Price July 30th FULL DATA ON 85 TUBE 15¢ 1932 Per Copy

T -R -F Set Using 55 Detector -Amplifier

REG. U.S. PAT. OFF. Measuring A -C Voltages with D -C Current Meter

The First and Only National Radio Weekly New 1 -Tube Set Eleventh Year -540th Issue

TUBE'S SOCKET CONTACT ASSURED

Sometimes a tube pops out of a socket. Poor contact. One provisional remedy is to niche the tube prongs with a pair of pliers.

Grid Bias Device Gives Portable Supply from You Access Power Amplifier Separate to Set's Currents for Radio, Phono Rectifier and Voltages or Microphone

www.americanradiohistory.com RADIO WORLD July 30, 1932 TREASURE CHEST Nationall 3 TUBE AMPLIFIER For use with Mike and Phonograph Ultra- Frequency Circuit Complete with Tubes 8 -tube superheterodyne, 40 -80 megacycles. AC- and operated; total of eight plug -in coils (four pair); R.C.A. - Hand Mike - - $17 95 two -stage intermediate at 1550 kc. Tubes required, Complete Kit Parts with (3) 224, (2) 235, (1) 227, (2) 247. True vernier laboratory precision dial. Separate oscillator with Cabinet - - - and Tubes $15 e 95 switch enables c -w reception and aids all station - finding. Complete parts (Cat. HFR) with coils, TRY -MO RADIO CORP. less tubes and power supply $52.63 85 Cortlandt St. 178 Greenwich St. Power supply (Cat. 3258 AB, wired), less 280 NEW YORK tube. $25,13 BIG BARGAIN BASEMENT 179 Greenwich Street Guaranty Radio Goods Co., 145 West 45th Street, New York, N. Y.

