home television demonstrated...general electric's broadcast of moving vision on 37.8 meters...

15cJAN. 28 THE DAVEN AC FIVE

U.S.PAT. oFE, :

'14 .

America's First and Only National

Impedance of Condensers Explained for Novices

3 -TUBE PRE -POWER UNIT

A Quality Analysis of Resistance Coupling

AERIAL COUPLING METHODS

An AC Audio Circuit with B Supply

ELECTRO-DYNAMIC SPEAKERS

Broadcast Bouts Debated

HOME TELEVISION DEMONSTRATED

TELEVISION PROJECTOR used for transmitting vision from the laboratoryof the General Electric Company, Schenectady, to homes in that city. The largedisc, in revolving rapidly, causes the beam of light from the arc light to coverthe picture to be transmitted. The reflected light falls on photo -electric cells,which convert the light fluctuations constituting the picture into equivalent elec-

tric current fluctuations. See article on Page 3.

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The great Morecroft has a new messagefor you. The second edition of his master-piece, "Principles of Radio Communication,"just off the press, is offered to you byProfessor John H. Morecroft of the Elec-trical Engineering Department of ColumbiaUniversity and past president of the Insti-tute of Electrical Engineers.

The outstanding book on radio principlesand practice is something that you mustnot be without. Every set builder, everydesigner, every engineer, every service man,simply must have this book. Ready refer-ence to all intricate problems makes thisvolume invaluable. Distributors and dealers,salesmen and teachers, students and opera-tors, all find Morecroft their standby, andnow the new second edition awaits you.1,001. pages and 831 illustrations in thiscloth -bound volume.

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RADIO WORLD January 28, 1928

"Double -R" Meters With Resistance of

1,000 Ohms Per Voltto Measure Voltages of B Eliminators, Bias Resistors, Batteries0 -300 volts, handsome full Md.! Pith!,convenient portable type meter, accurate towithin 2%% plus or minus, with & resistanceDer volt of a little more than 1,000 ohms.hence more than 300,000 ohms total re-sistance. Fully guaranteed. To manufacturethis meter requires 35 different dyes. Novoltmeter but n high resistance one will en-able you to toll the voltages of B eliminatorsand across C biasing resistors. This meterIs excellent for general D.C.use. It la furnished with

Catalogue No. 346 $4.5°long connecting cor s.

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0-500 volts. this meter; of same externalappearance and general construction as the0-300 voltmeter; particularly appeals to thecustom set builder, service man. experi-menter, etc., who deal with power packs.B supplies. etc.. that feed 210 or 310 tubesand otherwise require measurements up to500 volts. A meter with resistance of morethan 1,000 ohms per volt; excellent for allD.C. measurements. Nickel

cords. Catalogue No. 347. $5450finish; long connector

It is absolutely necessary to use a high resistance voltmeter inmeasuring the voltage of B eliminators, either across the totaioutput or at any intermediate voltage. A low resistance meter9t least partly short-circuits the eliminator and causes the volt-age reading to be away off. Sometimes the reading is as littleas 25 per cent of the total actual voltage. The Double R meters346 and 347 are accurate to 2% per cent plus or minus and havethe highest resistance per volt of all popular priced meters for

this work more than 1,000 ohms per volt!

COMPLETE CATALOGUECat. No. Type Price

POCKET AMMETERNo. 1 For testing dry cells, 0-40 ampere DC

scale pooket meter $1.00

POCKET AND PORTABLE VOLTMETERSNo. 8 For testing A batteries, dry or stor-

age, 0-8 volts DC scale $1.65No. 10 For testing A batteries, dry or stor-

age, 0-10 volts DC scale 1.65No. 13 For testing A batteries, dry or stor-

age, 0-16 volts DC scale 1.65No. 50 For testing B batteries, dry or stor-

age, but not for B eliminators, 0,50volts DC scale 1.65

No. 39 For testing B batteries, dry or stor-age, but not for B eliminators, 0-100volts DC scale 1.85

No. 40 For testing A and B batteries, dry ofstorage, but not for B eliminators;double reading, 0-8 volts and 0-100volts DC scale 2.25

No. 42 For testing B batteries, dry or stor-age, but not for B eliminators; 0.150volts DC scale 2.00

No. 346 For testing B battery eliminators, gridbias voltage across resistors, bat-teries, etc.; 0-300 DC scale 4.50

No. 347 For same as No. 346, except scale is0.500. 5.50

No. 348 For testing AC current supply line,portable, 0-150 volts 4.50

VOLTAMMETERSNo. 18 For testing amperage of dry cell A

batteries and voltage of dry or stor-age A batteries, double reading, 0-8volts, and 0-40 amperes DC $1.85

No. 35 For testing amperage of dry cell Abatteries and voltage of B batteries(not B eliminators); double reading,0-50 volts, 0-40 amperes DC 2.00

6 -VOLT A BATTERY CHARGE TESTERNo. 23 For showing when 6 -volt A battery

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PANEL AMMETERNo. 338 For reading amperage, 0.10 amperes

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Cat. No. Type

PANEL VOLTMETERSNo. 326 For reading DC voltages, 0-6 volts....$1.65No. 335 For reading DC voltages, 0-8 volts.... 1.65No. 310 For reading DC voltages, 0-10 volts... 1.65No. 316 For reading DC voltages, 0-16 volts... 1.65No.337 For reading DC voltages, 0-50 volts... 1.65No. 339 For reading DC voltages, 0-100 volts.. 1.75No. 342 For reading DC voltages, 0-150 volts.. 1.75No. 340 For reading DC voltages, double read-

ing, 0-8 volts, 0-100 volts 2.25

PANEL AC VOLTMETERSNo. 351 For reading 0-15 volts AC V.25No. 352 For reading 0-10 volts AC 2.25No. 353 For reading 0-6 volts AC 2.25(See No. 348 under "Pocket and Portable Volt-

meters.")

PANEL MILLIAMMETERSNo. 311 For reading 0-10 milliamperes DC $1.95No.325 For reading 0-25 milliamperes DC 1.85No. 350 For reading 0.50 milliamperes DC 1.65No. 390 For reading 0.100 milliamperes DC 1.65No. 399 For reading 0.300 milliamperes DC 1.65No. 394 For reading 0-400 milliamperes DC 1.65

DC PIN JACK VOLTMETERSNo. 306 For No. 25 and No. 28 Radiolas, 0-6

volts DC $2.50No. 308 For No. 20 Radiola, 0-6 volts DC 2.50No. 307 Desk type voltmeter with cord, 0-6

volts DC 2.50

TUBE CHECKERNo. 210 For experimenter, professional set

builder, dealer and service man.Consists of 0-6 DC voltmeter, 0.10DC milliammeter, grid bias switch,rheostat, socket and binding post,instruction sheet $6.50

CORD AND PLUGNo. 21 For connecting meters in A and B

leads of a receiver -without any dis-_conneotions. Terminals correspondwith posts on No. 210 tube checker $1.85

Price

A pocket type meter will fit easily in a man's vest pocket.A portable type meter will fit in his sack -coat outside pocket.The other meters -panel type -are intended for panel mounting,

2 5/64 -inch hole. - - - - -GUARANTY RADIO GOODS CO.,145 West 45th Street, New York City.

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ALL METERS SOLD ON FIVE-DAY MONEY -BACK GUARANTY.

SIXTH YEAR

Vol. XIINo. 19

Whole No. 305January 28, 1928

15s per Copy. $6.00 per Year.

RADIOPCG. V 5 PAT Orrl

WORLDA Weekly Paper Published by Hennessy

Radio Publications Corporal Ion, 11.0(I1Publication Office, 145 West 45111 Street,

New York, N Y.Phones: BitYant 0553 and 0559

Technical Accuracy Second to None.

[Entered as second-class matter, March, 1922, at the post office at Nr,. Vork, N. u.1 is:: 9I

Home TelevisionDemonstrated

Alexanderson's Receivers in Three Points in Schenectady Pick UpGeneral Electric's Broadcast of Moving Vision on 37.8 Meters Whilethe Voice of the Subject Is Brought In on egular Radio Set on 379.5Meters -Curl of Cigarette Smoke and Flash of an Eye ClearlyVisible-Forerunner of Machines for Home Use Still Under Experiment

Schenectady.RADIO television leapt the barrier be -

tween the laboratory and the homein the first demonstration of televisionbroadcasting, arranged by the Radio Cor-poration of America and the GeneralElectric Company. At three differentpoints in this city, including the home ofE. W. Allen vice-president of the Gen-eral Electric Company, groups of engi-neers, scientists and newspaper men,standing before the first "home televisionsets" ever to be demonstrated, saw themoving images and heard the voices of aman and a woman transmitted from theresearch laboratories of the General Elec-tric Company, several miles away.

So lifelike were the lights and shadowsreproduced from the research studiosthat the curl of smoke from a cigaretteand the flash of an eye were transmittedby radio just as a picture unfolds on amovie screen.

The first home television set is of verysimple construction, not unlike the fa-miliar phonograph cabinet in size and ex-terior appearance. It was developed byDr. E. F. W. Alexanderson, consultingengineer of the Radio Corporation ofAmerica and of the General Electric Com-pany, and his assistants in the laboratoryhere.

Uses Short and Long WavesIn this instance the transmission of the

moving object was made on 37.8 meterswavelength, while the voice was simul-taneously sent through the air on 379.5meters, the normal wavelength of WGY.

The receiver which Dr. Alexandersonused differs from the ordinary short wavereceiver in that it converts the electro-magnetic wave into light instead of intosound, and the light becomes an imagecorresponding in movement to the actionof the artist at the transmitting end.

"While this is an historical event com-parable to the early experiments in soundbroadcasting, the greatest significance ofthe present demonstration," declared Da-vid Sarnoff, vice president and generalmanager of the Radio Corporation ofAmerica, "is that the radio art has bridged

(Continued on page 5)

E. F. W. ALEXANDERSON, CHIEF CONSULTING ENGINEER OF THE GEN-ERAL ELECTRIC COMPANY AND INVENTOR OF A SUCCESSFUL TELEVI-SION APPARATUS FOR HOME USE, SEATED IN FRONT OF A TELEVI-SION RECEIVER AND VIEWING AN ANIMATED PICTURE SENT BY RA-DIO FROM THE LABORATORY IN SCHENECTADY. SYNCHRONIZATIONBETWEEN THE TRANSMITTER AND THE RECEIVER IS EFFECTED MAN-UALLYIWITH THE LITTLE DEVICE SEEN IN THE HANDS OF THE IN-

VENTOR.

4 RADIO WORLD January 28, 1928

Dr. Alexanderson OutlinesTechnique of Home Television Machine

By Dr. E. F. W. AlexandersonChief Consulting Engineer, Radio

BEFORE we could think seriously oftelevision broadcasting we had to

convince ourselves that a television re-ceiver could be simplified to the pointwhere it could be made available in thehome of the average man.

To test out the practicability of a tele-vision receiver for the home we con-structed a model receiver of the greatestpossible simplicity and distributed severalduplicates of it in some homes in Sche-nectady.

Television receivers may be worked outin a variety of ways according to well-known principles. The first choice to bemade was to select the source of light.This choice was soon narrowed down totwo alternatives: the light control de-veloped by Professor Karolus of ,Leipsigand the Neon lamp developed by D. Mc-Farlan Moore of the Edison Lamp Worksof the General Electric Company.

Tests of these two sources of light fortelevision soon convinced us that each hasits own distinct field of usefulness.

When a large volume of light is neededfor projection on a screen the Karolussystem is preferable. The work on tele-vision which I described in a paper lastYear was built around the idea of usingthe Karolus light control for projectingtelevision images on a large screen.

Moore's LampThe other light source available for

television was the lamp invented by Mr.Moore, who proposed this lamp for tele-vision in a paper as early as 1906 but itwas not until 1913 that he received aquantity of neon from Sir William Ram-sey which enabled him to construct apractical lamp.

While the Neon lamp does not comparewith the Karolus light in brilliancy it isMore sensitive and easier to operate.

'The distinct 'fields of 'usefulness ofthese two systems thus become evident,the Karolus light for the large televisionprojector and the Moore light for the'home receiver.

Most experiments with television inEurope, as well as America, have usedthe Moore lamp.

Mr. Moore has developed one tele-vision lamp which gives "a uniform glowover a fiat plate and'another which givesa concentrated light in a cavity in theelectrode. An enlarged arid improvedlamp of the first type was one of theimportant elements used in the demon-stration of television by Dr. Ives of theBell Laboratories last April. The tubu-lar lamp, with 2,500 electrodes was alsobased on the Moore invention.

Photo -Electric Cells

One of the features of the demonstra-tion by the Bell Laboratories at that timeappears to be a valuable contribution tothe art of television,-the arrangementof large photoelectric cells for intercept-ing the reflection from a moving spot oflight. The system saves the eyes of thesubject from the glaring light to whichotherwise he would be exposed.

The Bell Laboratories photoelectric sys-tem has ben adopted in our equipmentfor broadcasting television and will prob-ably prove to be one of the factors in thedevelopment of practical television.

Returning to the design of the tele-vision receiver, we had the choice betweenthree well known systems,-the mirror

Corporation of America, and General Electric Co.

radiated simultaneously by two transmit-ters.

We feel that the inauguration of thisnew development will be the startingpoint of practical and popular television.The transmission is the expensive partof such an undertaking and we feelthat it is our privilege to provide it. Weshow the television transmitter which isnearly completed at our South Schenec-tady plant.

THE RECEIVER OF THE ALEX -ANDERSON TELEVISION SYSTEMSET UP IN. A HOME NEAR THEGENERAL ELECTRIC COMPANY ATSCHENECTADY. THE LARGE DISCDETERMINES WHAT PART OF THE

FIELD IS RENDERED VISIBLE.

drum, the disc with lenses and the discwith holes. Our conclusion was that,while the mirror drum and the lens discmay have certain advantages for televi-sion production on a larger scale, from thepoint of view of television in the homea hole is more economical than a lensand 48 holes are more economical than48 lenses.

Whenever television has been discussedin the past there has always been somepessimist who has wound up the discus-sion by asking: "How are you going tosynchronize?" The answer has alwaysbeen that we will have a synchronousmotor and transmit a special synchron-izing wave or synchronize to the picturefrequency or to a tuning fork. But allthese devices mean higher cost,' specialamplifiers, and more things that may getout of order. We, therefore, simply de-cided to leave out all of this complication.

Uses Household MotorWe took a standard electric motor

made for household use and are manipu-lating its speed by an electric hand con-trol. With a little practice and coordina-tion between the eye and the hand it ispossible to hold the picture in the fieldof vision as easily as one steers his caron the middle of the road. In specialcases when the transmitting and receiv-ing system are on the same power net-work the machines may be operated by 60cycle synchronous motors.

Experimental television programs' willbe continued to be broadcast from a labo-ratory transmitter on a wavelength of37.8 meters with the accompanying voicetransmission on the regular 379.5 metersof WGY. As soon as it is found that therange can be extended the televisiontransmitter will be transformed to thehigh power short wave experimental sta-tion at South Schenectady. A new trans-mitter is being built for this purpose spthat the voice and the television can be

New Type AntennaA part of this equipment is a new type

of projector antenna which is now beingtested with music and voice modulation,and favorable results have already beenobserved in San Francisco and Europe.We have called this a projector antennabecause it does not pretend to be a beam.The radiation that would be wastedbackward and sidewise is saved and pro-jected in the general direction where it isdesired.

After trying several types of projectorsystems we have arrived at a type whichwe call the checkerboard antenna, builtin a checkerboard pattern, the sides ofeach square being a wire half a wave-length long. All these half -wave an-tennas are connected in such a way thatthey oscillate in phase and require notuning or adjustment.

A duplicate of is be-ing installed in the San Francisco broad-cast station of the General. Electric Com-pany. This plan was decided on to pro-vide means for systematically studyingthe physical phenomena of wave propa-gation over long distances.

Television will here serve as a meansto an end, but in the determination ofwave phenomena one thing is certain,that the eye is infinitely superior to theear for ascertaining facts and for a criti-cal analysis and comparisons. This hasalready been proven by our televisiontests in Schenectady.

Delving Into Secrets of SpaceOccasionally when we "look -in" on tele-vision at our homes uptown we observe

a visual echo of the wave from the elec-tronic layer on the upper atmosphere.The evidence of the echo is that two im-ages appear side by side instead of ope.The echo image is usually displaced a dis-tance, corresponding to one fifteen -hun-dredths of a second, showing therebythat the echo wave had traveled about200 kilometers and yet the echo image isoccasionally as strong as the direct im-age which traveled only a few kilometers.Such phenomena obviously can not beobserved by the ear.

What we may learn about wave propa-gation by systematic study of televisionacross the continent is something we canonly vaguely imagine, but we do feelwithout any doubt that television is thenew tool by which we are going to ex-plore the secrets of space.

COMPOSER BROADCASTSSchenectady, N. Y.Zez Confrey, the composer and pianistwith the twinkling fingers, broadcastsevery Thursday evening at 6:30 fromWGY. Mr. Confrey is the composer of"Kitten on the Keys," "Dizzy Fingers,"

"Stumbling" and many other pieces whichrequire dexterity and accuracy in theplaying. Mr. Confrey and his recordingorchestra play at the Hotel Kenmore inAlbany.

January 28, 1928 RADIO WORLD 5

The Daven AC FiveA Batteryless Receiver of Excellent Quality

By Henry Harbord Chisholm

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THE COMPLETE CIRCUIT DIAGRAM OF THE DAVEN AC FIVE. IT COMPRISES A VOLUME CONTROL, OSCIL-LATOR PREVENTERS, FILAMENT PROTECTORS, GRID B 1AS RESISTORS, AND A FILAMENT TRANSFORMER.

