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tic Capacitors mark much morethan an advance in an art. Theymean that filters now occupyless space, cost less, have longerlife because of permanent seal-ing, are used in single units tosimplify both production andstock -keeping, and are "stand-ard" parts.

Solar engineers have been thepioneers in advanced methodsof making radically smaller dryelectrolytic capacitors. "littlegiants," introduced three yearsago, were the original ultra -com-

pact drys. Now we announcefurther size reduction, superiorcharacteristics and outstandingutility in the new Minicaps. Youwill find them in thousands ofradio sets,- to stay there.

SOLAR MFG. CORP., 599-601 BROADWAY, NEW YORK, N. Y.

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A. W. FRANKLIN

THE Franklin Mechanical Pusit Eu-_ton Tuner repre-sents fourteen months of constant experimentation

and devel.)pment-more than a yea. of thanges, improve-ments and rejections. It is an instrument that boasts nointricate assemblage of gears, racks, pilior* and stuff-no complicated, trouble -making mechanism& Here is anengineering triumph of which the radio industry will bemighty proud -a precision -built unit magnificent in itssimplicity - positive in its permanent accuracy.

To meet requirements of receiver manufacturers for indi-viduality, push buttons can he supplied in a variety ofshapes and designs. The mechanism arid application of theFranklin Mechanical Push Button Tuner for all types ofhome and automobile receivers, covering all price rangesis described in technical bulletins available upon request.

A.W. FRANKLIN MFG. CORP., 175 VARICK ST., NEW YORKMANUFACTURERS OF SOCKETS, SWITCHES, TERMINALS, PLUGS, AND OTHER DEVICES

COMMUNICATIONS FOR MARCH 1938 1

COMMUNEI© Til NSMember of Audit Bureau of Circulations

RAY D. RETTENMEYER Editors W. W. WALTZ

CONTENTS FOR MARCHCover Illustration: A large air-cooled transmitting tube, RCA -86I, under exhaust. A power

of more than 15 kilowatts is used in heating the metal parts to incandescence. Here

the anode of the tube has reached a temperature of 2500°F.; it will rise higher forbrief periods. Heating of the interior metal parts facilitates the vacuum pumping byreleasing the hard -to -get occluded gases from the metal parts. Photo courtesy RCAManufacturing Co., Inc.

With the Editors 4

Selenium Rectifiers 7

Cathode -Ray Electron Ballistics By F. Malcolm Gager 10

The Broadcast Engineering Conference 12

High -Frequency Triode Oscillators By Grote Reber 13

Report of the NAB Convention 16

Recent Developments in Push -Button Tuning 18

The Delta -Star Mixer By J. N. A. Hawkins 20

New Tubes 21

Compromises in Allocation Engineering By Raymond M. Wilmotte 23

Background Noise Corrections By L. E. Packard 24

Some Notes on Snow Static By Dr. Victor J. Andrew 25

Book Review 28

Telecommunication 30

Veteran Wireless Operators Association News 32

Over the Tape 36

The Market Place 42

Index of Advertisers 48

VOLUME 18 NUMBER 3

BRYAN S. DAVISPresident

JAMES A. WALKERSecretary

Published Monthly by the

BRYAN DAVIS PUBLISHING CO., INC.19 East 47th Street

New York CityNew York Telephone: PLaza 3-0483

Chicago Office -608 S. Dearborn St.Telephone: Wabash 1903. <CV:.

SANFORD R. COWANManager

PAUL S. WEILAdvertising Manager

A. GOEBELCirculation Manager

Wellington, New Zealand-Te Aro Book Depot.Melbourne, Australia-McGill's Agency.

Entered as second class matter October 1, 1937, at the Post Office at New York, N. Y., under the actof March 3, 1879. Yearly subscription rate: $2.00 in the United States and Canada, $3.00 in foreign coun-tries. Single copies: twenty-five cents in United States and Canada, thirty-five cents in foreign countries.

2 COMMUNICATIONS FOR MARCH 1938

Western Electric's NEW 5KW

has the DOHERTY CIRCUIT, too!

Final amplifier stage of the new5KW. At right, W. H. Doherty of BellTelephone Laboratories inspect", thenew transmitter.

In the new 5KW (as in tke new 50KW) the famJus Doherty Circuit increasespower amplifier e ii ciency by more than 100% - cuts operating and maintenancecosts-saves space. One more proof that Bell Telephone Laboratories and West-ern Electric are continuing to set the pace in better equipment for broadcasters!

A FEWFEATURES OF THE

5KWDoherty Circuit ncretteos effi-ciency of final amplifier stagefrom the usual 30 g t over 60%.Requires lees primary power,greatly reduces ope-atin; andmaintenance cosh.Automatic line vt.ltrge regale -tor.Improved stabilized feed -back

Automatic circuit breakers andan automatic reelcsing con-tactor in the power circ tit tothe rectifier.Cathode ray oscil ograph con-nections in all important Mr -elute.Engineered to permit increasein power to 10KW, 50KW and500KW by adding selectedapparatus."ASK YOUR ENGINEER"

WesternElectric

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'butorsCreyber Electric Co Graybar

/n Canada one NewfoundlandNorthern Electrie Co.. Ltd.

In other countries:International Standard Electri. Corp.

RADIO TELEPHONE BROADCASTING EQUIPMENTCOMMJNICATIONS FOR MARCH 1938 3

TH THE EDITORS

HIGH -POWER HEARING

IT HAS BEEN announced that the FederalCommunications Commission will hold ahearing on May 16 to determine the ad-visability of amending the Commission'sRule 117, which provides that the author-ized power of a dominant clear -channel sta-tion shall be not less than 5 kilowatts andnot more than 50 kilowatts.

At this hearing all pending applicationsfor permits which request power increasesin excess of that permitted by the existingrule will be heard. Among these will be theapplication of WLW, which is now operat-ing under an experimental license with 500kilowatts power, as well as stations WHO,KFI, WGN, WSM, WSB, KDKA, KNX,KSL, WBZ, WGY, WHAS, WJR, WJZ,WOR, and WOAI.

The Commission's present regulationsprovide for 40 clear channels. However,under the existing arrangement there is du-plication on about 12 of these channels.

As is usually the case, there are two sidesto the problem. It is sincerely hoped, how-ever, that engineering advance will not beretarded for a questionable economic gain.

A CURB ON HIGH POWER?

AND, while on the subject of increasedpowers, we should like to mention the so-called "Wattage Tax" bill on radio stations.This bill proposes a tax of $1 per watt forstations having powers of 1000 watts andless, $2 per watt for stations between 1000and 10,000 watts, and $3 per watt for allstations over 10,000 watts.

Frankly, we fail to see any sound reasonfor imposing additional taxes upon broad-casters. But even if we go so far as to as-sume that additional taxes might be justified,we still fail to see any logic behind the pro-posed tax. In the first place, net incomesfor radio stations, we believe, are somewhatless than in direct proportion to power,while the bill under consideration assumesa net income considerably greater than indirect proportion. In other words, a 100 -watt station would pay a tax of $100, whilea 50,000 -watt broadcaster would be taxed


$150,000 . . . if applications were grantedfor 500,000 watts, the tax on these stationswould be $1,500,000!

If such a tax were to be levied, it wouldcertainly represent a most effective curb onincreased powers. As a matter of fact, thetax would probably be so heavy on a num-ber of the present higher powered broad-casters as to render continued operation un-economical, resulting in a deleterious effecton the entire radio industry. Everyone inthe radio field should voice opposition tothis proposed tax.

COMMITTEE ON INTERNATIONALBROADCASTING

ACCORDING to Frank R. McNinch, Chair-man of the Federal Communications Com-mission, the President has appointed an In-terdepartmental Committee to study inter-national broadcasting.

The Committee is composed of the follow-ing members : Frank R. McNinch, Chair-man ; Attorney General Homer S. Cum-mings ; Harvey B. Otterman and George H.Butler, of the Department of State ; RoyNorth, Deputy Third Assistant PostmasterGeneral; E. K. Burlew, Administrative As-sistant to the Secretary of the Interior andJohn Ward Studebaker, Commissioner ofEducation ; Leslie A. Wheeler, Chief, Divi-sion of Foreign Agricultural Service, Bu-reau of Agricultural Economics, and E. N.Bressman, Special Adviser to the Secre-tary of Agriculture ; Dr. Alexander V. Dye,Director, Bureau of Foreign and DomesticCommerce ; and Warren Lee Pierson, Presi-dent of the Export -Import Bank.

The Committee is to study and reportto the President on international broadcast-ing problems.

IRE CONVENTION

THE TWENTY-SIXTH ANNUAL Conventionof the Institute of Radio Engineers is to beheld in New York City on June 16, 17 and18. The place is the Hotel Pennsylvania.Further information on this gathering willappear in a later issue of COMMUNICATIONS.

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SELENIUM RECTIFIERS

A DEVELOPMENT of increasing importancein communications and other fields ofelectricity is the selenium rectifier. Thecombination of metals which makes aselenium rectifier effective was discov-ered during research with light-sensitivecells. Metal rectifiers have been in usefor many years, and their efficiency anddurability have been well established.They hold an important advantage overother types of rectifiers because they re-quire no maintenance and no replace-ments. Although the rectifying prop-erty of selenium has been known forsome time, it has remained for this newapplication to put it to its maximum use.A reliable rectifier of high efficiencyand wide versatility has resulted. Pres-ent indications are that its service lifeis practically unlimited, and, inasmuchas there are no moving parts, no assist-ing agents, there is no question of main-tenance. It is a particularly versatileproduct varying in its application fromthe rectification of currents as low as afew milliamperes for polarizing direct -current relays, to that of thousands ofamperes in electro-plating uses.

The widespread extension through-out the world of alternating -current elec-trical power has, of course, increasedthe demand for compact apparatus whichwill convert the a -c into direct currentsilently and efficiently.

It is, in effect, an electronic switchwhich changes the direction of the al-ternating current at the instant that itpasses through zero, but, unlike a me-chanical switch, it has no inertia, nomoving parts to wear out and requirereplacement. The selenium rectifierelement consists of a nickel -plated irondisc to which metallic selenium is ap-plied. This is subjected to a series ofheat treatments. The selenium surfaceis then coated with a thin layer of spe-cial alloy which provides a uniform con-

tact surface to distribute the currentevenly over the working material. Oneof the outstanding features of the seleni-um rectifier is its uniform performanceregardless of contact pressure.

Current will flow easily in the direc-tion from the iron to the selenium, butwith great difficulty from the seleniumto the iron. The rectifier presents sucha low resistance to current in one di-rection and such a very high resistancein the reverse that if a curve is drawnof current density against voltage dropin the forward and reverse directions,the reverse current is so small that itcan hardly be shown on the same scale

Note: -Scale of reversecurrent ordinate -1/400 of forward

current ordinate.

Reverse

VoltsDirection

16 14 a 10 8 6 4

120MA

CM2 100

80

60

40

20

11E21111MEN1111MIIIMMEN

2 4 voltsForward Direction

.20

40

60

Fig. 1. Static characteristic of a

selenium rectifier disc having effect-ive surface area of 1 cm2.

with the forward current. This is il-lustrated in Figs. 1 and 2 presentingthe static characteristics of a seleniumrectifier disc having an effective areaof one square centimeter. Note shouldbe made that the current scale of Fig.1 in the reverse direction is magnifiedone hundred times.

The discs and associated parts of Fig.3 are assembled on an insulated spin-dle. Connections are made from onedisc to another by spring washers whichmake contact with the alloy layer onthe face of the discs and only normal

pressure is required to ensure good con-nection. The discs are ruggedly built,completely rigid and are not liable toaccidental damage. They are unaffectedby vibration and are suitable for use ininstallations where apparatus is subjectto mechanical shocks, as exemplified bytheir success in train lighting sets andother mobile services.

A problem a-ising with the use ofdry rectifiers has been the effect of theoperating temperatures. In the solutionof this, the use of selenium has beenan important step, inasmuch as it canoperate with a relatively high ambienttemperature. It is obvious that no metalrectifier can operate if the temperatureof the cooling air is higher than thepermissible temperature of the discs.The latter, then, determines the maxi-mum ambient temperature at which therectifier can be used, and it is importantthat this working temperature be suf-ficiently high to permit flawless opera-tion of rectifiers without the use of fanswhich means moving parts, possiblenoise, and increased maintenance. Thenew selenium rectifier has been devel-oped to withstand relatively high tem-peratures and it is usually not necessaryto apply any special means of coolingalthough, when heavy currents are used,cooling fins are added to the discs.

This high working temperature andthe high permissible back voltage ofthe selenium discs have furthered com-pactness, an important factor in a rec-tifier assembly.

Since the current output from a seleni-um rectifier is not limited by emissivepower but only by maximum tempera-ture, a rectifier which is initially coldcan be loaded to many times its normalcarrying current for a short time. Itis only necessary that the load, whenthe maximum temperature is reached,should be decreased to the normal value.


112 in in. Bridge Frith Cooling {-ins.112 MM. Bridge

Output 6o v.rto v.

to amps.4

`C 84 m in. Half wave -17o v. 1.2

" B.45 rn. Half wave35 m m. Half wave

115 V.250 V.

0.3150 M.A.

" F " 25 in m. Bridge 27 v. 15o" G ""Fr, 25 m in. Bridge

ID m m. Half wave40 v.52 V.

15040

IF 5000

In

4000

a 3 3000

il .000

0 2 3VOL,"5

Fig. 10. Showing varioussizes, assemblies and rat-ings of selenium rectifiers.

Fig. 2. Rectification ratio,or the ratio of forward toreverse current plotted

against voltage.


Fig. Power board forTotalisator equipment (tworectifiers, each with an out-put of 50 volts at 40

amperes.)

Fig. 4 shows the relation between theoperating time and load rating for atemperature rise of 40 degrees C.

The current overload capacity indica-ted in Fig. 4 as a function of the operat-ing time applies only to cases where theinterval (at least half an hour) betweeneach operation is sufficient to allow forthe cooling of the rectifier. For shortcooling periods, the curves of Fig. 5

apply. One curve shows the relationbetween percentage operating time andpermissible overload of the rectifier ;the other, the corresponding maximumoperating time in seconds.

The efficiency of the selenium rec-tifier varies from 65% to 85% accord-ing to the method used for measuringit. It is highly uniform varying littlefrom 15% to 150% of full load. Thisis due to the fact that the internal re-sistance falls as the current increases.This is an important factor on a fluc-tuating load, since the efficiency stayshigh when the load is reduced. In thisrespect this rectifier differs from mostother electrical apparatus where maxi-mum efficiency is attained only in theneighborhood of full load. To illustratethe efficiency with various types of loads,Fig. 6 shows efficiency as a function ofload current for 3 -phase currents andsingle-phase currents of both batteryand resistance loads.

A distinction must be drawn betweenthe efficiency calculated as the ratio ofthe output to the input, when both aremeasured with a wattmeter, and the ef-ficiency obtained when the output ismeasured with voltmeter and ammeterof the moving -coil type. The figure inthe case, the watt efficiency, is about85% at full load for all sizes of discs,types of load, and rectifier circuits be-cause the current ratings are determinedso that the same final temperature isreached in each case by the rectifier.The volt-ampere efficiency, on the otherhand, depends on the form factors ofthe output voltage and current, and thesefactors vary considerably for differentloads and rectifier circuit arrangements.

As mentioned previously the life of ametal rectifier is practically unlimited,and the selenium rectifier has provedthat it is no exception in this respect.

Fig. 6. Efficiency of selenium recti-fier operating at full -load voltage.

It has been in use for about seven years.The experience gained shows that, incommon with other metal rectifiers, it"ages" slightly-what is, the forwardresistance increases-during the first10,000 hours and then tends toward aconstant final value. The resulting dropin output voltage is slight and is fre-quently compensated for by a 5% tap-ping on the transformer when it is nec-essary to maintain output voltage atoriginal value.

Selenium rectifiers are being appliedin communications operations as fol-lows: Telephone and telegra'ph-rec-tifier for operating d -c relays from a -csource, employment of its voltage -re-sistance characteristic (for relay breakdelay and for contact spark quenching ),polarization of d -c relays, power sup-ply for small telephone exchange,P.B.X.'s and signalling installations(with reserve engine generator), float-ing battery chargers in signal circuits,in voltage protection circuits, as meterrectifiers; Radio-rectifiers for filamentor anode supply, avc and detectors inreceivers, loudspeaker field supply. Dif-ferent European designs of rectifierequipment are shown from the large in-stallation in Fig. 7 to the water tightspecial installation in Fig. 8 and thegarage battery -charging equipment inFig. 9. A view of the various sizes,assemblies and ratings are given in Fig.10.

This product is of increasing com-mercial importance among the manycommunication items manufactured anddistributed by associated companies ofthe International Telephone and Tele-graph Corporation throughout the world.It is being used extensively in Europe.Selenium rectifiers are being purchasedalso in North and South America,Australia, and other parts of the world.

RADIO -EQUIPPED AMBULANCEA STREAMLINED AMBULANCE, equippedwith a General Electric radio receivingset, was recently purchased and put intooperation by the New York City FireDepartment.

The radio equipment is capable of be-ing tuned to either police or fire depart-ment frequencies.

Fig. 4. Short period current -over-load capacity of a selenium rectifier.

IL C

IC.

Yso gum

3 ... ..MuLTMLE OP TM!. POW., CURRENT

Fig. 8. Left: Battery -charg-ing equipment in water-tight container. Fig. 9.Right: Portable charging

equipment.

Fig. 5. Overload rating andoperating time for a selen-ium rectifier on intermit-

tent operation.

Fig. 3. Component parts ofa Standard selenium recti-

fier.

-,....;:.,,,,,,

4-.04My......-

I

034


CATHODE-RAY ELECTRON BALLISTICSBy F. MALCOLM GAGER

Department of PhysicsBOSTON COLLEGE

HOLLMANN1 and subsequently Libby' have indicatedthat high -frequency cathode-ray deflections as a functionof frequency for sinusoidal charge forces on the electronstream are accounted for by a single correction factor andconstants. The substance of this paper reveals a gen-eralized correction chart for any cathode-ray tube ofknown geometry and applied potentials when deflectedmagnetically or electrostatically by sinusoidal or non -sinusoidal forces. In addition, the treatment calls for arecognition of two dissimilar constants and a more logicalreference point for deflection expressions which is morein line with recognized differences between theoretical andexperimental deflections.

Let the following represent the quantities :-The peak value of the deflecting voltage

E, -The electron -gun velocity voltage giving rise to the hori-zontal component of particle velocity from the expression(1/2) mv2 = Eve

v -Horizontal electron -gun velocity 5.97 X 10' Vff,T -Time of electron flight under the deflecting platest -The period 1/ff -The frequency of the deflecting force1 -The physical length of the deflecting plates1E -The effective length of the deflecting platesy -The distance of electron fall at the effective tip of the

deflecting plates 1Edy/d1E-The derivative at the point of entrance of the stream

electrons into a field of "no force"D. -The maximum ray deflection from the neutral axis A -A,

Fig. 1, on the screen S due to electrostatic forces

e, Condition whereT is largecompared with t

Condition whereT is twice t

- Conditionintermediate

AccelerationUnity --)1

e2

Fig. 2. Half sine wave with superimposed angles offlight.

