 kc andlet the second be 170 kc. Then F,-F=280 'kc and F0 -1-F=620 kc. Let us also as-sume that the condenser we added, that is,C, had a value of 250 mmfd. Substitutingthe values in the formula we obtain L=3millihenries.

* * *

Adjusting SupersIS IT practical to line up superhetero-

dynes without the use of an oscillator? Howshould it be done, if it can be done?-W.T. C., Oklahoma City, Okla.

It is quite possible to do it but it isnecessary to guess at the intermediate fre-quency. Try to tune in a short wave stationnear the zero end of the dial. As soon asa,nvthing comes through tune all the inter-mediate circuits until the sound from thestation is loudest. That tunes the inter-mediate to some frequency which is closeto the one that is required. For example, itmay be 170 kc instead of 175 kc, or it maybe 180 kc. The slight deviation is not veryserious. As soon as the i-f has been tunedin adjust all the trimmers for the same sta-tion until the signal is as loud as possible.Next convert the circuit to a t -r -f set bymoving the grid clip from the first to thesecond detector. Tune in a station about600 kc. Leave condenser set, return the cir-cuit to a superheterodyne, and then adjust

the series padding condenser until the signalis loudest. Touch nothing else but the pad-ding condenser at this time.

* * *

Diode Power DetectorIS IT correct to call a diode detector a

power detector or should that term be re-served for grid bias detection?-E. W. R.,St. Paul, Minn.

The term power detection has not beenreserved for any particular kind of detec-tion, nor has it been defined. If it. is aquestion of output voltage any of the de-tectors with the exception of the grid leakdetector could be called a power detector.with a diode detector it is possible to get avery high output voltage without distortion,and that is as good a criterion as any for apower detector. There is no amplificationin the diode detector and it is really for thatreason that a large output without distor-tion can be obtained, for the distortion usu-ally occurs in the amplifier. The so-calledgrid leak detector is really a diode rectifierwith a diode biased amplifier following it.The reason it overloads quickly is that theplate voltage on the amplifier is low.

* * *

Changing Auto SetMY EIGHT TUBE automobile set wasbuilt for -a car in which the negative of

the storage battery is grounded but now Iwant to change it so that it can be usedon a car having the positive grounded. Willyou kindly show how it can be done? In-cidentally the receiver contains automaticvolume control and diode detection.-W. R. T., Akron, Ohio.

If you wire the set as shown in theaccompanying drawing you can use the seton any car provided you change two connec-tions only. You will notice that whereveressential the cathodes return to the positiveside and the grids to the negative of theheater circuit. The two leads to be re-versed according to the grounding of thestorage battery are marked X and Y. Theproper way of connecting them is given inthe note on the drawing. If these connec-tions are not made right the circuit will notwork. The 300 ohm resistor terminating inthe sign plus must be connected to the posi-tive side of the heater circuit or the a.v.c.will not work the same way under the twocases.

* * *

Cathode Ray OscillographWHY are cathode ray oscillographsapplicable to frequencies where ordinary

mirror oscillographs fail? Are there anyother devices that can be used for study-ing wave forms that are not so expensivea's cathode ray tubes and the mirror oscillo-graphs, and if so, can they be used on radiofrequencies ?-C. W. Y., Springfield, Ill.

The only reason cathode ray oscillo-graphs can be used on radio frequencies isthat they are fast enough to follow thewave. The ordinary mirror oscillographis so slow that it is not useful above thecommercial power frequencies, unless theyhave been especially designed to follow high-er frequencies. But even so they cannot beused on the high audio frequencies. Thereis another instrument that has been calledthe Phonodeik, devised by Dayton C. Mill-er, for the study of musical sounds. It maybe used on frequencies as high as 4,000 cyclesprovided that certain corrections be appliedfor its inability to follow the higher fre-quencies accurately. But it is not useful onradio frequencies. The cathode ray oscillo-graph is the only device so far developed .that will follow radio frequencies accurately.It is so fast that it is useful on the veryhighest frequencies. The cost of a suitablecathode ray tube with the necessary voltageequipment is now so low that it is aboutthe same as that of a good radio set. Theentire outfit need not cost more than about$50, and possibly can be assembled for halfthat amount.

* * *

Voltage RegulationWHY DOES the voltage output of a B

battery eliminator rise when the current isreduced or when it is stopped entirely?-G. A. P., Jersey City, N. J.

It rises because the drops in the powertransformer, the rectifier tube, and the filterchokes decrease. The effective voltage inthe circuit is the same all the time as longas the primary voltage is constant. Thechange in the output voltage therefore is onlya change in the distribution of the voltagedrops. When the change in the output volt-age with given changes in current is smallthe device is said to have a good regula-tion. That simply means that the resist-ance of the device, looking from the outputterminals toward the transformer, is low.The same thing applies to a battery. Thehigher the internal resistance of the batterythe lower the measured voltage is, and themeasured voltage is lower the more currentthe voltmeter takes.

WORTH THINKING OVERg7 HO IS THE MOST POPULARentertainer on the air' Why go tothe trouble of starting a poll and getting

everybody excited! Just ask one of thosecocksure, can't -be -mistaken personal pressrepresentatives and he'll tell you that-well,possibly he'll select the blonde lady or thecrooning chap on whose Payroll he happensto be at the moment. Of course, you prob-ably won't believe him, but that will notdisturb the 1932 model P. A. He's builtfor hard wear!


STATION SPARKSBy Alice Remsen

The FootstepsFOR "TALES OF TERROR"

WLW-Sundays and Mondays, 11:00 p. m.

One night as I sat dreaming,In reverie profound,With thoughts uncanny, teeming,Unconsciously I frowned;The night was cold and dreary,The evening I had squandered,With heart so cold and drearyThrough shadowland I wandered-Until my faithful houndGrowled at a ghostly sound.

Then I heard footsteps plainlyUpon the oaken floor;The silver moon shone vainlyThrough the glass -windowed door;But not a shadow fell thereThe while I sat and waited;No, not a shadow fell thereAs I still hesitated-Reluctant to exploreBeyond the fast -shut door.