THE success of an AC operated re-ceiver is simply a matter of correct

design. If care in balancing has not beentaken, the receiver may hum. If precau-tions have not been taken to protect thefilaments of the tubes, the life of thetubes may be very short. But hum and

brevity of life of the tubes can alwaysbe traced to poor design or incorrectassembly of parts. The AC tubes are notinherently short-lived. The hum in manyAC sets is avoidable.

Let us consider briefly the Daven AC5 as an example of correct design.

The correct filament voltages and cur-rents for the various tubes are derivedfrom a Karas AC Former which hasthree secondary windings of PA, 2,4 and5 volts. The low voltage winding sup- ,

plies the filament current to three AC -26AContinued on next page)

Trained Observers to Test Television Models(Concluded from page 3)

be taken towards the development oftelevision receivers for the home.

"With all that has been accomplishedthere are still many experimental stagesto be travelled before a commercial tele-vision service can be established.

"The first step contemplated is theplacing of laboratory models of the pres-ent television receiver at central andstrategically located points so that withthe aid of technically trained observers,future experiments may be continued notonly in the reception of but in the simul-taneous transmission both of sight andsound.

"Sound broadcasting has now developedto an art and industry of world-widescope and significance.

"The television receiver as at presentdeveloped will supplement and not re-place the modern radio receiving. set inthe home. Broadcasting of television, itseems clear, will develop along parallellines with broadcasting of sound, so thateventually not only sound but also sightthrough radio broadcasting, will be avail-able to every home."

The elements of the television home re-ceiver are a light source, the scanningdevice and the synchronizing system.The signal, or electro-magnetic wavefrom the television transmitter, is receivedin equipment designed to receive modula-tions as high as 40,000 cycles.

The amplifier is substantially the sameas the amplifier of the home loudspeaker.

The receiving system differs from amodern loudspeaker system in that aneon gas filled lamp is substituted for theloudspeaker. The amplified current isdelivered to this lamp, known as theMoore lamp, and which responds -to theintensities of the current and gives fluc-tuations of the light intensity just as adiaphragm. of the Youdspealker repro-duces pulsations of the air waves.

Field for ExperimentThe scanning disc is 24 inches in diam-

eter with 48 small holes, each hole 35 milsin diameter and arranged in a spiral sothat each of the 48 holes will pass eachother and trace successive lines of thepicture, completing or literally paintinga picture in one revolution.

In other words, if the disc were re-volved very slowly a ray of light throughsuccessive holes would trace over the en-tire object. The disc is revolved by astandard motor, similar to those used inhousehold devices such as the washingmachine or vacuum cleaner.

'The revolutions occur at a speed of 18per second, slightly faster than a filmpasses through a motion picture camera.An observer, looking at this revolvingdisc as the light from the Moore lampshines through these small holes, wouldsee the image being sent by radio, but

this picture would be only PA inchessquare.

Magnifying lenses enlarge the picturetwice, so that it is 3 inches square in theaperture in the front of the receivercabinet.

Synchronization of the scanning discof the receiver with the scanning disc ofthe transmitter is obtained by manuallyoperated control, a push button held inthe hand. By means of this button, ofthe bell ringing type, the picture may beheld in the field of vision with a littlepractice, as naturally after a time asdriving an automobile or steering a bi-cycle.

The reproduced picture or object hasa pink color, which is characteristic of theneon gas used in the lamp. D. McFarlanMoore, inventor of the lamp and an en-gineer at the Edison Lamp works of theGeneral Electric Company, found in earlywork that this gas was most efficient andmost sensitive for reproducing a lightwhich will go on and off in a millionthpart of a second.

The transmission system is of the typeusing a disc with spiral holes, a duplicateof the disc in the receiving machine. Aspot light is projected on the objectthrough the moving disc and the reflec-tion of this light is intercepted by photoelectric cells, which converts the light toelectric waves, ready for the short wavetransmitter.


L L2

C, C2

IMO

02

AN ELIMINATOR ESPECIALLY DESIGNED FOR THE DAVEN AC FIVE RE-CEIVER. IT MAKES FULL USE OF A FULL WAVE THERMIONIC RECTI-FIER THE OUTPUT OF WHICH IS ADEQUATELY FILTERED.

8+ F;Nk

8+ AMR

8+

Bl-DET

tubes, two of which are RF amplifiersand one of which is the first AF ampli-fier. The 2,/s volt winding supplies theheating current to one AC -27 detectortube. The 5 volt winding supplies the-71A type power tube.

Long Life Assured.

As a protection against surges in theline voltage and consequent possible dam-age to the filaments, Daven AC ballastsare used. These help maintain the volt-age across the filaments constant forvariations in the line voltage as great as20%. This action is due to the fact thatthe resistor material has a very high tem-perature coefficient of resistance changeat the normal operating temperature.Thus these ballasts, which are markedRa and Rb in Fig. 1, stand guard over thefilaments and insure their long life aswell as consistent operation of the re-ceiver throughout the life of the tubes.

The ballasts marked Ra are DavenAC 26 and the ballast marked Rb is aDaven AC 27 ballast. The ballast Rain the filament of tube No. 5 may beomitted if desired, as this tube is notcritical. A 5 -volt pilot light is conectedacross the filament circuit of the powertube next to the transformer. This isa part of the Hammarlund drum.

How Hum Is Banished.The use of ballast resistors in the fila-

ment circuits upsets the balance so thatthe center taps on the filament trans-former cannot be used without introduc-ing hum. In place of the center taps onthe transformers artificial center taps areprovided with the aid of four 10 ohmDavohms, which are accurately centertapped. These are connected across thefilament terminals on the sockets so thateven the resistance of the filament leadscannot enter to upset the accurate bal-ance of the center tapped resistors.These center tapped resistors are markedR2, R4, R7 and R9 on the circuit dia-gram.

R11 is a similar center tapped resistoracross the filament of the -71A type tube,but its resistance must be higher thanthe resistance used for the other tubes.This is due to the fact that the voltageacross it is higher and that the resistanceof the filament is higher than the resist-ances in the other tubes.

Suppose the 10 ohm resistance be' con-nected across the filament.

The current through it would be IAampere. But the filament of the tubeonly takes Vq. ampere. Hence the re-sistor would take twice as much currentas the tube, and the drain from the 5volt winding, exclusive of the pilot light,would be the same as 3 of the -71A tubewould draw. The total resistance of R11should be at least as high as the resist-ance of the filament, so that the currentis no more than doubled. This might beclbtained by putting two of the 10 ohm

resistors in series and using the junctionbetween the two as the center tap.

Grid bias for all the tubes in the re-ceiver is obtained from drops in resistors.One resistor is used for each amplifiertube as a means of minimizing interstagecoupling and the resulting distortioneffects on the output. Resistors R3, R6and R10 serve AC -26 tubes and there-fore they are all of the same value. Eachshould have resistance of 1,500 ohms andshould have a wattage rating of 1 wattor more.

Resistor R12 gives the negative bias tothe grid of the power tube, and since thisis of the -71A type the resistance shouldhave a value of 2,000 ohms. The resistorshould have a rating of 1 watt or morebecause its dissipation will be .8 watt.

Condensers C2, C7, C10 and C11 areconnected across the respective resistorsto prevent the plate circuit of a tubefrom feeding back voltage into its owngrid circuit and thus decrease the ampli-fication. C2 and C7, which handle onlyradio frequency currents, need not belarger than .01 mfd., but CIO and C11which handle audio frequency currentsshould be at least 4 mfd. each.

C3 is also a radio frequency condenserused mainly for by-passing the leads tothe B battery eliminator. C8 is an audiocondenser and should be at least 2 mfd.but C12 is a radio frequency condenserand it should not exceed .0005 mfd.

R8 is a resistor inserted in the grid cir-cuit of the first audio tube to preventaudio feed -back. Its value is 100,000ohms and it is by-passed with a condenserC9 of 2 mfd.

L7 is a Hammarlund j5 millihenrychoke coils which is used to prevent thetransmission of radio currents to theaudio amplifier.

L1L2, L3L4 and LSL6 are three Daventuning coils which fit the three Hammar-lund .0005 mfd. condensers CI, C4 andC5.

The volume is controlled with a vari-able resistance R1 of 2,000 ohms resist-ance, which is placed in shunt with theprimary of the first RF coil.

(Part II next week)

Rubber Company TriesShort Wave to Liberia

Washington.The Firestone Tire and Rubber Com-

pany, of Akron, Ohio, has been grantedan experimental three month license, toenable it to use' a transmitter with callletters 8XAS to communicate with themen in charge at their rubber plantationsin Liberia.

The license permits the use of from200 to 5,000 watts of power on waves from.5.35 meters to 16.6 meters and from 42.8to 52.6 meters.

LIST OF PARTSL1L2, L3L4, L5L6-Three Daven RF

coils for .0005 mfd. condensers.L7-One Hammarlund 85 millihenry RF

choke coil.AF1, AF2-Two Halldorson overtone

audio frequency transformers.Cl, C4, CS-Three Hammarlund .0005

mfd. midline condensers.C2, C3, C7-Three Carter .5 mfd. con-

densers.C6-One Carter .00025 mfd. grid con-

denser.C8, CO-Two Carter 2 mfd. by-pass

condensers.C10, C11.-Two

condensers.Cr -One Carter .0005

denser.C-One Carter 1 mfcL condenser.R1-One Centralab 2,000 ohm variable

resistor.R2, R4, R7, R9-Four Daven 10 ohm

center tapped resistors.R11-Two Daven 10 ohm center tapped

resistors.R3, R6, R10-Three Daven 1,500 ohm?

resistors 1 watt type.R5-One Daven 2 megohm Glastor grid

leak.R8-One Daven 100,000 ohm Glastor.R12-One Daven 2,000 ohm resistor, 1watt type.Ra-Four Daven AC -26 ballasts.Rb-One Daven AC -27 ballast.GR1, GR2-Two 1,000 ohm Daven grid

resistors.PL-One 5 -volt pilot light.Thirteen resistor mountings.One Karas AC Former (filament trans-

former).Four Benjamin sockets.One Benjamin 5 -prong socket.One Hammarlund drum dial.Six XL binding posts.Two Frost pup jacks.One Cortlandt Panel, 7x24 inches.Three Daven AC -26 tubes.One Daven AC -27 tube.One Daven AC -71 tube or UX1NA or

CX371A.Two rolls Acme flexible Celatsite.

Carter 4 mfd. by-pass

mfd. fixed con -

Different Colors UsedIn Benjamin Sockets

The Benjamin Electric Mfg. Co., 120South Sangamon Street, Chicago, Ill., arenow making their famous spring-cush.'ioned sockets according to the color -codeadopted by the Radio Manufacturers'Association and the National ElectricManufacturers' Association.

According to this code the sockets forgeneral purpose tubes are made in a richmaroon color and the sockets for detec-tor tubes are made in a dark green color.The green detector sockets are made forboth four and five prong tubes, so thatboth the special detector and the heatertype of tubes are provided fora The ma-roon sockets fit all the standard ampli-fier tubes such as -01A and the -26types.

The Benjamin sockets, besides adher-ing to the standard color code, have ex-clusive features which make them non-microphonic even when used with tubeswhich are most sensitive in this respect.The tubes are held suspended on suppleand well balanced springs.

A. ATWATER KENT-Recognitionby the great leaders in the musical, politi-cal, industrial, educational, financial andreligious world is a sure indication of theimportance and permanency of radio.There can he no doubt of that. Theonly question should be, now that wehave this powerful medium, how are wegoing to use it for the greatest good ofthe greatest number of people for thegreatest length of time.


The Impedance of CondensersExplained in a New Way for du- Novice

By Brewster Lee

FIG. ITWO SIMPLE HARMONIC WAVES OF EQUAL AMPLITUDE, ONE OFWHICH HAS A FREQUENCY 6 TIMES THAT OF THE OTHER. THESHADED PORTION SHOWS THE QUANTITY OF ELECTRICITY TRANS-

PORTED BY A CIRCUIT DURING ONE HALF PERIOD.

THERE are few radio fans indeedwho do not know that high frequency

currents pass through condensers muchmore easily than low frequency currents.It is well known that an audio frequencycurrent of 100 cycles is practicallystopped by a condenser of .001 mfd. andthat a radio frequency current of 1,000,000encounters practically no obstruction inpassing through the same condenser.Why does a high frequency current passthrough so easily and why does not alow frequency current get through?

The answer to that question will bemore readily understood if the readerrealizes that no current actually passesthrough a condenser but that electricitypasses into the condenser and out again.The alternating current in the circuitsurges back and forth and charges anddischarges the condenser. The currentis the rate of change in the amount ofelectricity in the condenser, or it is therate at which electricity passes in or outof the condenser. For example, if thecharge on the condenser changes at therate of one coulomb per second the cur-rent is one ampere. Also if the chargeon the condenser changes at the rate ofone micro coulomb per microsecond thecurrent is also one ampere. Again if thecharge on the condenser changes at therate of 60 coulombs per minute the cur-rent is one ampere.

The charge on the condenser cannotchange unless electricity flows in or outof the condenser, and it takes an electro-motive force to drive electricity in, andit requires a path for the electricity toleave the condenser.

Question AnsweredThe answer to the question of why a

condenser of a given capacity admits highfrequency currents better than low fre-quency current lies in the definition of cur-rent that it is the rate of change ofcharge on the condenser. Suppose twocurrents have the same amplitude butthat one has a frequency 6 times that ofthe other. The average value of the cur-rent in a half period is the same for bothcurrents because the amplitude is thesame and the average current during thehalf period is 2/sr times the amplitude, or.636 times the amplitude.

The total amount of electricity thatflows in a half period is average currenttimes the time of a half period. Sincethe frequency of one of our assumed cur-rents is 6 times that of the other, the halfperiod of the higher frequency is only1-6 that of the lower. Thus if the dura-tion of a half period of one is T that ofthe other 6T. Since the total quantityof electricity in a half period is equal tothe average current times the time of ahalf period, the quantity that flows in one

case is .636IT and that in the other is3.8161T, where I is the amplitude of eitherof the two currents. The total change inthe charge of the condenser is therefore6 times as great for the lower frequencycurrent as for the higher frequency cur-rent. Generally, if T is the time of ahalf period and Ia is the average currentduring that period the quantity of elec-tricity moved during the half period isTIa.

Graphic RepresentationIn Fig. 1 two sine curves are given

which represent two alternatidg currentsof the same amplitude I but one having afrequency 6 times that of the other. Theperiod of the high frequency current is T1and that of the low frequency current isT2. The corresponding half periods areshown in the diagram as ,./zT1 and Y2T2.The mean current is represented by Iaequals 2I/ir. The total quantity of elec-tricity moved during a half period is rep-resented by the area of one loop boundedby the axis and by the curved line asshown by the shaded portions. It is ob-vious that the quantity represented bythe low frequency at the right is manytimes greater than that at the left. Cal-culation shows that it is 6 times as great.If one current has a frequency of 100cycles per second and another 1,000,000cycles per second the ratio is not 6 toone but 1,000,000 to 100, or 10,000. Thequantity in one loop of the audio fre-quency current is 10,000 times as greatas that in one loop of the audio fre-quency current.

Now it will be recalled that the quantityof electricity that can be put into a con-denser of a given capacity is directly pro-portional to the voltage used in chargingthe condenser. Doubling the voltagedoubles the charge. It follows that ittakes 6 times as high voltage to force a6 unit charge into the condenser as toforce a unit charge into it. Since an al-ternating current through a condenser issimply a periodic charging and discharg-ing of the condenser it is obvious that ittakes a much higher voltage to maintaina given amplitude when the frequencyis low than when it is high. The voltagedepends on the charge or quantity in eachloop of the alternating current, and thatdiffers widely for radio and audio fre-quency currents of equal amplitude.

Actual Values GivenSuppose we consider the relative quan-

tities in single loops of two currents eachhaving an amplitude of one ampere butone having a frequency of 1,000 cycles andthe other a frequency of 1,000,000 cyclesper second. The mean value of currentis the same for both and is .636 ampere.The duration of a half period of the 1,000

FIG. 2

TWO SINUSOIDAL CURVES OFEQUAL FREQUENCY ILLUSTRAT-ING HOW THE FLOW LEADS THEPRESSURE BY A QUARTER PERIOD.THIS IS THE RELATIONSHIP BE-TWEEN THE VOLTAGE AND THE

CURRENT. IN CONDENSER.

cycle current is .0005 second. Hence thequantity is 318 microcoulombs. The du-ration of a half period of the 1,000,000cycle current is r/2 microsecond. Hencethe quantity in this case is only .318 mi-crocoulomb. Thus the ratio is 1,000 to 1,just as the ratios of the frequencies.

Perhaps the action can be visualizedbetter with the aid of an airpump and anair tank. The pump represents the sourceof emf or the battery. The tank repre-sents the condenser. The pump may be

. operated with a short stroke at a veryhigh rate of speed, or it may be operatedwith long strokes with a very slow speed.It is obvious that in either case the rateat which the air is forced into the tankmay be the same, that is the amplitude ofthe air current may be the same in bothcases. But the short stroke may forceinto the tank only a thimble full of air,while the long stroke may force a 1,000thimble fulls into the tank. One thimblefull will not alter the pressure in the tankvery much, and there will be very littleback pressure on the piston because ofthe addition of a thimble full. But whena 1,000 thimble fulls are forced in thechange in the back pressure is much great-er-a 1,000 times greater-and the pistonmeets a greater impedance. Yet in bothcases the rate at which air enters thetank is the same. In one case the airenters at the rate of one thimble full inone millisecond for example, and in theother case at the rate of a thousandthimble fulls per second, which are justtwo ways of stating the same thing.

Current Leads the VoltageAnother fact about a condenser not

easily visualized is that the current inand out of it leads the voltage by 90 de-grees, or by a quarter period. Whenthe voltage is zero the current in or outof the condenser is maximum and whenthe voltage has reached its maximumvalue the current is zero.