1 1 5 DIAGRAMS 360- Degree Condenser FREE! FULL LINE 20 375 mmfd. 116 Cuntll Diagrams of Commercial Receivers au to ca- Power Supplies supplementing the dlagrame L John F. pacity variation, ef- Rider's 'Trouble Shooter's Manual." These ecbesatle OF RECEIVING fected over full 360 diagrams of factory -made relielver', giving the menu degrees, affords wide facturer'd same and model number on mash diagram. L apreadout, better dial dude the MOST IMPORTANT iCRaiN OBID 11 TUBES, INCLUDING for legibility. Great The 116 diagram, each L black and white. en diem test oscillators and dt/e I 11 inches, punched with three standard boles fe all -wave tuning. loose -leaf binding. constitute a supplement that mast b LATEST ONES -r obtained by all polaeesord of "Trouble Shooter's Manual. to make the manual complete. We guarantee ao duplica %ion of the diagrams that appear In the "Manual EVEREADY -RAYTHEON 4- PILLAR TUBES Cireuitr include Bosch 64 D. C. serest) grid; Balkh, Model f. Croeley 20, 21, 21 screen grid; R dy aerie, Consult the List for Tube You Want Si scree grid; Iris 114 A. C. saw grid; Perl.a, DIRECT RADIO COMPANY e lectrostatic series; Philco 16 screen grid. PRICE YOUR PRICE YOUR COST 145 WEST 45TH STREET Subscribe for Radio World for 1 mosthe at tn. regale, TYPE LIST COST TYPE LIST subscription me of 11 50. add have chess diagrams de NEW YORK, N. Y. 11 $3.00 $1.95 '34 $2.80 $1.82 Livered to you fall 12 3.00 1.95 '35 1.65 1.08 Present subscribers may take advantage of tks. 112 -A 1.55 1.01 '36 2.80 1.82 EBY Ant.-Ground twin binding post assemblies offer Pleas, out a cross here lo es *glib '20 3.00 1.95 '37 1.80 1.17 30e each. Guaranty Radio Goods Co., 143 W. 45th extending four expiratiow date '71 -A .95 .62 '38 2.80 1.82 St., N. Y. C. Radio World, 145 West 45th St., New York, N. Y. V-'99 2.75 1.79 '39 2.80 1.82 X -'99 2.55 1.65 '40 3.00 1.95 '100 -A 4.00 2.60 '45 1.15 .75 '01 -A .80 .52 46 1.55 1.01 START RIGHT! Use These ... '10 7.27 4.73 47 1.60 1.04 '22 3.15 2.05 '50 6.20 4.03 '24 -A 1.65 1.08 55 1.60 1.04 Superb Condensers for Short Waves! '26 .85 .56 56 1.30 .87 '27 1.05 .69 57 1.55 1.01 THE most popular '30 1.65 1.08 58 1.55 1.01 capacity for short- '31 1.65 1.08 '80 1.05 .69 '32 2.35 1.53 '81 5.20 3.38 wave use, and the one '33 2.80 1.82 82 1.30 .87 for which virtually all We will ship C.O.D. on receipt of 10 %. commercial short - wave When remitting in full enclose postage. coils are wound, is 0.00014 mfd. The Ham - GUARANTY RADIO GOODS CO. marlund condensers of 145 West 45th Street New York City this capacity, both single Single 0.00014 mfd. Ham - and double, are compact marlund condenser; non - Inductive pigtail; single and efficient. They have hole panel mount and two - Isolantite insulation and point base mount; Isolan- tite insulation; brass plates. Hammarlund precision Quick- Action Single 0.00014 mid. sent workmanship. See offer r free with a 3-months sub- at lower left. Present scription for Radio World Classified (19 Issues. $1.50). Double subscribers may extend 0.00014 mfd. sent free with their subscriptions under a 6- months subscription (26 Issues. $3.00). this offer. . Advertisements 145 45th Steet, New York, N. Y. 7c Word - $1.00 Minimum RADIO WORLD, West Casts With Order NATIONAL S. W. FIVE, A.C. Condition perfect. Complete tubes, fifteen dollars, cash with order. BLUEPRINTS OF STAR CIRCUITS T. Christian, Georgetown, Ohio. 8 -TUBE AUTO SET 5 -TUBE AC, T -R -F WANTED: Broadcast vacuum tube transmitter, of 10 microvolts per meter charac- 150 to 200 W. Racon 20 W. speaker or any other Sensitivity 662 -N. 8 -tube auto receiver designed by good make- also trumpet. Ajax Electric, terizes the Five -tube a -c receivers, using variable Ill. J. E. Anderson, technical editor of Radio mu r -f, power Clark St., Chicago, World, and therefore stations come in with detector, pentode out- only six feet of wire for aerial, and without put and 280 rectifier, are not all alike NATIONAL RADIO INSTITUTE COURSE, texts, ground. Most cars will afford greater aerial by any means. Forty circuits were complete, ten dollars. Pilot Super Wasp, battery. pickup, and besides the car chassis will be fifteen dollars. Stephen Plavetich, 1597 East 47th used as ground, so with this receiver you will carefully tested and one selected as Street, Cleveland, Ohio. get results. The blueprint for construction of far superior to the others. This prized this set covers all details, including directions circuit was the 627, and if you built THE FIVE NEW TUBES, 46, 56, 57, 58 and 82, for cars with negative A or positive A it, you will always be glad you fol- characteristics, installation data, uses, fully de- grounded. The circuit features are: (1) high scribed and illustrated in the April 30th issue (7 sensitivity; (2), tunes through powerful locals lowed our authentic Blueprint, No. pages) 7th Send and gets bX stations, 10 kc either side; (3), 627. This is the best 5 -tube a -c t -r -f two copies. Radio World 145 45th latest tubes, two 239 pentode r -f, two 236 screen broadcast circuit we have ever pub- Street, New York, N. Y. grid, two 237 and two 238; push -pull pentodes, all of 6 -volt automotive series; (4), remote lished. Price 2Se S. GERNSBACK'S "RADIO ENCYCLOPEDIA," tuning and volume control on steering post, SECOND EDITION. A Guide -Book of Radio plus automatic volume control due to low Information topically arranged in Alphabetical screen voltage on first detector; (5), running A -C ALL -WAVE SET Order. Radio in all its branches, described, ex- board aerial. The best car set we've published. plained and illustrated. Size 9 x 12, 352 pages, This circuit was selected as the most highly An all -wave set is admittedly what Red Morocco - Keratol Flexible Binding. Loose - prized after tests made on several and is an many persons want, and we have a Leaf Arrangement. Price $3.98 postpaid (Foreign outstanding deign by a recognized authority. circuit that gives excellent and Canada add 35e extra). Radio World, 145 for Bluetuint 631, @ Sic broadcast York City. Send results, and is pretty good (not great) W. 45th St., New SHORT -WAVE CONVERTER on short waves. No plug -in coils SITUATION WANTED: High School Graduate If you want to build a short -wave converter used. Cost of parts is low. and student of R.C.A. Institutes, Inc., 20 years of that costs only a very few dollars, yet gives Send for age. Have four years electrical work: Three years good results, furnishing all its own power from Blueprint, No. 628 -B, @ 25e. of servicing radio receivers and one year selling 110 volts a -c, and uses no plug -in coils, you In preparation, an 8-tube broadcast sw er- radio and electrical equipment, do some experi- can do so from Blueprint 630, Price roc deterodyne.for 110v d -c. Write for particulars. menting in sound, short- waves. and television. Member of the Official Radio Service Men's Asso- WORLD, 145 West 45th Street, New ciation. Will consider any radio work for which RADIO York, N. Y. eligible. Chas. W. Hancuff, 5105 Broad Ave., Altoona, Penna.