D.-The maximum ray deflection due to magnetic forces on thecharge stream

L -The distance from the screen S to the effective tip of thedeflecting plates is

L' -The distance (L 1E/2)s -The deflecting plate spacingH -The magnetic intensity.

Fig. 1 indicates a cathode-ray tube with one set ofdeflecting plates for the purposes of analysis. Due tothe fringing of the electrostatic flux at the edges of the

,Hollmann-W.E.&E.W.. No. 10-1933.'Libby-Electronics, Sept. -1936


deflecting plates of length 1, the effective length lE ismuch larger than the physical length3. When the electronstream's particle acceleration is constant during theflight time T, the deflection sensitivity is straight forwardand given by

D. L' lE IS= - (L + 1E/2) (1)

E. 2sE, 2 sE,

and

D., vL'lE v IE- - -H 2 E. 2 E,

(L 1E/2) (2)

Fig. 1. Skeleton structure of cathode-ray device.

Epdy

dl,

Electron I/Gun

Deflecting Plates L

These expressions are similar to those idealized in thetextbooks by making l, equal to 1.

THE GENERAL DEFLECTION

When frequency and waveform are considered, thereis a definite need for more valid expressions than (1)and (2), and furthermore they cannot be corrected bya single constant. To this end the problem is consideredone of particle mechanics and before revealing the re-sults of such an investigation, it is timely to considerparticle conditions. First, no matter what path the elec-tron takes to arrive at the effective tip of the deflectingplates, it is clear that the velocity at this point will bedetermined by the derivative dy/d1, at the point. Thelatter is definitely a function of the waveform of theapplied E, (or the current which produces H) and thetime of flight T when E, is a function of time. Secondly,the distance y at the effective tips of the deflecting platesis not only dependent upon the latter considerations butin addition the full time of flight is not always effective inproducing electron fall from the neutral axis A -A.

With the above physical conditions in mind, one canrefer to Fig. 1 and write the general deflection expressionwithout immediate regard for the character of the forceson the electron stream. Accordingly the maximum de

(Continued on page 15)'R.C.A. 906 and 911 have 1= 1.5 cm whereas le = 1.9 cm.

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A group photo of those in attendance at the Conference.

THE BROADCAST ENGINEERING CONFERENCE

THE FIRST Annual Broadcast Engi-neering Conference, held at Ohio StateUniversity, Columbus, Ohio, from Feb-ruary 7-18, was a distinct success. TheConference had ninety-six registrations,coming from twenty-five states andthree Canadian provinces. These regis-trations included a large number ofoperating broadcast engineers, represen-tatives of industry, teachers, and a num-ber of governmental representatives. Asa matter of fact, the gathering was sosuccessful that plans are under way tohold it annually in Columbus.

The excellent program of the con-ference included three timely topics each

day, a period of two hours being as-signed to each topic. Logically, thefirst hour was devoted to a formal lec-ture, while the second hour was givenover to a round -table discussion.

Briefly, the speakers and their sub-jects were as follows: "Field StrengthSurveys," by J. F. Byrne, Collins RadioCompany ; "Coupling Networks," byW. L. Everitt, Ohio State University ;

Left: Candid shot of JohnMorrison (with pipe) talk-

ing to Dr. Brown.

Right: Dr. Geo. H. Brownthe center of interest at an

informal discussion.


"Studio Acoustics," George M. Nixon,National Broadcasting Company; "Ul-tra -High -Frequency Propagation," byH. H. Beverage, RCA Communications ;"Propagation of Broadcast Frequenciesat Night," by J. H. Dellinger, Bureauof Standards ; "Broadcast Antenna De-sign," by George H. Brown, ConsultingEngineer ; "High -Power Radio -Fre-quency Amplifiers," by W. H. Doherty,Bell Telephone Laboratories ; "Modula-tion and Distortion Measurements," byA. E. Thiessen, General Radio Com-pany ; "Indicating Instruments," by H.L. Oleson, Weston Elec. Inst. Co.;

(Continued on page 35)

HIGH -FREQUENCY TRIODE OSCILLATORS

By GROTE REBER

TRANSIT TIME EFFECTS

RECENTLY considerable work has been done on electrontransit -time effects in triode amplifiers and diode recti-fiers. These same principles apply to negative -grid triodeoscillators. Ferris' gives

K -roc).= seconds (1)

5.95 10'\/Vg

- 1 I

e`' dx seconds ( 2)

.15.95 1(h/E' Eit/E' \, l,, E'

wherer1 cathode -to -grid transit timer2 grid -to -plate transit timeK a function of rgjrkrK cathode radius in centimetersro grid radius in centimetersr, plate radius in centimetersER plate potential in volts with respect to cathode

3 InVg=

2 S. / k 1 + + -2 log rp/roit 314

"'Input Resistance of Vacuum Tubes as Ultra -High -Frequency Ampli-fiers," by W. R. Ferris, PIRE. p. 82, January, 1936.

ER -

log rp/r,-;and

In plate current in amperesS,,, transconductance in mhos

amplification factor

Table I gives a summary of data taken from currentliterature as a basis for computation. The results areshown in Fig. 1.

These results show that efficiency is primarily de-pendent upon the ratio TIT (where T = 1/f) as indi-cated by the mean heavy line and independent of absolutefrequency. t2 appears to have little or no effect onefficiency since all points fell below a tenth of a periodand 75% fell below a twenty-fifth of a period. Since theloading conductance is proportional to t2 the grid -cathode conductance will be over 50 times the grid -plateconductance so that even though in the average feedbackoscillator where the grid -plate voltage will average twicethe cathode -grid voltage t, will still be the controllingfactor.

THE PRINCIPLE OF SIMILITUDE

If a series of tubes are built exactly similar and havinglinear dimensions of U, U/2, U/3, , U/n, from the

Fig. 2 Performance curves of triode oscillators when operated at constant plate dissipation cnd constant platecurrent.

20

1111 11111 In 1111! flu1E13 igm Illh inii30

II 1111 IFAIII 11111 111111II 11111/i nllIl MIMI IIIIII

40

50 1111111...1.0.1

60

`') 70.1.-> 80>)0 900wt71 100

..,..

MNIIMMIIIIMONIIMMIMMNii11=IIMMENIIIIIMENEMEMINE

MEMNON MEM

4 .......im..m.....NIMIIIMMNiiillamlvAIMIMIMMEMI EMU'=NFIIIIIIIMIIMI=MESIIMW

MINIVAMIIIIIIMN IIIMIll'AMENII

6MEN 4=MEN/AMINMEIMM

INIIIIIIIIIIIMMINMI.IMIIIIIMEEMMa

MINI 11111111E MillMIIIIINIMMIIIIIMINII

MMIIIIIIMMENommommimIMMININIIIIIMI

liall

=Man

2

1=1=7INVIVAIIMN=MEMIIMMIMINIM=MIMI

1/1.11"

MEIMEM=INE MMI

=W111161111UMMEINIMOI111111

Mr MN=MWIN= MN/ AN

WM=Pill'AMIEMINIIIIIIINIIAIIIIMENIIM=MMEN

=

10

IIM'IMMIPAIMPFAMIIIMIIIIIIIIMINEI1.111111WAIMMIKAMMOMFAMIMMINNMEMZrATIVIIIrmimi

Allir.....-.11111anlry

/MEM IIIIIMINIVAIIIIMMIIIIIMMIN

meMi M7!...tOP7.mAlAMIMW.,1111:Mlle

illiffillim=ri ...M.P.7:17f,-,m

III , IIIeip 150 -ca

IHI mo.... II I MP'10 SHIM 11111

,

11111,

III 11111 11111,200

iii,_

300 WIEWARIMI111FAME II INN insmi

1111 o Indicates 100/0 efficie-ncy 11111MN!MEM

ii 11111!2M 1111 . Indicates 20 0/0 AMMI effici?..ny UM111012111400

50060o M_W *ailiRiNilMMIIM4111====lina700

1

=IANIF/111mixartossimmoimommiummommosoniir.wwwwmoi

MMIIIIIMENMIIIIIIIMMIIImisio=mo

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8 EnaMIIIIMIIIMIIMIINIIIIIIIIIIIIIMIINM11=111M11.111111101

INIIIMMIIIIMMI=INN =INIMMEN

miiIIIINIMMN

MEM x Indicates slope of curvy equals -4 Millmu1111111111111=1111IIIIIMINIMMIIIIIMIIIIIMMINIIIIIIINIIIMM=MBINMENIN=so

102

Output Power

111111111111M MIBM1111=11111NIMIMIMMEMI= MN MIMS

IMIIIIIIIIIIMIIIMINIMI __IL...

MIIIMMENZ_I MIIIIIIMII=MEIBME

imMommem1

in Watts

in IM11111=11OMM3 404 105


Model theorem2 the R, S., Rp will be substantially thesame. When Eb, Eb/2, Eb/3, , Eb/n are applied withthe same load resistances, a series of plate currentsIb, Ib/2, 'b/3....., Ib/n will result. The power inputswill be Pi, P1/4, P,/9, .... , P1/n2. Since t, is pro-portional to (rg - rb)/1/Ib the_series of t1 will beTi9 ti/V29 tr/V39 9 TI -/n. From the resultsof Table I and Fig. 1 the ratio ti/T will produce agiven E independent of f. Therefore for any given Ethe series of frequencies obtained will be f, V2f, V3f,

, Vnf. With fixed efficiency the power outputswill be P., 130/4, P./9, , Po/n2. D will remainconstant and the dissipating areas will be A, A/4, A/9,

, A/n2. When power output versus frequency isplotted on log -log paper and points of equal efficiency areconnected together a line of slope -4 will result. Simi-larly the line drawn tangent to all the curves will havea slope - 4. The equation of this line is

log P. = s log f + log B (3)

where s is the slope and B the intercept value. This in-tercept value is important as it is the figure of merit ofthat design and operating condition.

POWER OUTPUT

Table II gives a summary of data plotted in Fig. 2.The intercept values for these curves have been com-puted as follows. Equation (3) is transformed to

13= Pf4 (4)

by taking the antilog and inserting the value - 4 fors obtained from the above discussion.

The parameters of which B is a function are notIf, however, the following empirical relation

is set up

B = J (5)

where J is a constant to be determined

Pi... is plate dissipation in wattsVolume is ir(re-rk2)1 in cubic centimeters

and J is computed for various efficiencies ; the resultsplotted in Fig. 3 are obtained. The radius of the circlesis equal to the probable error of the point in question. The!"Recent Developments in Miniature Tubes," by Bernard Salzberg and

D. G. Burnside, PIRE, p. 1142, October, 1935.

Fig. 1. Values of cathode -grid transit time in fractionsof a period versus efficiency.

60

t 50

gCL 40

..5

'.,;' 30I:

4...4, 20

40

N \A PeA

HG F

N

IN

Mir

kg

E4'

A

ti

\,,,, .40,s \ , 0H L

,G

5

K N I

-...,k ouF

SE

,LIf

aA C a P

A

I

A

cc

e

'

,.,

a4:o.App f

C

P,:1,5,,,ir° ""'L"---

`A

.05 .to .15 .20Ratio 7',/T

.25 .30 .35


numbers in circles indicate number of readings used tocompute value of J at point indicated. The fact thatmaximum J is obtained fors between 10% and 20% canbe checked qualitatively by noting on Fig. 2 that linesof slope -4 become tangent to curves 1, 2, 3, 5, 8, 9, 12between points s = 10% and s = 20% and tangent tothe others near 20%. At E below this tangent point ofslope -4 the output decreases very fast and as B ap-proaches zero so does J with the result that the curve ofFig. 3 will turn back below 15% and end at zero -zero.

GRID TEMPERATURE

Application of the Stefan -Boltzmann law to the triodestructure involves the following additional notation.

UVR

MN

T kTgTC

energy dissipated at the cathodeenergy dissipated at the gridratio of grid -mesh hole area to grid cylinder

area (always less than one)radiated cathode energy intercepted by gridradiated cathode energy through gridlength of elements in centimeterscathode temperature Kelvingrid temperature Kelvinplate temperature Kelvina constant for radiated energy per square

centimeter per degree Kelvin

Then

M (1-R) (Tx*- T0`) 27r1CrxN=R (Tx` - T54) 27r1CricM N -U

(6)(7)(8)

M + V = (1 -R) (Te- Tp4) 271-1Crc (9)U + V= [(1-R) (Te-Tp4) +R (Tie- T P` ) I2r1Crp (10)

from these we may eliminate M, N, 23t, 1 and C whichgive

rK [VR (Tie- Tp4) + (1-R) To') (U + V)]ro = (111U (1 - R) (T0' -and

VR (Tie - Tp4)+(1-R) [(U V)rfc TIE4 + Ur o

TG = . . (12)(1-R)[Uro + (U V)ric]

Using R from 0.6 to 0.9, V will be the controllingfactor above V = .25U. This is important because highefficiency demands that I -e be small.

EFFICIENCY

Power output can be expressed asP. = DAe/(1- e) (13)

where P. is power outputD is dissipation per unit areaA is units of areae is efficiency

Using existing materials D cannot be increased verymany times over present values. Since the fundamental

-!X:: SS!:

alternating -current generator is limited to one wave-length in size A will be proportional to the square ofthe wavelength and P0 will be inversely proportional tof. The only way (outside of cascading many generators)to obtain high power output is to increase E. Inspectionof (13) shows the nearer it approaches unity the moreprofitable it is to increase it.

CONCLUSIONS

(a) Efficiency is determined by ratio TIT as shownin Fig. 1. Its importance increases approximately as thesquare of the frequency.

(b) Absolute power output islations of (4) and (5) and Fig. 3.

(c) Grid temperature may be importantmined from equations (11) and (12).

CATHODE-RAY BALLISTICS

dependent upon re -

as deter -

(Continued from page 10)

flection from the neutral axis is given by (D - y) /Ldy/d1, orD = Ldy/d1 y (3)

This expression is as expected. The first term involvesthe derivative and the second the distance of fall y.

60

50-I.-C

':':

W 400. CO

.S. 030i).?ca)

.64.- 204 -kJ

(E)

10 002 3 4 5 6 7 8 9 10 20 30 40 50 60 70

J times 10-6

Fig. 3. Variation of empirical constant J withefficiency.

WAVEFORM AND FLIGHT -TIME CONSIDERATIONS

When the period t of the deflecting voltage E., (orthe current producing H) is comparable with the elec-tron's flight time under the deflecting plates 1, the forceon the electron's charge (e) is not constant. In supportconsider Fig. 2 where a half sine wave of unit amplituderepresents charge acceleration as a function of electricalangle or time, along with the constant upper line indica-tive of constant acceleration. Superimposed upon thesetwo is a slot suitably representing the electron flight time.If 0, represents a width of slot where t is large comparedwith T, the acceleration force on the charges which pro-duce maximum deflection is substantially constant dur-ing the time T, because the areas under the constantcurve and that under the sine curve are substantiallyequal'. The latter is to be expected over a considerablerange of frequency from zero (d -c) to some high fre-quency. The integrated curve area, or the terminalvelocity in the vertical direction at the tip of the de-flecting plates I, when made a deinite integral overthe time T = 1, /v, when expressed as a ratio for thatof a constant force is the correction factor altering theterminal velocity which would be expected for a constantforce.

Let the acceleration be a function of a. The ratiobetween the two terminal velocities in the vertical direc-tion is given by

KP

- f18i f (a) da/e- (4)

where 01 = - 0/2), 132 = (0 + 0/2) and [35 thereference angle or time. When (4) is evaluated for asine -wave accelerating force the expression for K be-comesK = 2 sin (0/2)/e (5)

The derivative dy/dl5 involves a ratio between theterminal velocity in the vertical direction and the gunvelocity, thus K dy/dl, is said velocity corrected for anyK evaluated. In order that (4) and (5) be made ex-perimentally useful for any tube K, from (4), wasevaluated for three specific waveforms and plotted-curves 1, 2, and 3, Fig. 3-as a function of frequencyon a general frequency axis applicable to any tube

(Continued on page 28)'Considering high frequencies increase the slot width A because the

effect is the same if the slot width is fixed and the frequency increased.50 is chosen to produce maximum deflection over the flight time

angle 9.


Mork Etl-idge, WHAS.

Elliott Roosevelt, Hearst Radio

Harold Fough. WBAP.

REPORT OF THE

HELD

AT THE HOTEL

WILLARD, WASHINGTON, D. C.,

FEB. 14-16

THE SIXTEENTH ANNUAL convention ofthe National Association of Broadcast-ers, which was held at the Hotel Wil-lard, Washington, D. C., from February14 to 16, was well attended, about 350broadcasters being present. As expected,the business sessions were primarilyconcerned with reorganization. Therewas even less opposition to the proposedplan than had been anticipated.

BOARD OF DIRECTORS

The new Board of Directors is com-posed of twenty-three members, seven-teen district representatives and sixdirectors at large representing the clear,regional and local channels.

The district representatives are asfollows : John Shepard, 3rd, YankeeNetwork, for District 1; Harry C.Wilder, WSYR, Syracuse, New YorkDistrict 2; Clair McCollough, WDEL,Wilmington, Delaware, District 3; JohnA. Kennedy, WCHS, Charleston, WestVirginia, District 4; W. Walter Tison,WFLA, Tampa, Florida, District 5;Edwin W. Craig, WSM, Nashville,Tennessee, District 6; Mark Ethridge,WHAS, Louisville, Kentucky, District7; John E. Fetzer, WKZO, Kalamazoo,Michigan, District 8; Walter J. Damm,WTMJ, Milwaukee, Wisconsin, Dis-trict 9; John J. Gillin, Jr., WOW,Omaha, Nebraska, District 10 ; Earl H.Gammons, WCCO, Minneapolis, Min-nesota, District 11; Herb Hollister,KANS, Wichita, Kansas, District 12;0. L. Taylor, KGNC, Amarillo, Texas,District. 13; Gene O'Fallon, KFEL,


Denver, Colorado, District 14; RalphR. Brunton, KJBS, San Francisco, Cal-ifornia, District 15; Donald W. Thorn-burgh, KNX, Hollywood, California,District 16; C. W. Myers, KOIN, Port-land, Oregon, District 17.

DIRECTORS AT LARGE

The six Directors at Large are :Clear Channels Harold Hough,

Edward A. Allen. WLVA.

WBAP, Fort Worth, Texas, and Lamb-din Kay, WSB, Atlanta, Georgia;Regional Channels-Frank M. Russell,WRC, Washington, D. C., and ElliottRoosevelt, Hearst Radio, Incorporated;Local Channels-John Elmer, WCBM,

NAB CONVENTION

Edwin W. Craig, WSM.

Baltimore, Maryland, and Edward A.Allen, WLVA, Lynchburg, Virginia.

EXECUTIVE COMMITTEE

From the above Board of Directorsthe following men were named to acton the Executive Committee : MarkEthridge, Edwin W. Craig, Herb Hol-lister, John Elmer, Frank M. Russelland Walter J. Datum. Philip G. Loucks,

Lambdin Kay, WSB.

former Managing Director of the NAB,has been retained as special counsel forthe organization.

It was announced that the Board ofDirectors will meet again in Washing-ton on March 21. It is expected that

the matter of a paid President for theassociation will receive attention at thattime.

REBUILDING TRANSMITTER TUBESONE OF theradio is theNo one can

most interesting phases ofrebuilding of power tubes.imagine the difficulties en-

countered in rebuilding practically anykind of tube that may come in for re-pairs of some kind of other, unless hehas been associated with this kind ofwork for many years.