There is nothing unique about that be-havior. Analogous phenomena abound inphysics. Referring to the air tank andpump again we have a perfect analogy.At the beginning of a stroke the pistonis stationary and there is no compressionof the air in the tank. The instant thepiston begins to move the air rushes intothe tank 'but the rush decreases in vio-lence as the tank fills up. When the pis-ton is at its greatest displacement thepressure is greatest but the piston is notmoving. Hence there is no current flow-ing into or out of the tank. This is il-lustrated in Fig. 2. The current is in-dicated by "flow," and it is either anelectric current or an air current accord-ing as the "pressure" is electric or pneu-matic. The maximum of flow is a quarterperiod ahead of that of pressure.


The Pre -Power UnitBy H B. Herman

THE PRE -POWER UNIT CONSISTS OF A STAGE OF TRF, A REGENERA-TIVE DETECTOR AND A RESISTANCE COUPLED AUDIO STAGE. ATRANSFORMER STAGE IN A POWER PACK, WITH 11 OR 10 TUBE, IS TO

BE USED WITH THIS.

AFTER you have built any set you areexceedingly anxious to determine its

capabilities, but how do you go about it?Perhaps you give the set just a general

tryout, with no particular point in mind.Perhaps you note carefully the selectivity,and appraise the other factors later. Ormaybe the tone quality engages your firstattention.

With me it is different.I test a receiver first for its sensitivity

on the high wavelengths. Let me hear KYW,Chicago, (526 meters, 570 kilocycles) orWHO, Des Moines, Ia., (535.4 meters, 560kc), in my home in New York City, andI will appreciate the sensitivity of the set.

I know that on the lower wavelengths-higher frequencies-about the only problemwill be safeguarding against too much am-plification. This is because of the risingcharacteristic of tuned radio frequency am-plification, whereby the higher the frequen-cy, the higher the amplification.

By that test the Pre -Power Unit (Fig. 1)stood up beautifully, for scarcely a night haspassed during the three weeks that I havebeen experimenting with the set without'my bringing in KYW soon after WNYC,New York .City's municipal station, signedoff. Both occupy the same wavelength, butdo not broadcast simultaneously. AndWHO, occupying the second highest as-signed wavelength, is another steady visitor.

Not a Usual ThingThis amplification at the lower frequen-

cies is a decidedly advantageous feature,and is something not too commonly encoun-tered. It marks the radio part of the Pre -Power Unit as something well worthy ofconstruction.

Granting good tubes, properly voltaged,this sensitivity at the higher wavelengths,with its assurance of even greater sensitivityat the lower ones, is accounted for largelyby the coils and by-pass condensers. Thecoils are of adequate proportions, where thediameter comes close to the formula's re-quirements for low -loss design, when thatdiameter is compared to the axial lengthof the winding. The primaries are gener-ous, too, and this is particularly necessaryin a radio amplifier consisting only of twotubes, if high -wavelength amplification is tobe of the desired amount.

With this attainment of adequate sensi-tivity on the higher wavelengths come cer-tain problems. One is selectivity andanother is stabilization at the lower wave-lengths. The selectivity is sufficient toseparate WABC, New York City (309.1

meters, 970 kc) from KDKA (315.6 meters,950 kc). This is done without critical ad-justment of the ticker coil, L5, but whenthe regeneration is pressed a bit fartherthe selectivity, increases considerably.Hence the selectivity.

If you want the ultimate in practicalselectivity you gain it -at the expense ofvolume and sensitivity for the same num-ber of amplifier tubes. A middle coursewas struck, so that the number of tubes inthe radio amplifier (one RF and one de-tector) is kept at a minimum.

Resistance RF in First StageOne audio tube is included in the cabinet,

this being a resistance coupled stage. Fin-est tone quality is preserved and full utili-zation is made of the high RF gain by usinga resistance coupled step here. The otheraudio stage (not shown) is to be a part ofthe B supply that will be constructed. Or,if you have a B supply, then you may putthe second audio coupling in a containerwith the output filter and run the A andB supply leads thereto, as well as thespeaker cords.

The design was settled upon as shown inFig. 1 because of the popularity of home -constructed or custom-built eliminators witha stage of transformer coupled audio in-corporated. Hence the circuit as shown ispreliminary to a power pack, feeding nicelyinto it, without distortion. That is why itis called the Pre -Power Unit.

The design may be followed economically,also, for while only first-class parts areused, there are no non -essentials and noitems that run into money, excepting per-haps the bypass or filter condensers C2, C3,C6, C8, C9 and Cll. The set willwork without these, and work well, butnot so well as with them in, nor shouldas much DX be expected with them. out,so if possible one should include them.Their object in the radio part of the cir-cuit is to bypass the radio frequencies,keeping them out of the B supply andout of the leads running to that supply,as well as negativing the antenna effectof those leads. Such effect is injurious toselectivity. On the audio side they helppreserve the purity of tone, tend to re-duce self -oscillation at audio frequenciesand reduce stray noises.

You'll Be SatisfiedOn the radio side their effect is gainful,

hence with them in the 'set will be morelikely to be too regenerative at the lowerwavelengths. That is as it should be, since

LIST OF PARTSLl, 12, L3, IA, L5-One Hammarlund

antenna coil and one Hammarlund TCT23coil, constituting HR23.

L6-One Samson 85 millihenry chokecoil.

121-One Lynch 800 -ohm suppressor,(optional).

R2-One IA Amperite.R3-One Lynch 5 meg. leak, with

mounting.R4-One IA Amperite.RS-One Lynch 100,000 ohm (.1 meg.)

metallized resistor.R6S-One Frost S 1895 Potentiometer

(switch attached).R7-One IA Amperite.R8-One volume control Clarostat (used

as grid bias resistor).C-One Polymet .5 mfd. filter condenser.CI-One Remler twin rotor .0005 mfd.

condenser (649 S. L. Frequency or 639S. L. wavelength).

C2-One Polymet .5 mfd. filter conden-ser.


C4-One Remler twin rotor .0005 mfd.condenser (649 S. L. Frequency or 639S. L. wavelength).

CS-One Polymet .00015 mfd. mica fixedcondenser.

C6-One Polymet mfd. filter conden-ser.

C7A, C7B-Two Polymet .0005 mfd.mica fixed condensers.



C10-One Polymet .5 mfd. filter con-denser (optional).

CII-One .5 mfd. Polymet filter conden-ser.

C12-One .5 mfd. Polymet filter conden-ser.

Two binding posts (Ant. and Gnd).Three Frost sockets No. 530.Two Remler standard dials, type 636.One 7x21x3-16 Celeron front panel.One 7x18 Celeron panel (for subpanel).One pair of Benjamin or Bruno brack-

ets (for front panel attachment).One pair of Benjamin brackets (for

extra support of subpanel).One four -lead cable.

ACCESSORIESOne Corbett 7x21x8% cabinet, 2" slop-

ing front.One CeCo type F (112) tube (socket 1).One Q. R. S. type 200A detector tube or

CeCo type H (socket 2).One CeCo type A tube (socket 3).

when we have too much amplification wealways know what to do about it, but whenwe have not enough we are often at a lossto know what to do, except add more tubes,and that means building a new set. It isa poor inducement to build any receiver ifthe net outcome is a conclusion to buildsome other set. In other words, you mayfollow the outline as in Fig. 1 with assur-ance of success, even elation.

The Pre -Power Unit was operated witha Victoreen B Supply, with built-in audiostage, including the last audio tube, andthere was amplification aplenty at both radioand audio frequencies. Indeed, on stronglocal signals, such as WEAF, WJZ andparticularly WOR, the final audio tube willoverload, but that is easily taken care ofby loosening the tickler coupling.

(Part II, conclusion, next week)


Radio UniversityWhen writing for

A FREE Question ad n- sewer Department con-

ducted by RADIO WORLDfor its yearly subscriber,only, by Its staff of Experts.Address Radio University,RADIO WORLD, 14S West45th St.. New York City.

Information give yet Radio University subscription number.

FIG. 597WIRING OF FILAMENT CIRCUIT, WHEREBY IT IS POSSIBLE TO CON-NECT A BATTERY USED FOR SET, TO OUTSIDE SOURCE.

I WOULD like to know how to hookupthe filament circuit of my three tubes,using three lA Amperites, with two fila-ment switches in series with each other.The idea is to connect up the A batterythrough one switch and then disconnectthe filaments from the battery, so thatthe battery can be used for testing.-FRED EDGEWORTH, Brawley, Ark.

See Fig. 597. Si is used to connect thebattery to the filaments through S2, whenit is closed. When S2 is opened, the bat-tery can be used for external purposes.

* * *

I AM very much interested in thefive -tube on pages 10and 11 of the November 12 issue of RA-DIO WORLD.

(1)-Could I use two separate variablecondensers of .0005 mfd. capacity?

(2)-In winding my own coils, I am go-ing to use 3 inch diameter tubings andplace 15 turns on, for the primaries, and50 turns for the secondaries, using No. 22double cotton covered wire. Is this allright?

(3)-I have several 1 mfd. fixed conden-sers around my workshop. Could theybe used anywhere in this receiver?-JIMMY CROSTER, Chicago, Ill.

(1)-Yes.(21-Use 12 turn primaries. Your

other data are all right.(3)-Place one between each B plus

post and the minus A terminal.* * *

PLEASE ANSWER the followingquestions regarding the Winner 4 -tubereceiver, which w4s described in theOctober 1, 8, 15, 22 and 29 issues ofRADIO WORLD.

(1)-I have all the necessary parts forthis receiver, except one ballast, but Ihave an extra 20 -ohm variable resistance.Could this be used in place of R3 in thedetector stage?

(2)-Can all fixed condensers, of the .5and 1 mfd. fixed capacity type, be placedin a single metal container?

(3)-This will necessitate placing theaudio transformers closer to each other.Is this all right?-ARTHUR BLATNER,Troy, N. Y.

(1)-Yes.(2)-Yes. Be sure to keep the leads in-

sulated from each other.(3)-Yes.

* * *

I DESIRE to build the Tone Controldescribed in the January 7 issue of RA-DIO WORLD.

(1)-Will a 30 henry choke coil servethe purposes where the choke coil is tobe used?

(2)-Can I use a Clarostat (0 to 5 meg-ohms) across the output ?-ANTONYGRAPIDO, Houston, Tex.

(1)-Yes.(2)-Yes.

* * *

HOW MANY milliamperes will pureNo. 24 copper wire pass?

(2)-How much current will pure No.40 copper wire pass?-SED FRANCIS,Basin, Mont.

(1)-From 275 to 400 milliamperes.(2)-Prom 5 to 10 milliamperes.

* * *

SOME OF my friends have toldthat the silver coat on the glass envelopeof a tube is a determining factor as tothe efficiency of the tube. That is, themore silvery it is, the better the tubeworks. Is this correct?-ARTHUR K.LONTREN, Johnston, S. C.

No. This silvery coat you see is nothingmore than the deposit of magnesium,which accumulates on the inner surfaceduring the process of getting rid of gassesinside of the glass envelope. That is,after the tube has been evacuated asmuch as possible with mercury pumps, asmall piece of magnesium of which 'is at-tached to the plate of the tube is heatedwith a radio frequency coil, until it va-porizes and then flashes. When thishappens, the metal is deposited on theinside of the glass walls, at the same timecombining with any of the gases presentand completely eliminating them. The de-gree of silvery deposit is not a factor.

I HAVE built a 4 -tube Diamond of theAir, and ant having some trouble with it.

(1)-I can hear signals on the ear-phones, but when 1 plug in on my loud-speaker, I don't hear a thing.

(2)-The detector tube does not regen-erate either. Anything you can suggestwill be gratefully appreciated.-WARDTIAMDOM, Delaware, Ind.

(1)-The trouble is in the jack at thedetector output. Either one of the innersprings probably does not make contactwith the upper or lower springs, whenthe plug is taken out. Suggest you in-sert a new jack.

(2)-Place a .00025 mfd, fixed conden-ser across the tickler leads. Reverse theseleads and increase the plate voltage.

* * *

REGARDING THE construction of adirect current A and B eliminator.

(1)-Can't the standard 30 henry chokecoil be used in the A filter side of theeliminator? 1 have two of these.

(2)-In the diagram, I have, three fixedresistors are connected in series with themain output line to drop the voltage.Can a single variable resistor be used,instead? I wish to use only 90 volts forthe audio and radio tubes, and the othervoltage for the detector.-PERRY MAN-ZAN, Lexington, Ala.

(1)-No. You will have to use aheavy duty choke, having an inductanceof about henry and being able tostand 2 amperes, at least. The 30 henrychoke can only stand a couple hundredmilliamperes.

(2)-Yes, you can use the variable re-sistor. Do not forget to by-pass it witha 1 mfd. fixed condenser.

* * *

IN LOOKING over some issues ofRADIO WORLD I noticed the circuit dia-gram of a 6 -tube receiver on page 11 ofthe Feb. 26 issue, which I would like tohookup. There are, however, severalthings, about which I am in the dark.

(1)-What are the capacities of thecondensers connected between the B plusposts in the radio frequency circuits, andthe minus A posts?

(2)-The grid returns of the radio fre-quency, detector and first audio tubetubes are all returned to a minus C post.What voltage battery is used here?

(3)-Is it all right to us a 2 ohm rheo-stat, which will pass 14 amperes in se-ries with all the filaments?-JOHN K.ORERT, Maple Lake, Minn.

(1)-They each have a capacity of 1

mfd.(2)-Use a 4i' volt battery.(3)-Yes. It would be better, though,

to use lA Amperites in each of the fila-ment legs.

Join RADIO WORLD'S University ClubAnd Get Free Questions and Answer Service for the Coming 52 Weeks

This Service for Yearly Subscribers OnlyHave your name entered on our subscription and University lists by special numbers.Put this number on the outside of the forwarding envelope (not the enclosed returnenvelope) and also put at the head of your queries. If already a subscriber, send S6for renewal from close of present subscription and your name will be entered in RadioUniversity. No other premium given with this offer.

[In sending in your queries to the University Department please paragraph them so thatthe reply can be written under or alongside of each query. Write on one side of sheetonly. Always give your university number.]RADIO WORLD, 145 West 45th Street, New York City.Enclosed find $6.00 for RADIO WORLD for one year (52 nos.) and also enter myname on the list of members of RADIO WORLD'S University Club, which gives mefree information in your Radio University Department for 52 ensuing weeks, and send

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City and State


v

An AC Audiofor Phonograph and

PT,

C>C>C.

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Lz

I

DET. AF, -26 AF2 -71

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By Chester

Ch

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O

THE DIAGRAM OF A POWER SUPPLY AND POWER PUSH-PULL AUDIO FREQUENCY AMPLIFIER DESIGNED FORUSE WITH EITHER A RADIO TUNER OR A PHONOGRAPH PICK-UP. SPECIAL CONNECTIONS HAVE BEEN

MADE IN THE FILTER TO ELIMINATE HUM AND DISTORTION.

THE use of the audio channel of a ra-dio receiver in conjunction with a

phonograph electric pickup is growing inpopularity. A man may search out hisfavorite record and put it on the phono-graph. But somehow that alone won'tsound just right. It does not please as itdid formerly. Is the fan suffering froman acute attack of ennui? Is he in astate of mind where nothing will pleasehim? Or has a change taken place inhis favorite record so that he no longerlikes it?

A change has crept in, to be sure, butit is not in the record. That is as goodas ever. The change is purely psycho-logical and is centered about the fan whois ill at ease. He has heard good radioreproduction of his favorite selection andis disappointed if his phonograph doesnot reproduce it as well. He wants oneto be as good as the other and both tobe the best.

Where Difference LiesThe difference does not lie in the

record, for that is of the latest electricallyrecorded type. It is not in the rendition,for the record is the same as that whichpleased him before. The difference liesin the mechanism between the record andthe listener. The mechanical reproduc-tion with the formerly prevalent sound -box does not have the brilliancy charac-teristic of the reproduction with the elec-trical pickup, e.g., the Phonovox.

And then the thought occurs to thetroubled fan that what has been electri-cally recorded should be electrically re-produced. The idea seems logical to himand he resolves to try it out. He hasbeard of the possibility of this both fromthe phonograph and the radio interests.

Investigation brings out that certainconditions must be met if the electrical

reproduction is to be comparable to thebest in radio. He must have a good mo-tor and turn table; he must have a goodpickup unit; he must have a high power,high quality audio frequency amplifier;and he must have a steady and depend-able power source which will deliver allthe power required.

The motor and turntable in his old pho-nograph will suffice provided that thespring is good, and also provided thatthe speed governor is functioning proper-ly. If the motor will turn a record satis-factorily in the old phonograph, it willserve very well in the electrical repro-ducer. We pass to the next condition.

Good Pick-up EssentialIt is absolutely necessary that a good

pick-up be used. It is that which con-verts the mechanical vibrations intoelectrical vibrations, and the value of thepick-up depends on how faithfully theconversion is made. The pick-up is theheart of the electrical reproducer, and itis as important in this connection as themicrophone is in the broadcasting studio.

There are several electro-magnetic pick-up units on the market having a balancedmagnetic system which give satisfactoryresults.

The third condition requires that ahigh type audio frequency amplifier beused. It must be capable of handling thehigh quality music stored in the recordwithout adding to or subtracting anythingtherefrom. Such amplifiers are nowavailable and are even used in radio setsquite extensively. The amplifier mightwell be push-pull in at least one stage.Such an amplifier is incorporated in theunit illustrated in Fig. 1.

It is assumed at this point that theradio fan who is equipping his outfit forelectrical reproduction of phonograph

records will want to use his audio ampli-fier and power source for both the radioset and the phonograph. The unit shownin Fig. 1 is designed on that basis.