The hound still growled a warningWith ivory fangs unbared;Stark terror in them dawning,His red -rimmed eyeballs glared;With hair upright and bristlingHe crouched beside me, shaking;With coarse red hair all bristling,His noise the night awak'ning;With noble spirit he dared-A challenge he declared.

There in my chair still sittingChained by a ghostly whim,Strange terrors 'round me flittingFrom gloom obscure and dim-I felt the THING draw closer-I felt that I was dying-As that dread THING drew closer-I felt my soul was flying;And in that presence grimI could not move a limb.

My gallant hound crouched nearer-And then my senses fled;The atmosphere was clearerWhen I awoke with dread;I always shall rememberThat moment full of sorrow-That sight I shall rememberIf I should die tomorrow;His proud throat gushing red-My faithful hound lay dead.

-A. R.* * *

If You Like Your Hair to Stand UpStraight with horror, listen in to DonBecker's "Tales of Terror." You'll likethem !

* * *

The Radio RialtoMust tell you what a thrill I experienced

last Sunday evening. Was just leaving theNetherland Plaza for rehearsal at the WLWstudio, when who should I bump into butthe one and only Amelia Earhart. What asweet unaffected woman she is ; did not havetime for more than a very short chat, butduring that time learned she was in townfor a lecture and was going right away with-out even staving overnight. Of course, youall know what she looks like so I don'thave to tell you, but she was wearing a longvelvet gown, which clung to her and madeher seem even more tall and slender ; herresemblance to Lindy is actually remark-able. . . . A grey day today. . . . No snowyet. Not even really cold. . . . "Showboat"

is here at the Shubert and I'm going to seeit tonight; wouldn't miss Helen Morgan. . . Lucky Strike program has changedfrom WSAI to WLW, which changes thetime of my Thursday program with TheFlying Dutchmen; exact time has not beensettled yet. . . .

The latest piece of news to drift this wayfrom WABC is the signing of Ruth Etting,Bing Crosby and Tom Howard for the 1933Chesterfield program; Etting was retainedby popular demand and will be heard eachMonday and Thursday night; Bing Crosbyeach Wednesday and Saturday ; the ToniHoward program will feature him togetherwith his partner, George Shelton, and Jean-nie Lang. . . . Lennie Hayton's orchestrawill replace that of Nat Shilkret. . . . Ofcourse, the irrepressible Norman Broken -shire will still continue to announce. . . .

Another old feature has returned to the air,Goldy and Dusty, who for five years werea popular feature of the pioneer days ofnetwork broadcasting. They may be hearddaily from 9:15 to 9:30 a. m. over a groupof ten Columbia stations: Albany, Buffalo,Hartford, Philadelphia, Pittsburgh, Syra-cuse, Harrisburg, Rochester, Wheeling andWorcester; the program will not go outover WABC. Harvey Hindermeyer andEarle Tuckerman are "Goldy and Dusty";they will be assisted by two little girls whowill be known as the Silver Dust Twins... .

Enoch Light and his orchestra are now lo-cated at the Plantation Gardens in Phila-delphia, broadcasting locally through WCAUsix times weekly. . . . Joe Haymes and hisorchestra are at the Village Nut Club inNew York, broadcasting over WABC threetimes weekly. . . . The Bohemia Club, locat-ed at 53d St. and Broadway, is a new danc-ing spot in New York; Ben Selvin and hisorchestra make the music, which is broad-cast through WABC. . .

Are you listening to WLW nowadays?and have you heard any of your girl friend'sprograms? Cincinnati seems to grow on abody. I'm liking it better each week ; andif it were only a little cleaner I could ac-tually love it. . . . A new program is beinginaugurated this week-dramatizing the hu-man interest angle of big business-bring-ing business down so that its intricacies maybe understood by the average man on thestreet; should prove to be a great program;it will be heard on Thursday nights I be-lieve. Don Becker will be responsible forthe continuity; this youngster is a marvelat dramatic effect-and you should hear himplay a ukulele. . . . Billie Dauscha is ex-pected to go commercial very soon. Shehas taken a little apartment in the down-town section of Cincinnati. . . . BarneyBarnes, remote control man for WLW, andhis cute little wife, have an apartment inthe same building ; so we play bridge, eatgrapes and candy and get the cards allsticky. . . . A good program on WLW isChime Reveries, 11:30 p. m., Mondays, and11:00 D. m. Fridays ; if you like good mu-sic, well played, be sure to tune them in... .

And now for some NBC news. . . . LuckyStrike will make a radical change in itsprogram idea, canning "The Magic Carpet"and substituting three different name bandsto be used permanently; Jack Pearl willstay on the job, but Walter O'Keefe will nothave his contract renewed. . . . Peter deRose and May Singhi Breen celebrated theirthird wedding anniversary on December8th. . . . Jan Garber broadcasts over WJZand the blue network on Sundays at 12:30a. m. from the Netherland Plaza Hotel inCincinnati; Jan has a good band and workslots of little tricks while directing. He isa friendly little person with a great audi-ence personality. . . . Our old pal, LarryFunk, gets through to New York from theHotel Gibson, but he is in Cincinnati for just

a short time, going from here to the Lowy"Hotel in St. Paul for two weeks, then theBellerive in Kansas City. Larry has a mil-lion fans through this part of the countryand his Band of a Thousand Melodies morethan lives up to its reputation as a goodname band. . . . Frank Black, an earnestmusician, arranger and pianist for the Re-velers, a quiet, conservative man, succeedsErno Rapee as general musical director forNBC when Rapee takes over the director-ship of Radio City. . . . Rumor has it thatthe Stebbins Boys will be back on the airagain in the near future.. . . A program I'dlike to see back is Peter Dixon's "RaisingJunior." . . . Understand that "FriendshipTown" is going off the air, for the timebeing at least. . . .

As I write this Joe Emerson is singing"Home on the Range" over WLW. Joehas a mellow pleasing baritone, which comesover very well. . . . Anne Seymour, well-known Broadway actress, featured on manydramatic programs over WLW, wrote herfirst radio script last week, a skit on theCourtship of Miles Standish; and was Annetickled to see her name on the productionsheet-"Continuity by Anne Seymour." Itwas produced on the Crosley Follies pro-gram and proved to be richly humorous. . . .