When a tube is received, it is testedfor vacuum with a high -frequency coilto determine if there is a slow leak orcrack somewhere in the tube-also asto whether or not there is any vacuumin it.

Next is to determine whether the gasis air or if it is gas that has been liber-ated from the electrodes. If the gas isair, new stems are needed. If the job isa water-cooled tube, the metal -to -glassseal may be cracked or leaky which cangenerally be repaired if it is hard glass.If it is soft glass, it will probably re-quire a new bulb and a glass -to -copperseal.

We are now ready to break the vac-uum at the tip off and open the tubewith a hot wire. The grid and plateare examined for defects. Then thefilament is measured with a micrometerto determine the diameter. A new fila-ment is formed of the same diameterand spot welded to the leads. The grid


Herb Holl'sPer, KANS

John Elmer, WCBM.

Frank Russell, WRC.


Fig. 1. The Franklin push-button tuner.

PUSH-BUTTON TUNING has received agreat deal of attention during the pastyear. While automatic tuning was atfirst confined to the higher priced re-ceivers, push-button tuned sets sellingfor less than twenty dollars are nowavailable. Additional interest will nodoubt be evidenced in the subject during1938. Hence, it is the purpose of thisarticle to briefly review some of themost recent developments in this field.

The push-button tuner mechanismshown in Fig. 1 is a mechanical system

Fig. 7. The Harbray tuning unit.

recently announced by A. W. FranklinMfg. Co. The mechanism essentiallyconsists of six or more station selectorbuttons mounted on a suitable frame,with a corresponding number of camson a common drive shaft assembled ontwo pedestals. The action is transmit-ted from the cam shaft to the variablecondenser by means of two pulleys anda connecting wire cable. A dial is alsoattached to the condenser by the pulleyand drive cable arrangement.

Adjustments for desired station fre-quencies are made from the front ofthe radio by removing a snap -in name

Fig. 6. Meissner's push-button system.

RECENT DEVELOPMENTS

Fig. 3. Sprague's back -adjusted unit.

plate on the face of the escutcheon. Theset screws for adjusting the cams arethus made easily accessible. The desiredstation is tuned in by the tuning knob,then the proper selector button is de-pressed and the corresponding cam is setusing a screw driver. The selection ofstation frequencies may be made in anydesired sequence. When any button ispushed in, a latching bar automaticallylocks it to tune -in position and releasesall other buttons. Manual tuning isaccomplished by pressing a tuning knoband adjusting the variable condenser tothe desired station frequency. Thechange from manual to push-button tun-ing requires no additional button.

Fig. 8. Automatic Devices B-6 tuner.

The principle of operation is simple-the mechanism utilizes the downwardstroke of a sliding member to rotate acam to a pre-set adjustment. At thepoint of adjustment, the radius -edge ofthe push button meshes with the face ofan inverted V-shaped cam. A stroke offive -eighths of an inch rotates the camthrough a maximum arc of 60°. Thisrotary motion is transmitted to the shaftof a variable condenser by a system of


two pulleys (ratio of 3 to 1) connectedby a drive cable of stainless steel. Allpush -buttons, cams, pedestals, and thebutton bearing plate are of one piece diecastings. The individual parts aresolidly assembled and the bearing sur-faces of all moving parts are kept toclose tolerances. The arrangement anddimensions are given in Fig. 2.

An automatic tuning system employ-ing trimmer condensers has been an-nounced by Sprague Specialties Co.

Fig. 2. Arrangement of tuner of Fig. 1.

This system, which is available only tomanufacturers, can be obtained in vari-ous combinations. In Fig. 3 is showna two -circuit six -button back -adjustedunit, while Fig. 4 shows a two -circuit,six -button, front - adjusted assembly."Back -adjusted" refers to a unit inwhich push buttons are operated fromthe opposite face to that from which thetrimmers are adjusted; while "front ad-justed" means an assembly in whichpush buttons operate on the same facefrom which the trimmers are adjusted.

The manufacturer of these latter as-semblies furnish : three -gang tuners ina six -button, back -adjusted type; four-,six- and eight -button, back -adjustedtypes for two -circuit tuning; and four-,six-, and eight -button, front -adjustedtypes for two -circuit tuning. Thesestandard units, further, can be varied tomeet special situations ; for example, asix -button unit can be obtained withfive buttons for station selection and thesixth as a double -pole -single -throw dis-

IN PUSH-BUTTON TUNING

connect switch, or a double -pole -double -throw change -over switch.

A push-button tuner circuit with per-meability tuning is shown in Fig. 5.The permeability tuning on push-buttoncontrol is provided in the oscillator, us-ing a Colpitts circuit. The antennacircuit is tuned by use of the regularantenna coil and the push -button -switched tuner condensers of the typejust described. Good stability in theoscillator circuit can be obtained through

P- Push-button tuning 1-FAmpM. Manual tuning

.Z(.LTTTTTT_L

CARRIER RANGE520 - 1/20 Kc.675 - 1380 Kc.900 - 1680 Kt

Fig. 5. Circuit with permeabilitytuning.

careful design of the permeability -tunedcoils, and the use of a Colpitts oscillatorcircuit with the high -capacity fixed con-denser minimizes the variable circuitelements.

The automatic push - button tunershown in Fig. 6 has been developed bythe Meissner Manufacturing Company.It may be used with any superhetero-dyne or t -r -f receiver having a two- orthree -section tuning condenser. It isrecommended by the manufacturer forsingle -band two -gang receivers, provid-ing full automatic operation on suchsets. On receivers with three -gang con-densers, only two sections are tuned bythe push-button condenser assembly. If,however, the signal strength of thestations selected is adequtae to givegood reception on a four -tube receiver,a receiver with five or more tubes willgive satisfactory performance whenused with this push-button condenserassembly. The Meisner tuner provides

Fig. 4. Sprague's front -adjusted tuner.

for selection of any of six pre -deter-mined stations. A seventh push buttonis used to return the receiver to normaltuning condition when desired.

The Harbray Company's push-buttontuning unit is shown in Fig. 7. Thisassembly permits the selection of fivestations, the sixth button being used toshift from manual to automatic tuning.Like the previous one, this unit can beused on any two -gang superheterodytr%

The Automatic Devices Manufactur-ers' B-6 tuner is shown in Fig. 8, whilea typical superheterodyne application ofthe unit is given in Fig. 9. The opera-tion of the switching unit is completelyautomatic, so that when one button is

BLACK - Tb van cond...frame in receiver

_14 Jr

Tt -t t -t

r" r" r" r"

:JA 1.11 J4

Fig. 9. Application of tuner of Fig. 8.

pressed it remains in position until re-leased automatically by pushing any ofthe remaining buttons. In operationthe push-button switches connect thesmall variable condensers to the oscil-lator and antenna circuits of the radioreceiver.

A push-button station selector switch,which is similar in action to the wellknown apartment house lobby telephoneselective ringing switch, has recently

Fig. 10. Mallory% ten -button switch.

been introduced by P. R. Mallory. ThisYaxley station selector switch is adapt-able to both motor drive and condenserapplications. Flexibility of tool designmakes combinations possible up totwelve buttons and allows adaptation tothe mechanical requirements of the in-dividual designer. A ten -button switchis shown in Fig. 10, while Fig. 11

shows an 8 -button unit for use in sta-tion selection, and other applications.The switches are available in two cir-cuit combinations-one designed for cir-

"$r $1144.04:1----

41114; rati

.444010'

Fig. 11. A Mallory eight -button switch.

cuit closing applications and the otherfor circuit transfer applications.

The unit shown in Fig. 12 is a push-button switch which has been designedby Oak Manufacturing Co. Silver-plated, double -wiping contacts are em-ployed and the contacts are entirelyfloating. This switch also features aslide latch -bar to automatically com-pensate for wear. It is available withany number of buttons from four totwelve. A variety of circuit applica-tions may be used. It is adaptable eitherto trimmer or permeability tuning andmay be used for band changing.

Fig. 12. An Ook push-button switch.


THE DELTA -STAR MIXER

SPEECH -INPUT MIXERS are used to mixthe outputs of two or more soundsources into the input of an amplifierchannel. The output of the amplifierchannel may modulate a radio transmit-ter or it may be directly reproduced byloudspeakers as in a public-address sys-tem. Also the sound may be stored tobe reproduced at some later time, as indisc and film recording.

Mixers may be either electronic orresistive. Electronic mixing has bothadvantages and disadvantages, but asresistance mixing is almost standard inhigh -quality mixing circuits, this dis-cussion will describe a new resistance -mixer circuit.

Resistance mixers use either seriesmixing, parallel mixing, or a combina-tion of the two methods. These oldermixing methods will not be discussedin detail as the common circuits can beseen in any broadcast or recordinghandbook. It is enough to say that somefour -position mixers average a 700%impedance mismatch and 17 decibelsminimum insertion loss.

In the four -position mixer circuitshown in Fig. 1 the impedances arematched looking forward or backward,and standard variable pads can be usedfor any number of inputs from two tosixteen. The inherent mixer loss (mini-mum insertion loss) is 6 db up to fourpositions and only 12 db for the six-teen -position mixer.

The same impedance pads whichserve as master gain also serve for eachinput channel, which reduces the num-ber of spare pads necessary. The inputand output circuits are identical and canbe used interchangeably as either in-puts or outputs.

The mixer can do a number of thingsthat the average mixer circuit cannotdo. Two inputs can feed up to fourseparate outputs, each with its own gaincontrol. Four inputs can feed two out-puts, or three inputs feed three outputs,with always a separate gain control oneach input and output channel.

However, one precaution must be keptin mind. The inputs and outputs mustbe chosen with care due to the hybridbalance which exists between inputs Aand B, C and D, and between E and F.Thus if terminal A is used as an input,terminal B cannot be used as an outputas there is nearly infinite loss betweenA and B regardless of the pad settings.

By J. N. A. HAWKINS

Fig. 2. Equivalent circuit of delta -starmixer of Fig. 1.

Likewise there is nearly infinite loss be-tween terminal C and terminal D, andterminal E and terminal F. However,the minimum loss between terminal Aand terminals C, D, E or F is only 6 db.Thus, while there are six pads shown,this particular arrangement can onlybe used as a four -position mixer, withthe other two pads acting as separatemaster gain controls in two separate out-put channels. These two output channelsare useful in many services; such as,feeding the main and monitoring ampli-fiers, feeding a network and a localtransmitter, etc. Note that the nearlyinfinite loss between the two output cir-cuits prevents line noise, switchingclicks or other unwanted sounds appear-ing in one output channel from reach-ing the other output channel.

The high loss between the terminalsin the same vertical plane in the dia-gram of Fig. 1 (AB, CD, EF) can be

Fig. 1. Schematic of the 4 -position mixercircuit.


visualized more easily by examiningthe equivalent circuit of Fig. 2. It isfrom this equivalent of the four -posi-tion mixer that the arrangement getsits name. Fig. 2 will be seen to be adelta network combined with the com-mon star network, both borrowed fromcommon three-phase practice.

Each of the resistances in Fig. 2 rep-resents the output resistance of the vari-able pads shown in Fig. 1, and they areall equal. In Fig. 2 it will be seen thatany voltage applied across A will notappear across resistance B becauseboth ends of B are at the same potentialas long as C equals F and E equals D.However, any voltage impressed acrossA will produce a voltage across theother four resistances C, F, E and D.

By the same token it is seen that anyvoltage impressed across C will not ap-pear across D. Likewise nearly infiniteloss exists between E and F. The circuitresolves itself into a balanced bridge,but it is shown in this form to show thatin certain balanced bridges three condi-tions of balance exist and not just one.

This matter of infinite loss betweenthree pairs of terminals has an unusualand interesting aspect. It means thatthree studios, for example, can be in-terconnected by means of microphonesand monitoring speakers, so that eachstudio can talk or listen to the other twostudios without singing or audio feed-back as long as the acoustic loss in eachstudio, from speaker to mike, is greaterthan one-half of the net gain betweenany mike and loudspeaker. This condi-tion is easy to realize in practice withoutspecial mike or speaker placement.

While it is rarely necessary to inter-connect three studios for full triplexconversation, the use of two studios withfull duplex facilities is not uncommon.At the present time it requires the useof headphones at one end of the conver-sation, at least, but with this mixer ar-rangement loudspeakers can be used atboth ends without trouble.

One of the main advantages of theDelta -Star mixer is that standard andsimilar pads are used throughout. Inthe four -position arrangement of Fig. 1,six 200 -ohm pads may be used workingout of four 200 -ohm sound sources andfeeding two 200 -ohm lines or amplifierinputs. Mixing transformers are notshown in Fig. 1, but they might consist


Fig. 7Taylor T-40

A NUMBER of new tubes, both transmit-ting and receiving, have recently beenmade available. The purpose of thisarticle is to briefly review the most re-cent developments in this field.

Shown in Fig. 1 is a television ampli-fier pentode, designated as the RCA -1851, and for use by experimenters andamateurs in experimental television re-ceivers. This pentode features highgrid -plate transconductance (9,000 mi-cromhos). It is designed for use in ther -f and i-f stages of the picture ampli-fier as well as in the first stages of thevideo amplifier when several videostages are used. This RCA Radiotronrequires a heater voltage (a -c or d -c)of 6.3 volts, while the heater currentshould be 0.45 ampere. Direct interelec-trode capacitances are given as follows :grid -to -plate, 0.02 mmfd maximum; in-put, 11.5 mmfd; output, 5.2 mmfd.

A new RCA triple -grid amplifier tubehas been made available to radio -equip-ment manufacturers. This tube, desig-nated as the RCA -657, is a pentode typeof metal vacuum tube intended for serv-ices in the r -f and i-f stages of radio re-ceivers designed for low heater -powerconsumption. Its heater requires only

Fig. 6. The Eimac RX21.

NEW TUBES

Fig. 3. The Gammatron 54.

0.15 ampere at 6.3 volts. Its direct in-terelectrode capacitances are as follows:grid -to -plate, 0.005 max. mmfd; input,6.5 mmfd; output, 10.5 mmfd.

Information has also been released onthe RCA -6K8 triode-hexode converter.This tube is a multi -unit type of all -metal vacuum tube incorporating a tri-ode unit and a hexode unit. It is in-tended primarily for use as a converterin superheterodyne receivers, especiallythose of the all -wave type. In such re-ceivers, performance of the 6K8 is char-acterized by improved frequency stabil-ity, according to the manufacturer. Itrequires a heater voltage of 6.3 volts,the heater current being 0.3 ampere.

A 6K8 metal -type triode-hexode con-verter has also been announced by Ray -

Fig. 4. United's 312-E.

Fig 1

RCA -1851

theon for use in superheterodyne receiv-ers. It may be used satisfactorily ina-c/d-c receivers inasmuch as the screen,oscillator plate, and mixer plate may allbe operated from the same 100 -volt sup-ply. The heater of this tube also re-quires 6.3 volts while the heater currentis 0.3 ampere.

A type 6J8G triode-heptode converterhas been released by Hygrade Sylvania.This tube consists of a triode unit anda heptode unit having a common cathode.The applications of this unit are simi-lar to those of the separate oscillatorand mixer tube combination. However,new construction is said to make pos-sible some circuit simplifications andto give improved performance at highfrequencies.

A 6J8G triode-heptode converter hasbeen announced by Ken-Rad. It was de-signed especially for converter opera-tion in high -frequency receivers.

Among other new tubes which havebeen made available to radio -equipmentmanufacturers are the following: Syl-vania 6AC5G high -mu power -amplifiertriode; Sylvania VR150 voltage regula-tor ; Sylvania 6F8G double -triode ampli-fier ; Sylvania 6G6G power -amplifier

Fig. 5. Eimac Type KY21.

'U


Fig. 8. The Collins C -849A and C -849H.

pentode ; Sylvania 6W7G triple -gridamplifier; Raytheon 6W7G pentode -typeamplifier; RCA -1G5 -G power -amplifierpentode ; RCA -6C8 -G twin -triode ampli-fier ; RCA -6F8 -G twin -triode amplifier ;RCA -6G6 -G power -amplifier pentode;RCA -6V6 beam power amplifier ; RCA -6Z7 -G Class B twin amplifier ; andRCA -25A7 -G rectifier pentode.

Still another recent development inreceiving type tubes are the glass "Ban-tam" tubes developed by Hytron (seeFig. 2). A complete series of thesetubes are available, and they are said tobe identical in electrical characteristicsto the larger glass types. These tubeswere designed for applications wherespace economy is required. The shortconnection leads in conjunction with

Fig. 2. Hytron's "Bantam" tubes.

the metal shield band about the base issaid to increase the stability of opera-tion. Lower interelectrode capacitiesare a result of the geometric construc-tion and short connection leads in thebase, according to the manufacturer.

For ultra -high -frequency usage,Heintz & Kaufman have announced thetype 54 Gammatron shown in Fig. 3.This tube is a 50 -watt plate triode hav-ing an amplification factor of 27. Theelectrical characteristics of this tube areas follows : filament voltage, 5.0 volts;filament current, 5.0 amperes ; normalplate dissipation, 50 watts; maximumaverage plate current, 150 ma ; maxi-mum average grid current, 30 ma; aver-age plate impedance, 7500 ohms.

Another recent development of Heintz

Below: Fig. 9. Raytheon's RK-11, 12, 51, 52. Right: Fig. 10. Amperex 849A.


& Kaufman is the Gammatron type 654.The electrical characteristics of this tubefollow : filament voltage, 7.5 volts ; fila-ment current, 15 amperes ; normal platedissipation, 300 watts ; maximum aver-age plate current, 0.6 ampere; maxi-mum plate voltage, 4,000 volts ; maxi-mum average grid current, 0.10 am-pere; average plate impedance, 3,700ohms ; average amplification constant,22; grid -plate capacitance, 5.5 mmd;grid -filament capacitance, 6.2 mmfd;plate -filament capacitance, 1.5 mmfd.

A redesigned version of the Unitedtype 212 is the new United type 312 -


Among the interest-ing developments att h e InternationalAir Show was thetwo-way radioequipments shownby Bendix Aviation

Corporation.

Ranging in powerf om 10 to 100watts, these equip-ments provide mul-ti -crystal controlledoperation and re-mote electrical fre-

quency shift.

COMPROMISES IN ALLOCATION ENGINEERING

THE BROADCASTING INDUSTRY has forgedahead since its inception in all itsbranches ; administration, engineeringand in its final product, entertainment.It has been fortunate in working on anexpanding market. It seems that theindustry may be entering a new phaseshortly, which may be akin to whatpsychologists term a plateau. Thisstatement should be limited to the regu-lar broadcast band, for the opening ofthe ultra -high -frequency bands, the de-velopments of facsimile and the labora-tory successes of television are not likelyto let the industry settle down to rest,however, well earned that rest may be.

In the regular broadcast band, itseems likely that international agree-ments, particularly the one recently ne-gotiated in Havana, will lead in one wayor another to the clarification of broadpolicies, such as power, number of sta-tions, quality of reproduction permis-sible, and broad allocation principles,which, while fairly well defined at anyone time, have always operated underthe assumption that some day, in thenot distant future, these allocationstandards might be changed. The effecthas been to keep broadcasters on thealert all the time to make sure that theywould not lose any opportunities toimprove their position. There must havebeen a tremendous duplication of work.Here is a job in which the National

RAYMOND M. WILMOTTE

Association of Broadcasters could beof valuable assistance; it could preventmuch of this duplication, by analyzingthe decisions of the Commission andkeeping the industry informed of thecases in which the engineering andother standards were not rigidly ad-hered to.