The terminals of the pick-up unit areconnected across the points (1) and (2)on the primary of the first audio fre-quency transformer AF1. This trans-former excites the grid of a -26 typetube, which in turn feeds its output intothe primary of the push-pull input trans-former AF2. The secondary of thistransformer excites the grids of the two-71A tubes connected in push-pull relation.In the output of the two power tubes isa high inductance choke coil Ch which istapped at the center point. The loud-speaker is connected across this coil with-out the intervention of any stopping con-densers whatsoever.

Grid Bias ObtainedR4 is a double slider potentiometer in-

serted in the plate circuits of the tubesto yield a grid bias to the tubes. Notethat the resistor is placed so that theplate current of all the tubes flowsthrough it. The -71A tubes draw about40 milliamperes and the -26 tube takesabout 6 milliamperes. Hence the totalcurrent through R4 will be 46 milliam-peres. A total drop of 40,A volt in R4 isrequired. A 1,000 ohm potentiometerwhich will carry at least 50 milliamperesis suitable, provided that it has twosliders so that the bias for both the -26and the -71A tubes may be obtained fromit.

'The question of the introduction of dis-tortion and hum into the signal throughR4 must be disposed of before this cir-cuit is acceptable.

As the last stage is push-pull therewill be very little AC from this stage inR4. It will be appreciable only when


AmplifierSet with B SupplyCharlton

LIST OF PARTSPT1-One Samson transformer No. 132.PT2-One Karas AC Former.LI, L2-Two Samson 30 henry chokes No.

30.AFI-One Karas Harmonik audio fre-

quency transformer.AF2-One Samson Type Y push-pull

transformer.Ch-One Samson Type Z output choke.RI, R3-Two Centralab 3464 ohm resist-

ors No. FT -3464.R2-One Centralab 10,000 ohm heavy duty

variable resistor HR -010.R4-One Centralab 2,000 ohm 4th termi-

nal potentiometer.Cl, C2-Two Tobe 2 mid., No. 602 con-

densers.C3-Two Tobe 4 mfd., No. 404 conden-

sers.C4-Two Tobe No. 304 4 mfd. condensers.CS-Two Tobe No. 304 4 mfd. condensers.C6-One Tobe No. 304 m 4 mfd. conden-

ser.C7-One Tobe No. 404 4 mfd. condenser.Six Eby binding posts.Four Benjamin standard sockets.

ACCESSORIESOne CeCo R-80 full wave rectifier.One CeCo M26 type amplifier tube.Two 71A type amplifier tubes or CeCo

type J.

the two push-pull tubes are much alike.For practical purposes any two -71A tubescan be considered alike. Hence even ifno other precautions had been taken toprevent hum and distortion as a result ofthe use of R4, the last stage will intro-duce no appreciable amount of them.

The absence of stopping condensers inseries with the loudspeaker and the useof high inductance chokes (Ch) also helpto reduce to the vanishing point the badeffects of R4. Only pure DC flowsthrough R4 as far as the last tubes areconcerned.

But the plate current of the -26 tubealso flows through R4,, and since thereis nothing to balance out the effects ofthis it is possible that hum and distortionmight creep in at this point. Let us seeabout that.

Residual CurrentBy virtue of the size and special con-

nection of condensers C3 and C7 relativeto the grid bias resistor R4, practicallynone of the AC current from the plateof the -26 tube can get into R4. The by-pass condensers C5 and C6 further pre-vent any of the AC from flowing throughR4. Of course the by-pass condensersalso prevent the residual current from thelast two tubes from getting into R4,that is, the AC current which is due tothe lack of absolute equality of -71A tubes.

Any residual current from the first

tube through R4 cannot act as an inputto the push-pull stage as the effect is bal-anced out by the push-pull system.

Neither can any of the hum from theeliminator enter the signal in any appre-ciable amounts. This is due to the spe-cial connections employed in the elimi-nator, to the push-pull stage, and to theadequate by-passing that has been pro-vided for.

The fourth condition calls for steadyand dependable power supply with an ade-quate ripple filter. A thermionic rectifiertube of the -80 type is satisfactory. Asit is a full wave rectifier the hum will beof 120 cycles per second and will be rela-tively easy to filter.

Two choke coils Ll and L2 in serieswith the line prevent any of the ripplefrom circulating in the main circuit, andtwo by-pass condensers Cl and C2 pro-vide paths for the ripple currents to cir-culate without going through the outputresistances.

The New WayNote that CI and C2 are connected

across the entire line whereas the remain-ing condensers are connected across onlyportions. The method of connection isthe same as described by J. E. Andersonin RADIO WORLD Jan. 21, and which is de-signed to provide a power supply andpower amplifier with a minimum of humand the least possible signal distortion.

Cl and C2 should be 600 volt conden-sers and each should have a capacity ofnot less than 2 mfd. and preferably 4mfd. C3 can be 400 or 300 volt conden-ser since the normal voltage across itwill not be more than 180. Its capacitymay be either 4 or 8 mfd. Ordinarily alarge condenser would be recommended atthis point but due to the fact that itserves mainly a push-pull stage the 4mfd. size may be used.

C7 is an important condenser in thiscircuit in that it prevents AC from. the-26 tube from entering R4 and thuscause distortion. The voltage across itwill not be greater than 135 volts andtherefore a 200 volt condenser may beused. Its capacity should preferably be8 mfd. or more.

Another Important CapacityPerhaps the most important condenser

in the filter system is C4. It steadiesthe detector tube plate supply and thusprevents any small ripples in the platevoltage from entering the detector andmodulating with the signal. Certainly thiscondenser should be an 8 mfd. Since it isconnected across a 45 volt source ofvoltage it need not be designed for morethan 100 and 200 volts.

C5 may be a duplicate of C4. It servesto by-pass R4 and thus to minimize humand distortion. C6 by-passes that portionof R4 which gives bias to the -26 tube.It may well be combined with C.5.

The resistor strip R1, R2 and R3 con-nected across the filter output providesthree different voltages, 45, 135 and 180volts. These not only provide the re-quirements of the power tubes and thefirst audio stage, but also the voltagesfor the radio frequency tubes and thedetector in the receiver.

Two separate transformers are used toprovide the required voltages. PT1 hastwo secondaries both of which are mid -tapped. One is of 5 volts and heats thefilament of the rectifier tube. The otheris a high voltage winding and it suppliesthe current to be rectified, The secondtransformer has three secondary wind-ings, .5, 21/2 and 11/2 volts, though the21/2 volt winding is not shown on thedrawing. The 21a volt winding can beused for heating the cathode of a -27tube.

He Wields Wide InfluenceEDITOR RADIO WORLD:

I am a professional set builder.As may be assumed, I move a lot of

parts in the course of a year, and these Iorder from regular distributors. My ownopinion of any new or other circuit forhome construction has some effect on thenumber of such circuits that will be builtby persons who have confidence in my judg-ment. Also, of course, it has everythingto do with my own adoption or rejectionof the circuit for customers' use. I tryout nearly all circuits as they are publishedin radio magazines, and have become espe-cially familiar with those which I like. Iknow what helps to make a circuit success-ful, what helps therefore to sell parts formanufacturers. and I sometimes wish thatsome manufacturers would follow my ad-vice and thereby sell more parts.

The time may not be far distant wheneven professional set builders will be ableto adopt time payment methods, because ofthe interest of finance corporations in thisgrowing and solid branch of the radio busi-ness. Indeed one of my good friends, LeoFenway, has adopted it for the corporationof which he is president, and is blazing thepath. It is quite possible, I realize, to de-vise a plan whereby time payments wouldprevail, and without extra cost to the cus-tomer, because if he will pay fair prices forparts and equipment, and there is enoughturnover, the credit extension cost can beabsorbed by the business. But the turnoverin my particular business is not great enough.Fenway's business is much, much larger,and I believe his plan will work.

J. C. FOSSET,Nyack, N. Y.


Why an Electro- DynamicL./9,57- /70.0/0TUBE -//2 OR 7/

- /77" 5- 57'

L /9,5 T /910/0TUBE - 2/0

/9- /9-/-

L/257- AL/P/0TUBE - 2/0

(B)

44 /27fcl.

30 TO /00h'E/YR/E5

FIG. 1(c)

OVi

A. THIS SHOWS HOW AN ELECTRO-DYNAMIC REPRODUCER MAYBE CONNECTED TO THE OUTPUT OF A 112 OR A -71 TUBE. THE CON-DENSER Cl IS USED TO ELIMINATE TUBE AND BATTERY NOISES.

B. WHEN A -10 TUBE IS USED WITH HIGH VOLTAGE IT IS PREFER.ABLE TO INTERPOSE A 1 TO I TRANSFORMER BETWEEN THE SPEAK-

ER AND THE TUBE.C. OR THE SPEAKER CAN BE PROTECTED BY THE USE OF A SERIES

CONDENSER AND A CHOKE COIL AS SHOWN HERE.

By Billy HondurasTHE power of audio frequency ampli-

fiers has been increased greatly dur-ing the last year. Tubes to handle highervoltages and greater plate currents arepopular and devices have been developedto supply the increased power.

Along with this development, amplifiercoupling devices have been improved sothat all frequencies in the audible bandare amplified with remarkable fidelity andimpartiality. The improvement has beengreatest at the bass end of the scale. Thelower musical notes now come throughwith amplitudes comparable to the ampli-tude of the original, and in the same re-lationship to the amplitudes of the highernotes. Realism in a startling degree is theresult. The reproduction now sounds likethe original and no draughts on the imag-

ination are necessary to convince thecritical ear that this is so.

Blasting OccursBut now and then on the lower notes

the reproducer is overworked. The ordi-nary loudspeaker can swing only a cer-tain distance before the armature strikesagainst the pole pieces. When that oc-curs it is said the speaker is blasting.

The exact sound of this blasting de-pends on the frequency at which it oc-curs, but usually it can be described as abuzz. It is most unpleasant, not per se,but because it happens at important pas-sages in the music or speech.

One remedy for blasting is obviously toturn down the volume to a point wherethe loudspeaker used is able to handle the

N0600000000OG

~-A5IRON

5000660060000

N

(8)FIG. 2

A.-THIS SHOWS A CROSS SECTIONOF ARMATURE AND POLE PIECESOF AN ELECTRO-DYNAMIC SPEAK-ER, ILLUSTRATING THE FREEDOMOF THE ARMATURE TO MOVE AXI-ALLY WITHOUT DANGER OF

STRIKING ANYTHING.B._- THIS SKETCH ILLUSTRATESTHE PRINCIPLE OF MANY PER-MANENT MAGNET TYPE OF LOUD-SPEAKER UNITS AND IT SHOWSHOW THE POLE PIECE PREVENTSA WIDE SWING OF THE ARMA-TURE AND HENCE THE SOURCE OF

BLASTING ON LOUD VOLUMES.

signal without any buzzing where thereshould be only true tone emphasis. Butif that is done there is no object of havinga power amplifier. It is just a waste ofequipment and of power.

Another remedy is to remove any amplifi-cation peaks from the reproduced signal.Of course there are no such peaks of ap-preciable altitude in the output of the bestamplifiers, but loudspeakers are not al-ways used with the very best amplifiers.This removal can usually be accomplishedwith by-pass condensers placed across thesource of plate voltage or the source ofgrid voltage. They must be very large tobe of much effect, say 8 mfd. or more.

Stop Those BlastsAnother method of avoiding blasting is

to separate the AC from the DC in theoutput of the power tube and use only theAC in the reproducer. This can be donewith an output transformer as is shownin Fig 1B. This transformer, having aratio of 1:1, has no other object than tokeep the DC component of the plate cur-rent out of the speaker winding. Thisprotects the speaker winding against ex-cessive heating from the DC, yet the.speaker gets all the AC in the output.The separation also eliminates the unbal-ance which the direct current introducesinto the speaker, and hence it enables thespeaker to handle greater power beforeblasting occurs.

Still another way is shown in Fig. 1C.The speaker winding is connected in series


Speaker Prevents Blastingwith a condenser and then the combina-tion is connected across a choke coil offrom 30 to 100 henrys inductance. Thishas the same effect as the transformer.

When blasting occurs on the high notes,as it sometimes does, this may be rem-edied by connecting a condenser acrossthe speaker winding, as has been done inall three cases in Fig. L The condensermay have as high a value as .01 mfd., butit is preferable to use smaller values whenthey are effective. The larger by-passcondensers have the effect of cuttingout the higher audio frequencies; andmany designers deliberately put con-densers of more than .01 mfd. across thespeaker to eliminate background and bat-tery noises. But this impairs the repro-duction of speech perceptibly in that ar-ticulation becomes poor.

The Electro-Dynamic PrincipleThe best way of preventing blasting on

the low notes is to replace the repro-ducer with one that is able to handlethe requisite power and amplitudes. Aspeaker designed to handle high power onlow notes must have a wide clearance be-tween the armature and the pole piece,so that the armature can swing widelywithout striking.

But in the ordinary type of loudspeakerthe sensitivity is greatly reduced bywidening the possible swing. Hence inpractical loudspeakers of this type it isnecessary to compromise between sensi-tivity and volume.

Therefore little will be gained by re-placing the old speaker unless a type isfound in which the pole pieces do not puta limitation on the swing of the arma-ture.

Such a type is found in the Magnavoxeleotro-dynamic reproducer. The possiblemotion is practically unlimited, and in itthere is no necessity of compromising be-tween volume and sensitivity. The unit isultra -sensitive and it can handle enormousvolumes without any danger of blasting.

Fig. 2 illustrates the difference betweenthe two types and shows clearly why theelectro-dynamic is far superior. In Fig.2A is shown a cross section of the electro-dynamic speaker. The small shaded cir-cles labeled A represent the turns in asmall coil which constitutes the armature.This coil is placed in an annular gap ina specially shaped electromagnet. It hasa central core which is one of the polesin the electro-magnet. In the figure thisis marked as the south pole. The northpole of the electro-magnet surrounds thearmature coil and it is marked NN.

An Exclusive VirtueThe turns of the armature coil move

axially in the strong magnetic field estab-lished by the magnet. The force on thecoil is the same no matter where thecoil may be, within practical limits, andtherefore the sensitivity of the unit doesnot depend on the position of the arma-ture. No other unit has this virtue.

The sensitivity does depend on the in-tensity of the magnetic field across theair gap in which the armature coil is mov-ing. That in turn depends on the magnet-izing coil used (not shown) and on thedistance across the gap. If the movingcoil is small and mounted accurately thelength of the airgap can be made verysmall and still leave the armature per-fectly free to move. How far the arma-ture can move axially without strikingdepends more on the external require-ments of construction than on any re-quirements in the unit itself.

It is different with the ordinary type ofloudspeaker motor. Fig. 2B shows a typi-

FIG. 3AN ELECTRO-DYNAMIC REPRO-DUCER CONNECTED TO THE PLATECIRCUIT OF A POWER TUBETHROUGH THE MEDIUM OF ASERIES CONDENSER AND A CHOKECOIL. THE FIELD COIL OF THEDRIVING UNIT IS CONNECTED SOTHAT IT SERVES AS ONE OF THECHOKE COILS IN THE FILTER CIR-

CUIT IN THE ELIMINATOR.

cal construction. The armature is markeda, the permanent magnet M, the arma-ture winding W and the air gap g. Thesmaller g is the more sensitive this unitis, but the sooner will the armature hitthe pole carrying the coil W. And whenit strikes there is a buzz. If the gap gbe made large enough to handle the largeamplitudes met in high power, low notereproduction, the unit will be so insensi-tive that a great deal of power is re-quired to give any response at all.

While the construction shown in Fig.2B represents one type of speaker, thepreceding objections apply to all havinga permanent magnet and a moving ironarmature. It includes the balanced types.

Another AdvantageThe electro-dynamic reproducer has

one other advantage above all others. It

has a high inductance field coil whichmaintains the steady magnetic flux acrossthe armature gap. The coil can be usedas one of the choke coils in a filter cir-cuit, provided it is proportioned to workon suitable voltages and currents. Thismethod of use is shown in Fig. 3. Whilethe field coil is shown as part of the filtercircuit it is actually built into the speakerlabeled cone. It carries all the direct cur-rent delivered by the B battery eliminator.There is supposed to be another coil inthe filter but this is not shown. The fieldcoil is put in second place because in thatposition there is less current fluctuation,and it is desirable to have a steady fieldfor the loudspeaker.

The speaker and its series condenserare put across an inductance coil of from30 to 100 henrys in order to force mostof the AC output of the last tube throughthe speaker. The series condenser shouldbe from 4 to 12 mfd. to facilitate the pas-sage of the low notes through the speakercircuit.

When the output of a high power andhigh quality audio frequency amplifier isput into an electro-dynamic reproducerlike the Magnavox R-4 and R-5, there isno blasting whatsoever, and the quality isas realistic as the transmission permits.

Melhuish New Head ofN.E.M.A. Radio Work

H. T. Melhuish, former manager ofsales administration of the Radio Corpo-ration of America, has joined the staffof the National Electrical ManufacturersAssociation as director of the Radio Di-vision.

Prior to joining the R. C. A., Mr. Mel-huish practiced law in Pittsburgh, Pa.for five years, leaving his law practiceto enter business in New York.

Custom -Set BuildersCUSTOM-BUILT SET EDITOR:

Reading your magazine suggested thatI write a few words of encouragementto the parts manufacturers.

I believe the custom set builder is hereto stay, and no amount of commercialcompetition can dislodge him from hisrightful field. No commercial manufact-urer making a generalized, compromiseset can give the value the custom -setbuilder can in a special-purpose receiver.