www.americanradiohistory.com ROLAND BURKE HENNESSY J. E. ANDERSON Editor Technical Editor HERMAN BERNARD J. MURRAY BARRON Managing Editor Advertising Manager

The First and Only National Radio Weekly ELEVENTH YEAR Vol. XXI JULY 30th, 1932 No. 20. Whole No. 540 Published weekly by Hennessy Radio Publications Corporation, 145 West 45th Street, New York, N. Y.

Editorial and Executive Offices : 145 West 45th Street, New York Telephone: BR -gant 9 -0558 Price, 15c per Copy; $6.00 per OFFICERS: Roland Burke Entered as second -class matter Mare, 1922, at the Post Office at New Year by mail. $1.00 extra Hennessy, President a n d York, N. Y., under Act of March 3, 1879. Title registered in U. S. per year in foreign countries Treasurer; M. B. Hennessy. Patent Office. Printed in the United States of America. We do not Subscribers' change of address Vica4President; Herman assume any responsibility for unsolicited manuscripts, photographs, becomes effective two weeks Bernard, Secretary. drawings, etc., although we are careful with them. after receipt of notice. Latest Model T-R -F Set Diode Full- Wave Detector, 3 A -F Stages By Herman Bernard

Resistance and voltage values are given on this diagr am of a six -tube tuned radio frequency set of latest design, using the 55 as full -wave detector. Supreme tone quality is the feature.

HERE is the latest tuned radio frequency tion, with the triode of the 55, the 56 and the regards the 55. as used here, as two tubes, set, using two stages of t -r -f, with 58 '45 power tube. and a 280 rectifier. It is a which technically it is. Somebody will have tubes, a full -wave 55 diode detector, six -tube set, on the basis of one tube ascribed to decide officially what the count shall be. three stages of audio frequency amplifica- to each socket, but a seven -tube set if one (('oulinned on next page)

LIST OF PARTS Coils Resistors One shaft type a -c switch (SW) with knob Two two- winding r -f transformers, LI, Two 1000 -ohm resistors One a -c cable with plug Li, and L3, L4, and one three -winding One 0.005 meg. (5000 ohm) resistor Two tube shields for 58's, two for 55 and r -f transformer, L5L6L7. Two 0.1 meg. resistors 56 One power transformer Three 1.0 meg. resistors One dynamic speaker, for '45 single -sided One 0.01 meg. (10000 ohm) resistor output, with 1800 -ohm field coil. output Condensers One 0.5 meg. (500000 -ohm) resistor transformer and speaker plug One 0.00035 mfd. three -gang tuning con- Three 0.05 meg. (50,000 -ohm) resistors Three six- spring sockets (for two 58's denser, Cl, C2, C3, with equalizers, E. (Above are pigtail resistors, 1 watt rating) and one 55), two UY sockets (for 56 One shielded block of three 0.1 mfd. One 10 -ohm center tapped resistor and speaker) and two UX sockets (for fixed condensers (black lead in com- One 25000 -ohm potentiometer with knob '45) mon, to ground) Three grid clips One 0.1 mfd. tubular fixed condenser Other Requirements One table model cabinet Three 0.01 mfd. fixed condensers Two 0.0001 mfd. fixed condensers One chassis, 1394 x 731 x 214 inches [Note: The speaker specified above may One 1 mfd. condenser One travelling light type vernier dial, with be of the tapped field type, 800 ohms and Three 8 mfd. electrolytic condensers pilot lamp 1,000 ohms.]