Allocation standards are bound to beand should be subject to exceptions.At best they are compromises betweenideal engineering standards and the eco-nomic and social forces of the countryas a whole. These economic and socialforces are not the same all overthe country, nor are they the samefor all stations. To the extent thatthey change, so should the standardschange also. Rigid standards can onlybe countenanced on the assumption thatall the details of engineering, economicsand sociology, affecting the problemhave been fully taken into account in theestablishment of the standards. Unlessit is believed that there will be nochanges in technique or in the natureof the demand by the public, it is essen-tial to have a flexible system to meetthese changes.

It is, therefore, important for the in-dustry to be kept in continual touch withthe direction and degree of compromises

made in special cases, so that an intelli-gent analysis of trend may be evolved.

What are desirable trends? The Fed-eral Communications Commission canfoster them, and the coming period ofre -allocation may prove to be an oppor-tunity. It could foster desirable trendsby granting special protection from in-terference to special stations or to sta-tions that operate in a way that theCommission thinks desirable, or for theestablishment of stations in certain lo-calities.

On the program angle, most of theCommission's attention has been prop-erly directed toward the elimination asfar as possible of undesirable or ob-noxious entertainment or advertising. Astation that has a consistently bad recordof that kind should have its service re-stricted, if not eliminated. But the in-fluence of the Commission should notstop at this point. If a station has un-usually good programs, which are sub-stantially different in type or qualityfrom the other programs that are re-ceivable in its service area, it would bein the public interest to give such a sta-tion as broad a service area as possible,so that more listeners would be able tohave a variety of programs at their com-mand. The Commission could make useof the special qualities of this station



BACKGROUND NOISE CORRECTIONS*

IN MANY PLANTS soundproof rooms areeither not available or are not practical,and it is found necessary to make soundmeasurements under existing noise con-ditions. It is always advisable to reducethe level of extraneous noise as muchas possible, but satisfactory sound meas-urements can usually be made, even un-der adverse conditions. Separate meas-urements are made of the backgroundnoise alone and the background plus theunknown noise. The difference of thesereadings is then taken and, from thechart of Fig. 1, the correction in db forthe background noise is determined.This correction is subtracted from thedb reading obtained in the second meas-urement to obtain the level of the un-known noise.

Assume, for instance, that the prob-lem is to measure the noise produced bya machine mounted in an assembly roomor test room where an appreciable back-ground noise level is present. Thesound -level meter is placed in the de-sired test position, and a measurementis made of the general background noise

*Reprinted from the December, 1937, GeneralRadio Experimenter.

Fig. 1. A curvegiving the rela-tion betweenthe db differ-ence betweentotal noise andthe backgroundalone and thedb error (to besubtractedfrom the totalnoise.) Thiscurve is ofvalue in de-termining t h ebackgroundnoise correc-tion for sound -level measure-

ments.

7

By L. E. PACKARDGENERAL RADIO COMPANY

without the machine running. An aver-age measurement of the backgroundnoise in db will be sufficient, although,if a widely fluctuating noise is present,it is often desirable to note the peakreadings. As an example, let this read-ing be 72 db. The machine under testis then set in operation and, when it isoperating at the desired conditions ofload and speed, a second measurement ismade of the total noise level. Let theresult of this measurement be, say, 78db. The difference between these tworeadings is then 6 db. Entering thechart of Fig. 1 at 6 db, along the hori-zontal axis, we find the correction to be1.25 db. This subtracted from the soundreading of 78 db gives a result of 76.75db which is the true noise level of themachine itself.

To obtain this correction it is as-sumed that the power in the backgroundnoise and the power in the measuredsound are added arithmetically by thesound -level meter. From the relation

'A general expression for which the curve ofFig. 1 can be calculated isError db = d -20 logo (2 sink 0.1151 dwhere d is the difference in decibels between the

two readings.

Padb = 10 log. -

P1the power ratio corresponding to the6-db difference is found to be 3.981.This means that the total noise is 3.981times the background. The desired noiseand the total noise level are therefore

3.981 - 1in the ratio or .75, which

3.981corresponds to 1.25 db. The actual noisebeing measured is then 1.25 db lowerthan the reading of the sound -levelmeter'

If actual sound -power levels corre-sponding to the db readings are desired,these can be calculated from the expres-sion given above. An easier method isto refer to a set of decibel tables.' Areading of 72 db, for instance, corre-sponds to a power ratio of 1.585 X 101.Since the reference level (correspond-ing to zero db) is 10-" watts per squarecentimeter, sound -power level for 72 dbis 1.585 X 10-9 watts per square centi-meter.

'See tables published on pp. 162.167 of GeneralRadio Company's Catalog J.

as

05

20

0h.id 4

CZ

CD3

2cc

ccccu.s

ml

0 2 3 4 5 6 7 8 9DB DIFFERENCE BETWEEN TOTAL NOSE AND BACKGROUND ALONE


10

In use, separatemeasurementsare made ofthe backgroundnoise alone andthe backgroundplus the un-known noise.The differenceof these read-ings is thentaken and dbcorrection forbackgroundnoise is de-termined fromcurve. Cor-rection is sub-tracted fromsecond meas-

urement.

William A. Ruggles atwork in the GeneralElectric ResearchLaboratory at Sche-

nectady.

Mr. Ruggles is incharge of the glass -Mowing and exhaust-ng facilities for the

organization.

SOME NOTES ON SNOW STATIC

THE LION'S SHARE of recent develop-ment work in aviation radio communi-cation has been devoted to eliminationof "snow static" or "rain static." Thiskind of disturbance is relatively uncom-mon, but when it does appear, it is ofsuch intensity as to totally block com-munication, and unfortunately, the timeit occurs is during bad weather whenradio -range signals, bearings, and com-munication are most needed. Certainair accidents are believed to have oc-curred when communication was dis-turbed by such static.

The usual characteristic of this staticis a steady hiss or roar, rather than thebursts of the more familiar form ofstatic. It usually starts and stopsabruptly, and lasts for only a few min-utes. It is often heard over only a smallarea, or at one point only. It is morecommonly heard on a plane than in aground station.

Before this type of interference canbe eliminated, its cause must first bedetermined. Much of the work to datehas been in studying and trying to dupli-cate in the laboratory the source of in-terference. The cause is not yet fullyunderstood, although it has becomeevident that there are really severaldifferent mechanisms producing similarinterference, and now all known by thegeneral name, "snow static."

One of the first opinions was that thisinterference was due to snow flakes,

By Dr. VICTOR J. ANDREW

rain drops, or dust particles carryingstatic charges which impinged on theantenna proper and discharged into it.Ship and shore stations, particularly inthe Great Lakes region, found this kindof static many years ago. It is also oftennoticed when fresh smoke, such as thatfrom a locomotive, blows across an an-tenna. On the Great Lakes, many shipsuse direction -finder loops with the loopwires encased in a metal tube. The tubeis open at one point to prevent it fromacting as a short-circuited turn on theloop. The loop is then sensitive to elec-tromagnetic fields, but is insulated fromelectrostatic fields or direct contact withcharged particles.

Transcontinental and Western AirLines studied the application of loopswith static shields to aircraft, over a yearago. Recently, government regulationshave required the installation of suchloops on all transport planes. Whilethese loops are entirely satisfactory instopping this one kind of snow static,it has been found that there are otherkinds on which the loop has little or noeffect. The loops are usually installedwith provision for rotating them, sothat they may also be used for takingbearings on ground stations.

Even when the antenna proper isshielded from impinging charged par-

ticles, these random discharges into theloop shield of the body of the ship setsup some disturbance. This is probablynegligible in amount.

A somewhat greater source of inter-ference is probably the accumulation ofcharge on insulated metal bodies or oninsulating surfaces such as the wind-shield, and then a spark discharge tothe body of the ship. Such causes maybe eliminated by adequate bonding, andpossibly by applying high resistancefilms to the surface of insulated bodieson the outside of the ship.

The engineering staff of United Air-lines are now actively engaged in furtherstudy of causes and remedies for snowstatic.' They have found evidence thatmuch of this interference results fromthe plane building up sufficient chargeto start brush discharge from points.Such discharges are sometimes seen bypilots at night. The charge may orig-inate by friction with the air, by col-lision with charged particles, or bypassing into a space where the atmos-pheric potential is different from that ofthe plane.

When interference results from thedischarge of a body, it is usually defi-nitely periodic, and often repeats at anaudio frequency. It is equivalent to a

(Continued on page 39)1 "Snow Static Effects on Aircraft," by H. M.

Hucke, Communication and Broadcast Engineer-ing, p. 7, July, 1937.


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Made from thin sheets of importedruby mica, plated with pure silver andmounted on a ceramic base.

Extreme stability due to low coeffi-cient of expansion of mica. Tests showdrift of .002% per degree, Centigrade.Initial "Q" of 3000 or better, main-tained under widely varying condi-tions of temperature and humidity.

Any capacity up to 500 mmf. in singleor double units. Small in size. Easilymounted.

Also New High -

Stability MicaTrimmers.'Special treat-ment giveneach piece ofmica used toassure maxi-mum stability.

Mechanical improvements result innew smoothness of operation andlong life. Complete line of capacitiesin single or multiple units.Units available for push-button receiv-ers and top -tuned triple -circuit I. F.transformers.

Write for DETAILS . .

Ask us for details regarding theseand other Sickles Products. Also sub-mit your coil and other r.f. problemsfor engineering aid and quotations.

'Sickles trimmers are protected by1I S. Patents 2,031,910 and 2,003,431

Quality ApparatusExport Department: Ad. Auriema, Inc.

116 Broad St., New York CityCable Address: Auriema, N. Y.

NEW TUBES


E. This triode, which is shown in Fig4, has a thoriated filament suspendedfrom four instead of three spring re-tained hooks on the top lava member.Electrically floating anode is anotherfeature of this tube. Characteristics ofthis tube are as follows: filament volt-age, 14 volts; filament current, 6.0 am-peres; max. d -c plate voltage modu-lated, 2,000 volts; max. d -c plate volt-age unmodulated, 3,000 volts; max. d -cplate current modulated, 325 ma; max.d -c plate current unmodulated, 350 ma;max. plate dissipation, 325 watts; max.d -c grid current, 80 ma; max. r -f gridcurrent, 10 amperes; amplification fac-tor calculated at 150 ma plate current,16; plate resistance at 150 ma, 1,900ohms; grid -to -plate capacitance, 18.5mmfd; grid -to -filament capacitance, 15.0mmfd; plate -to -filament capacitance, 8.5mmfd.

The Eimac KY21 (Eitel-McCullough)is shown in Fig. 5, while the EimacRX21 is illustrated in Fig. 6. Both ofthese tubes are mercury-vapor rectifiershaving filament voltages of 2.5 volts,filament current of 10 amperes, peak in-verse voltage of 11,000 volts, and peakplate current of 3 amperes. Using areasonable input choke to the filter, apair of these tubes are said to supply ad -c output power of 3,500 volts at 1.5amperes in a conventional full -wave cir-cuit.

The tube shown in Fig. 7 is desig-nated as the Taylor T-40. It is a gener-al-purpose triode with an r -f output of86 watts. The T-40 has a rated fila-ment voltage of 7.5 volts, while theplate current is given as 2.5 amperes.Other characteristics are as follows :plate resistance, 8,700 ohms; amplifica-tion factor, 25; plate -to -grid capaci-tance, 4.5 mmfd; max. d -c plate volts,1,000; max, d -c plate current, 40 ma.

The Taylor TZ-40 is a recently an-nounced high -mu triode designed forzero -bias Class B audio operation orfor frequency multiplying. Operatingat rated input, an output of 175 wattsof audio can be obtained. It is rec-

ommended by the manufacturer for allClass C amplifier purposes. Generalcharacteristics are: filament volts, 7.5;filament current, 2.5 amperes; amplifi-cation factor, 62; plate resistance, 17-500 ohms.

The Collins C -849A and C-350 tubesare shown in Fig. 8. The C-350 is aslightly enlarged version of the typeC-300. Three of these 350's can beused as a Class C modulated 1000 -wattamplifier. The filament voltage of theC-350 is 11.5 volts while the filamentcurrent is 4.0 amperes. Amplificationfactor is 24, and the plate resistance is5,500 ohms. The maximum plate dissi-pation is given as 250 watts.

The general characteristics for theC -849A and 849H are as follows: fila-ment volts, 11.0; filament amperes, 7.7;maximum plate dissipation, 500 watts;plate resistance, 3,300 ohms; amplifica-tion factor, 19; max. d -c plate volts,4,000; max. d -c plate ma, 500; max.d -c grid ma, 125.

Raytheon is now offering four newRK triodes for use as power amplifiers,oscillators, or frequency multipliers.These tubes are shown in Fig. 9. TheRK-11 has an amplification factor of20 and a power output of 55 watts. TheRK-12 is a zero -bias modulator tube hav-ing an output of 55 watts. The ampli-fication factor of the RK-51 is 20, whilethe output is 170 watts. The output ofthe high -mu zero -bias RK-52 is 135watts.

The Amperex type 849A and 849Htubes are redesigned versions of theolder 849. The 849A is shown in Fig.10. These tubes utilize an 11 -volt, 7.7 -ampere filament. The electrical charac-teristics of the 849A are identical withthose of the 849. The new tube carriesan FCC rating for use in the final stageof low-level modulated broadcast trans-mitters of 250 watts. The 849H differsfrom the 849A in that the grid isbrought out the side of the bulb, extend-ing the capabilities of the tube to fre-quencies in the vicinity of 30 mega-cycles.

REBUILDING TRANSMITTER TUBES


and plate are accurately put back inplace and the necessary getter cupsmounted.

The bulb is washed out to removethe old magnesium getter and metallicdeposits from the original exhaust pro-cedure with acids and water, then driedout with acitone. After the bulb is dry,the tube is ready to be sealed togetherand the exhaust tube attached.


It is now ready to exhaust and issealed to the vacuum manifold. A pre-liminary vacuum test is made for leaks.If ok up to this point, it is baked in anelectric oven, at from 400°C for leadglass to 500°C for hard glass, for atleast one hour or until the gas andwater vapor is completely exhausted.

An ionization gauge gives a constant(Continued on page 30)

All Wire Is Not The Same!

SHIELDED WIRE HOOK-UP WIRE

I Holyoke shielded wire, under criti-cal inspection, proves to be properlysheathed with high quality, corrosive -proof strands that afford maximum,long -life service. The rubber (or gutta-percha) covering the cotton servedconductor wire itself is specially treat-ed, uniformly applied-has no "thinspots," is perfect moisture -proof insu-lation.

2 The inherent (but not easily seen)defects found in inferior brands ofshielded wire are numerous. Poorlyspun sheathing "bunches." Vibrationwears it through the (ofiiimes porous)rubber insulation causing leaks andshort circuits.

MULTI -CONDUCTOR CABLE

I Holyoke hook-up wire has a braided,heat resistant, fire retardant coveringof the highest possible quality. The

smooth outside finish speeds produc-tion. The rubber insulation, uniformlyapplied, prevents moisture absorptionor oxidation under the severest condi-tions, strips easily and leaves the barewire strands clean, ready for assembly.

2 Inferior insulation on cheap gradesof hook-up wire deteriorates quickly,affording but little protection againstheat, moisture and climatic conditions.Current uniformity is impossible toobtain. Rejects and high productioncosts result.

I Holyoke specializes in making har-nesses for mass -production users. Thefinest quality wire and materials areused throughout. Each conductor liesuniformly in its place. The outside cov-ering and finished -ends prevent fric-tion, insuring long -life, efficient service.Every harness is subjected to criticalinspection, guaranteeing uniformitythat helps reduce production costs.

2 Defects in harnesses made of poorquality materials are not easily dis-cernible. Loose outside covering or un-finished end -wrappings allow frictionto damage the conductor's insulation.Non -uniformity of cables to specifica-Fions causes increased production costs.

All buyers and users of wire should study the above reasons as to why "All Wire Is Not TheSame." For over a quarter of a century Holyoke has been recognized as the Quality WireSupplier. Leading radio, communications and electrical equipment manufacturers through-out the world know Holyoke quality wire costs no more, and in many cases less, than inferiorbrands. Communicate with us so we may prove it to your entire satisfaction.

Holyoke Makes A Wire -Cable or Cord -Set For Every PurposeWrite for Engineering Data, Samples and Quotations

HOLYOKE WIRE & CABLE CORPORATION, 730 MAIN ST., 'HOLYOKE, MASS.

Holyoke Wire & Cable CorporationCOMMUNICATIONS FOR MARCH 1938 27

DICTIONARY OF RADIO TER-MINOLOGY IN THE ENGLISH,GERMAN, FRENCH AND RUS-SIAN LANGUAGES, by A. S. Lit-vinenko, edited by Prof. V. I. Bash-enoff, M.I.R.E., Moscow, U.S.S.R.,1937, 559 pages. Price $4.00. Ob-tainable from Bookniga Corporation,255 Fifth Avenue, New York City,N. Y.

According to its author this dictionaryis an initial attempt at a systematic com-parative review of modern radio ter -

BOOK REVIEW

minology in knglish, German, Frenchand Russian. Approximately five thou-sand terms encountered in communica-tion engineering and related fields arelisted with their equivalents for eachof the four languages. The alphabeticalarrangements are such that it is pos-sible to go directly from one languageto any of the other three. Thus, this onevolume is comparable to twelve one-waydictionaries.

Wherever possible English terms stand-ardized by the Institute of Radio En-gineers or given in the InternationalElectrotechnical Dictionary are em-ployed, and in general care has beenexercised in a difficult task. However,partly as a result of the profusion andrapid extension of our own terminology,this reviewer discovered omissions.

This volume should serve as a valuablesupplement to non -technical dictionariesin the translation of material pertain-ing to communication engineering.

CATHODE-RAY ELECTRON BALLISTICS


geometry. Thus far general waveform deflection cor-rection with frequency has involved the terminalvelocity. One can now proceed with the results of studyas it relates with the distance of fall y.

THE DISTANCE OF FALL Y

y, the second term of expression (3) is a function ofthe terminal velocity in the vertical direction and thussubject to K of expression (4). In addition the timethrough which the charged particles have to fall in con-junction with K is also a function of frequency by in-spection of Fig. 2. Let the correction for the latter bek = f (f) such that kl, will be the effective deflectingplate length corresponding to the time allowed forparticle fall at the plate tips. k is determinable for anycharge stream force function but surprisingly well givenfor any waveform by curve 2, Fig. 3, which has a dualpurpose; representing K for a square waveform andk for any waveform.

DEFLECTION EXPRESSIONS

Expression (2) was shown in two forms, the purposeof which was to allow comparison. When expression (3)is properly filled in, the following represent deflectionand sensitivity expressions :

Ep L' le E, 1ED.= 1E/2)

2 s E. 2sE.