For instance, down here in Floridathere is a demand for a reasonably pricedset that will consistently tune in theWEAF chain programs with the highestquality reproduction and ample volume

I built such a set at a wholesale costof about $100, not including tubes and bat-teries. What manufacturer could 'dupli-cate the special features listed below forthis sum? Here is one of my standardlayouts:

Choice of several very excellent repro-ducers in cabinet, with a concert grandor other high grade unit. RCA Unirectronor any other approved 210 power amplifieror 171 type push-pull amplifier. Any goodcircuit, three tuber containing one stageof high frequency and regenerative de-tector, such as the Diamond of the Airwith only one audio circuit.

This combination in the hands of a rea-sonably expert tuner will do anything anyone can expect a set to do, with wonder-ful quality and volume, at a reasonableprice. For those willing to pay more, Iadd a conventional three circuit tuner

with inductances adjusted to receiveWGY's short wave rebroadcasts, placingthis side -by -side with the broadcast re-ceiver on the top of the air column cabi-net. This combination will bring in chainprograms every day in the year from thispoint.

If the customer will stand still more, Iadd a light motor and turntable and elec-tric pick-up.

What manufacturer is likely to put meout of business for the next few years?

Yet every single part that goes in mysets is of the highest possible quality.and may be the highest priced item inits class.

My last set contained genuine Brown-ing -Drake coils, Hammarlund tuning as-sembly and condensers, Vedee metal cabi-net, Ferranti transformers, Silver -Mar-shall Unipac, Bremer -Tully short wavecoils, a well -performing u n it, withfinest quality, standard parts built toperform. There is no sales or promotionexpense attached to my overhead, noservice charges, nor returned merchandiseloss. The reproduction is of the highestpossible quality at the present state ofthe art, selectivity is adequate for localconditions, the sets are highly sensitiveif properly operated, both on broadcastand short waves, and the cost is reason-able. I have no trouble finding buyers.

ARTHUR SMITH,President, Arthur Smith Music Co.

1107 Franklin St., Tampa, Fla.


mANY experimenters like resistancecoupled audio frequency amplifica-

tion because of the excellent quality ob-tainable therefrom, but certain problemsare introduced in the up-to-the-minuteapplication of this system that bafflesthem. Frequency distortion and unevenamplification, besides self -oscillationand quantitative values of constants arepuzzling, but all soluble.

The predominating difficulty is self -os-cillation, because with the recent growthof B supplies in popular favor the chiefcause of such self -oscillation has been in-troduced.

When a B supply (eliminator) is usedin a direct coupled circuit, such as re-sistance, impedance, double impedance orother variant circuit, the audio amplifierand its plate supply source constitute aunited circuit in which there is much com-mon resistance. This is most likely to bea source of coupling, and if the phasesare right the coupling introduces toomuch self -oscillation.

A little is a benefit.It is the same thing, but it ap-

pears in different and variously audibleclothes. So new is this condition that notonly is the category of remedies still in-complete but the terminology for the ills,not to mention the remedies, has yet to beconstituted. Only two expressions standout-motorboating and peanut whistle.

All One LineThe total power supply and biasing

system for any circuit are one continu-ous branching line, even if batteries areused. Assuming batteries, you start withthe most negative C, come to minus A,then to positive- A, (B minus connectedto A minus or A plus), and then reachthe successive B voltages. Hence youcan trace a line from the grid return ofany tube in any radio or audio circuitand simply move up the voltage scale astep at a time. There is union among tubecircuits, and it is said that in union thereis strength. But it may be destructivestrength, and that smacks unwhole-somely of weakness, so one must neces-sarily, address himself to devising theremedies.

Any oscillating circuit can be tamed,whether it oscillates at audio or radiofrequencies. You have only three thingsfrom which to write the prescription-inductance, capacity, resistance-and youmay combine them in any of thousandsof ways, or use one or two and omit theothers.

Effect of Different CapacitiesIf you encounter motorboating you may

not know it, for its frequency will varyfrom, say, 1/4 cycle to 50 cycles, and ulti-mately become a "peanut whistle" at2,000 cycles. If it reaches high frequen-cies the remedy becomes simpler. In fact,the rule of the higher the frequency thesimpler the solution is pretty sound, sincea condenser of suitable capacity, placedacross the line, would be the remedy.

If the frequency is high enough thiscondenser need not be inordinately large,not more than .006 mfd., put across thespeaker terminals. Maybe up to .02 willhave to be used, but that would be unfor-tunate, since the higher broadcast fre-quencies would be by-passed in thisfashion. The remedy has been applied foryears in elimination of hissing strays,forms of tube noises and other high audiofrequency forms of interference, with.006 mfd.

Indeed, although the remedy of conden-ser -across -the -line is a good one only for

uality Factors inhigher frequency interference, whetheroscillatory or merely parasitic, it is truealso that a condenser will cure everyform of motorboating, and it need beplaced only across any grid leak in theaudio channel, or across any grid choke,if impedances are used.

But in such a case the remedy is worsethan, the ailment, for the high notes arecompletely cut off, by even .1 mfd., andif much larger capacity is used, the mid-dle frequency scale is invaded. Naturally,as motorboating of any frequency is os-cillatory in origin, a condenser of suitablecapacity will remove the oscillation, andif the capacity is large enough will godown far enough to remove all the modu-lation, so you get no reception whatever.The condenser by-passes all of the signal.

Where It Is ConstructiveNevertheless, equipped with a variety

of capacities of fixed condensers, any onedesiring to stop low frequency oscillation-the only kind to which the word "motor -boating" is applied in common technicalspeech-he may connect in parallel withany audio leak or plate coupling resistora condenser of the smallest capacity thatwill perform the estoppel. At least thetrouble will be cured.

Low note suppression is no evil at allcompared with a four cycle oscillationthat sounds like the outboard motor of arowless rowboat. Moreover, more thaneighty per cent. of all radio sets arelow -note suppressors of a high order, ifnot outright discriminators against allreproduction below 150 cycles, because ofabuse of the biasing resistor, inclusion oftoo small value of audio leaks and stop-ping condensers, overbiased grids and,most particularly, the coupling and speakerused. So the condenser across the lineto stop a receiver from put -putting likea motorboat engine is not only pardon-able but orthodox and constructive.

While in certain regions of the higheraudio frequencies self -oscillation is easiestto cure without detriment to quality, inthe lower regions the difficulty not onlyis greater but easy injury may be done toan otherwise highly acceptable amplifier.

Slow MotorboatingTake the slowest form of motorboating

one is likely to notice-and he may haveto be truly observant to notice it at all-the motorboating in the fractional cyclefrequency realm. Assume the frequencyto be one -quarter. That means that onecycle takes four seconds for completion.If the degree or severity of the motor -boating is not unduly large this form oftrouble may pass unnoticed by the ear be-cause all it does is to vary the intensityof the signal in such gradual and limitedmanner as to be a sly evader of atten-tion.

While this self -oscillation is takingplace some distortion is being intro-duced, but it is not sustained, since theplate current change (DC component)is accomplished over a period of fourseconds, during which the current value iswithin the distortionless swing for longerduration than it is out of that wholesomearea, hence as the fidelity is a major frac-tion the distortion often passes unnoticedby the ear. But the slow motorboatingmay always be read on a DC milliammeter(0-50 ma) connected in series with thechoke coil in the last audio tube (Ch inFig. 1), or, if there is no choke or othersuch device there, in series with the speak-er itself.

You can determine the frequency of theslow motorboating by looking at the sec -

AudioBy Herman Bernard

and hand of your watch and observingthe swing of the needle at the same time.

How to Determine FrequencyTake the mean plate current reading

and count how long it takes the needleto swing to one side, then to the otherside, then back again to the mean point.If it takes four seconds, the frequency isone -quarter of a cycle per second. Inother and quicker forms of motorboatingthe needle oscillates so fast you can notcount the frequency. Also, when the fre-quency gets considerably farther up (intothe audible scale) the needle stops wob-bling and the motorboating is just sound-so fast in frequency the needle, 'sluggishthing, can not follow. So it is, indeed, withthe plate current in all receivers that arebringing in a station-the DC milliam-meter does not follow the modulation atall, except to kick slightly one way or theother on too strong a note for the char-acteristic of the tube circuit as consti-tuted. If the needle kicks up (towardhigher reading), decrease the negativegrid bias; if it kicks down, increase thenegative grid bias; that is the rule, al-though not an infallible one, since thetrouble may necessitate a different rem-edy than mere bias alteration will afford.

Slow motorboating is something thatdeserves a great deal of consideration, ex-perimentation and analysis, and will re-ceive more attention in time to come.One reason why it has been almost ig-nored-except in the pages of this publi-cation-is that the world is not generallyaware of its presence or existence, since itis elusive, a sort of trouble that must behunted, and most persons are content toinvestigate only such troubles as impedetheir personal enjoyment.

The simplest ready remedy I have foundfor correction of the evil of slow motor -boating is to use a low mu tube in theoutput, e.g., a CeCo type 3, CX-371A orUX-171A or Armor 571, and to increasethe intermediate grid bias. If the radioamplifier is biased from the same sourcethe variation should include this part ofthe circuit, too. But this suggestion isnot a panacea; rather an ameliorant.

Bias Through ResistorMuch more likely these days is that

the bias is obtained through the voltagedrop in a resistor. This method is dia-grammed in Fig. 1, where R7 is the re-sistor, a 2,000 -ohm Centralab fourthterminal potentiometer. B minus is mostnegative and is used as the connectingpoint for the grid return of the final audiotube, that being the desired most -nega-tive voltage. The plate current flowingfrom A minus through R7 produces avoltage drop across the resistor, so bymoving the upper arm, to which pointsrequiring lesser C voltage are connected,one may obtain the desired voltages. Inthe diagram two points, lower right, aremarked A and B, and if these are inter-connected no vdltage will be wasted,since less than the total of 2,000 ohms


Resistance CoupledAmplifiers

Managing Editor,Associate, Institute of Radio Engineers

will be required, and by this method youdrop only what you need.

Unless the by-pass condenser be used,and its capacity be 4 mfd. or larger, and8 to 10 mfd. may well be used, low notesuppression, particularly below 150 cycles,will be almost complete. Use I mfd. andthere will be small improvement, 2 mfd.fair improvement, 4 mfd. good improve-ment, 8 mfd. excellent improvement-andhere you may add 2 mfd. to play doublysafe. This single condenser in a circuitusing the biasing resistor method will domore to improve the quality of any audio

great gain in low note restoration in-cludes the 60 cycles of the DC line and thesecond harmonic (120 cycles). If the humgrows too strong the condenser is vindi-cated and the B supply is corrected. Add4 mfd. to the last filter capacity.

Amplification itself has much to dowith the construction of a stable amplifierof any sort. Any radio or audio circuitcan and will oscillate if the amplificationis great enough. That was the principalreason for suggesting a low mu outputtube for any resistance, impedance ordouble impedance audio channel. The

the efficiency of the amplifier. The plateresistors usually will be on the order of100,000 ohms (.1 meg.), although 250,000ohms is the usual value recommended forhigh mu tubes.

There is no use adopting high mu tubesunless the volume from type A tubes isnot great enough, for the resistancecoupled amplifier has a definite volumelimit before motorboating begins, andhigh mu tubes help to bring about motor -boating by reason of the high amplifica-tion. You will read that 30 mu tubes giveactual amplification of 20, when 250,000ohm plate resistor is used at 180 volts.

Frequency DifferenceBut any cr-cuit will oscillate if the am-

plification is high enough, and in thecase of high mu tubes a resistance coupledamplifier may, and usually does, oscillateeven if only two stages are used, when theamplification is not high enough. Theoscillation is due to the B supply, thecharacteristics of the tube and the adventi-tious coupling in the common imped-ances. The only difference between themotorboating with two stages and three

FIG. 1

A RESISTANCE COUPLED AUDIO AMPLIFIER.

amplifier-including transformer coupled-than any other single thing, even in-cluding the substitution of a good fre-quency characteristic speaker for a poorone.

You Can Hear Difference EasilyWhen the capacities are increased as

suggested you can actually hear the dif-ference-and if you are musically trainedyou can hear and distinguish the instru-ments in an orchestra that were notbrought out or indentifiable under theprevious conditions. That is one outstand-ing reason why a man who builds his owncircuit can reproduce ever so much betterquality on his receiver. He knows that heis spending his money to put a vital con-denser across a biasing resistor-a con-denser likely omitted from all quantityproduction specimens except in fancy -priced installations. Yet if you are buy-ing tone values you can not get them inany batteryless or "electric" set thatomits the 8 to 10 mid. across the biasingresistor, although it may well be thatthe final condenser across the B supplyline may be made to include the biasingresistor. Also you quickly find out with8 mfd. across R7 how poorly or well isthe filtering in your B supply, since the

output signal intensity is less, but it isall that it need be, and more, especiallywith one B plus serving detector andfirst and second audio. This is desirableas tending to stabilize the circuit, reduc-ing the network of impedances thatcouple the components in the amplifierand contribute to oscillation troubles.

Effect of BiasNo doubt the bias adjustment for in-

termediate grid voltages (C minus in Fig.1, as distinguished from CC minus), helpsget rid of slow motorboating for thesame reason: the higher bias reduces theamplification. Tube operation may thusbe slightly off the straight portion of theplate current -grid voltage curve, but thatis entirely tolerable, as also is the identi-ty of grid voltages for the first and sec-ond audio tubes with the RF amplifiergrid voltage, since about 3 volts will suf-fice, if the plate voltage is around 100.

The extra bias also makes the imped-ance of each such grid circuit a smallerpercentage of the common impedance.

A poor way to reduce the amplificationis to use low values of grid leaks in theaudio channel as this tends to cut off lownotes, unless IC is 1 mfd. or so, whereastoo small value of plate resistor injures

stages is in the frequency, for in a two -stage amplifier it is faster.

Remove the detector tube ahead of anyoperating audio circuit. If there is nomotorboating then, most likely none willbe encountered at all. By this test a stageof resistance coupled audio followed by atransformer coupled stage, comprising acomplete audio amplifier, does not motor-boat, and indeed in laboratory experi-ments it was impossible to make it motor-boat except by forcing a wrong connec-tion whereby no broacast signals could beheard anyhow.

In line with the reduction of amplifica-tion and the alteration of impedance val-ues so as to minimize coupling, the vari-able resistor, put in series with the plateresistor in the first audio stage (R8 inseries with R3) often will completely stopmedium motorboating. But the higherfrequencies suffer reduction of amplifica-tion more than do the low ones, notice-able when the esses and zees become lesspronounced.

Remedy for ChatteringThe plate coupling resistor in the de-

tector tube is important. If a specialdetector tube of the gaseous variety is

(Continued on page 201


FIGHT or No Fight ?Two Writers Take Issue on WhetherRing Encounters Should Be Broadcast

By Tim TurkeyTHE door bell rang one evening while

was enjoying a classical programplayed by an orchestra. The sound ofthat bell crashed in on the music bothelectrically and acoustically. It was adiscordant crash and it jerked me out ofa peaceful reverie.

A stranger was at the door. I knewthat, for none other would ring the hallbell and remain below until invited up.There was a promise of a different eve-ning. It was nine o'clock when the bellrang, but that had no significance at thetime.

The stranger came up, and he turnedout to be no stranger at all, but an oldfriend 'disguised by the changes that'years effect.

"Well, Bill, it's good to see you againafter all these years," said I after my oldfriend had been seated. "You certainlyhave prospered physically," I added no-ticing that the anemic boy had grownup into a man of heavyweight champion-ship calibre.

"Yes, Tim, I have prospered in everyway except in love. I never got to firstbase in that game. But my failure hasnot worried me any, for I have foundcompensation in other forms of strife. Iam partial to fights in which a man hasat least an even break."

My old friend was a humorist, a traitby which I knew him well; but his phi-losophy dealt with love and strife, oneof which is strange to me. As he talkedhe gradually left the romantic and turnedmore to pugilism. He dragged pugilistafter pugilist into the conversation, noneof whom had any part in our commonpast. By this fact I should have knownthat he had some other purpose for com-ing than to review the past. I did noteven suspect his motive.

His Real MotiveWhile my friend was talking pugilism

my radio set was reproducing softly themusic of an orchestra. It was pleasingmusic yet it became apparent to me thatmy visitor did not enjoy it. I asked himwhether he liked that type of music.

"Yes, it's good stuff all right," he ad-mitted out of courtesy, "but you knowthere is a championship fight on tonight,and I thought perhaps they would broad-cast it."

"Sure, some station will broadcast it,and if it is within range of this re-ceiver we'll listen to it," I said, welcomingthe chance to listen to a good fight withsomebody.

Together we scanned the daily radioprograms to find what station was broad-casting the fight. We located it underWABC, at 9 o'clock. Fifteen or twentyminutes had passed since the first gongand some of the preliminaries. Whenthe signal from WABC was first tunedin that night the announcer was tellingabout the semi-final bout. We got someof the blow-by-blow description of thisfight, and it was a real treat. I had nottuned in a more interesting radio pro-gram for a long time.

The Main BoutWe would have been satisfied, or at least

I would, if the pugilistic broadcast had

ended at the conclusion of the corkingsemi-final bout. I had had my money'sworth and would gladly have gone backto one of the repeats of the weekly fea-tures. It was not necessary that night.There was something more interestingand exhilarating in store for us. Wewere to be the recipients of the samemental kick that the ringsiders received;we were to be jarred by the same emo-tional wallop that is so dear to the in-veterate fight fan.

The main bout had no sooner startedthan the reproducer began to count oneman out. At the stroke of nine thespeaker eased the tension a bit by an-nouncing that the recumbent championhad risen. While the announcer chat-tered about the fight my friend grew en-thusiastic about the opponent.