Paul Stewart has added announcing to hismany accomplishments; Paul acts andwrites.. . . Well, think I'll call it a day. Domy weekly biographical stunt and then EAT-because I'm starving-and speaking offood makes me remember that Octavia isgetting married on December 10th; by thetime this is in print she'll be a "Mrs."-butshe'll still continue to superintend myhousehold in Astoria.

* * *

Biographical BrevitiesABOUT WILLIAM STOESS

William C. Stoess, musical supervisor anddirector of "The Nation's Station," Cros-ley's WLW of Cincinnati, was born exactlythirty years ago in that city and has spentpractically all his life in his birthplace andyet has attained a coast -to -coast reputationas a musical director. Bill, as he is af-fectionately known to his friends and asso-ciates, is a post -graduate of the CincinnatiCollege of Music; while studying there hedid considerable concertizing with the Wag-nerian Quartette of the New England Con-servatory of Music, and solo violin workfor the concert platform and various musi-cal organizations.

His start in radio came through disappoint-ing Fred Smith, who was then studio directorof WLW. Bill had promised to come out tothe studio and play a program of violin selec-tions; he didn't show up-in those daysschedules were not adhered to as strictly asthey are now; nevertheless Fred Smith wasmad; he called Bill up and bawled him out-and then-at the end of the hot and heavyscolding he hired him-as assistant studiodirector ; now Bill is the head of the musicalactivities of this great station.

Yes, he's married to a charming little ladynamed Rosemary Ellerbrock; they have onechild, a girl, Betty May, seven years old.Bill's hobbies are good music and good ci-gars ; his sports-well, he plays a bad gameof golf; used to be a speed skater when aboy; I can just imagine Bill on rollerskates; he drives a car these days. He hasa favorite author, Theodore Dreiser ; and afavorite composer, Debussy.

Goes on the air once in a while, playingviolin, under the name of Elliot Brock, justto keep his fiddle fingers in good conditionand to satisfy his musical cravings. Hisambition is to become a really great conduc-tor. In appearance Bill is of medium height,slender, blondish, with an impish sense ofhumor which shows in the twinkle of hiseyes and a gorgeous grin. Usually has acigar in his mouth. When he is conductinggood music his eyes are almost closed andhis sensitive fingers keep tempo on the ba-ton; with popular music he is on his toes,swaying rhythmically and humming the tune.It is a delight to sing with him, for he hasa rare sense of just what a singer needs.


Twin Short -WaveStations Open

The British Broadcasting Corporation hasinaugurated powerful twin short-wave trans-mitters at the new Empire station at Daven-try, England. Each transmitter has carrieroutput of 20 kilowatts and is capable ofworking on six wave lengths between 13.9and 49.6 meters.

To provide transmissions at convenientlistening times for various regions of theBritish Empire, five zones have been pro-visionally named for broadcasts and havebeen designated as follows: one, Australia;two, India; three, South Africa; four, WestAfrica; and five, Canada.

The seventeen antennas, built around ahill -top site, give the station the appearanceof a giant pin cushion. Eleven of these an-tennas are directional and six omni-direc-tional. Thirty thousand feet of cable areused to link up the apparatus and sixtygallons of water per minute are circulatedaround the transmitters for cooling.

On Christmas afternoon, the Christmasspeech of H. M. King George V will bebroadcast, recorded, rebroadcast and relayedto all zones by British Empire stations andby many stations in other countries. Thiswill mean that King George will be heardby possibly 150,000,000 persons, an audi-ence of scope and size that has never beforebeen approached.

The apparatus for this British Empire sta-tion was manufactured and installed byStandard Telephones & Cables, Ltd., asubsidiary of the International StandardElectric Corporation, which is a companyof the International Telephone & TelegraphCorporation.

ANSWERS TO CORRESPONDENTSMRS. THOMAS OLMSTEAD, La

Crosse, Wisc.-Am sending you the inform-ation on "miniature photographs."

JUDITH KINNON, Cambridge, Ohio.-The George Hall, of the Don Hall Trio,is not the same George Hall who is maes-tro of the Hotel Taft orchestra. Your in-formation as to the latter is correct. Thefirst named artist used to be in Cincinnatiat WLW.

Literature WantedReaders desiring radio literature frommanufacturers and jobbers should senda request for publication of their nameand address. Address LiteratureEditor, RADIO WORLD, 145 West 45thStreet, New York, N. Y.

T. R. Morris, do Jones Russell & Co., Colorado,Texas.

Jack Perry, 42 Fairholt Road S., Hamilton, Canada.Robert Robbins, 1411 Hicks Ave., San Antonio,

Texas.Gordon Murray, 53 Elm Grove Ave., Toronto,

Ont., Canada.J. K. McConomy, 37 Bougainville Ave., Quebec

City, Canada.Jack LeClair, 101 Eastern Ave., Fall River, Mass.Hartwell Jones, 1009 Cross St., Little Rock, Ark.Fred Salmar, 2615 So. Emerald Ave., Chicago, Ill.Ira McMullan, 340 The Brooklands, Akron, Ohio.John S. Barss, Johnson Hall, Andover, Mass.Harold 0. Grimsrud, R. R. 1, Wembley, Alta.,

Canada.Frank Demoizes, Box 37, Grayn, Penna.Floyd E. Cates, 629 S. E. 2nd St., Minneapolis,

Minn.G. A. Swinford, c/o Service Hardware Co., Syla-

cauga, Ala.O. Burgett, Box 71C, Lima, Ohio.H. W. Haile, 6570 Scanlan Ave., St. Louis, Mo.John E. Helms, Jr., Daily Gazette & Mail, Norris-

town, Penna.Wm. B. Smith, 14 Winfred St., West Haven,

Conn.Elmer N. Boyer, 330 N. Pine St., York, Penna.

SHORT-WAVE CLUBClarence Cain, 1310 Minneapolis St., Sault Ste.

Marie, Mich.

TRADIOGRAMSBy J. Murray Barron

The many friends and followers of Silver -Marshall circuits will be pleased to learnthat McMurdo Silver, a real pioneer in radio,has organized a company bearing his nameand has brought out what is termed hislatest, greatest triumph. It is an all -wavereceiver manufactured under his personalsupervision.