D. L'(L 1E/2)

Ep 2 sE. - 2 sE.

vHL' lE vH1EDm = = (L + 1E/2)

2 E. 2 E.

Dm vL' lE vIE= = - (L 1E/2)

H 2F,. 2F

standard electrostatic de-flection. Not applicableat high frequencies.

standard electrostatic de-flection sensitivity. Notreliable at high fre-quencies (1)

standard magnetic de-flection. Not reliable athigh frequencies.

standard magnetic de-flection sensitivity. Notreliable at high fre-quencies (2)

WITH WAVEFORM AND FLIGHT TIME CONSIDERED

E. Kis kDe- (L -

2 s 2

D. KIE k 1EL -F, 2 s

electrostatic deflectionfor any K (6)

electrostatic deflection -sensitivity for ally K (6)'


vHK1E k 1EDm= L -

2 E.

Dm vK1E k 1EL

H 2E. 2

magnetic deflection forany K (7)

magnetic deflection -sensitivity for any K... (7)'

The last four expressions (6) to (7)' are especiallyuseful to communications, television and high -frequencyexperimenters where accurate determinations are inorder.

Of importance is the next relation. The manufacturergives the ratio (De/E,) for several Ey's in the tubespecifications. Since L' is measurable, or available fromthe manufacturer upon request, the effective length ofthe deflecting plates is given by the expression

2sE.( D.- (8)L'

where (De/Ep) is the corresponding sensitivity for theE. given.

FIGURE 3

This figure-which is an absolute magnitude plot-is applicable to any tube of known geometry and ap-plied potentials. The frequency axis is general forany v of E., and lE. Since T = 1,/v the frequency axisis fixed for any tube when Ev is set and lE determinedby expression (8). The ordinates for the curves ofFig. 3 are fractions for both K and k. With the fre-quency axis located as mentioned above, a known deflec-tion or sensitivity can be interpreted or corrected withthe aid of the expressions (6) and (7). Fig. 3 is ar-ranged with all the necessary data for ready use by theexperimenter and, inasmuch as the chart and the ex-pressions of this paper consider the waveform as well asthe existence of two correction factors which are not theequivalent of the ones to date proposed, it is more in-clusive and exacting.

From Fig. 3 it is also to be noted that the frequencyat which any cathode-ray device deflected magnetically,electrostatically or both, will begin to lose sensitivity andthus require data correction for quantitative work isgiven by

for. egaeN c I es) =2.985 L'

sVE.(Ep/De)

for a sine wave. f is much higher for waveforms ap-proaching a square wave and lower for those simulatinga saw -tooth form.

Your Condenser Problem

A. A. E.-ALHOVOX APPLICATION ENGIN-EERING-costs you nothing. Yet in addition toInsuring the RIGHT condenser for your job, it fie-quently means marked savings in other compon-ents for your assembly. Case histories indicatelens of thousands of dollars saved for manufacturerslarge and smal. alike. So just submit that prcb-:em. Our engireers will provide the specifications,samples, quotctions.

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Wes Officea in All Principal Cities


TELECOMMUNICATIONPANORAMA OF PROGRESS IN COMMUNICATIONS

RCA WORLD'S FAIR EXHIBIT

PLANS were made public recently byDavid Sarnoff, President of the RadioCorporation of America, and GroverWhalen, President of New YorkWorld's Fair, 1939, for the erection ofan exhibit building of unique design tohouse a panoramic display of the latestdevelopments of the radio art and in-dustry as reflected by RCA products andservices. The exhibits will embrace allthe products of RCA companies includ-ing RCA Manufacturing Co., RCACommunications, Radiomarine Corpora-tion of America, the Radio Institutesand the National Broadcasting Com-pany.

Experimental television programs willbe shown to the public in viewing roomsin the building. Ample opportunity willbe given for visitors to view variousforms of television entertainment insurroundings approximating those inAmerican homes.

The building, as viewed from the air,will be shaped somewhat like a hugeradio tube 136 feet in length, resting ona broad base 190 feet wide. The entirefront of the two-story structure will beof glass, which will be brilliantly lightedat night. Working models of variousradio devices will be placed in the largerotunda, around the sides of which willbe six television viewing rooms.

Proceeding further into the "tube"section of the building, the visitor will

Architects' model of the RCA building to be built for the New York World's Fair.

see the latest radio receiving sets andtubes in actual process of construction,together with animated demonstrationsof some of the principal RCA services.A picked crew of expert workers fromthe big RCA Victor factories at Cam-den, N. J., will assemble radio sets atone exhibit, while at another tubes ofvarious types, including those used intelevision will be constructed.

Behind the building a large garden oftrees and fountains, 200 feet wide by150 feet in length, will provide spacefor novel outdoor exhibits of the RCACommunication and Marine services.

A precision lathe for fusing the deflecting electrodes into the side walls of acathode-ray tube bulb. In the larger tubes, the bulbs are sealed together insections to facilitate pumping. Head and tail chucks are gear -driven so thatboth rotate at same speed. Photo courtesy RCA Manufacturing Co., Inc.


Plans for the structure were drawnby Skidmore and Owings, architects,New York, with Paul Cret acting asconsultant.

REBUILDING TRANSMITTER TUBES


check on the gas liberated. The nextstep is to carbonize the filament to itsproper conductance, about 80 per centof its original conductance, if it is athoriated filament. If it is a pure tung-sten filament, no carbonizing is needed.A high -frequency water-cooled vacuum -tube furnace or coil is put around thetube and the parts outgassed slowly atfirst, then the temperature is raised to1300°C or higher while there is an airblast on the tube which keeps the glassfrom collapsing.

The parts are bombarded alternatelyinternally and externally at the highesttemperature they will stand and stillhold their correct shape from 6 to 18hours or until there is no more gas lib-erated. It is baked again to clear theglass from gas deposited during thebombardment of the metal parts.

The getter is flashed and the elementssparked out with a coil. The tube isgenerally bombarded again before seal-ing off. The bases are mounted andbaked on, after which it is put in anaging rack for some time to stabilize itsoperation.

JOHN W. JAFFRAYGeneral Electronics Co.

CHEAPER ...yes, but

-mg This photomicrographshows why we do not offer

electroplated strip. Notethe effect of corrosion onthis nickel plated strip assold for radio tube use.

WE CANNOT AFFORD THE RISK! CAN YOU?YOUR PROTECTION IS SVEACOTE whichis well worth the slight additional cost

Here is a photo-micrograph of Svea-cote with the samemagnification (100X)made after the samecorrosion test.

(Darkness due to low reflection from math" surface.)

THE REASON

Sveacote is a definite alloy made by a special processto resist rust. Note compact structure, uniformity and

freedom from impurities.

Swedish Iron & Steel Corporation17 BATTERY PLACE NEW YORK, N. Y.


vo

W. J. McGONIGLE, President

VETERAN WIRELESS OPERATORS

ASSOCIATION NEWS

RCA Building, 30 Rockefeller Plaza, New York, N. Y. H. H. PARKER, Secretary

THIRTEENTH ANNUALTHE THIRTEENTH ANNUAL Dinner -Cruise ofour Association was held in the NorthBallroom of the Hotel Astor, TimesSquare, New York City, on the eveningof Friday, February 11, 1938, and simul-taneously Chapter cruises were held incities throughout the country and theworld. The Cruise at the Astor was ad-judged by most of those present as thebest cruise in the history of our Associa-tion.

A feature of the evening was the presen-tation of our Association's Marconi Me-morial Gold Medal of Valor to Lieut. Carl0. Petersen, a member of both Byrd Ex-peditions. A coast -to -coast broadcast overthe Blue network of the National Broad-casting Company accompanied the presen-tation and after the announcer made knownthe origin of the broadcast, he introducedour President, William J. McGonigle, whodedicated the broadcast to the memory ofMarconi and then spoke of the ideals andobjectives of our Association, in turn, in-troducing Mr. Sarnoff who detailed someof the background of our profession andour Association. Mr. Sarnoff in present-ing our Medal of Valor to Lieut. Petersenpaid high tribute to his resourcefulness andcourage under trying circumstances. Lieut.Petersen responded with profound thanksfor the high honor bestowed upon him byour Association and expressed his heart-felt gratitude to Admiral Byrd who madeit possible for him to accompany the twoByrd Antarctic Expeditions. (The textof the addresses will appear in a laterissue.)

A message from Admiral Richard E.Byrd : "To the members of the VeteranWireless Operators Association : I deeplyregret that I will not be able to be present

on the occasion when the Veteran WirelessOperators Association is honoring Carl 0.Petersen, by presenting to him the MarconiMemorial Gold Medal of Valor.

"Lieut. Petersen was a member of bothmy expeditions to the Antarctic ; on thefirst as Radio Operator ; and on the sec-ond, Photographer and Radio Operator.On both of these expeditions by his hardwork, endurance, and great efficiency,working under the most trying of circum-stances, and at times with inadequate equip-ment, he made great contributions to thescience of radio and to our expedition. Onthe second expedition he took part in anumber of flights of exploration, helpingto solve the mysteries of the Antarctic.Above this, and what I believe to be evenmore important, Petersen is a most loyalfriend and comrade and has the good -willand respect of all his shipmates.

"I am glad that he is to be rewardedwith this Medal which he so richly de-serves." Signed, R. E. Byrd.

Seated at our Distinguished Guests tablewere the following: Geo. P. Smith, Execu-tive in the Concessions Department of theNew York World's Fair 1939, and ChiefRadioman aboard the Flagship on theround the world trip of the United StatesNavy Fleet in 1908 ; Theodore Haubner,who sent the first SOS signal in March1909 from the Steamship Arapahoe andhad the honor of receiving the second SOSsignal later in the same year. He re-cently donated the headphones used in boththese cases to the Ford Museum at Dear-born, Michigan ; H. H. Parker, General -Secretary of our Association ; Paul Boro-voy, Acting Soviet Consul General whowas present as our guest to receive theMarconi Memorial Testimonial Scrolls ofHonor awarded to his fellow countrymen,


TI=15,10411:ANIWAL DINtri R.CPUIStVETERAN WIRELESS OPERATORS ASSOCIATION

ROTEL AwritAk ptimuARy.,, 143/11

heroes of the Russian Trans -Polar flights-Alexander Beliakoff, Serge Danilin,Georgi Baidukoff and Andrey Yumasheff ;A. F. Wallis, Vice -President of our As-sociation and Sales Manager of the Ma-rine Department of the Mackay Radio andTelegraph Company; Rolf Christensen,Norwegian Consul General who was pres-ent to pay tribute to Norwegian born Carl0. Petersen ; Lieut. Carl 0. Petersen,USNR, our Guest of Honor and recipientof the Marconi Memorial Gold Medal ofValor; William J. McGonigle, Presidentof our Association, who acted as Masterof Ceremonies ; David Sarnoff, Life Mem-ber of our Association, President of theRadio Corporation of America and Chair-man of our Marconi Memorial Committee,who presented the Gold Medal to Lieut.Petersen ; Ibrahim Mahmoud, Representa-tive of the Royal Egyptian Consulate inNew York ; Admiral Luke McNamee,President of the Mackay Radio and Tele-graph Company and the Federal TelegraphCompany and our most recent HonoraryMember (Admiral McNamee was presentto accept his Honorary Membership in ourAssociation) ; J. R. Poppele, Chairman ofour Scholarship Committee and Secretaryand Chief Engineer of the BambergerBroadcasting Service, Inc., and RadioQuality Group, Inc.; J. W. Scanlin, theNumber One Radioman in the UnitedStates Navy, whose service dates back to1901, who made the trip up from Wash-ington especially to be at the dinner ; H. F.Coulter, Comptroller of the RadiomarineCorporation of America and a pioneer inthe Department of Commerce ; Miss LenaMichelsen, one of the few of the fair sexwho worked commercially as a wirelessoperator for some few years ; Fred Muller,


116W-a5j6ta"jeti lOn (v5

AUDAXadds fresh weightto its slogan :-

"The Standardby Which OthersAre Judgedand Valued"

ENGINEERS and soundtechnicians will surely wel-

come this announcement-thatpractically flat response at "ceil-ing" frequencies can at lastbe assured. To 5,000, then to 6,000; then to 7,000-AUDAX has steadilyraised the standard, till now the most difficult special studio work, involv-ing real wide range, reproduces with uniformly flat characteristic. All theaccustomed facsimile realism, the uncompromising conformity to originalmicrophone recording-with this added feature which only AUDAX couldprovide!

THREE DISTINGUISHEDMICRODYNE MODELS

AT RIGHT

A pick-up for every purpose, from thehumble portable to the most elaboratesound system.

List $7.50 to $260.00

ADDAX

tcrodYED-FREQUE

MICRODYNE RF-6 Substantially flat to 10,000 cycles;for records up to 18 inches; needle impedance practi-cally nil; feather touch on record; list $125.00

MICRODYNE RF-5 Identical with RF-6, except thatits response is not quite so uniformly flat; list..$98.00

MICRODYNE RF-3 Substantially flat to 8,000 cycles;for records up to 12 inches; very low needle im-pedance; feather touch on record; list $60.00

The above models may be had with a permanentpoint at small extra cost. Also available for

Hill and Dale at slightly higher prices.

AUDAK COMPANY500 Fifth Avenue, New York

"Creators of High Grade Electrical and Acoustical Apparatus Since 1915"


COMMUNICATIONS19 East 47th Street,New York, N. Y.

Gentlemen:Please enter annual subscriptions (12 issues) for

each of the undersigned for which payment is en-closed at the rate of $1.00 each.

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COMMUNICATIONS!"

Progressive engineers obtain first-hand technical informationconcerning all phases of the communi-cations and radio industries by readingCOMMUNICATIONS each month.Present day design, manufacturing,production and maintenance problemsare covered in an understandablemanner.

To help every radio, electrical, com-munication or industrial engineer, ex-ecutive, department head and factorytechnician secure his own individualyearly subscription (12 issues) foronly $1.00 per year, the Group Sub-scription Plan was devised.

Regularly a yearly subscription toCOMMUNICATIONS is $2.00-butin groups of four or more, the sub-scription rate is only $1.00 each peryear. Each subscriber's occupationmust be stated.

Now, by using the form printedherewith, you and your co-workerscan sign up at the half-price rate.Most of the technical data publishedis ideal for filing and may be usedfor reference guidance during theyears to come.

COMMUNICATIONS

19 EAST 47th ST,NEW YORK, N. Y.

VWOA NEWS


a past President of our Association, LifeMember and at present a member of ourBoard of Directors.

MESSAGESWE REPEAT, here, the last message fromour late beloved member, Guglielmo Mar-coni, wireless veteran number one, in whosehonor we have named our Year Book for1938 and our awards, Gold Medal and Tes-timonial Scrolls of Honor and the Certifi-cate of Merit which will now and hence-forth be known as Marconi Memorialawards : "As the original wireless veteranmay I participate your reunion and wishyou all best of luck." This message wasreceived at the Twelfth Annual Cruise lastyear at the Great Northern Hotel.

The Royal Italian Ambassador the Hon.Fulvio De Suvich felicitated our Cruiseas follows : "It is with distinct pleasurethat I associate myself with the membersof the Veteran Wireless Operators As-sociation in doing honor to the memoryof Italy's illustrious son Guglielmo Mar-coni whose inventions made possible themodern science of radio communication.His name will be remembered as long asthe human voice is heard and his careerwill serve as an inspiration not only tothe people of Italy but of all the worldwhich with each passing year will be moreprofoundly affected by the remarkableachievements of radio."

From California we received the follow-ing message from our Honorary MemberDr. Lee De Forest:"Dear Fellow Vets:

There is tonight a spell of sadness aboutus, of a deep and personal loss, which we

dispel, even if we would. ThePioneer of pioneers, the Veteran of allWireless Veterans has passed over theboundless horizon, whither each one of us,when the Skipper summons, must bravelyfollow.

"Marconi, Commendatori, the etherwaves which your daring spirit first sum-moned to do man's bidding are bearing thatspirit with the speed of light into therealms of eternal light.

"But the effulgence which marked yourlife among us here on Earth, that gloryremains unfading and undimmed, for ourencouragement and inspiration!

"What blessings have come to manthrough the work and genius of that ex-ceptional man ! None are so qualified toappreciate the full magnitude of this giftas ourselves, Veteran Wireless Operatorsof America. Let us realize then that themantles of great men who have passedbefore have fallen especially upon ourshoulders; of Faraday, Hertz, Edison, Fes-senden, and now Marconi. Be enheartenedthus to follow on, to sail the seas wherethey first piloted.

"In recalling scenes of my early wire-less labors, memory carries me fondly tothose days in Key West when I was in-stalling one of the large Naval Stations.It was then all so new, so wonderful,before this triumph of Science had becomecommonplace and un-romantic and in-cidental.

"This is how it then impressed me-reading from my Diary of 1905:

"'Fascinated I stand and watch, seekingto fathom its significance, the great wierdmystery of it all, these shining pillarsholding aloft an invisible vault of ethericechoes, silent voices whose echoes never-theless resound over a thousand miles ;

strangely fashioned listening things thatharken silently, by night, by day, and hearthe inaudible calling from distant citiesacross the sea.'

"Let us not today become so lost in themazes of our headlong, dizzy or routineliving that we fail ever to realize, andpause before the wonder, the mystery ofwhat we first knew as Wireless.

"And let us not as Veterans forget theearly thrills of sending and then receivingthose first signals from some ship lostbeyond a hundred wide horizons-thosememories should keep alive a never waningpride in the profession which we chose solong ago, or helped to found.

"And now, be I in California or oncemore in your midst as of yore, as I longto be tonight, please know that on eachsucceeding Cruise I am still with you,fellow Veterans, in heart and spirit, untilthe last sign -off.

"'Beyond the light of far Cathay,Beyond all mortal dreams,Beyond the reach of night and dayOur El Dorado gleams,Revealing-as the skies unfold-A star without a stainThe Glory of the Gates of Gold

Beyond the Spanish Main.'And so -

73 forever!Lee de Forest."

SMOKER

THE APRIL MEETING Of the NeW Yorkgroup will take the form of a Smoker andBeer party and will be held on Mondayevening, April 4, 1938, at the Castle Gar-den Cafe, 62 Pearl Street, New York City.Admission, $1.50-all the beer you candrink. Don't fail to be there. Let us knowhow many in your party.

DELTA -STAR MIXER


of 200 -ohm to 200 -ohm isolation trans-formers to allow the one side of eachincoming and outgoing circuit to begrounded. The mixer may be extendedup to 16 inputs and 2 outputs, still using200 -ohm pads throughout, and with allimpedances matched regardless of thenumber of inputs. This means that astation can standardize on one impe-dance for its inputs, outputs, lines, padsand mixing transformers, and yet beflexible enough to meet future mixingrequirements.

BROADCAST CONFERENCE


"Snow -Static Effects on Aircraft," byH. M. Hucke, United Air Lines; and"Aeronautical Ground Radio StationDesign," by P. C. Sandretto, UnitedAir Lines.

The Broadcast Engineering Confer-ence was sponsored by the Departmentof Electrical Engineering of Ohio State,and much credit for its success is dueProfessor W. L. Everitt, the Directorof the Conference.