"I saw him fight in Youngstown," hesaid, "and believe me, he is a fightingfool." He got no further for the speakerwas counting again, ". . . six, seven,eight, nine." The ten did not come; in-stead of that the announcer said that thefighter who was down before was upagain. But the "fighting fool" hadscored a second knock -down in the firstround. My friend found relief from theexcitement of the moment by joining inthe cheering that the receiver broughtfrom Madison Square Garden.

White Hot ExpectancyThe activity in the first round of that

fight created an intense state of ex-pectancy in the minds of the listeners,and this did not end until the fighter whohad been down twice had been declaredthe winner on points. That expectancyhelped to keep interest at white heatthroughout the fifteen rounds, but therewas enough activity in every round tokeep hundreds of thousands of listenersglued to the loudspeaker until the lastannouncement had been made.

I am glad my old friend visited methat night. Without him I would havespent an average radio evening. Insteadwe sat in on an exciting contest betweentwo young gladiators held in the great-est arena, in which two healthy menwillingly fought each other and with anequal chance to win.

The game may be brutal and degrading.Be that as it may. The fact is that itappeals to every red-blooded man. Allappreciate any fair contest in which thecontestants take part willingly and inwhich each of the fighters has an equalchance. The game appeals as strongly tothe reformer as to the men who attendthe fights openly. But the reformer feelsit his public duty to condemn the sportin which the adversary is real and tangi-ble.

From now on I am a radio fight fan.I get more kick out of it than I do outof a great symphony; I sense more dramain it than I do in a modern production ofHamlet; I hear more noise in it than I doin a brass band; I hear more dischord init than I do in modern jazz and in rhap-sodies; I love the element of chance in it.T am delighted to know that it is the otherfellow's nose that gets caved in and notmine, that his ears get shriveled up andnot mine, that lie takes the blows underhis heart and not I.

The fight game is all right with me.

By Cuthbert Spencer WellsMI:RELY for comparative purposes

I listened in recently to the broad-casting of a description of a pugilisticencounter. I have always been opposedto this form of sport, but was willing toacquire some new data and indeed changemy mind if any reason presented itself,but none did.

I am aware that large numbers of per-sons enjoy listening into the descriptionof a ring contest and that considerableopposition develops when any suggestionof curtailment or prohibition of ring activ-ities is suggested. Education can changethis state of mind, since education focusesour minds and tastes on wholesome things.

My principal objection to pugilisticfights is their brutality, and I believe any-thing even suggesting brutality shouldbe kept off the air. Bull fights are il-legal in this country and I assume thatthe Government is as much interestedin a pugilist as in a matador, a toreadoror a bull.

Fighting DangerousThe clash of fists that entices so many

is dangerous to the human mind andbody, since the fighters suffer injuriousblows, the sounds of which come withthwacking realism right into our homes.Although any one may tune out such aprogram, so many tune it in that thewomen and older children of the house-hold are subjected to the doubtful "enter-tainment."

Hand-to-hand combat, unfortunately,still has an appeal to the "red blood" ofa man, but this is the blood inherited fromprimitive life and does not representthe real blood of the race, which has beenrefined by centuries of education and re-ligion.

The second greatest accelerant offight popularity is the commercialism ofthe sport-the great fortunes that changehands with titles-and so fine an instru-mentality as radio should take no partin this commercialization of a brutaliz-ing sport.

Not for the Love of ItFighters do not fight for the love of

fighting but for the money and glorythat is in it. Take away the big moneyand the glory still has some appeal tothem, but it is much less than manysuppose. Hence all who listen to or at-tend fights contribute toward the com-mercialization of physical suffering.

I do not propose any radical move atthis time, but it behooves the public toconsider the bad side of pugilism and toact toward it in that courageous mannerthat the situation requires. Personally, Ishall not listen in to another fight broad-cast. I hope that many converts willfollow my course and that the better ele-ment of the community will take up thecudgels in behalf of real manhood andwomanhood.

Suggests Mothers DecideThe mothers of the land. if given a

chance to vote on pugilism or itsbroadcasting, probably would side withme. Therefore I ask every radio listenerwho does tune in fights, if God still blesseshim with a mother's love, to ask motherwhat she thinks of the subject, and beguided accordingly.


Flashlight Real Needto Operators of CircuitsOften a radio fan wants to take a pee&

into the cells of his storage battery toascertain whether the cells are gassingor whether they need more distilledwater. Light on this operation is alwaysneeded and there is a great temptation tostrike a match to furnish it. Striking amatch there is a risky procedure. It mightlead to an explosion with painful andcostly consequences.

Now and then a radio fan must go outon a dark night and inspect his antennaand ground equipment. He needs light.Without the light he cannot inspect andwithout light he might stub his toe withpainful results. Striking a match willavail him little if the night is wet andwindy. And when is it not windy enoughto blow out a match?

Occasionally a radio fan finds it neces-sary to explore the inside of his radioset. And he can't do it without a light.He cannot very well employ a flame suchas that of a match or a candle. He needsanother light.

The Need of a Portable LightIn all these and in countless other cases

the radio fan needs a portable light whichis dependable, flameless, and sane. Aflashlight meets these conditions, a lightwhich operates with electricity. Just pressa button and point the light toward theobject that needs illumination, and theobject stands out in plain view.

A battery flashlight may be used, or apower plant carried in your coat pocket.A power plant in the coat pocket! Whata ridiculous idea! Power plants are lo-cated by the riverside or by the railwayside, and they usually cover many squareblocks. Even the smaller plants developthousands of horsepower of electricalpower. Sure enough, but still you canhave a power plant in your coat pocket,and what is more, you can carry the wholeelectrical distributing system in your pock-et as well.

A prime mover, a dynamo, ,a distributing circuit, and a load are the essentiaelements in a power plant. Size has noth

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What is the prime mover in a pocket -sized power system[ There are twoparts to the prime mover. You are thefirst part and a clock mechanism is thesecond. You yourself are really the fur-nace while the clock is the mechanismwhich converts your heat energy intokinetic energy or energy of rotation. Yousimply wind the clock spring and let thewheels turn.

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J18 RADIO WORLD January 28, 1928

A Comparison of Seven

FIG. 1SIX DIFFERENT ANTENNA ARRANGEMENTS AND METHODS OF COUP-

LING. (A) TUNED ANTENNA WITH A SERIES CONDENSER.(B) TUNED ANTENNA BY DIRECT COUPLING TO THE SECONDARY

CIRCUIT.(C) UNTUNED ANTENNA WITH A PROTECTIVE CONDENSER IN THE

GROUND LEAD.(D) UNTUNED ANTENNA WITH A WAVE TRAP IN THE ANTENNA LEAD.(E) APERIODIC ANTENNA WITH A VARIABLE SERIES RESISTOR FOR

VOLUME CONTROL.(F) APERIODIC ANTENNA WITH A SHUNT VARIABLE RESISTOR FOR

VOLUME CONTROL.(G) APERIODIC ANTENNA WITH VARIABLE COUPLING BETWEEN THE

PRIMARY AND THE SECONDARY.

(Cr-NO you think if I added 50 feet ofwire to my antenna that I would get

greater distance, greater selectivity andbetter tone on my set?"

That is just one of the thousands of.questions asked about antennas.

A good antenna is necessary on anyset. It does not matter what the set maybe nor how many tubes are used in it.But an antenna may be good for one setand no good at all for another.

The antenna must be suitable to the set.A small indoor antenna or a loop may

be all right on a Super -Heterodyne, butsuch an antenna may give poor resultson a three tube set.

The purpose of the antenna is to pickup the signals from. space and transferthem to the amplifying system. The in-tensity of signal picked up by an an-tenna depends on the height of the an-tenna for one thing. The pick-up is di-rectly proportional to the effective heightabove ground. An antenna twice as highas another will pick up just twice as much.

But there are other factors that enterand that affect the amount of the signalthat is transferred from the antenna tothe amplifying system, and some of thesefactors are the capacity, the inductanceand the resistance of the antenna. Thesedepend also on the height of the an-tenna, consequently the effect in the loud-speaker does not always indicate that thepick-up is directly proportional to theheight.

Length of wire deceptiveThe amount of wire used in the an-

tenna is not all important. If 200 feetof wire is strung two feet above theground the pick-up will not be as greatas if 100 feet of wire is erected straightup. But the capacity of the low-lyingantenna is much greater than that of the

vertical wire, even if that wire is 200 feethigh. The inductance of the longer an-tenna is also greater than that of theshorter, as is the resistance. The resis-tance particularly is likely to be great inthe low-lying antenna, due to the prox-imity of the wire to absorbing substances.

The length of the ground wire has agreat deal to do with the effectiveness ofan antenna. If a coil is used for coup-ling .the antenna to the amplifier, that coilshould be placed as close to the groundas possible, for the greatest antenna cur-rent is near the ground. Therefore theground lead should be as short as possible.

The antenna has nothing to do with thetone of the set. If the reproducer deliv-ers the signal as pure and undistorted asthe antenna delivers it to the amplifyingsystem the tone would be practically per-fect, and any deviation from perfectionwould not be the fault of the antenna.

This, however, does not mean that theeffectiveness of the antenna and the qual-ity of the signal are not related in prac-tice. If the antenna is ineffective so thatit is necessary to increase the amplifica-tion to bring the volume up to the de-sired level, many forms of distortion enterwhich would not enter if the antennawere effective.

For example, if the antenna is ineffec-tive it is necessary to tune the circuitsharply, and high selectivity cuts off thehigher audio frequencies. If it is alsonecessary to introduce a good deal of re-generation the higher frequencies are stillfurther reduced in intensity and the out-put becomes boomy.

Also, if it is necessary to increase theamplification in the set to make up forthe deficiencies of the antenna, all tubeand battery noises become relativelygreater.

This all goes to show that the antenna

By PeterContributing

should pick up a strong signal, and there-fore that it should be fairly high.

Broad tuning may resultBut the price of a strong signal may be

extreme broadness of tuning as well asan increase in the amount of interferingnoise. From this point of view, then, itis necessary to limit the effectiveness ofthe antenna. Therefore it is necessary tocompromise and call an antenna goodwhen it picks up a moderately strong sig-nal which does not require excessive am-plification in the receiver.

For ordinary purposes we might pickon an antenna made of 100 feet of wire.As much of this as possible should bevertical. As little of it as possible shouldbe between the set and the ground. Andwhat is left over should be horizontal. Thehorizontal adds a little to the effectiveheight of the antenna so that all of it isnot lost.

Again, the radio wave is not always ver-tical but it tilts forward a bit. The hori-zontal portion of the antenna catches thehorizontal component of the wave.

In Fig. IA the antenna coil is large anda variable condenser is put in series withit. This is an old-timer and used to bea favorite. Condenser C is in series withthe capacity of the antenna itself, so thatthe effective capacity in the primarycircuit is small.

If C is to be used for tuning it mustbe a small condenser, smaller than thecapacity of the antenna. This limits thesize of the condenser to about a .00035mfd. The coil in series with it must alsobe quite large, much larger than coilsordinarily used for tuning. The size can-not be given, for it would be a differentone for every antenna. It will probablylie somewhere between .4 and I millihenry.

If both the antenna circuit and the sec-ondary are tuned it is necessary to makethe coupling between them loose, andthat, in view of the large coils used,means that the coils should be far apart.The correct separation can only be foundby experiment. If the coupling is tooclose, only one of tuned circuits will beeffective and the secondary tuning con-denser might as well be omitted,

Condenser volume controlBut in modern receivers C is more often

used for controlling the volume by throt-tling the antenna current than for tun-ing the circuit. In that case the primarycoil has the ordinary value of from 10to 30 turns and the variable condensercan be an ordinary tuning condenser.

Under these conditions the secondarycircuit is selective and the volume is undercomplete control except for the shortestwaves.

When the antenna in A has a smallprimary coil it is usually spoken of as anaperiodic circuit, but really it has a periodwhich is below the lowest wavelength inthe broadcast band. When a condenseris connected in series the circuit is alsoof the same type but the wavelength isstill shorter.

In Fig. 2B the antenna is connecteddirectly to the top of the tuned circuit,or to the grid itself. In this case the an-tenna capacity is connected in parallelwith the tuning capaciy, as is the resis-tance of the antenna. The coupling be-tween the antenna and the tuned circuit

is very close. The circuit is very broad

Taman- 28, 1928 RADIO WORLD

Antenna Coupling Types.Il O'Rourke

Editor

on account of the close coupling and theresistance which is connected across thetuned circuit. But the signal intensityas transmitted to the amplifier is veryhigh.

The principle objection to this circuit isits limited tuning range. The capacityacross the coil can never be made lessthan the capacity of the antenna, andsince this is considerable, the tuning coilhas to be small if the circuit is to reachthe shorter wavelengths in the broadcastband.

The fact that the capacity in the circuitis relatively large and the inductance isrelatively small lowers the input voltagefor a given pick-up, and thus part of the'signal is sacrificed. But even so, this isa very effective connection when volumeis the main consideration. As not allwavelengths can be tuned in this fashionthe higher ones usually are tuned, thelower ones not, so that the rising charac-teristic of TRF is flattened out somewhat.

When this hook-up is used the requiredselectivity in the circuit must be obtainedin the subsequent tuners.

The arrangement shown in Fig. 1C isessentially the same as that in A, exceptthat the condenser is put in the groundlead and that it is fixed in value. It canbe used for a variety of purposes. If thecircuit is too broad the condenser can beput in with some advantage. In this casethe condenser should have a small value,say about .00025 mfd. if it is to be effectiveat the short and medium waves.

This condenser in the ground lead canbe used also as a protection against shortcircuits in certain cases, particularly whenthe antenna is metallically connected tothe amplifier and when the circuit is con-nected to a direct current power source.For that purpose it may be large and ofhigh voltage rating.

A condenser in the ground lead mayprevent a short-circuit.

Wave Trap Circuit

In Fig. 1D the antenna is of the so-called ap_eriodic type but a parallel tunedcircuit is connected in series with theantenna lead. The values of inductanceand capacity in the trap circuit are notmuch different from the values ordinarilyused in tuned circuits for the broadcastrange. For example a condenser of .0005mfd. capacity and a coil consisting of 40turns of No. 24 double cotton coveredwire on 3 inch tubing can be used.

The object of the parallel tuned circuitin the antenna lead is to trap out thesignals from an interfering station. It re-jects only one station at a time but doesit effectively. The trap circuit is tuned tothe station that is interfering and the sec-ondary circuit containing Cl is tuned tothe desired station. The two tuned cir-cuits are mutually dependent to a cer-tain degree and it is necessary to tuneand retune two or three times before thedesired signal is maximum and the inter-ference is rejected completely.

The circuit in Fig. 1E contains a trulyaperiodic antenna, provided that R is nottoo small. The purpose of the variableresistance R is to control the volume inthe set, which it does by reducing theantenna current as in case A. But in thiscase the reduction is the same for allfrequencies and the present device is

FIG. 2.A CIRCUIT SHOWING A CHAIN OF TUNED CIRCUITS FOR INCREASING.THE SELECTIVITY OF A RECEIVER WHEN THE DETECTOR IS NOT IN-HERENTLY SELECTIVE. RF TRANSFORMERS A'RE USED, WITH PRIM-

ARIES CONNECTED TO PRECEDING SECONDARIES.

therefore a better volume control. Rshould be a variable resistor having amaximum value of 5,000 ohms. The useof this type of volume control does notreduce the selectivity of the secondarytuned circuit but rather has the oppositeeffect. This phenomenon is due to reduc-tion of the radiation resistance.

Fig. 1F shows a variable resistor inshunt with the primary of the inputtransformer. This is a very effective vol-ume control and it operates by detour-ing the antenna current around the prim-ary coil. Its range may be the same asthe series resistor in Fig. lE but it shouldhe so arranged that the shunt circuit canbe opened completely for maximum vol-ume and sensitivity.

Effect on Selectivity

The effect on the selectivity of theshunt resistance R is just opposite to theeffect of the series resistance. It reducesthe selectivity at the same time it de-creases the volume. It also tends to de -tune the secondary circuit. Both of theseeffects are due to putting a partly short-circuited coil in the field of the tuningcoil. The lower the value of R, the loweris the volume and the lower is the selec-tivity.

In case G we have perhaps the near-est approach to the ideal method of con-trolling the transfer of energy from theantenna to the tuned circuit and the am-plifier. It is the old time variocoupler,the primary of which is adjustable in po-sition or in orientation with respect to thesecondary. The coupling between the an-tenna and secondary can be varied' frompractically zero to maximum by meansof this device by simply turning a knob.

The adjustment of the primary of thevariocoupler with respect to the secon-dary has little effect on the tuning of thesecondary or on the selectivity of thecircuit. It simply controls the amountof energy that is transferred from the an-tenna to the amplifier.

The volume control methods shown inFig. 1E, F and G are especially applicableto receivers employing AC heated tubesin which the volume cannot be controlledsatisfactorily with filament rheostats orplate circuit resistors.

Tandem Tuning

There is another antenna connection,and that is the single circuit, directcoupled connection. In this the grid isconnected metallically to the antenna insuch a manner that the voltage acrossthe tuning coil is made use of. This isabout the most effective collector of radio

energy but it is also the least selective.It is not shown because it is wholly un-suitable to present broadcast reception.It ceased to be useful when the secondbroadcasting station went on the air.

In one of the early attempts to gainselectivity when neither the- transmitternor the receiver was capable of greatfrequency discrimination the method oftandem tuning was employed. This meth-od is illustrated in Fig. 2, which shows noless than four tuned circuits throughwhich the signal must filter before reach-ing the detector. While the drawingshows a regenerative tube detector thescheme was ordinarily used with crystaldetectors.

In this arrangement the several tunedcircuits are loosely coupled so that theywill be as independent of each other aspossible and still leave enough couplingto transfer a readable signal to the detec-tor. The only difference between thisarrangement and that used in TRF re-ceivers is that in the present case thereare no amplifiers interposed between twoadjacent tuned circuits.