* * *

Try-mo Radio Co., 85 Cortlandt Street,New York City, has stocked the replace-ment parts of Philco and has on display thenew and unique display cards illustrating thecircuits for various parts. If you are indoubt as to whether you can use a particularpart for other than a Philco, the circuitcards will aid you.

* *

Thor's Bargain Basement has a com-plete new window dressing of unusualdesign featuring small parts and muchneeded essentials of radio. Downstairs thekits and parts department is running tofull capacity. Even in these days of veryefficient factory -built receivers at reason-able prices there are still thousands offolk who want their receiver as they wantit and therefore prefer to build their own,hence the demand for an efficient kit atreasonable price.

* * *Lansing Mfg. Co., Los Angeles, Calif.,

announces it has brought suit in the U. S.District Court of Arizona against the Mag-navox, Fort Wayne; Utah Products Co.,Chicago; Jensen Radio Mfg. Co., Chicago,and the Lektophone Corp., Jersey City,through John H. Klenke, patent attorney forthe plaintiff. It is understood the purposeof the suit is to ask restraint on the fourcompanies from mailing further letters tothe trade, from filing any patent actionagainst individual Lansing customers andretail trade until and unless they bring suitagainst Lansing Mfg. Co., itself.

* * *

There is an interesting and helpful tubechart that assists greatly in giving data onthe new tubes. It gives all the data andshows the pin arrangement. It is for freedistribution and issued by the Postal RadioCo. Copies may be had by addressingTrade Editor, RADIO WORLD.

* * *

Philco Radio & Television Corp. has acomplete parts catalogue for the servicemanwhich gives valuable information. Sendyour name to Trade Editor, RADIO WORLD,for one.

NEW INCORPORATIONSInternational Television & Broadcasting Corp.,

Wilmington, Del.-Attys., Corporation Fiscal Co.,Dover, Del.

Radio Center, New York City, realty-Atty., M.Paxson, 64 West 52nd St., New York City.

Radio Sales, New York City, broadcasting-Attys., Rosenberg, Goldmark & Colin, 165 Broad-way, New York City.

Dynamic Acoustical Products, New York City,sound amplifying horns, etc.-Atty., E. A. Stern,120 Wall Street, New York City.

S. & S. Electric Products Co., Lynbrook, L. I.,N. Y.-Atty., L. Weinstein, Lynbrook, N. Y.

ASSIGNMENTSIn Kings County, New York City

Atlantic Radio Corp., radio parts, etc., 1,072 Atlan-tic Ave., Brooklyn, has been assigned to AaronL. Palmer, 26 Court St., Brooklyn, N. Y.

In New York CountyPenn Electric Co., at 22 Dey St.,New York City,

to Harry Smith, 80 Broad St., sTew York City.William Vance Co., Inc., plumbing, 301 West 127th

St., New York City, has assigned to IreneNaiman, 6201 Bay Pkway, Brooklyn, N. Y.

CORPORATIONS REPORTSPilot Radio and Tube Corporation-November: Net

sales, $134,263, compared with $108,587 for thecorresponding month last year. I. Goldberg,President, said November was the fifth consecu-tive month in which the company's sales hadshown an increase over last year's.

Kent AuditionPrizes Awarded

The winners of the national audition ofthe Atwater Kent Foundation were WilsonAngel, 19, basso, Winston-Salem, N. C., andLydia Summers, 25, contralto, New York.They receive $5,000 each.

Second places were awarded to ThomasL. Thomas, 21, baritone, Scranton, Pa., andFrances de Voice, 23, Minneapolis. Theyreceive $1,000 each.

The remaining six of the first ten se-lected by the judges receive $500 each. Theyare Peggie Jo Lobb, 23, coloratura soprano,Concord, N. C.; Robert Miller, 23, baritone,Dallas, Texas; William Felix Knight, 24,tenor, Santa Barara, Cal., Laura Lodema, 19,mezzo-soprano, San Francisco, Clyde- F.Kelly, 24, baritone, St. Louis, and EdytheHoskinson, 23, mezzo-soprano, Hutchinson,Kan.

The judges were Maria Jeritza, RosaPonselle, Lawrence Tibbett, Richard Bo-nelli and Tito Schipa, all of the Metropoli-tan Opera Company; Reinald Werrenrath,Marcella Sembrich, teacher, and MarshallBartholomew, director of music, Yale Uni-versity.

Bellows Assigned byC.B.S. to Washington

Henry A. Bellows, vice-president of theColumbia Broadcasting System, has beenassigned to Washington, D. C., where hewill be in charge of Columbia's activitieswithin the Capital district. He will assumehis duties in Washington on January 1.

Mr. Bellows, one of the pioneer broad-casters in the north central states, will con-tinue to supervise the operation of WCCO,in Minneapolis, and will spend a part ofhis time in that city.

DX CORNERJust why it is that so many DX-ers re-

peatedly pull in the "hard -to -get" stationsand yet rarely ask for a verification? Ofcourse there are a great many who have theverifications, but nowhere near the numberthat has not. It isn't because the station hasnot been heard, because we know of toomany cases that offset that opinion. Itcannot be lack of interest, for the same sta-tions are pulled in repeatedly, sometimes forthe purpose of listening to definite featuresat stated periods. It may be that there area great many more verifications receivedthan the DX-ers admit, and possibly theydo not want to let them out of their pos-session, or go to the trouble of sending themin. That will work both ways,. for if allfelt that way, then there would not be anyexchanging of ideas. We will publish veri-fied reception records.

We want to publish lists from all overthe country, and while we have received finesupport in the way of letters of good -willand also a large number giving lists of sta-tions received, the big list of verified stationshas not come along, so please bear this inmind when writing.

From Oak Forest, Ill., comes a reportfrom W. E. Smith, with verification cards,showing reception of VK2ME, "The Voiceof Australia," 31 meters ; also a card show-ing reception from "The Voice of theTropics," Honduras, C. A., on 1370 kc.

Readers interested in DX should addressthe condition of this column, J. Murray -Barron, clo RADIO WORLD, 145 West 45thSt., N. Y. City.