SPEECH INPUT COMPONENTS

EQUALIZERMODEL 3A-The UTC universalequalizer will equalize telephonelines, recording systems, pickupsand cutters, microphones and allother broadcast equipment. It isaccurately calibrated and quicklyadjustable for both low and highfrequency equalization. Low fre-quency controls permit maximumequalization at 25, 50 or 100

cycles with zero to 25 DB control.The high frequency end permitsmaximum equalization at 4,000,

6,000, 8,000, or 10,000 cycles withzero to 25 DB control.Net price to broadcastand recording studios

stations$85

STUDIO PREAMPLIFIERMODEL 5A-The UTC 5A preampli-fier can be used as a two stage, threestage or four stage amplifier. The rela-tive gains under these respective con-ditions are 55 DB, 77 DB and 100 DB.A tri-alloy shielded input transformerplus additional design features devel-oped in the UTC Laboratories effectextremely low hum level. The fre-quency response is uniform from 30 to14,000 cycles and the power output isplus 7 DB. A switch and milliameterare provided to permit checking platecurrent of all tubes.

POWER SUPPLYMODEL 6A-This is a highly filteredpower supply for use with the 5A pre-amplifier. 250 Volts at 15 ma is pro-vided and 6 Volts at 1.2A.The Model 5A -6A unit is suppliedcomplete, wired and calibrated withtubes, net $125

STUDIO -MONITORING AMPLIFIERMODEL 7A-With MODEL 8A POWER SUPPLY-This

amplifier is suitable for all medium power broadcast applications including driverservice. It provides 15 or 25 watts power output using pushpull 2A3's or 300 A's.Three pushpull stages effect 85 DB gain with hum level 50 DB below normal output.A switch and meter are provided on the audio panel to check plate current of alltubes, and a control is provided to balance the plate current of the output tubes.The power supply panel incorporates a pilot light and fuse. The frequency responseof this unit is uniform from 30 to 14.000 cycles. The model 7A -8A unit is suppliedcomplete, wired and calibrated, with tubes, net $160

72 SPRING STREETlrhET

NEW YORK, N. Y


OVER THE TAPE . .

NEWS OF THE COMMUNICATIONS FIELD

BENDIX EUROPEAN REPRESENTATIVEAppointment of H. F. McEnness as spe-

cial European representative for the Ben-dix Aviation Export Corporation and theopening of a new Paris office at 51 Ave-nue George V have been announced byHoward S. Welch, Vice -President andGeneral Manager. Traveling out of hisParis headquarters, Mr. McEnness willcover the Continent, the British Isles andthe Near East.

GARRETT W. LEWISIt has been announced that Garrett W.

Lewis, San Jose, California, is the suc-cessor to National Radio Tube Co., of SanFrancisco. Mr. Garrett W. Lewis, who forfourteen years served as Chief Engineerfor the old company, heads the new organ-ization, which will engage exclusively inthe repair of electron tubes. Associatedwith Mr. Lewis on the engineering staffwill be Mr. Eldreth Hodges of San Jose.

CENTRALAB BOOKLETCentralab now has available an engi-

neering data booklet on carbon composi-tion fixed resistors. This 8 -page bookletcontains dimensions, general specifications,cold -voltage and hot -load curves, power -temperature characteristics, noise -limitcurves, life and humidity test data, as wellas resistance -frequency and voltage -limitcurves. To secure a copy write to Centra-lab, 900 E. Keefe Ave., Milwaukee, Wis.,for form No. 647.

PA U LEY -JAM ES CORP.

The Pauley-James Corporation, of 4619Ravenswood Ave., Chicago, Illinois, hasbeen formed for the purpose of manufac-turing and distributing a new auto -radioreplacement vibrator. Sales Manager ofthe concern is Hal. M. Pauley, who wasGeneral Service Manager of Grigsby-Gru-now Co., and connected with Stewart War-ner Corp. Stephen F. James, formerly withGrigsby-Grunow Co., is acting in the capac-ity of Chief Engineer and as a Director ofthe Corporation.

GENERAL RADIO BULLETINThe General Radio Company, 30 State

Street, Cambridge, Mass., have recentlyissued an interesting 4 -page bulletin cover-ing an improved standard -signal generator,Type 605-B. A general description, cir-cuit diagram and specifications are given.A copy may be secured by writing to theabove organization.

SOLAR APPOINTMENTSolar Manufacturing Corporation have

announced an addition to their executivestaff. Mr. J. I. Cornell has joined the or-ganization as Consulting and Field Engi-neer. Mr. Cornell was formerly Chief En-gineer of the Magnavox Company, and pre-vious to that was Section Engineer incharge of audio components with RCAManufacturing Co., Inc.

TRANSMITTING TUBE MANUAL"Air -Cooled Transmitting Tubes- is the

title of RCA's Technical Manual TT -3.This 192 -page manual covers general vacu-um tube considerations, generic tube types,transmitting tube installation, application,technical description, ratings, design con-siderations, etc. In addition, useful formu-las and transmitting tube charts are given.Also special sections have been devotedto rectifiers and filters as well as to cir-cuits. To add further to the value of thismanual a reading list is provided. Copiesof the manual may be obtained from RCAtransmitting tube distributors or by send-ing 25c to the Commercial EngineeringSection, RCA Radiotron Division, RCAManufacturing Co., Inc., Harrison, N. J.

LOVEJOY PLANT AT WINDSORLovejoy Flexible Coupling Corporation,

Chicago, Illinois, makers of L -R flexiblecouplings, are opening a Canadian factoryat Mercer Street, Windsor, Ontario. L -Rflexible couplings are made in severaltypes for use by manufacturers in Canadaas well as the United States.

OPERADIO APPOINTMENTThe Operadio Manufacturing Company

announce the promotion of Howard A.Wilson to the position of Sales Managerof the Public -Address, Sound and Ampli-fier Trade Division, according to a state-ment issued by Larry King, General SalesManager. Howard Wilson has been withOperadio for several years.

SHALLCROSS BULLETINBulletin No. 835 has recently been is-

sued by the Shallcross Mfg. Co., Coiling -dale, Pa. This bulletin describes the 800series of Decade Resistance Boxes. Com-plete descriptions and specifications aregiven. Copies are available from theabove organization.

MICROPHONE BULLETINUniversal Microphone Co., Inglewood,

California, on March 1 issued a specialbulletin showing various types of handmicrophones. It covers the subject ofhand microphones exclusively and showsthe exterior appearance as well as circuitdiagrams for use as call systems in hos-pitals, paging systems, sports announcing,ship -to -shore, police car transmitters, air-craft use, etc.

BULLETIN ON BUSHINGSIsolantite Inc., announces the issuance of

a new 8 -page bulletin on bushings for lead-in, transformer and condenser service. Thebulletin, identified as Bulletin No. 104, listsall of the company's standard bushings. Allthe insulators listed are of the low -lossceramic type, suitable for high -frequencyservice. Mechanical drawings give com-plete working dimensions. Bulletin No. 104is the third of a series listing groups of thecompany's insulators. Copies may he ob-tained from Isolantite Inc., 233 Broadway,New York City.


HARRY TERRY MOVES OFFICESHarry Terry has moved to 8 So. Michi-

gan Ave. Until Feb. 1, 1938, he had officesat 360 N. Michigan Ave., Chicago. Mr.Terry, who was Vice -President of TheCramer-Krasselt Co. for ten years, resignedJan. 1, 1937, to open his own offices as Ad-vertising and Sales Economist. He workswith both advertising agencies and adver-tisers in co-ordinating sales and advertis-ing plans by making sales and market stu-dies and advertising audits at the point -of -sale.

GATES CATALOGSThe Gates Radio & Supply Company

announce the release of three new catalogsdevoted to speech -input equipment, remote -control equipment and accessory equipment,all for broadcast station and associatedfields. Copies of these catalogs may behad by writing to either the Gates Radio &Supply Company of Quincy, Ill., or theGates Radio & Supply Company, 5334Hollywood Blvd., Hollywood, Calif.

SPAULDING DATA BOOKSpaulding Fibre Company, Inc., 310

Wheeler, St., Tonawanda, N. Y., have madeavailable their 1938 Engineering DataBook. This 32 -page booklet covers theirline of fibre sheets, tubes, rods, radio coilforms, etc. To secure a copy, write di-rectly to the above organization.

RCA LICENSES HEINTZ & KAUFMANRadio Corporation of America have an-

nounced that they have granted a non-exclusive license to Heintz & Kaufman,Ltd., of San Francisco, California. Thelicense extends to various commercial radioapparatus for use on ships and aircraft,and by governments. The agreement ef-fects termination of certain patent litiga-tion pending between the parties.

"THIRD HAND INFORMATION""Third Hand Information" is the title

of an interesting 4 -page bulletin recentlyreleased by the American Screw Companyof Providence, R. I. This bulletin de-scribes the patented Phillips recessed headtype of screw, which is said to save con-siderable time in production operations. Acopy of "Third Hand Information" may besecured from the above organization.

THORDARSON TRANSMITTER GUIDEThe Thordarson Transmitter Guide, No.

344-C, has just been issued. This 48 -pageguide is offered as a practical work -bookto aid the builder and operator of amateurtransmitters. It contains descriptions of5 and 10 -meter transmitters, as well asother transmitters ranging in power from100 to 1000 watts. In addition, about 15pages have been devoted to technical data,calculations, circuits, etc. To secure a copyof this guide, write to Thordarson ElectricMfg. Co., 500 W. Huron Street, Chicago.The price is 15c.

RAYTHEON DATA BOO K

The Raytheon Production Corp. haverecently issued a pocket databook on Ray-theon radio -receiving tubes. This databookcontains information on tube elements,classification by structure and function,characteristics, application and circuits, op-erating practice, conversion curves, resist-ance -coupled amplifier design curves, etc.Copies may be secured from Raytheon Pro-duction Corporation, 55 Chapel Street,Newton, Mass. The price is 25c.

WESSNER JOINS WEBSTER-CHICAGOAbsent for a long time because of ill

health, the many friends of Fred Wessnerwill be glad to welcome him back into theradio business. Mr. Wessner has acceptedthe position of Sales Promotion Managerof Webster -Chicago and will be located atthe home offices in the Bloomingdale Ave-nue plant, Chicago.

HOFFMAN HEADS WESTINGHOUSETUBES UNIT

Foreseeing an enlarging field of useful-ness for electronic tubes, the WestinghouseElectric & Manufacturing Company has re-organized its manufacturing facilities atBloomfield, New Jersey, to form the Spe-cial Products Division, under the manage-ment of H. J. Hoffman. The new Divisionembraces the design, manufacture and saleof electronic tubes, according to an an-nouncement of D. S. Youngholm, Vice -President.

The new Division will continue themanufacture of a complete line of radio -transmitting tubes, including the 50 -kwtype AW-200, the largest ultra -high -fre-quency television tube made. It will alsocontinue the manufacture of special ultra-violet devices, and complete lines of elec-tronic tubes of industrial types, as well asX-ray tubes and associated rectifiers.

VARNISHED CAMBRIC CABLE DATAA carefully prepared study on the cor-

rect uses of varnished cambric cable, thevarious types, physical properties and char-acteristics is now available. In additionto this information, a new booklet containsa series of new tables relating to recom-mended thickness of insulation, tests andnew current capacities data for use of thiscable in both air and ducts. The concludingpages give recommended instructions formaking straight joints on varnished cam-bric cable. This publication is availablethrough the Anaconda Wire and CableCompany, 25 Broadway, New York, N. Y.

MILLER BULLETINSJ. W. Miller Company, 5917 Sofith Main

Street, Los Angeles, California, have re-cently made available two interesting bul-letins. One bulletin describes the Series813 dual -wave interference traps and theSeries 812 standard wave trap. The sec-ond bulletin gives a complete descriptionof a band-pass tuned -radio -frequency coilkit including circuit diagrams of a high-fidelity tuner and a high-fidelity receiver.

GENERAL ELECTRIC BULLETINSThe General Electric Company, Schenec-

tady, N. Y., have recently made availabletwo bulletins on capacitors. One bulletincovers Pyranol-treated radio -transmittercapacitors for amateur radio equipment,while the second deals with d -c Pyranolcapacitors for radio and X-ray equipment,impulse generators. etc. Write to the aboveorganization.

ACOMPLETE, Iwo speed, sixteen inch, high fidelity recorderand reproducer mounted in a single case . . . the recorderyou have always wanted for your shortwave truck and

remote pickups where size and convenience in handling areimportant.

SpecificationsSize: Width, 21"-Depth, 24" --Height, 131/2".Weight: 79 pounds.Turntable: Sixteen inch with two speed drive mechan-

ism and PRESTO instantaneous speedchange.

Cutting Head: . Presto 1-B high fidelity lateral magnetic head,range 50 to 6600 cycles, impedance 8 ohms.

Pickup: Lateral magnetic, impedance 5000 ohms.Amplifier: . . . . Gain 115 db, power output 4 watts, response

uniform within 2 db from 60 to 9000 cycles.Speaker: Eight inch, PM dynamic.Mounting Case: Black leatherette finish.Microphone: . . . Velocity with adjustable floor stand.

Price $560.00 F.O.B. N. Y.A bulletin describing the Presto 16-X recorder will be sent at your request.

PRESTORECORDING CORPORATION

145 West 19th Street, New York, N. Y.

COMMUNICATION!. FOR MARCH 1938 37

LEPELVacuum Testers

Will ionize gas as low as onemicron of pressure.

Cannot puncture the glasscontainer.

Will operate continuously. Ground free and shock -proof. Facilitates production testing

of electronic tubes and in-candescent lamps. Weighs 8ounces.

Write for Bulletin 103

LEPELHIGH FREQUENCY LABS., Inc.Mfrs. of Spark -Gap Converters

39 West 60th St., New York CityCable Address: LEPELSPARK

5'

Grip -To -TalkDESK STAND

Astatic Engineers now offer the newType G Grip -to -Talk Desk Stand. Madewith relay operating switch for remotecontrol of amplifiers and transmittersthrough suitable relay systems. Inter-changeable socket connector to accommo-date microphones illustrated. Most prac-tical combination stand made. Chromeand black. Complete with cable.

(Combination List Prices)GT-3 Mic. and Stand $30.00GD-2 Mic. and Stand 30.00GK -2 Mic. and Stand 32.50GD-I04 Mk. and Stand 27.50

Type G Stand Alone 10.00

ASTATIC MICROPHONELABORATORY, INC.

Dept. M-7 YOUNGSTOWN, OHIOLicensed under Brush Development Co. Patents

REMCO BULLETINThe Remco 3A portable remote amplifier

is described in a bulletin which has re-cently been issued. Write to Radio Engi-neering & Manufacturing Co., 26 JournalSquare, Jersey City, N. J.

AIEE CONVENTIONS, MEETINGSThe American Institute of Electrical En-

gineers, 33 West 39th St., New York City,have announced the following schedule ofnational conventions and district meetings :

National Conventions1938

Summer Convention-Washington, D. C.,June 20-24.

Pacific Coast Convention-Portland, Ore-gon, August 9-12.

1939

Winter Convention-New York, N. Y.,January 23-27.

Combined Summer and Pacific Coast Con-vention-San Francisco or vicinity, Calif.Dates to be determined.

District Meetings1938

North Eastern District-Lenox, Mass.,May 18-20.

Southern District-Miami, Florida, No-vember 28-30.

1939North Eastern District-Springfield, Mass.,

May.South West District-Houston, Texas,

Spring.Middle Eastern District-Location to be

determined, October.Further information may be secured from

H. H. Henline, National Secretary of theabove organization.

WILCOX BULLETINThe 45-M portable remote amplifier is

described in a bulletin available fromWilcox Electric Company, 1014 West 37thSt., Kansas City, Missouri. Completedescription and specifications are given.

TAXATION OF BALLAST RESISTORAND TUNING "TUBES"

Ballast, or resistor, tubes and also ca-thode-ray tuning eye tubes are exemptfrom the federal 5 percent excise tax, whensold separately from a chassis or receiv-ing set, according to an informal rulingsecured by the RMA from Internal Reve-nue Bureau headquarters at Washington.When the ballast or resistor tubes or thetuning tubes are incorporated in a chassisor receiver, they are, of course, part of thecomplete chassis or receiver which is thusassembled and subject to the excise tax.

Regarding the ballast or resistor type of"tube," so far as the excise tax law is con-cerned it is not regarded as a "tube." It isa resistance unit or voltage regulator, inthe opinion of Internal Revenue Bureauofficials, who are of the opinion that a tubemust consist of at least three elements inthe modern receiving set to perform thefunctions of a tube and be subject to excisetaxation.

PIERSON-DE LANE CATALOG

Pierson -De Lane, Inc, Los Angeles,manufacturers of communications receivers,the middle of January published their firstcatalog. The organization was establishedseveral months ago and manufactures anddistributes PR 15 communications receivers,and the PR 15 UH, special police receivers.Address requests to the above organizationat 407 I. N. Van Nuys Bldg., Los Angeles.


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OF CONDENSERS

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ZOPIIARMILLS, INC.

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Radio Engineerswho are

RADIO AMATEURSbuy a fresh copy today of the

RADIO AMATEURCALL BOOK

The CALLBOOK is the only publication thatlists all licensed radio amateurs in the UnitedStates and over a hundred and seventy-fivedifferent foreign countries.Each issue also contains a world map show-ing amateur prefixes, press time and weatherschedules, amateur prefixes listed alphabeti-cally and by countries and a world time con-version chart.Complete ... Accurate ... Up -to -Date

Issued QuarterlyMARCH .. . JUNE . . . SEPTEMBER

and DECEMBERAnnual subscription $4.00

Single copies $1.25Buy your copy note from your radio jobber

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Radio Amateur Call Book, Inc.608 S. Dearborn St., Chicago, Ill., U. S. A.

SOME

NOTES

ON

SNOW

STATIC


relaxation oscillator, such as, a con-denser charged steadily through a highresistance, and discharged periodicallythrough a neon tube which has an un-stable resistance. The audio waveformof such a discharge is jagged, whichgives a tone harsh, or right in audioharmonics. If conditions are suitablefor generation of r -f oscillations in themetallic structure near the discharge,then the audio wave appears as modula-tion on the r -f carrier. Such a carrieris highly damped, and therefore verybroad in frequency. If no actual r -foscillations are present, still the steepwave front of the audio wave is actu-ally equivalent to harmonics of theaudio frequency across the radio fre-quency spectrum, and consequently pro-duces interference.

Such a periodic discharge gives atone or whistle readily distinguishablefrom the roar or hiss which results froma random discharge such as impingingparticles. Often the periodic dischargeis confused by several independentsources at different frequencies. Whis-tling static with distinct and varyingtones is heard at times. In an urbanlocation, such as the usual broadcast re-ceiver, it is probably taken for a man-made interference.

It appears impossible to prevent acharge from building up on a plane.It is necessary therefore to try to findsome way to discharge the plane withoutgenerating radio interference. UnitedAirlines are working experimentally ondischarge through a small trailing wire,with a series resistor. The effects ofthis wire are (1) to offer a sharp pointwhere discharge will occur before theplane reaches a high potential, andtherefore generate lower amplitude ofinterference, (2) to locate the dischargesome distance behind the plane, and soquite remote from the receiving an-tennas, and (3) to damp out r -f andpossibly audio oscillations by passingthe discharge current through a seriesresistor.

The snow static discussed thus faroriginates in the plane, or in the caseof a ground station, results from windpassing the receiving antenna. Thereis now abundant evidence that somesnow static originates some distanceaway from the receiving station, and isdue to a natural cause at present beyondthe reach of the engineer to stop at thesource or to discriminate against in the


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SNOW STATIC


receiver. A relaxation oscillator typeof discharge between two clouds, be-tween a cloud and the earth, or betweenan insulated object and the earth is aprobable source of such interference.