Why Show it?

The only object of the circuit shown inFig. 2 is to increase selectivity, and theincrease can only be gained at a consid-erable loss in signal strength. Why then,it might be asked, is the circuit shown?Because of a new development in radio,one which calls for greater selectivity andat the same time supplies amplificationenough more than to compensate for thelosses in the tandem tuned circuits: Thenew development is the shielded grid tube(UX222, CX322, Shieldplate 122).

The new tube has a high amplificationconstant, which makes it possible to at-tain a radio frequency voltage amplifica-tion per stage of from 30 to 50 dependingon the circuit constants with which thetube is operated. This gain is much morethan would be lost in a reasonably welldesigned and coupled chain of tuned cir-cuits.

But when two or more of these shieldgrid tubes are used in a receiver the tun-ers can be distributed just as in ordinarysets, although in so doing the net selec-tivity of a given number of tuned cir-cuits will not be so great as if used accord-ing to the arrangement shown in Fig. 2.

The stability and ease of tuning, how-ever, would be greater when the tunersare interspersed with the amplifiers.

Next week: The Tyrman Shielded gridsuper, the Four Tube Diamond of theAir and other big features.


Per Agate Line

A THOUGHT FOR THE WEEKRADIO is much like poetry in the

sense that you know whether it isgood or bad by its appeal to the ear.That more or less abused person, "the manin the street," might not know the where-fore of good reception, but if his hearingis acute, his ears will register satisfaction.

SIXTH YEAR

The First and Only National Radio Weekly

Radio World's Slogan: "A radio set for every home."

TELEPHONES; BRYANT 0558. 0559PUBLISHED WERT WEDNESDAY

(Dated Saturday of same week)FROM PUBLICATION OFFICE

HENNESSY RADIO PUBLICATIONS CORPORATION145 WEFT 45TH STREET, NEW YORK, N. Y.

(Just east of Broadway)ROLAND BURKE HENNESSY. President

M. B. HENNESSY, Tice -PresidentPENMAN BERNARD, Secretor -9Chicago: 55 West Jackson Bivd.

Kansas City, 110.; E. A. Samuelson, 300 Coca Cola Bldg.Loa Angeles: Lloyd Channel, 611 S. Coronado St.

European Representatives: The International News Co.Breams Bldg., Chancery Lane, London, Ihtg.

Paris, France: Bre:steno's, 8 Avenue de l'Opera

EDITOR, Roland Burke HennessyMANAGING EDITOR. Herman BernardTECHNICAL EDITOR, J. E. Anderson

ART EDITOR, Anthony SodaroCONTRIBUTING EDITORS:

James H. Carroll, John Murray Barron andCapt. Peter V. O'Rourke

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Receipt by new subscribers of the first copy of RADIOWORLD mailed to them after sending in their orderautomatic arimowleclgment of their subscription order.Changes of address should be received at this office twoweeks before date of publication. AlwaN give old address;also state whether subscription is new or a renewal.

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Entered as second-class matter March 23, 1922, atthe Poet Office at Now York, N. Y., under the Act ofMarch 3. 1879.

Deaf Indian Listens InThrough Wife's Fingers

Glacier Park, Mont.While at work in his log cabin studio

on the St. Mary Road in Glacier Na-tional Park, during the long shut-inWinter months, John Clark, deaf anddumb Indian artist -genius, gets inspira-tion from the wide world over the radio.

Mrs. Clark, a former reservation schoolteacher, sits nearby, occasionally drop-ping her knitting or fancy -work to trans-mit in the "finger language" to her hus-band things of interest that are broughtin "out of the air."

Clark, besides doing some painting,hews trunks of trees out of the forestand from these he carves bears, goatsand mountain sheep, using a bowie -knifeand chisel as his sole tools. Some ofClark's carvings, including his master-piece, "The Bear in a Trap" have a per-manent place on exhibition in the ChicagoArt Institute.

Station EliminationOpposed by Some Fans

Two Readers Well Satisfied, Ask Toleration-ThirdWriter Complains Middle West Is Unfairly Treated,Due to Stations In East and West, on Same Wave,

Killing Each Other Off.

STATIGN EDITOR:As far as I am concerned the latest re-

allocation work by the Federal RadioCommission was very good. It suits mefine. But it seems that some personscannot be pleased at all. They demandthe impossible of the Commission. Forexample, these people demand that theCommission so allocate wavelengths andpowers as to insure all the people con-stant and unfailing radio reception, notonly free of heterodyne disturbances butalso free of fading troubles.

I think that consolidation of stationsas much as possible should be urged andthat no more new licenses should be is-sued. But to order a station off the airoutright or to confiscate it takes moneyand the cost would ultimately have to beborne by the taxpayers.

I repeat that I think that the radiosituation as it is at present is good. WhenI want a good radio I turn to the locals.When I want DX I can have that too,for my set has reached out 2,000 milesmany a time. I am satisfied and I do notcrave the impossible.

What is really needed today is tolera-tion rather than station elimination.-LOUIS T. THOMA. Cincinnati, Ohio.* * *STATION EDITOR :

In my opinion we should keep the sta-tions which are now licensed but weshould refuse to license any more. Somestations from time to time will drop out,of their own accord, so that after a lit-tle while this should afford some relief in

the congested part of the broadcast band.It is desirable to have as many non -

interfering stations as possible, for it al-lows the man with a good receiver to tunein on a good program at any time.-R.E. BROWN, Highland, N. Y.

* * *

STATION EDITOR:I appreciate the effort made by the

Federal Radio Commission to clear theair of heterodyne interference, but Iprotest against the method it used forbringing it about.

The Commission ignored the fact thatpersons living in the middle of the UnitedStates cannot tune in either one of twostations operating on the wavelengthwithout having their programs impairedby interference. If they try to tune inthe Eastern station, the Western stationcomes in with almost the same intensityas the station desired, and if they try totune in the Western station, the Easternstation interferes. The result is thatpersons living in the middle part of theUnited States cannot enjoy either stationwith any degree of pleasure.

KFI and WRC come in with aboutequal volume; KFI and Atlanta inter-fere; as do WEAF and Ft. Worth;KRLD and WRR; and KFNF andWCEA. KOIL and one of the stationsin Seattle also interfere with each otherand New Orleans is interfered with byone of the stations in New York.-A. L.NELSON, Clarksdale, Miss.

Licenses of StationsExtended to March 1

Washington,Extension of all broadcasting licenses

until March 1 was ordered by the Fed-eral Radio Commission, the acting chair-man of the Commission, Judge Eugene0. Sykes, announced. Sixty-day licenseswhich were granted by the CommissionDecember 1 in accordance with its policyto issue them only for short terms tomake for flexibility in wave, power, andtime assignments were accordingly madeeffective for an additional month.

Judge Sykes issued the following state-ment :

"In view of the fact that three of thefour present members of the Federal Ra-dio Commission are yet unconfirmed bythe Senate, 1 have recommended to mycolleagues that the station transfers andother changes designed to improve recep-tion in the broadcasting band, be post-poned until confirmation of a quorum ofthe Commission's membership, and thatall broadcasting licenses be extended andmade to expire on next March 1,"

WGY INVITES THE WESTSchenectady.

For the entertainment of far Westernlisteners WGY is on the air until aftermidnight two mornings each week. Tues-days and Thursdays are the days on whichthese extended programs are put on theair.

Broadcast by BeechamFollows Radio Attack

Sir Thomas Beecham, well-known Eng-lish musician, conducted the New YorkPhilharmonic Orchestra recently on thestage of Carnegie Hall, New York City.This marked the first appearance of SirThomas as a conductor on an Americanstage, although he has been in this coun-try several times, and it also marked hisfirst appearance as a radio artist. Whenhe stepped on the stage three microphonesfaced him, all of which were connectedwith the transmitter of station WOR,which broadcast the concert.

Less than a year ago Sir Thomas classi-fied radio as "music's greatest menace,"and he has characterized English broad-casting as a "stupidity and a crime againstmusic."

Damrosch Music Lessonsfor Children Gets Trial

Walter Darnroch, conductor of the NewYork Symphony Orchestra, is giving a"sample" by radio of his plan for teach-ing music to the children of the UnitedStates in three broadcasting periods.

The first of these broadcasts was broad-cast January 21, from 8 to 9 am.; thesecond is scheduled for Saturday morn-ing, February 10 from 11 o'clock untilnoon, and the third one week later atthe same hour.


How Quality is Obtainedfrom Resistance Audio

(Continued front page 15)used (UX-200A, CX-300A or Q.R.S.200A type), a chattering or gurgling maybe heard when tuning. This disappearsat resonance, but is very annoying other-wise. It is due to an unsuitable load 1111-pedance, causing self -oscillation which isdetoured by the phenomenon of "infiniteimpedance" at resonance. Use a largervalue of load resistance. Instead of, say100,000 ohms for R1 use 250000. Thismay decrease the amplification slightly,unless the plate voltage is increased. But.amplification decrease is not to be takenas a shortcoming, since ample volume forthe home is taken as a prerequisite in allthese considerations.

If the suggested change is made in areceiver that has a regenerative detectorthe higher value of detector plate re-sistor may defeat regeneration on thehigher waves, but this can be overcomeby decreasing the intermediate grid biason the radio amplifier and in the audioamplifier as well (since there is one biasfor these).

It is not only true that there is a defi-nite limit to the total amplification whichmay be gainfully employed but it seemsto be true that this limitation is specificeven as to individual stages, includingthe detector. And in rating an audiochannel the detector tube must be in-cluded as an audio amplifier. Although itsamplification at audio frequencies may besmall with some tubes, the effect on phaserelationships in the audio amplifier ispresent at all times and with all detectortubes.

In the interests of best quality andstability of the amplifier the isolatingcondensers IC should be large, becauseif they are small they will suppress thelow notes slightly. The gain in, low noteamplification is bought so dearly that itshould not be sacrificed by too small ca-pacity here. If small capacities are therealready it may be well to put larger ca-pacities in parallel with them, so that .1mfd. or more is the total capacity of eachisolator. It so happens that best sta-bility was experienced in circuits using1 mfd., and that capacity is a good oneto use, as the low notes are not by-passed.

To support the just favoritism shown tolow notes, AF plate resistors should not bevery high. It is well to adhere to .1 mid.,especially where intermediate C minusis common to several tubes, including RF,for if the plate resistor is high the DCvoltage actually reaching the -plate willbe too low for the common bias. In otherwords, separate intermediate C biaseswould have to be introduced, but if bat-teries are used that is a simple matter.

On the other hand, the audio grid leaks.should be no less than 2 meg. The de-

tector grid leak, if resistance audio isused, may be of greater resistance thanusual, and 5 to 10 meg. is a suitable rangeof choice.

The condenser coupling the speaker tothe last tube, OC in Fig. 1, may be 2mfd. or more, but increase beyond 2 Illfd.produces no change noticeable to the ear.If that condenser is of a DC voltage testwell in excess of the total B voltage, thereturn connection may be made as shownby the dotted line, to negative filament.It is more usual to show this connectionto minus A, but that returns the speakerto a part of the C bias system, and thisis avoided for theoretical reasons-thesame reasons that deter one from makingthe return to B minus in Fig. 1.

The fine quality of which a resistancecoupled amplifier is capable thereforemay be preserved to full extent if neces-sary precautions are taken, particularlyif a B supply is used instead of batteries,and even if a biasing resistor is used tofurnish grid biasing voltage. As manyexperimenters possess and construct suchamplifiers this report of extensive ex-periences with such channels was pre-pared as a guide to the correction of er-rors in existing construction and in am-plifiers that are to he built.

As success depends 'partly yet stronglyon the values of the constants, the follow-ing are recommended for application toFig. 1:

Tubes: D (detector) Q. R. S. 200A type,the loudest detector tube I ever en-countered CeCo type H, CX-300A, UX-200A. First audio: CeCo typeA, CX-301A, UX-201A. Last audioCeCo type J, CX371, 13X171, Armor 571.(Do not use a 112.)

Lynch plate resistors: R1, -1 or .25meg.; R3 and R5, 100,000 ohms:

Lynch grid leaks:R (detector leak) 5to 10 meg.; R2, R4, R6, first, second andthird audio, 2 to 5 meg.

R8 (optional) : Volume Control Claro-stat.

25 CentsBrings ALL THIS!

One Official Blueprint of the Five -Tube Diamond of the Air

One Official Booklet describing in detailHow to Build this Famous Set,

Wind Coils, etc.

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Add $1.00 a Year for ForeignPostage; 50c for Canadian Post-age.

Filament resistors: IA Anun-ritesthroughout, unless a .5 ampere tube isUsed its the last Stage (types without thestub .\1; the,' lg.,. a 112 Amperite

ls,l,tling c.,mlensers of .1 to I mid,These may he of one capacity throughoutor sI aggCFC,i.

('I : , 'lid 'sit ch 'I: ,,f 35 henrys ormore, with lots Iris resistance, and usedwith a 2 to mid. 0,11dt:user OC; orthese tw,, nifiy will 1,, the National outputfill1:r.7:(life

t.,miralah f.,urth-tvrininal po-tenti,mieter, 2,000 idlins.

( loudcuscr f no less than 4 mid,under ally circumstances, but far prefer-ably 8 to 10 mid., with 4 as a sufficiencyand 10 as an extra precaution in favor ofquality. Low voltage type ample.

ileageWhen youQ buy a new

Radio Set or refitll an old one-insist upon

for Clarity, Tone, Longer Life

A type for every radio need.'Your dealer will help you selectthe types needed for your set.

C. E. MEG. CO., INC.Prortdcnct, R. I.. u S. A.

Everybody's Talking About ItThere'. a wealth of reliable, boiled -

doom, and Interesting InformationIn Thislatance the 'ControlValve' of Bailin" Slangy writ-ten-clearly Illustrated. Thisvaluable handbook on rIstaneeIn radio Is worth dollar-sendonly 25 gents for YOU, WIIY.

ARTHUR H. LYNCH, lee.1775 Broadway, New York City 25'

FULL OF USEFUL INFORMATION on 101 aspects of radio, the December 10 issue is one tokeep and study. It is a reference book all by it-self. Some of the features are "My Three Monthswith the Magnaforrner Si." by J. E. Anderson,Technical Editor (seven full pages, including illus-trations in colors-the presentation that evoked700 laudatory letters): "The Object of a PowerAmplifier, Wills Special Emphasis on Push -PullStage," by C. T. Burke, engineer, General RadioCo.; "The Floating Armature Coil Reproducer,"by H. B. Herman, acoustimi expert, featuring thenew Magnavox electrodynamic reproducer; "ABattery Powered Two -Tube Phonograph Ampli-fier," embodying the Phonovox. by James H. Car-roll; "Giving the Crackles the Gate," by TimTurkey; "The Everyman 4," by E. Bunting Moore;"The Analysis of the Concertrola," by Leo Fen.way, its noted designer; "Scientists Freeze Re-sistance Out of Metals"; other features, abundantillustrations. Send 15 cents for copy of Decem-ber 111th issue to --RADIO WORLD, 145 W. 45th St., New York City


The Big Thrill ofDX, and at verySmall Cost to You

Everybody who owns a radio set likes totune in far -distant stations now and thenbecause not only is there a thrill in hearinga voice or instrument thousands of milesaway but one verifies the fact that he hasa powerful receiver and that it is in goodcondition, if it is able to pick up theseweak signals. Now that the broadcastingstations are more suitably distributed as towavelength or frequency, fans are in abetter position to tune in distance. Be-sides, the weather is in their favor thesedays. But what kind of a set shall beused? You know very well that if theset can tune in distance once in a while,you can develop sufficient skill to make ittune in far -distant stations very often,virtually every night. Then when youhave visitors you need not boast aboutthe DX qualities of your set but simplytune the receiver and let them listen tostations thousands of miles away. Youmust be sure to have a receiver capableof responding to your distance -getting de-sires. You also want this set to have de-lightful tone quality, so that your owncritical ears cannot detect even a singleflaw in the reproduction. Indeed, evenmusic lovers who may be guests at yourhome will comment admiringly upon thebewitching tone of your receiver. Thenyou know you have something real. Theability to get distance and to reproduce theoriginal music without distortion dependslargely on the circuit design, and you willfind that the Diamond of the Air, eitherthe 4 -tube or the 5 -tube model, will liveup to your highest expectations. Howare you going to know which to build?Carefully Inspect the textual data as wellas the blueprints that fully expound thetheory, operation, charactenstics and am-plification of these two outstanding receiv-ers that differ principally in the type ofaudio amplification.

The 5 -Tube DiamondCan be constructed in a couple of hours.The authorized blueprints that make thisspeed and efficiency possible are just offthe press and will be shipped at once, to-gether with the new booklet of full textualexposition of construction, including thewinding of coils, how to connect terminals,what values of condensers and resistors touse, etc. The receiver consists of a stageof tuned radio frequency amplification, aspecially sensitized detector, first stage oftransformer audio and next two stages ofresistance audio. It is easily adapted toplaying phonograph records through theset and on your speaker. Get acquaintedwith this new delight.

The 4 -Tube Diamondrepresents the most that is obtainable fromfour tubes. A stage of tuned radio fre-quency amplification, a specially sensitizeddetector and two stages of transformercoupled audio. Follow the blueprint toamazing success. Build the set from partsyou have. Full instructions cover utiliza-tion of such apparatus. Thousands areeager to build an economical set of sur-passing perforinance and amazing achieve-ment and this one is the most economical,the most scientific, and the least expen-sive in cost of parts and upkeep. Workssplendidly from batteries, either type 99or type IA tubes' and can be used withA and B eliminators, power packs, etc.,with great success.

Look over both of theseblueprints and read the text in both casesbefore choosing the receiver you are tobuild.