6 -PinSHORT - WAVE

plug - in coils withthree separate

windings for detec-tor circuit producebest results as theyavoid the broadnessof plate -circuit tun-ing or the losses ofr -f choke load onplate circuit due todamping. The lowerwinding is for r -fplate circuit, if t -r -fis used, or for aerialotherwise, the cen-ter winding is thetuned secondary,while the top wind-ing is for feedback.The coils are accu-rately wound osi LIBinch diameter Bake-lite and have a At -inch flange for grip-ping. Thus the ac-tual winding neednever be touchedwhen you're hand-ling the coils, andthey are suitable forcalibration.

Plug -In Coils 200 to 15 Meterswith 0.00014 mfd.

Cat. SW B -Four plug-in coils, 6 -pin base; primary, secondary, fixed tickler $1.7econtrolCat. SZ-Six-spring wafer socket for use as coil receptacle for six -pin coils

$1i315,

Cat. SWA-Four plug-in coils, UX base, primary and secondary; primary may be used for feedback if condenserconnects serial to grid $1.35Cat. SX-Four- spring (UX) wafer socket for use as coil receptacle for four -pin coils 10eCat. H-14-Hammarlund junior midline 0.00014 mid. condenser with Isolantite insulation

Cat. H-20-Hammarlund junior midline 0.0002 mfd. condenser with Isolantite insulation. Used as feedback

HOW TO USE THE COILS FOR HIGHEST EFFICIENCY AND SMOOTHESTIn building short-wave receivers using our plug-in coils be careful to

locate the coils so that the centers of their cores are at least 6 inchesapart, otherwise in sets with t -r -f - the r -f tube may oscillate. Evenif a volume control in the r -f stage controls any oscillation presentthe recommended separation should be maintained, otherwise a criticalcircuit results.

THE secondaryis to be tunedwith 0.00014

mfd. capacity. Us-ing four coils, therewill be sufficientoverlapping of bands,also assured cover-age to above 200 andbelow 15 meters. Al-so, 0.00015 mfd. maybe used instead fortuning, with slight-ly greater overlap.Regeneration may becontrolled b7 a0.0002 mfd. variablecondenser from de-tector plate toground, or by aplate voltage rheo-stat or other means.

The standard six -pin tube socket maybe used for coilreceptacle.

For antenna stagetuning only twowindings are need-ed, where no stageof t -r -f is included,when use SWA.

OPERATIONThe connections to make are diagrammed

herewith. Bottom views of sockets are shown.For the 6 -pin coil P -B RF goes to aerialand ground if there is no r -f. For UX coilprimary is ant. and gnd.

HIGH- GAIN SHIELDED - COILS FOR T- R- FDIRECTIONS FOR BEST RESULTS

THE shielded coils for tuned radio frequencysets are supplied in matched sets of threeor four, with secondary inductance equalized

(plus or minus 0.6 microhenry). Thus any lackof sensitivity due to mismatched secondaries isavoided. As inductive discrepancies could notbe compensated for by parallel capacity trim-ming, this high degree of inductive accuracyis important. Complete coverage of the waveband with the specified capacity condensers isabsolutely guaranteed.

The coils may be used (set of three) fort -r -f, and with minimum value of negative biasfor r -f tubes may oscillate a little at the veryhighest frequencies, say 1500 to 1580 kc, asthey will be timed below the broadcast bandabout that much. The negative bias should beincreased until oscillation completely stops. Thusalso selectivity is improved by heightened per-manent or limiting bias.

. In using four coils (three stages of t -r -f andtuned detector) each screen and plate lead shouldbe carefully filtered, using 300 -turn honeycombcoils and 0.002 mfd. or higher capacity in thefilter, and the coil centers placed at least 4inches apart.

The diameter of the form is 1 inch, the alumi-num shield 23. inch diameter, 2% inches high.

The shield has a small protected opening attop so the lead for the grid cap may be broughtthrough. The opening is bevelled. This con-stitutes the protection against fraying the insu-lation of leadout wire to grid cap.

In the four -coil system, reversing connectionsto primary of second coil often stops oscillationin poorly filtered sets.

COILS FOR 4 -TUBE

MIXER

Cat. No. 1 -Three t -r -f coils for 0.00035 mfd.,80 -meter taP $1.35

Cat. No. 1 F -Four coils, 0.00035 mfd $1.80Cat. No. 3 -Three t -r -f coils for 0.0005 mfd , 80 -

meter tap $1.35Cat. No. 3- F -Four coils, 0.00035 mfd $1.80Cat. DC H -Diode r -f choke, center-tapped 5 .40Cat. 3 DS -Three -deck long switch for above

coils, to utilize 80 -meter tap $2.50

80 -METER TAP PROVIDEDEACH coil for the t -r -f sets has secondary

tapped, so that if desired a long switchmay be used to shift the tuning con-

denser stators to extreme of winding (200-555meters) or to tap (80-200 meters). The tapis represented by a ground symbol stampedon the shield base. Please note ground is notto be connected to ground symbol. Grid re-turn is the side lug inside the shield. P, Brepresent primary, G and side lug secondary.

The 80 -meter tap does not have to be used,but is advantageous to those desiring to timein television, amateurs, police calls, some relaybroadcasting and other interesting transmis-sions in a band of frequencies replete withnovelties for the usual broadcast listener.

High impedance primaries are used, thenumber of turns chosen so that the samecoils may be used for antenna coupler andinterstage couplers.

For diode t -r -f circuits, either full -wave orhalf -wave detector, a diode choke may be in-serted inside the detector form. This chokehas three terminals, with outleads: two ex-tremes and center. For full -wave use twoextremes to anodes of 55 or 85, center tocathode resistor. For half -wave use two ex-tremes and ignore center tap.

Except in rare hookups the diode circuit re-quires an input free from grounding, and asthe tuning condenser rotor and frame aregrounded the choke pickup affords any potentialoutput.

T -R -F sets using the 55 or 85 should havethree stages of resistance audio, e.g., firststage the triode unit of the 55 or 85, secondstage screen grid audio, third stage power tubeor tubes (output).