Snow static is sometimes presentwhen there is a thunder storm nearby.When a discharge of lightning occurs,the static disappears for a short timeand signals are heard normally. Thisindicates that the lightning has dis-charged the primary source of powersupplying the assumed relaxation oscil-lator. The whistling tone usually risessteadily, indicating an increasing volt-age in the primary source of power,until it is climaxed by the lightning dis-charge.' The author recently observed whis-

tling static in the El Paso ground sta-tion of the Continental Airlines. A thun-der storm was evident in the nearbymountains. At times several independ-ent tones were present. Local tests weremade to determine that the oscillationwas not occurring in one of the localantennas. The interference was presentin a broadcast receiver in an automo-bile, but of quite low intensity.

ALLOCATION ENGINEERING


on behalf of the public by insuring thatits service area was protected as far aspossible beyond the boundary to whichthat station would be normally limited.Such a station might be asked to in-crease its power in order to increase itscoverage, provided that it retained itsdesirable program and advertisingpolicies.

It might be possible to adopt a simi-lar attitude toward stations that cooper-ate together to increase each others'service area. A station can usually in-crease the service area of the other sta-tions operating on the same channelwithout materially affecting its own byusing directional antennas and othermeans. The increase in service areaobtainable will usually be several hun-dred percent, and would materially im-prove the coverage of regional and localstations. Moreover, it would make itpossible for some stations to give ser-vice to large surrounding rural areas.(Such rural service is seldom availablenow.) The protection of other stationswill involve substantial expenditures,and, unless there were a reciprocalpolicy on the part of these other sta-tions, there is no reason why a stationshould embark on such an altruisticpolicy. It is hardly debatable that co-operation between stations on the same

frequency is desirable for the service ofthe public. It should therefore be desira-ble to foster such cooperation within theindustry with the assistance of the Com-mission.

Another aspect of allocation is themarket area which a station serves. Alarge station in a small town is no moreeconomically reasonable than a smallstation in a large town, quite apart fromthe economics of the station itself, butfrom the point of view of the best dis-tribution of the energy of radio waves.As far as possible a station should begranted enough power to give good andsufficient service to the market area inwhich it is located.

The question of the relationship be-tween the power of a station and itsmarket area raises the question of hori-zontal power increases. While such in-creases are probably desirable in manycases, the general desire of the industrythat was indicated in the public hearingof October 5, 1937, that stations be per-mitted to operate at higher powers, maynot have disclosed all the facts. Therehas been considerable pressure from ad-vertising agencies to increase power onthe grounds that such an increase wouldpermit higher rates, and it is possiblethat such higher rates would be obtainedimmediately after a horizontal powerincrease were introduced. If, however,such an increase does not materiallyimprove the service rendered, and thatwill be the fact in some cases, it is notlikely that the initial increase in rateswill be retained for any length of time.These stations will then find themselveswith higher costs to meet and no betterrevenues, so that the quality of theirprograms will be affected. In such casesthe increased costs will not benefit thepublic, and on the contrary it may bedesirable to protect the industry againstbuilding up such unjustified operatingcosts.

Engineering principles are not theonly criteria for station allocation. Inthis article, I have considered a fewcases in which it may be desirable tomake compromises from the standardsbased on pure engineering in order tomeet other important factors from thepoint of view of service to the publicand to the industry. Such compromisesimply reasonably flexible rules, it ishoped, therefore, that rigidity will notbe a characteristic of the new allocationrules to be adopted, so that exceptionsmay be made to meet special cases suchas those described. It seems that itwould be to the benefit of the public togive special protection to cases of thiskind. There is no real need for rigidrules, for the industry and the Commis-sion should be able to and can workhand in hand to give the best servicein the most economical manner.

AN OLD IDEA -A NEW DRESSThe Cates "RECEIVING REMOTE"

A small self contained radio tuner built as part equipment into a complete A.C. operatedhigh fidelity remote amplifier describes the "Receiving Remote" is a nut shell. Flip a keyand listen to the preceding program for cues, depress the same key and radio is cut outand amplifier connected to the telephone line.Yes, it's an old idea but its brand new dress eliminates cumbersome equipment, chance oferror and best of all keeps the maintenance cost down by doing away with order wires.The "Receiving Remote" is fully described in the new Gates remote equipment catalogCE22. Write for it on your station letter head.

GATES RADIO&SUPPLY CO.MANUFACTURING ENGINEERS SINCE 1922

QUIMCY,ILLMOIS.U.S.A.CABLE ADDREti (GATESRADIO)

The time Pzaven .tine

LEAD-IN WIRES

CALFORHARD GLASS STEM

LITECertified lead-in wires of Tungsten, Molybdenum and Kulgridhave uniform, tested, proven quality-essential requirements for the pro-duction of radio and power tubes, lamps and neon signs.

TUNGSTEN. . Ground finish-free from longitudinal and other surface cracks-controlled crystal structure-excellent sealing quality.

KULGRID"C" Strands once welded stay welded and always remain flexible-does not oxidize or flake under high temperatures-nigh conductivity-eliminates shrinkage and rejection due to overoxiklized and brittle copperstrand.

MOLYBDENUM Ductile and easily shaped - high tensile strength - greatrigidity.

ANY combination and size of Kulgrid, Tungsten or Molybdenum can be suppliedto your specifications in cut pieces or finished welds.

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542. 39th STREET UNION CITY, N. J.


THE MARKET PLACENEW PRODUCTS FOR THE COMMUNICATIONS FIELD

RECEIVING REMOTEThe Receiving Remote is a combined,

complete high -gain remote -control ampli-fier and small radio tuner having self-contained loudspeaker and a -c powersupply. Nothing is needed to complete itsreadiness for broadcasting other than themicrophone.

The Receiving Remote is so arrangedthat all operation is handled by a singlekey -type switch. The radio is tuned bymeans of a slotted control and can not bechanged by the operator. When the keyswitch is up or to position "radio" thereceiver is in use and local program isreproduced through the small self-con-tained loudspeaker. When the key is downor to position "amplifier" the radio isshorted out, speaker cut off and the ampli-fier is connected to the telephone line. Theentire equipment is 20" long, 7" high and5" deep.

Additional information may be securedfrom Gates Radio & Supply Co., Quincy,

U NICATION S.

THORDARSON AMPLIFIERSA new line of amplifiers in modernly

styled, solid walnut cabinets has just beenannounced by Thordarson. Outstandingfeatures are: illuminated dials, protectedcontrols, window visibility dials, dual tonecontrol, multiple inputs with individualcontrols, universal output impedance se-lected by convenient plug-in connectors.Inverse feedback is employed.

The full line includes sizes from 8 to60 watts output. Amplifier and speakercarrying cases are available. Free CatalogNo. 600-C may be obtained from Thordar-son Electric Mfg. Co., 500 West HuronStreet, Chicago, Illinois.-COMMUNICA-TIONS.

BELL P -A SYSTEMAn announcement has just been made of

the Bell Model 424 portable public-addresssystem, which is of modern design, andwhich can be had with the amplifier in achoice of colors-red, blue or black. Ithas a 24 -watt output, and utilizes bothbass and treble compensators. By properuse of compensating controls it is said thatthe feedback difficulties encountered be-cause of different room acoustics can belargely overcome. The system has two12 -inch heavy-duty dynamic speakers.Matching terminals permit the use andmatching of as many as six speakers. Threeinput channels allow for simultaneous useof two microphones and a phono pickup.

For additional information write to BellSound Systems, Inc., 61 East Goodale St.,Columbus, Ohio.-COMMUNICATIONS.

CENTRALAB SWITCHESCentralab has made available a complete

line of selector switches assembled withIsolantite insulation. Two general classesof switches are available. The first of theseis designed primarily for the radio amateurand has sufficient clearance between allelectrical parts to operate safely at poten-tials up to 1000 volts d -c. The contactsare designed to operate in transmitters


Gates Receiving Remote.

Mallory Capacitors.

Thordarson Amplifier.

Centralab Switch.

Bell P -A System.

rated up to 100 watts. The second gen-eral classification of Isolantite switches issimilar in design to the present popularCentralab Bakelite type, but will differin that Isolantite insulation is used through-out. These will be available in all theusual multiple -pole multiple -position types.

Bulletin No. 684 covering the new lineof Isolantite switches will be forwarded tothose requesting it. Write to Centralab,900 E. Keefe Ave., Milwaukee, Wisc.-COMM UNICATION S.

MOTOR -STARTING CAPACITORSA complete line of motor -starting capaci-

tors designed to service all replacementneeds has been announced. The entire lineconsists of 106 units, only 22 of which arerequired to serve 90% of the field applica7tions. Nine "universal" units may be satis-factorily used on a wide variety of replace-ments even though they do not duplicatethe original capacitor in physical appear-ance. All units incorporate latest construc-tion improvements. A special folder, withmore than 160 replacement listings by mo-tor make and model number, will be senton request. Write to P. R. Mallory &Co., Inc., Indianapolis, Indiana.-COM-MUNICATION S.

TELEVISION TRANSFORMERSThree transformers, for use with the new

Kinescope television tubes, are announcedby Thordarson. T -16R50 delivers 3000/2000volts d -c at 3 ma for a type 1801 tube and2.5 volts at 1.75 amperes for an RCA -879.T -16R51 delivers 6000/4500/3000 volts d -cat 5 ma for a type 1800 tube and 2.5 volts at5 amperes for an RCA -878. T -16F55 deliv-ers 2.5 volts at 2.1 amperes for the heaterof either an 1800 or an 1801.

Three replacement type output trans-formers, for use with push-pull 6L6's,6V6's etc., single 25L6's, 6L6's, etc., andsingle 1F4's, 1F5G's etc., and a modulationtransformer for use with the new TZ-40tube, are also announced.

A copy of Catalog 400 -AX describingthese units is available from any Thordar-son jobber or will be mailed postpaid toany one writing to the Thordarson ElectricMfg. Company, 500 West Huron Street,Chicago, I l inois .-Com UNICATION S.

TRIMMER CONDENSERA new Solar trimmer condenser is avail-

able in two different constructions, TypeTP and Type TPB. The Type TP is theceramic base type which is available ineither individual units or in multiple unitsup to any desired number of sections withthe ceramic base fastened to an L channelsteel strip. The TPB units are mountedon a bakelite strip, and are available insingle or multiple units up to any desirednumber of sections.

In general, for push-button tuning wherea high order of stability is required, theceramic base units should be used.

Additional information may be securedfrom the Solar Manufacturing Corp., 599Broadway, New York City.-COMMUNICA-

N S.

LitiECRYSTAls3 6 e

0 .1 0

t

are manufactured for all fre-quencies frcm 20 Kc. to30 Mc. Bliley BroadcastFrequency Crystals are ap-proved by the F. C. C. Pre-cision manufacturing andcorrectly designed holdersassure full dependability.

BLILEY ELECTRIC COMPANYUNION STATION BUILDING ElUE. PA.

'TOPHET C"meets mechanicalend corrosion-resis--ant specifications.

High specific resis-tance for compactresistors and con-t-ols.

Bare or insulated.Tangle -proof spool-ing.

Pronounced TOF - FET - the always - uniformnickel -chrome alloy which beers the initials andendorsement of the pioneer. Made by alloyspecialists for resistants-dey ce specialists.

,LBUR B. DRIVER. CO.NEWARK, NEW JERSEY

WANUMNOMMON

PRECISION CAPACITANCEAfter two years of development and test,

a new type of precision condenser is beingoffered for radio production purposes. Thenew condenser is based on the use of con-ducting films of silver, chemically depos-ited on thin sheets of India ruby mica.Connection to the films is made by meansof silver-plated terminal clips which arepressed down over the ends of the mica.This assembly is fastened to a ceramicblock.

Adjustment of capacity is accomplishedby removing the required amount of silver.The maximum capacity using a single micais about 150 mmfd. This range may be in-creased by using additional plates connectedin parallel. Close capacity tolerances canbe maintained in production because of theease of adjustment. A special treatmentgiven the finished and adjusted assembly issaid to insure uniformly high Q, while awax dip provides protection against mois-ture.

Additional data may be secured fromThe F. W. Sickles Co., Springfield, Mass.-COMMUNICATIONS.

VIBRAPOWRVibrapowr is the trade name of a recently

announced auto -radio replacement vibrator.This unit is said to incorporate a differentmechanical design, and adjustability with aself-cleaning wiping action of the contactpoints. Filing and readjusting the pointsin a Vibrapowr unit is practically the sameas the method employed in automobile dis-tributor work, without the use of an oscil-

Sickles Capacitor.

.40

Pauley-James Vibrapowr.

Ohmite Tandem Assembly.

lograph, meters or gauges. Further infor-mation may be secured from Pauley-JamesCorp., 4619 Ravenswood Avenue, Chicago,Illinois.-Co rMI NICATIONS.

RHEOSTAT TANDEM ASSEMBLYA special type of tandem construction and

assembly has been designed by Ohmiteengineers for special use with the larger -size Ohmite rheostats. This assembly, likethe standard Ohmite tandem assemblies, isused for the control of electrical apparatuswhere several circuits are to be simul-taneously varied, as in the control of theindividual phases of a 3 -phase line, etc.

A four -unit assembly recently completedconsists of four Ohmite Model "U" rheo-stats rated at 1,000 watts each. The over-all length is approximately 3'2" and theheight 151/8". It is 12" in diameter, andhas a 3/4" through shaft.

Each rheostat is individually driven fromthe shaft through specially made universalcouplings, designed to eliminate lost mo-tion-the contacts thus remaining in align-ment.

This special construction and assemblycan be supplied for 2, 3, 4 or more rheo-stats in tandem, using any combination ofModel "N" (300 -watt), Model "R" (500 -watt), or Model "U" (1,000 -watt) units.Standard -type tandem assemblies are avail-able for use with all Ohmite rheostat mod-els from 25 to 1,000 watts, or with Ohm-ite tap switches.

Ohmite Manufacturing Company, 4835Flournoy Street, Chicago, Illinois.-COM-VUNICATION S.


-s--- 44011- ..,..

MIDGET MOTORSThe unit shown in the accompanying

illustration incorporates the new Utah 3 -wire reversible midget motor. It is oneof the mechanical arangements suppliedto radio manufacturers for push-button orautomatically tuned radio sets. The geartrain gives a reduction ratio of 34.56 to 1.A gear mounting plate is inserted betweenone end cover shell and the laminationstack, providing alignment of the low -speedshaft. As usually used in radio receivers,this shaft carries the manual tuning knobin addition to a pulley for the gang con-denser drive cord.

Complete specifications on this and otherUtah motors are contained in a bulletinrecently issued by Utah Radio ProductsCo., 820 Orleans Street, Chicago, Illinois.-COMMUNICATIONS.

POWER -LEVEL INDICATORS

For measuring levels of audio -frequencysignals a new line of miniature power -levelindicators has been developed. Usefulwherever audio -frequency signals are gen-erated, amplified, transmitted, received, andutilized, these instruments provide for ef-ficient operation of lines and circuits car-rying audio -frequency currents.

Power -level indicators are essentiallyrectox voltmeter. When provided withscales marked in decibels, overall powergain or loss in a system may be obtainedby adding algebraically the "db" gains orlosses of the individual devices or linescomprising the entire network.

Modified permanent -magnet moving -coilinstrument mechanisms are used in con-junction with selected rectox rectifiers.

All standard power -level indicators havescales marked -10/0/-1-6 decibels ; how-ever, power -level indicators can be fur-nished with special scales, speed, response,and damping, and special calibration tomeet any requirements within the possi-bility of design.

Further information may be secured fromWestinghouse Electric & Mfg. Co., EastPittsburgh, Pa.-COMMUNICATIONS.

AMERICAN MICROPHONE

A small dynamic microphone has re-cently been announced by American Micro-phone Co. The diameter of the instrumentis 1% inches and the weight is 8Y2 ounces.The frequency response is said to be good.Both high -impedance (D7T, 10,000 ohms)and low -impedance (D7, 50 ohms) modelsare available. For complete informationwrite to American Microphone Co., 1915South Western Ave., Los Angeles, Cali-fornia.-COMMUNICATIONS.

MINICAP TUBULAR CONDENSERS

Solar Minicap tubular condensers, small,dry electrolytic condensers, have been an-nounced. In addition to their small size,these condensers are produced in singlevalues only to prevent inter -coupling orinter -leakage between sections. They arehermetically sealed in metal cans, and be-ing in tubular form they are easy to mount,singly or in multiple. Electrical character-

istics are said to be as good as largertypes.

Additional information can be securedfrom the Solar Manufacturing Corp., 599Broadway, New York City.-COMMUNI-CATIONS.

BULL MARINE SPEAKER '

The Bull Marine Speaker, shown in theaccompanying illustration, is a large re-entrant type of horn, 28 inches in diameterand 21 inches deep. It is made of heavyaluminum casting and unbreakable bell andcenter section. It is designed to operatewith standard Racon marine receiving unit.or the 60 -watt Bull unit. It is saidto be entirely weatherproof and salt sprayproof. Additional information may be se-cured by writing to Racon Electric Co.,Inc., 52 East 19th St., New York City.-COMMUNICATIONS.


THERMIONIC AMPLIFIER

The Thermionic amplifier, shown in theaccompanying illustration, is said to bringhigh sensitivity to potential measurementsin high -resistance circuits. This unit, draw-ing negligible current, is also said to adaptany potentiometer of suitable range to themeasurement of glass electrode potentials.It is further useful for measuring poten-tials encountered in polarization studies,corrosion and oxidation-reduction poten-tials, as well as potentials and currents incircuits of very high resistance.

The thermionic amplifier is a product ofLeeds & Northrup Co., 4901 Stenton Ave.,Philadelphia, Pa.-COMMUNICATIONS.

DELCO MOTORS

Two new Delco fractional horse -powermotors have recently been announced. Oneis of the split -phase reversible type, whilethe other is a series reversible unit. Uni-directional models of both are available,and they are said to be non radio inter-fering. Rotation is reversed as desired bymeans of remote control.

Bulletins .describing these motors areavailable Delco Appliance Divi-sion, General Motors Sales Corp., Roches-ter, N. Y.-COMMUNICATIONS.

HEAVY-DUTY RESISTORS

As a result of engineering research, anew and improved coating for tubular typewire -wound resistors has been announced.This is known as the IRC Type C coat-ing. It is now available on all IRC powerwire -wound resistor types at a slight in-crease in cost over standard units usingthe IRC Type A coating.

Tests on the new coating are said toprove its superiority under abnormal at-niospheric conditions. Among other fea-tures, tests indicate greater life on ac-celerated salt solution immersion tests, itis said.

This development is detailed in the 1938IRC Resistor Catalog just off the press.Write to the International Resistance Co.,401 N. Broad St., Philadelphia.-COM-MUNICATIONS.

Mr. EngineerYOU'LL FIND a big

sales advantagewhen you include theBrush "Hushatone"(pillow speaker) in yournew model midget radio.It's easy to modify youroutput circuit to accom-modate this popular ac-cessory.

In the home the"Hushatone" is ideal foruse in bed, on a couchor a comfortable chair.