Guaranty Radio Goods Co.145 West 45th Street, New York City

Please send me one newly -printed officialblueprint of the 5 -tube Diamond of theAir, one newly printed official blueprint ofthe 4 -tube Diamond, and the textual datagiving full directions for constructing thesesets. Enclosed please find SO cents to de-fray all expense.

Name

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Maximum Sun SpotsAid Long Waves by Day

The results of scientific studies of solaractivity on broadcasting were announced bythe Department of Commerce. The state-ment, based on findings of the Bureau ofStandards, was in full as follows:

It is reasonably certain that long wavedaylight radio signals, both from distantstations and from those only two or threehundred miles away, were stronger in1927 when the 11 -year sunspot cycle isnear its maximum. than in 1923 when itwas at its minimum. This was one of theconclusions of Dr. L. W. Austin and MissI. J. Wymore of the Bureau of Standards.

A commercial radio expert, G. W. Pick-ard, has shown, on the other hand, thatat night in the broadcasting range, signalsgrow weaker when the number of sun-spots increases. Hence it appears thateffect of solar activity on signals is re-versed when day gives place to night.

Confirms Bell LaboratoriesThis corresponds to the conclusions of

the engineers of the Bell Laboratories,that magnetic storms which are knownto be connected with sunspots weakenmedium and long wave signals at nightand slightly strengthen them in the day-time.

The evidence regarding the influenceof magnetic storms and solar activity odultra short waves is somewhat conflicting.There are many authentic reports of poorreception at the time the long continuedobservations of Dr. A. H. Taylor of theNaval Research Laboratory, as averagedby Mr. Pickard, indicate an increase ofnight signals with increasing sunspots orthe reverse of the effect on longer waves.

Very few observations have been pub-lished -on long wave night transmission,on broadcasting day transmission nor any,so far as is known, on broadcasting nightsignals extending over more than oneyear. This offers a very promising field

of experiment for those interested in thescientific side of radio.

"Enormous developments",in the field oflong and short wave radio communicationwere predicted by H. A. Bellows, formermember of the Federal Radio Commission,testifying at a subsequent session of thecommmittee.

Testimony, while first designed to ex-plain some of the actions and policiesof the Federal Radio Commission since itsinception with respect to radio broadcast-ing, turned almost exclusively to the mat-ter of short waves and other technical de-velopments in the radio art when Sena-tor Dill (Dem.), of Washington, sponsorof the Radio Act of 1927, asked for Mr.Bellows' opinion as to the proposed pro-longation of the Commission for anotheryear.

"The Commission," said Mr. Bellows,"during the first year has been greatlyhandicapped by the deaths of Col. JohnF. Dillon and Rear -Admiral William H.G. Bullard, and has been unable to doanything like the job Congress intended.

"Another year will enable it to take upother questions than broadcasting, suchas the short and long wave lengths, whichwill present a problem even more im-portant to the public interest than broad-casting.

Television Discussed

"These represent a perfectly enormousdevelopment, largely technical, primarilywith respect to the use of short waves fordistance code communication, and pos-sibly later for television fascimile repro-duction and other phases of the art forwhich the channels in the lower end of theradio band are being developed.

"The Commission needs experts and en-gineers to aid it, and it needs technicalequipment to continue its work."

Take Your Choice of 7Other PublicationsFor NEW RADIO WORLD Subscribers Ordering NOWRadio World has made arrangements-To offer a year's subscription for any one of the following publications with one year'ssubscription for RADIO WORLD-RADIO NEWS or POULAR RADIO or SCIENCE AND INVENTION or BOYS' LIFEor RADIO DEALER or RADIO (San Francisco) or RADIO AGE.

This is the way to get two publications-for the price of one:-Send 58.00 today for RADIO WORLD-for one year (regular price-for 52 numbers)-and select any one of the other-nine publications for twelve months.

-Add $1.00 a year extra for-Canadian or Foreign Postage-Present RADIO WORLD subscribers-can take advantage of this offer by-extending subscriptions one year-if they send renewals NOW!

Radio World's Special Two -for -Price -of -One Subscription BlankRADIO WORLD, 145 West 45th Street, New York City.Enclosed find $6.00 for which send me RADIO WORLD for twelve months (52 number.),beginning and also without additional cost, Popular Radio, orRadio News, or Science and Invention, or Radio Dealer, or Radio (San Francisco), orRadio Age, or Boys' Life (or $10.00 for a two-year subscription to one address). No otherpremium wtib this offer.

Indicate if renewal.

Offer Good Until

February 15, 1928 City and State

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January- 2S, 1928 RADIO WORLD

Metal Shield Patentfor Tubes is Granted

The Orange Research Laboratories, 247McKinley Ave., East Orange, N. J., havebeen granted U. S. Patent No. 1,564,694,covering a mz_stallic shield to be placedover vacuum tubes for preventing unde-sired interstage coupling. "Vac -Shield"is the name of the device. It is made intwo types, one for the -01A type tubeand the other for a -22 shielded grid typetube. The only difference is a hole inthe top of the shield for the control ele-ment of the 22 tube.

The Vac -Shield prevents interstagecoupling by acting as a static screen; itmakes tuning in distant stations easierby minimizing stray capacity effects; itprotects the tube from breakage by offer-ing a mechanical guard; and it minimizesthe tendency toward microphonism byloading the tube down and lowering itsnatural period of mechanical vibration.

Volume Control ModelClarostat Announced

Differentiating between the heavy -cur-rent requirements of the usual radio powerunit and the relatively light -current re-quirements of the usual radio receiver,there has been added a smaller andmoderately priced type to the well-knownClarostat line of micrometric variable re-sistors.

The new type is known as the VolumeControl Clarostat. It is of about the samediameter as the standard type, but onlya third as deep. The current -handlingcapacity is approximately one-third thatof the standard type employed in radiopower units and for the heavier receiverrequirements. In several turns of itsknob, the Volume Control Clarostatcovers a resistance range of approxi-mately zero to 500,000 ohms. It hassingle -hole mounting. It is provided withscrew terminals for ready wiring.

NEW NBC WASHINGTON STUDIOSThe new Washington Studios of the

National Broadcasting Company, whichfurnish programs to the Radio Corpora-tion of America's station WRC and theNBC's Red and Blue Networks, are inoperation. The studios are located in theNational Press Building at F and Four-teenth Streets, N.W., Washington, thenewest and largest office building in thatcity. The building is in the center of thecapital's business and theatrical section.

INDEPENDENTS ELECT RUSSWalter C. Russ has been elected sec-

retary and patent counsel for the RPALaboratories, Inc., an organization of ra-dio manufacturing companies, membersof the Radio Protective Association, ac-cording to A. D. Lord, president of theRPA Laboratories and receiver for theDeForest Radio Company.

Subscribers : Look at theExpiration Date on

Your WrapperWe do not like to take your name from

our subscription list without specific in-struction to do so, because many of ourreaders wish to keep a complete file of thepaper.

Please therefore, look at the subscriptiondate stamped on your last wrapper, andif that date is earlier than the issue con-tained in the wrapper, please send checkto cover your renewal.

In this way you will get your copieswithout interruption.Subscription Dept, Rim° WORLD, 145 W.

45th Street, New York City.

LiteratureWanted

THE names and addresses of readers ofRADIO WORLD who desire literature

on parts and sets from radio manufactur-ers, jobbers, dealers and mail order housesare published in RADIO WORLD on re.quest of the reader. The blank below maybe used, or a post card or letter will deinstead.

RADIO WORLD,145 West 45th St., N. Y. City.

I desire to receive radio literature.

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Quilty and Burke Radio Co., 252 Water St.Quincy, Mass.

Frank G. Babylon, N. S. Pittsburgh, Pa.Alexander Solo, 507 Bankers Trust Bldg., Phil-

adelphia, Pa.Kendall M. Pratt, Beechwood St., Cohasset,

Mass.F. G. Buhrendorf, 463 West St., N. Y. City.William G. Barger, 356 N. Liberty St., Jackson,

Tenn.,N. H. Shoup, 2723 4th Ave., Huntington, W. Va.Charles Stoltz, 281 Cooper St., Brooklyn, N. Y.William Supper, 3439 Hillside Ave., Cincinnati, 0.Frank E. Adamson, 812 S. Broad St., Winston-

Salem, N. C.F. P. Crossan, Fox Chase, Philadelphia, Pa.George Kornblatt, 1747 N. 33d St., Philadelphia,

Pa.Bill Grieiks, 7500 Hillmont Ave., Oakland, Calif.Frank Flanagan, 4723 East Marples St., Tacony,

Pa.Chas. Maier, Jr., 399 Liberty Ave., Jersey City,

N. J.J. C. DePina, 82 Kingston Ave., Brooklyn, N. Y.Reginald Todd, P. 0. Box 16, Caledonia, Ontario,

Canada.Edwin Shafer, 335 East 88th St., N. Y. City.Harold W. Pitt, 126 East 31st St., Oklahoma

City, Okla.W. C. Massett, Box 34 R. F. D. No. 2, Shakes-

peare. Drive, Berea, 0.Edwin Helfenstein, 132 South 57th St., Philadel-

phia, Pa.Clinton Klinge, 7305 Penn, Kansas City, Mo.Fred Wittwer, P. 0. Box 262, Rock Island, Ill.Al Skollar. 667 Crotona Pk. N., N. Y. City.Fred G. Tresselty, 2419 Jefferson St., Philadel-

phia, Pa.Berbard S. Shav, 2610 Fremont Ave. S., Minne-

apolis, Minn.Olive H. Zane, 120 N. 34th St., Camden, N. J.Archibald Curror, P. 0. Box 66, Crane St.,

Schenectady, N. Y.Robert Falla, 168 Pape Ave., Toronto, Ontario,

Canada.George A. Nicoud, 2221 Ashland Ave., Racine.

Wis.'. Bergner, 948 Bergen St., Brooklyn, N. V.

Professional Set Builders!SEND NOW for full size X -Ray, two-

color, Wiring Diagram for Magnaformer9.8-fully described by 7. E. Anderson. inDecember 10 issue of Radio World. Theonly set ever constructed that fully livesup to its advertising claims. Every setinstalled, by its superior performance, auto-matically sells many others. Address Ra-diart Laboratories Co., Dept. 69, No. 19South La Salle Street, Chicago, Ill.

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HERMAN BERNARD, managing editor oRadio World, discusses radio topics of 119Pillainterest every Friday at 5:40 P. M. from WOBS,348.6 meters, the Gimbel Bros. station in NewYork City. Listen in.

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AttractiveParts

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DRUM CONTROLGives that Ritzy appearance to your set.Consists of two drums, onealuminum mounting frame,one bronze panel plate (es-cutcheon) and two bronzemounting screws. CatalogueNo. 1001

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Tuning Coil, with va-Low Loss R.F. riable third winding.Transformer,wound for .01305 Catalogue No. 1003.mid. condenser;80% air dielectric; $3.30useful for antennaor interstage coup-Itg. . 1oS2a t a l o g II i

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36 -Inch Come KitFor superb tone qual-ity build this speaker.

$10.00FREE! With each 36"cone kit order we willgive a Corbett Tel -FootPedestal (Illustrated). Kitconsists of licensed GiantCone Unit; designed frontsheet Fonotex, plain backsheet Fonotex; two metalrings; ono bracket: onoapex; one tube of cement;screws, nuts. COMPLETEINSTRUCTION SHIM.Cat. No. 1160.

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I am to pay the postman the advertised price, plusa few cents for postage.Name

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RADIO WORLD January 28, 1928

KARAS AGAINSPECIFIED BYRADIO WORLD

IN THIS ISSUEKARASA -C -FORMERFilament Supply

This remarkabledevelopment ofKarat engineers,when used withany of the adap-ter c able har-nesses now avail-able, makes itpossible to haveANY set, operate

directly from 110 -volt, 60-eyoleA.C. current. No

rewiring-no hum. Brings In distant stations withmarvelous clearness and volume. Easily installed inany set. Insist upon using the Karns A -C -Formerin order to protect the life of your A.C. tubes.Write tale.), for complete details on converting yourset to A.C. at less than the cost of a good batteryand charger. List price of Karns A -C -Former.$13.50.

KARASHARMONIKAUDIOTRANS-FORMERProvides themaximum ofdistortion-lesse p u r e,sweet audioamplification.H a s superbtone and tre-mendous vol-ume. T h oKarns Her-monik h a snever beenequalled byany competing transformer In performance, regard-less of prime. The NEW Harmonik. NOW. $5.00.Insist on getting the genuine Karns product whenyou build your receiver.

KARAS ELECTRIC CO.4039-B NORTH ROCKWELL ST.

CHICAGO

P%c.A.._.A.5

121115,9girk

AUDIO 1FABUFNCr u

IRANSTORMER,,

MI Sint Ratio

U. S. PatentNo. 1,564,694

Stabilize Your Set

"Vac -Shields"Bring in DX

THE invention ofthese non-magnetic

shields for Type 201-Aor the new Type 222Tubes prevents inter -stage coupling andelectro- static effects,overcoming stray ca-pacities that maketuning of distant sta-tions 'so difficult.Guard tubes ag-ainstbreakage. Attached ina minute.Order today at yourdealer's, or by mail,

postpaid, $1.00.

ORANGE RESEARCH LABORATORIES

247-249 McKinley AvenueEast Orange, N. J.

VICTOREENSuper CoilsSend for Folder

Geo. W. Walker Co.282S Chester Avenue

Dept. B Cleveland, 0.

SET BUILDERS pallogovriBIG NEW 1928 CATALOG -4,000 ItemsShows the latest A -C circuits, the newest

ideas in radio. at startling low prices. Getthe sets and parts you wont here. Savomoney. Orders tilled same clay re- .R.4 .1coined. Write for free copy now. re s,sBA RAW I K CO., Deg, 91 I, Chicago

VO LU P4.1E CONTROLCLAROSTAT

Do You Control Your Radio Set?Do you run your radio or does It run you?

Doubtless you would welcome positive control ofvolume. without distortion, to suit the occasion-from dance music for shuffling feet to soft back-ground for dinner conversation. You would enloytone control from sharp, crisp sPeech, to soft, mel-low, soothing mauls. You would have better re-sults with line -voltage control for that radio powerunit or those A -C tubes.

And It's all so simple with Clarostats--micro-metric resistance units available in three types andseveral ranges for every radio purpose!

Ask your dealer how. Or, better still, send forour booklet, "M icrometrio Resistance." which tellshow to get the best radio results. And when you

buy Clarostats, be sure youWatt.. ens Pet the genuine article Indistinctive green box andname stamped on nickeledshell.

AMERICAN MECHANICALLABORATORIES, INC.Specialists in Variable Resistors

235 N. Sixth Street Brooklyn, N. Y.

R IN A

For Best Resultswith

H. B. Herman'sPre -Power Unit

Use only the

Hammarlund CoilsSpecified by the Designer

3-crt, Bettax

arnmarlund-PREC/S/ONPRODUCTS

HERMAN BERNARD, managing editor ofRadio World, discusses radio topics of popularinterest every Friday at 6:40 P. M. from WGBS,348.6 meters, the Gimbel Bros. station in NewYork City.

Halldor.sonovertone=,

Chosen for theDAVEN A.C. FIVEDescribed in This Issue

SET BUILDERS!Henderson Overtone Audio and Output transformersare Droving a revelation to set builders all over thecountry. They will give you quality that you neverdreamed possible. Try them in your receiver; it theydon't astonish you with their lifelike reproductionyour money will be gladly refunded. At your dealeror sent direct Price, each, $6,00.THE HALLDORSON COMPANYFactory: 4746 N. Western Ave. CHICAGO,Office: 223 W. Jackson Blvd. ILL.

Condenser BlockFixed CondensersA. C. Switch

Specified-as usual-in

Daven A.C. Convertor[Carter Radio CO

CM I AGOA

Guaranteed "A" Power Unit-$13.75No better "A" Socket Power Unit ran be obtained

even at twice this amazingly low price. N. hum ornone. Operates on 50 or 80 moles at 110 volts A. 0.Approved by rigid laboratory tests of Radio News andPopular Radio. Fully guaranteed. Shipped complete,subject to inspection, on receipt of price-or C.0.0if you wish. 5% discount if cash in full is sent withorder. Send order NOW! WORLD BATTERY CO.,1219 South Wabash Ave., Dept. 64, Chicago, III.

End Radio BothersDO YOU KNOW what's wrong when your radio set isn't working right?

Ten to one, you don't. Twenty to one, you would if you had a copy of

Hoff's Radio Trouble FinderEver hear of M. M. Hoff, radiotrician, of Philadelphia? He was

One of the very first "radio bugs" and has been building andstudying sets ever since. And now, out of his broad experience,this man has written a book to tell radio owners how to keeptheir sets working right.

He tells in plain words and illustrations how a set is made, whattbe parts are called, what are the few usual troubles and how tofix them. Then he lists 103 troubles that sometimes happen andtells how to detect and fix each one.

The book is a regular cyclopedia of radio information-only it's in a language anyonecan understand. Read it five minutes and you'll know more about radio than you everdreamed of.It will save you many a repair man. It will save you hours of guessing and fussing andfuming. It will help you to keep the tone of your set always sweet and strong. It willkeep you from losing many programs. And, best of all-IT WILL MAKE YOU STOP SWEARING-MUCH TO THE SURPRISE OF YOURFAMILY-because radio repairs are expensive. Why hire them done when you can easilylearn bow to keep your set from needing them?

All It Costs Is $1Send cash with your order and you get also a Dictionary of Radio Terms and the latestlist of Radio Broadcasting Stations with call letters and the new Federal Radio Commissionwave lengths. Send your dollar today while the copies last.

CHICAGO BARGAIN HOUSE424 QUINCY BUILDING

CHICAGO, ILLINOIS

home television demonstrated...general electric's broadcast of moving vision on 37.8 meters...

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