DIAMOND (CAT. DP) @ 90c -COILS FOR 5 -TUBE DIAMOND (CAT. DT) @ $1.35

AND INTERMEDIATE TRANSFORMERSPADDED SETS

For circuits using 175 kc. or 400 kc.intermediate frequency we have two coilsfor stage of t -r -f and first detector,and accurately chosen inductance for thepadded oscillator for these intermediatefrequencies. There is no 80 -meter tapprovided on these mixer coils.

The coils are of the same type ofmechanical construction as the t -r -f coils.Since there is no secondary tap, the codefor connecting the t -r -f coils of thesuperheterodyne combination is different:P and B. Primary; 0 and ground symbol,secondary. P would go to plate or an-tenna, to grid cap, while B andground symbol are the returns.

The oscillator has a smaller inductancesecondary, for padding, and moreover isa three -winding coil. The three wind-ings are: pickup, secondary and tickler.The pickup winding consists of 10 turns,and is brought out to two side lugs. Thepolarity of its connections unusually isof no importance. The secondary is rep-resented by Gi and ground symbol. G go-ing to grid and ground symbol to gridreturn, usually ground. The tickler con-nections for oscillation usually requirethat the lug at B be conected not to Bpine but to plate, hence the P lug goesto B plus. In any case, if no oscillationresults, reverse the tickler connections.

Cat. No. 4 -Three mixer coils, for 0.00035 mid. Intermediate frequency in-tended, 175 kc. Price includes padding condenser, 700-1000 mfd $1.80Cat. No. 5 -The mixer coils for 0.0005 mfd., 175 kc., 700-100 padderCat. No. 7 -Three mixer coils, for 400 kc; padding condenser included is 350-

450 mfd. $1.80

SCREEN GRID COIL CO.145 WEST 45TH STREET, NEW YORK CITY

INTERMEDIATETRANSFORMERS

The Intermediate transformers consistof two honeycomb coils, wound with lowresistance wire,, coils spaced 1 inch apart.and thus affording loose coupling, stabil-ity and high selectivity. Primary andsecondary tuned.Cat. F F -175-Shielded intermediate fre-

quency transformer, 175 kc $1.10Cat. F F -175C7 -Same as above, center -

tapped secondary, for full -wave diodedetector $1.25

Cat. F F -450-Shielded intermediate fre-quency transformer, affording choice bycondenser adjustment of frequenciesfrom 380 to 480 kc $1.30

Cat. F F -450C7 -Same as above, center -tapped secondary $1.45Padding Condensers ea 45c

EachCat. PC -710 --For 175 ke intermediate.

Put in series with oscillating toningcondenser. Capacity 700-1000 inmfd.Hammarlund, Isolantite base.

Cat. PC -3545 -Same as above, except350-450 mmfd. for 380-480 kc inter-mediate.

Cat. C H -300-A 300 -turn r -f choke, in-ductance 1.3 millihenries $0.30

Cat. CH -800 -An 800 -turn r -f choke, in-ductance 10 millihenries

December 24, 1932 RADIO WORLD

rROLA SPEAKERSROLA dynamic speakers with output transformers matched for the specified

type of output tubes built-in, single -sided or push-pull, and affording threedifferent diameter sizes, 8, 10.5 and 12 inches, are offered as premiums for the

first time. Besides there is a 6 -inch diameter speaker offered (not made by Rola),so that a full range of sizes and types is afforded to those now subscribing forRADIO WORLD.

The Rola speakers are equipped with output transformer, 1800 -ohm field coil(tapped as designated), cable leads, plug and terminal cover. They are grouped be-low as to outside diameters of cone rings.8 -inch Diameter; sent free with one-year subscription, $6.00 (52 issues).Single pentode, '47 or '89, tapped at 300 ohms. Order Cat. PRE -F -P.Single 59, new heater power tube model, tapped 300 ohms. Order Cat. F -P-59.Push-pull pentodes, '47 or '89, tapped at 125 ohms. Order Cat. PRE -F -P-2.Push-pull 59's, tapped at 125 ohms. Order Cat. PRE -F -P-2-59.10.5 -inch Diameter; sent free with 60 -week subscription,$7.00 (60 issues).Single pentode, (47 or 89), tapped at 300 ohms. Order Cat. PRE -l -7-P.Single 59. Order Cat. PRE -K -7-P-59.Push-pull pentodes, tapped at 125 ohms. Order Cat. PRE -K -7-P-2.Push-pull 59's, tapped at 125 ohms. Order Cat. PRE -K -7-P-2-59.12 -inch Diameter; sent free with 68 -week subscription, $8.00 (68 issues).Single pentode, 47 or 89, tapped at 300 ohms. Order Cat. PRE -K -9-P.Push-pull pentodes, 47 or 89, tapped at 125 ohms. Order Cat. PRE -K -9-P-2.Single 59, tapped at 300 ohms. Order Cat. PRE -K -9-P-59.Push-pull 59's, tapped at 125 ohms. Order Cat. PRE -K -9-P-2-59.

(Speaker for any other type output .tubes, single or push-pull, obtainable on the same subscriptionbasis, determined by outside diameter of speaker as listed above).

Above speakers shipped express collect.

Besides the Rola speakers (illustratedabove) we offer a 6 -inch diameter speaker,1800 ohm field, bias through built-in re-sistor apportionment; single 47 or 89 out-put only. Free with six -months subscrip-tion a $3.00 (26 issues). Order Cat. PRE-AKMS. Shipped express collect.