In hospitals and sanitariums it has a natural use. Con-valescents and bedridden patients welcome the "Husha-tone" because of the pleasare and convenience it gives

them.

Get in your order today and gain a definite sales ad-vantage.

The BRUSH DEVELOPMENT Co.

3318 PERKINS AVE., CLEVELAND, OHIO

AMPEREXURBON ANODETNINSMITTING TUBES

ELECTRONIC PRODUCTS, Inc.

79 WASHINGTON ST., BROOKLYN, N. 7.

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Built-up Mica PlateMica Condenser Films

'DTIVE LITERFOR EESCR

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#111' °1frURE AND SAMPLES WRITE DEPARTMENT 304

WILLIAM BRAND & COMPANY268 Fourth Ave N. Y. 217 N. Desplaines Si., Chicago

NOW READY for DeliveryALLIANCE MODEL "R"

FOR PUSH BUTTON RADIO TUNING

IT'S HERE! After weeks of checking, testing, improving,the tiny Model "R" motor, specifically designed for push-button tuning, is ready for immediate delivery.Exclusive safety and dependability features make the Model "R"motor the most rugged and efficient of its kind. Securely mounted,self -aligning, oilless bearings guarantee permanent shaft alignmentand noiseless operation. Thermostatic protection against accidentalburning out, plus ample heat radiating area provided by the housing,make the Model "R" ideal for concealed positions. Yet the overalldimensions are only 21/4" x 2l/a" x 1%". The Alliance Model "R"motor can be had now in large quantities at low cost. Mountingand gear assemblies will be supplied to meet your particular demandsand specifications.

Write, Wire or Phone for Complete Details and Sample.

ALLIANCE MFG. CO., Alliance, Ohio


AUTO -RADIO CONTROLThe unit shown in the accompanying

illustration is arranged with three inde-pendent mechanisms ; the center, whichconsists of the dial and the lighting ar-rangement ; on the right is the tuning de-vice; and on the left is the volume con-trol. These units may be placed in anyposition on the instrument panel andfunction in a satisfactory manner. It isfurnished in the aeroplane type dial andwill fit the majority of the 1937 and 1938automobiles. Special care has been takenin arranging the dials so that they are at-tractive and may be illuminated either byedge -lighting or direct -lighting.

For details address F. W. Stewart Manu-facturing Corporation, 340 West HuronStreet, Chicago, I ll inois.-Com uN icn-TION S.

DEFLECTING YOKE & TELEVISIONTRANSFORMERS

Deflecting yoke Type T-700, recentlyintroduced, is designed for use with cath-ode-ray tubes of the electromagnetic -de-flection type. Special care is taken in thewinding and placement of coils in this yoketo reduce to a minimum any distortionwhich may occur due to unbalanced mag-netic flux or non -uniform fields. Couplingbetween high and low -frequency coils issaid to have been reduced to a negligiblevalue. An internal shield is effective inreducing the effects of external fields onthe image to be projected. The low -frequency coils are so constructed that alow -impedance line may be run to themfrom the new output transformers TypeT-112. This helps to minimize pickup andeliminate coupling condensers. Ampledeflection is obtained from the Type T-700yoke on nine -inch tubes at a plate voltageof 6000.

The new Type T-111 high -frequencysweep output transformer is wound withlow -capacity coils in order to pass thehigher harmonics of 13,200 cycles necessaryfor the production of a linear deflection.The power transformers T-203, T-204, andT-208 are said to be insulated for the highvoltages at which they must operate andat the same time compactness is retained.

Further information may be securedfrom Kenyon Transformer Co., Inc., 840Barry St., New York City.-COMMUNICA-TIONS.

TUNING MOTORThe motor shown in illustration is now

ready for immediate delivery, equippedwith mounting and gear assemblies tospecification. Securely mounted, oillessbearings guarantee permanent shaft align-ment and noiseless operation, it is said.Housing provides ample heat radiating areaplus thermostatic protection against ac-cidental burning out. Overall dimensions2A- x 2%" x 1W. The Allinance Manu-facturing Co., Alliance, Ohio.-COMMU-NICATION S.

MICA CAPACITORSThe new C -D Type 2R mica capacitors

have been designed to meet the stabilitylimits required by push-button tuning. Anew silver-plated mica construction methodis said to give a capacity tolerance within3%, high Q, and good retrace. The C -DType 2R's are encased in low -loss bakelite.For further information on these units,write to the. Cornell-Dubilier Electric Cor-poration, South Plainfield, N. J.-COM-MUNICATIONS.

Stewart Auto -Radio Control.

Cornell-Dubilier Beaver Capacitor.

Kenyon Deflecting Yoke.

Alliance Tuning Motor.

Cornell-Dubilier Mica Capacitor.


ELECTROLYTIC CAPACITORSThe small, etched foil, dry electrolytic

capacitors designated as the "Beaver Line"have been designed primarily for use in themore compact models of radio receivers.

The small physical size of the Beaverunit is said to result from an engineeringdevelopment in the etching of anodic ma-terials. The new etching method is saidto give a larger effective anode surface andno alkalies or acids are used in the etchingprocess. Also, the Beaver units employnewly developed electrolytes which arestable and free from tendencies toward cor-rosion of the anodic film during active aswell as idle shelf life, it is said.

A bulletin giving the general specifica-tions of "Beaver" etched foil, dry electro-lytic condensers is available from Cor-nell-Dubilier Electric Corp., South Plain-field, N. J.-Comm U N ICATIONS.

BALL -BULLET MIKEIn addition to their Bullet microphones,

Transducer has announced a new Ball -typedynamic microphone. Model MK -35. Thenew "Ball -Bullet" is housed in a sphericalmetal case 3 inches in diameter, finished in"satin black." It is equipped with a swivelbracket and can be used as either a direc-tional or non -directional microphone. Sen-sitivity of the Ball -Bullet is said to be -52db, impedance approximately 50,000 ohmsor approximately 200 ohms, frequency re-sponse flat, from 30 to 10,000 cycles.

To secure further information write toTransducer Corporation, 30 RockefellerPlaza, New York City.-COMMUNICA-TIONS.

BASS REFLEX ENCLOSURESThe new Jensen Bass Reflex enclosures

for speakers have been so designed thatthey can be used with 18 -inch and audi-torium speakers that are now being usedin the field. The enclosure is shippedknocked down and all that is necessary todo is to set up the enclosure and put thespeaker unit in place. All Jensen public-address speakers -8", 10", 12", 15", audi-torium and 18" speakers are now offeredas complete reproducers, no baffles beingnecessary. For further information on thenew auditorium and 18 -inch Bass Reflexenclosures, write for special folder to Jen-sen Radio Manufacturing Company, 6601South Laramie Ave., Chicago, Ill.-COM-MUNICATIONS.

ULTRA -HIGH -FREQUENCY CONDENSERBud Radio has just announced a new

series of transmitting condensers especiallydesigned for use in ultra -high -frequencycircuits. There are said to be no closedinductive loops in the frame. Metal tierods are used to permit a rigid type ofconstruction, but they are insulated fromthe end plates with ceramic bushings oneinch long. The rotor connection is saidto be placed at the electrical center of therotor. This contact is a 4 -point self-cleaning phosphor bronze spring.

Further information may be secured fromBud Radio, Inc., 5205 Cedar Avenue, Cleve-land, Ohio.-COMM UNICATION S.

NEW LEAR LABORATORYMr. Wm. P. Lear, President of Lear

Developments, Inc., announces that onMarch 14, 1938, the company opened theirnew office, laboratory, factory and serviceset-up at Roosevelt Field, Building No. 31,Mineola, Long Island, N. Y.

azkizeta.FOR ECONOMY

Throughout the radio industry Gardiner Rosin -CoreSolder has an outstanding reputation for savings Inboth time and material. Its uniform water whiterosin flux ... no solvent added . .. permits cleaner

work by both expert and inexperienced help. Its high tensile strength insureslasting bonds. Yet, due to modern production methods and tremendous de-mand, Gardiner Solder costs less than even ordinary kinds. Made in variousalloys and core sizes and in gauges as small as 1/32 of an inch. Availablein I. 5 and 20 -lb. spools.

Eastern Sales Office and Warehouse:DAVID M. KASSON & CO., 264 Canal St, New York

4319 S. CAMPBELL AVENUE, CHICAGO, ILL.

CHAS. EISLER'SEQUIPMENT HAS PRODUCED

MILLIONS

FOREMOST IN THE ELECTRONICSFIELD FOR OVER 20 YEARS!Charles Eisler's equipment for the productionof radio and electronic tubes, incandescentlamps, X -Ray and cathode ray tubes, mer-cury switches, photo -electric cells, and neonsigns has met the severest demands of in-dustry in operating at maximum productionand minimum cost. If you are in the marketfor any of the above or allied equipment

including electric spot welders up to 250 KVA, butt, and arc welders, get in touchwith us. Write for our "college and alas, working laboratory units" catalog.

EISLER ENGINEERING CO.750 S. 13th STREET (Near Avon Ave.) NEWARK. N. J.

TAYLOR FIBRE

PI- ENOL FIBRE

TAYLOR FIBRE CO., Norristown, Pa.

TAYLOR INSULATION

"THE CRYSTAL SPECIALISTS SINCE 1925"

PIEZO-ELECTRIC CRYSTALSGUARANTEED Accurate to BETTER than .01%

Send for FREE Booklet and Price List!

SCIENTIFIC RADIO SERVICEUNIVERSITY PARK - HYATTSVILLE,. MD.

RADIO IN IT S. ENTIRETY!13 A. the trade wit' every need In radio-complete 160 -page catalo, of nationally knownradio receivers. public addr ss, parts, supplies andequipment. Orders shipped same day received.

BURSTEIN-APPLEBEE CO.1012-14 McGEE ST. -:- KANSAS CITY, MO.

UP-TO-DATE CATALOG AVAILABLE

USED LABORATORY EQUIPMENTWeston - G.R. - L&N - G.E., Etc.

Meters - Bridges - Torsion balances - Inductors.Decade boxes - Analytical balances - Oscillographs.Tubular rheostats - Signal generators - Condensers.

Write for flew listLouis J. Winslow

200 PENNSYLVANIA AVENUE HILLSIDE, N. J.

April COMMUNICATIONSAnnual

Construction & Equipment NumberForms close April 4th

COMPLETE ELECTRIC PLANTSNEW 1938 MODELS

OPERATERADIOS AND TRANSMITTERSONAN A.C. PLANTS furnish same currentas city lows, 110 volt 60 cycle. Ideal foroperating PUBLIC ADDRESS SYSTEMS.SOUND CARS MOTION PICTURE EQUIP-MENT PORTABLE NEWSCASTERS or forEMERGENCY STANDBY.

Standard Sizes 350 to 5000Watts A.C.

6. 12. 32 and 113 volt D.C. Models, $57.50and an. Also combination A.C.-D.C. Units.

Write for details.

D. W. ONAN & SONS360 ROYALSTON AVE. MINNEAPOLIS, MINN.

GET RID OF "EXPENSIVE" DIRT !Blows - Vacuum, -Sprays

JUMBO "3 IN 1"ELECTRIC CLEANERDirt wears out machinerycauses trouble with delicateelectrical instruments, is a

"short" hazard.Keep your Plant and Electricalequipment clean with IdealCleaner. Has power to spare-yet is gentle enough to use aroundmost electrical instruments, apparatus, and wiring.Creates high -velocity, dry -air stream at low pressure.corners and "hard -to -clean" places.Portable-Easy to handle-Weighs 14 lbs.Particxlarly designed for use in broadcasting stations-communica-tion companies. Used extensively.

Ask About Free TrialIDEAL COMMUTATOR DRESSER COMPANY

1062 PARK AVENUE SYCAMORE. ILLINOIS

Gets dust in

ERMANENT MAGNETSWe make Permanent Magnets

for All PurposesStamped, Formed and Cast,Chrorr e, Tungsten, Cobalt

andALN I C 0' (cast or sintered)

uncle- G. E. license

THOMAS & SKINNERSTEEL PRODUCTS CO.

1113 E. 23rd ST. INDIANAPOLISLAMINATIONS FOR RADIC TRANSFORMERSTOO.S DIES HEAT TREATING STAMPINGS

ARE YOU Training OR Waiting FOR TOMORROW?New Equipment-New Problems Demand Men with Training

There is no mystery as to what "tomorrow willbring." Already we have seen highly complicatedreceivers. Foe -simile transmssion is HERE.Practical television Is slot far off! Men who wantto get ahead In Radio will find that NOW Is thetime to insure their future by increasing theirability. CREI home study course are PRACTICAL,and have been thoroughly tested and proved In allbranches of Radio.

Write Today for "A TESTED PLANfor a Future in

Practical Radio Engmeering"This FREE Informative and illiztrated booklet willprove helpful to men not satisfied with theirpositions in Radio. Wrte for your FREE COPY.

Capitol Radio Engineering InstituteWASHINGTON, D. C.14th and Park Rd., N.W.

DEPT. CO -3 NEW YORK OFFICE:29 Broadway

COMMUNICATIONS FOR (MARCH 1938 47

LETUS

LOWERYOURTUBE

COSTSWe REBUILD any type Wateror Air Cooled.

Since 1919, we have earned areputation for unrivaled qualityin workmanship.

This experience means longer life-greater satisfaction.

Our modern equipment and en-gineering skill assures you "tubesas GOOD as NEW."

Liberal CASH or TRADE allow-ances for old tubes.

List of Satisfied customers onrequest.

GENERALELECTRONICS CO.

DOBBS FERRY, N. Y.

"World's Lareest Tube Rebuilders"

Sii

HIGH FREQUENCY

RESISTORSSend your high frequencyresistor problems to re-sistance headquarters. LetIRC engineers help you-just as they have solvedsimilar problems for manyengineers and physicistsduring recent months. IRCResistors up to 200 wattsnow available for frequen-cies of 30 megacycles orover. When writing,sure to supply detailsyour requirements.

be

of

INTERNATIONALRESISTANCE CO.

415 NORTH BROAD STREET,PHILADELPHIA, PA.

Advertising IndexA

Aerovox Corp.Alliance Mfg. CoAmperex Electronic Products, IncAmperite Co.Astatic Microphone Laboratory, IncAudak Co.

B

294545483833

Bliley Electric Co 43Brand & Co., Wm 45Brush Development Co., The 45Burstein-Applebee Co. 47

C

Callite Products Division 41Capitol Radio Engineering Inst... 47Cornell-Dubilier Electric Corp. 6

D

Driver Co., Wilbur B

Eisler Engineering Co

F

Franklin Mfg. Corp, A. W

G

Gardiner Metal Co

43

47

47Gates Radio & Supply Co 41General Electronics Co 48General Radio Co Third CoverGoat Radio Tube Parts, Inc 39

H

Holyoke Wire & Cable Corp 27Hubbard Spring Co., Al. D . 39

IIdeal Commutator Dresser CoInternational Resistance Co

L

Lenz Electric Mfg. Co

4748

5Lepel High Frequency Labs., Inc 38

0Onan & Sons, D. W 47

P

Presto Recording Corp 37

It

RCA Communications, Inc 40RCA Mfg. Co., Inc Back CoverRadio Amateur Call Book. Inc 38Recoton Corp. 48

S

Scientific Radio Service 47Sickles Co., F. W 26Solar Mfg. Corp. Inside Front CoverSound Apparatus Co 40Swedish Iron & Steel Corp. 31

TTaylor Fibre Co 47Thomas & Skinner Steel Prod. Co 47

UUnited Transformer Corp 35Universal Microphone Co., Ltd 40Utah 43

WWestern Electric CO 3Winslow, Louis J

z47

Zophar Mills, Inc 38


DJUITABLE REPonteti

1E;made poilibla by

THE ACOUSTICCOMPENSATOR

111.,

With the flip of a finger you can now (1) loweror raise the response of the microphone... (2)adjust the microphone for most desirable re-sponse for close talking or distant pickup.. .(3) adjust the system to any "taste", room con-dition, or equipment.MODELS RBHk, RBMk, with Acoustic Compen-sator, frequency range 40 to 11000 cps, output,-65 db., complete with switch,, cable connectorand 25' of cable $42.03 LIST

NEW LOW-PRICED CONTACT "MIKE"ModelSKH SRL (200 ohms) $12.00 LIST

(pat. pond.)

*Higher orlower pitchwith thesame micro-phone.

MODELS RAH-RAL, excellent for speech andmusic. Reduce feedback $22.00 LISTWrite for Complete Illustrated Bulletins and

Valuable Sales Helps561 BROADWAY, N, Y.

MPERITE O. Cable AddressALkem.New York

ittatSV%014the

0041

At JUST ONE POINT in therecording process is Soundtransferred from the metalto the medium . . . wherethe Cutting Needle contactsthe record. That is whereprecision counts. RECOTONCutting Needles are preci-sion -made of the finest qual-ity tempered steel, highlypolished for minimum scratch.Used for Acetate and Cellu-loid.

RECOTONCORPORATIONI 78 Prince Street, New York

RADIO AIDS TO AIR NAVIGATION

CONTINUOUSLY on the alert for thelatest developments in radio safe-

guards to air transportation, the leadingairlines for years have been steadycustomers of General Radio Company.

General Radio measuring equipmentis used regularly to check the designand performance of aircraft transmittersand receivers by lines such as American,Braniff, Delta, Eastern, North American,Northwest, Pan American and United,to mention a few. In addition, the air-craft departments of the U. S. Govern-ment, including the Army, Navy, CoastGuard and Department of Commerce,are large users of G -R apparatus.

General Radio equipment for aircraft

GENERAL RADIO COMPANY New York

use includes standard -signal generators,primary and secondary frequency stand-ards, beat -frequency oscillators, power -level indicators, heterodyne frequencymeters, radio -frequency bridges, stand-ards of resistance inductance and capaci-tance, wave analyzers, noise and vibra-tion meters and many other instrumentsand accessories.

Air transportation demands the high-est precision, accuracy and stability andthe latest engineering design in radiolaboratory equipment. Airlines rely onG -R equipment. You can depend ontheir choice. Write for Bulletin 235 for completeinformation on all General Ratio prod-ucts.

CAMBRIDGE, MASSACHUSETTSLos Angeles

A Money -Saving,Air -Cooled

Power Tube!Year in and year out, the RCA Laboratories are thebirthplace of radio's great advances. Among manyof RCA's achievements in design is the new, money-saving, air-cooled power tube, now available in twotypes -891-R and 892-R.

These new tubes incorporate the design advantagesof the water-cooled tube construction -plus theeconomy and simplicity of air-cooling.

These new RCA air-cooled tubes are outstandingbecause they eliminate the need of very expensivewater cooling equipment. Pipes, machinery, tanks,cooling ponds- all are unnecessary. This results inlower installation cost. Because these tubes removethe intermediate step in cooling, there's no chanceof cooling apparatus going bad or leaking and thecooling system is more simple and reliable, assuringa maximum of time on the air.

Write for full technical details of this sensationalnew RCA achievement.

Ask your distributor or send 100 to Camdenfor a commemorative advertisement on RCA's

television tube announcement.

Better programs every day-when your station's tubes are RCA.

RCA MANUFACTURING COMPANY, INC. CAMDEN, NEW JERSEYA SERVICE OF THE RADIO CORPORATION OF AMERICA

communication - americanradiohistory.com · capacitor yet developed brand new molded silver-plated...

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