POWER TRANSFORMERSN the construction of small a -c receivers in general two types of powerI transformers are used, and we offer both types. These are distinguishedmainly by their B current carrying capacity and the capacity of theheater winding of the receiver tubes. The classification is generally nar-

rowed down to B current comparison, 50 ma and 60 ma.The two types, 508 for the smaller load (50 ma) and 509 for the largerload (60 ma), are in the same style case.The specifications are as follows :

No. $08, for four -tube receivers, including rectifier; primary, 110 volts, 50-60 cycles,high voltage secondary, 330-330 volts a -c (660 volts, center -tapped); heater secondary,2.5 volts, 7 amperes, center -tapped; rectifier filament secondary, 5 volts, 2 amperes,not center -tapped. On 1800 ohm field supplies about 275 volts d -c.No. 509, for five, six and seven -tube receivers, including rectifier; primary 110 volts, 50-60 cycles; high -voltage secondary, 330-330 volts ac -c (660 volts, center -tapped); heatersecondary, 2.5 volts, 9 amperes, center -tapped; rectifier filament secondary, 5 volts, 2amperes, not center -tapped. On 1800 ohm field supplies about 275 volts d -c.No. 508 sent free on receipt of $3.00 for six months' subscription (26 issues). OrderNo. 508 or No. 509 winding bulge fits into a panel Cat. PRE -508.

cutout of 2 TA x 1 11/16 inches, two mounting holes244 inches apart, at center, across the shorter sideof opening. Laminations 3/4. inch extra all around.

No. 509 sent free on reception of $4.00 for 34 -weeks' subscription (34 issues).Cat. PRE -509.Above transformers shipped express collect.

3 -Gang Condenser, DialThree -gang

0.00035 mfd. tuningcondenser, low min-imum capacity, ex-ceptionally widefrequency cover-age. The con-denser has brassplates, trimmers,and sturdy shield.Condenser, shieldand trimmers freeon receipt of $4.00for 34 -week sub-scription (34 is-sues) Order Cat.PRE-SHSCO.

Above with dialand knob sent freewith 39 -week sub-scription (39 is-sues) at $4.50.Order Cat. PRE-SHSCO - DL.Shipped express col-lect.

CABINETA cabinet for a 12 -inch speaker only.

A beautiful walnut, hand -rubbed, artisticcreation, with steel back cover in imita-tion cane, beautiful front grille, marqueterieup and down the front sides, and a lux-urious general appearance. Stands 32inches high and 19 inches wide. Room inthe back also for a small set to be tunedby remote control, but not for knob con-trol from the front. This cabinet, withspeaker, listed at $175. Given free (with-out speaker) with three-year subscription(156 issues) on receipt of $15.00. Shippedexpress collect.

CHASSISChassis can be supplied for four, five, six,

seven and eight -tube receivers. The gen-eral size is 14 inches wide, 3 inches high,8.5 inches front to back, for five, six, sevenand eight -tube sets, whereas the four -tubechassis is smaller. Any of these classessent free on receipt of $2.00 subcription on16 issues (16 weeks). Order Cat. PRE -CHAS -4, 5, 6, 7 or 8 (specify which bycorrect number at end.) Shipped expresscollect.

RADIO WORLD, now in its eleventh year, is the first and only na-tional radio weekly, and publishes the latest, up -to -the -second newsof circuits, both of kit types and of 1933 commercial receivers, as wellas news of happenings in the broadcasting field. Lists of broadcastand short-wave stations are published regularly. You get your infor-mation weekly -which means quickly -and you get it accurately, so besure to become or remain a subscriber for RADIO WORLD. We areable to offer now specially attractive premiums, and ask you to makeyour choice from the variety of parts offered herewith. When order-

ing, please remember that weproducts listed on this page.we pay cartage.

BLOCK

Order

A paper condenser black that standsthe gad and provides abundant ca-pacity for excellent filtration for thosewho desire the utter absence of humfrom a receiver. Stands up to 350volts d -c on any section. The highestQuality paper condensers are insidethe block (not electrolytical. The ca-pacities are 8.0 mid.. 6.0 mfd.. LOmfd., 1.0 mid. and 0.5 mfd. Of themany condenser blocks of this groupwe have supplied. not one has givendissatisfaction. Send $3.00 for sixmonths subscription (26 issues) and setthis free. Order Cat. PRE-B'LRCB.Shipped express collect.

do not pay shipping charges on anySee footnotes on pages as to whether

The regular subscription rates are: $6 for one year, 52 issues, oneeach week; $3 for 6 months (26 weeks); $1.50 for three months (13weeks); $1 for 8 weeks; 15c per single copy. All copies postpaid.Present subscribers may take advantage of any of our offers by stat-ing they are subscribers already. Subscription will be extended.

RADIO WORLD145 WEST 45th STREET, NEW YORK, N. Y.

We DO NOT

11/41144a.

pay the postage, express or freight on any products listed on this page, but will ship express collect on receipt of the subscriptionprices mentioned. If other shipping directions are to be followed, please advise us.


DIAMONDPARTS

FIVE -TUBE MODEL

A -C operated circuit, 50-60 cycles, 105-120 volts,using two 58 t -r -f stages, 57 power detector and47 output, with '80 rectifier. Three gang shieldedcondenser and shielded coils in a sensitive, selectiveand pure -tone circuit. Dynamic speaker field coilused as B supply choke. Complete kit of parts,including 8" Rola speaker and all else (excepttubes and cabinet). Cat. DSCK @ $15.18Wired model, Cat. DSCW (less cabinet) 17.19

Kit of five Eveready-Raytheon tubes for thiscircuit. Cat. D5T LOT

FOUNDATION UNIT, consisting of drilled metalsubpanel, 13-34 x 8% x 214"; three -gang Scovill0.03035 mfd., brass plates, trimmers, full shield;shields for the 58 and 57 tubes; six sockets (onefor speaker plug); two 8 mfd. electrolytic con-densers; set of three coils. Cat. D5FU 8.19

Super Diamond parts in stock.

FOUR -TUBE MODEL

The four -tube model is similar, except that thereis one stage of t -r -f, and a two -gang condenseris used. Tubes required, one 58, one 57, one 47and one '80. Complete kit, including 8" Rola dy-namic speaker (less tubes, less cabinet). Cat.D4CK $13.58

Kit of four Eveready-Raytheon tubes for thiscircuit. Cat 4D.TK 3.18

FOUNDATION UNIT, consisting of drilled metalplated subpanel 1334 x 234 x 7"; two -gang 0.00035mfd. SFL condenser; full shield; two shields for58-57; center -tapped 200 -turn honeycomb coil; fivesockets (one for speaker plug); two 8 mid. electro-lytics; set of two shielded coils; 20-100 mmfd.Hammarlund equalizer for antenna series con-denser. Cat. D4FU 85.49

INDIVIDUAL PARTSTravelling light ver-

nier dial, full -vision,6 -to -1 vernier, pro-jected indication pre-vents parallax, takes3.4" or $if shaft; dial,bracket, lamp, escutch-eon.

0-100 for 5 -tube Dia-mond, Cat. CRD-0,$0.91.

100-0 for 4 -tube Dia-mond, Cat. CRD-100,@ $0.91.

[If dial is desired forother circuits statewhether condenser

closes to the left or to the right.]8 mfd. Polymet electrolytic, insulating washers,

extra lug. Cat. POLY -8 @ $0.49Three 0.1 mfd. in one shield case, 250 volt d -c

rating. Cat. S-31 @ .21Rola 8" dynamic for 47, with 1800 ohm field

coil tapped @ 300 ohms. Cat. FP @ 3.832 coils for 4 -tube. Cat. DP @ .903 coils for 5 -tube. Cat. DT @ 1.35

DIRECT RADIO CO.

Quick -ActionClassified

Advertisements7c a Word - $1.00 Minmium

Cash With Order

WANTED TO BUY - One or more SilvertoneNeutrodyne radio sets, models 106, 108, 110 or 95.Purchased from Sears, Roebuck & Co.. betweenJune, 1930, and June, 1931. Need not be inoperating condition but must have manufacturer'snameplate. Will pay commission to service manlocating required set, if satisfactory. Box 1724,Radio World, 145 West 45th Street, N. Y.

"THE CHEVROLET SIX CAR AND TRUCK."(Construction-Operation-Repair) by Victor W.Page, author of "Modern Gasoline Automobile,""Ford Model A Car and AA Truck," etc., etc450 pages, price $2.00. Radio World, 145 W. 45thSt., N. Y. City.

BARGAINS IN FINEST PARTS! - Highestgrade, new parts, few of each on hand. Nationaldial, fiat type, modernistic escutcheon, type G,clockwise, $2.19; Pilot drum dial No. 1285 @ $1.89;a -c toggle switch, 19c; triple pole, four -throwBest switch, insulated shaft, $1.62; double pole,four throw, $1.08. Direct Radio Co., 145 West45th St., N. Y. City.

"TALKING MOVIES," by James R. Cameron.A History of the Talking Movie since 1899, withan elementary explanation as to how the picturesare produced and reproduced. Paper cover, $1.50.Radio World, 145 W. 45th St., New York, N. Y.

THE FORD MODEL-"A" Car and Model "AA"Truck-Construction, Operation and Repair-Re-vised New Edition. Ford Car authority. VictorW. Page. 708 pages, 318 illustrations. Price $2.50.Radio World. 145 W. 45th St., New York.

8 MFD. CONDENSERFour for Only $1.47

We are able to offer brand-new 8 mid. wet electrolyticcondensers, with insulatingwashers, mounting nut andlugs at four for $1.47. Thesecondensers are freshly madefor us in quantity by Poly -met Manufacturing Co. andare highly recommended byus for assurance of full ca-pacity and for their rugged-ness. They are of the in-verted mounting type. Singlecondenser, lugs, washers,nuts. Cat. Poly -8 @ 49cFour for the price of three,

Le., $1.47

DIRECT RADIO CO.143 West 45th St. New York City

SOLDERING IRONFREE!Works on 110-120 volts AC or DC, power,50 watts. A serviceable iron, with coppertip, 5 ft. cable and male plug. Send $1.50for 13 weeks' subscription for Radio Worldand get these free! Please state if you arerenewing existing subscription.

RADIO WORLD145 West 45th St. N. Y. City

"A B C OF TELEVISION," by Yates, $3.00.Radio World, 145 W. 45th St., N. Y. C.

Magnetic Pickup Outfit

INPUTTRANSFORMER

VOLUMECONTROLKNOB

PICKUP\PLUG mamma

GUARANTY RADIO GOODS CO.

A phonograph pickupmade by Stromberg-Carlson, equipped withvolume control knob,with matched inputtransformer, a connect-ing cord and jack plug,for using the audioamplifier of your set,to play phonographrecords. Outfit wa listed @ $30.00.

OUR PRICES:Cat. SC -3A, for grid

circuit connection, 117.115

Cat. SC -3B, for platecircuit connection, 7.95

Three differentweights, for choice inusing bead for record-ing, Cat. SC -W @ tea

143 WEST 45th STREETNEW YORK, N. Y.

Two for the Oneprice ofGet, EXTRA, one-year subscription for any One of thews magazines:

O Q.S.T. (monthly, 12 issues; official amateur organ).O POPULAR SCIENCE MONTHLY.O RADIO -CRAFT (monthly, 12 issues).O RADIO INDEX (monthly, 12 issues), stations, programs, etc.O RADIO (monthly, 12 issues; exclusively trade magazine).O EVERYDAY SCIENCE AND MECHANICS (monthly).O RADIO LOG AND LORE. Bi-monthly; 5 issues. Full station lists, cress indexed, etc.O AMERICAN BOY-YOUTH'S COMPANION (monthly, 12 issues; popular magazine).O BOYS' LIFE (monthly, 12 issues; popular magazine).O OPEN ROAD FOR BOYS (monthly, 12 issues).

Select any one of these magazines and get it free for an entire year by sending in a year's sub-scription for RADIO WORLD at the regular price, $6.00. Cash in now on this opportunity to getRADIO WORLD WEEKLY, 52 weeks at the standard price for such subscription, plus a full year'ssubscription for any ONE of the other enumerated magazines FREE. Put a cross in the square nextto the magazine of your choice, in the above list, fill out the coupon below, and mail $6 check,money order or stamps to RADIO WORLD, 145 West 45th Street, New York, N. Y. (Add $1.50, making$7.50 in all, for extra foreign or Canadian postage for both publications.)

Your Name

Your Street AddressDOUBLEVALUE!

City StateO If renewing an existing or expiring subscription for RADIO WORLD, please put a cross in square

at beginning of this sentence.O If renewing an existing or expiring subscription for other magazines, please put a cross in square

at the beginning of this sentence.RADIO WORLD, 145 West 45th Street, New York. (Just East of Broadway)

143 WEST 45th STREETNEW YORK, N. Y.

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