www.americanradiohistory.com 4 RADIO WORLD July 30, 1932 (Continued from preceding page) the resistor method is used for accomplish- anode, cathode. The grid cap is the control Meanwhile we shall call it a six -tube set, ing the same purpose. grid of the triode or first audio frequency, lest describing it as a seven -tube set gives amplifier, and the usual stopping condenser rise to the question, where is the seventh Voltage Distribution is inserted between the center -tap of L7 and socket? the grid of the triode, with a leak of 1 meg. The outstanding virtue of the receiver is The aim in resistor method is to establish from grid to ground. This method provides its tone. The sensitivity is about the same the minimum bias at no less than 2.5 volts fixed bias. as that of the familiar five -tube midget, negative, and such was the result, since until now a sort of standard, but to be re- the combined screen and plate currents for Virtue of Fixed Bias placed no doubt by designs of this sort, for the two tubes passes through the 10,000 - the 55 has virtues that must be capitalized ohm resistor that drops 50 volts, hence 5 It is necessary in a t -r -f set to use fixed even in modest sets. milliamperes flow, or 2.5 milliamperes per bias, as the signal amplitude would not be tube, equals 2.5 volts drop across each of great enough to provide always a sufficient The Detector Pick -up Coil the 1,000 -ohm resistors. negative bias if such bias were dependent The detector is one that can not be alone on the drop in the 0.5 meg. resistor. The two 58 tubes help boost the gain be- overloaded by this set, and also the volume Three or four locals would give fine tone, yond what it would be were '35 or other va- control is such that cross -modulation is prac- but all other stations would come in with riable mu tubes used as r -f amplifiers, but tically impossible, if the volume control is much distortion, due to little or no negative the detector is a diode, which is not an used to reduce the volume of sound at the bias on the first a -f tube. Of course, the amplifier, and besides it is used as full -wave output so it is not excessive. This protec- plate voltage on the triode of the 55 could fashion, therefore the voltage input is halved. tion against cross -modulation arises from the be reduced, but the remedy would be only If the winding 1,7 were considered as one nature of the tube and the added advantage of relative, not absolute as it is with fixed with only the two extreme terminals, and the reducing the signal input to and the ampli- bias. detector were half -wave, the voltage input fication of the first tube at the same time. The resistor in the plate circuit of the would be twice what it is when the center If only the signal input were reduced the triode part of the 55 is 100,000 ohms. Not tap is used for full -wave detection. This amplification obtained from the tube would only does this reduce the plate current but does not necessarily mean that the voltage be the same all the time, and for low vol- also provides greater volume of sound. The put in always must be half, but rather it ume levels the tube noise would be the usual recommendation in tube characteristic always could be double. The voltage de- same as for any other volume level, where- tables is 20,000 ohms, but this is not a crit- pends on the coupling, which must be tight as if the amplification alone were reduced ical value, and a 1 -watt resistor may be in all instances, and on the number of turns some very strong stations might lay down used in the plate circuit, if 100,000 ohms, on L7. So, in view of the full -wave detection, too great an intensity at the antenna and and likewise a 1 -watt resistor for the bias may we beat about the bush a little way result in some cross modulation. (5,000 ohms). This bias is sufficient, about saying that if L7 is made up of consider- 9 volts negative, which is the specific recom- Easy Combination mendation of some of the tube manufactures ably more turns than ' ordinarily would be for the 56 when resistance coupling is used. selected, that the halving of the greater A combination of the two functions is voltage results in not so much a depression It is not necessary to use the full recom- easily effectuated with the same type of vol- mended bias for the triode of the 55, or 20 of sensitivity ? ume control unit as used for the single-pur- So if the outside diameter of the coil form volts, especially as there is no possibility of pose methods. The arm or slider of a po- any rectified on which are L5 and L6 is 1 inch, and the voltage being fed from the tentiometer is connected to ground, the ex- diode that would require any such bias. On inside diameter about 7 inch, then the form tremes to aerial and to the limiting resist- on which L7 is wound should be 94 inch, signal considerations along 2 volts negative or in the cathode leg. Then as the arm is bias would be enough. However, we have whereby the L7 may be slid inside the other slid toward the aerial connection the ground tubing without contacting with it, and may combined the bias, making it the same for is moved toward the aerial and finally the two tubes, and used a large condenser (8 have 150 turns or more of No. 32 enamel two input posts are shorted and -tapped. size and -aerial mfd.) across the resistor. wire, center This insula- ground interconnected -and there is no sig- tion wire winds 115.6 turns to the inch. That the whole circuit is gaited properly nal input. This position comes in handy in to audio frequencies is the belief of the au- Values connection with the use of a phonograph thor, and the low frequencies are well Resistor pickup, when it is desired to exclude the handled, compared to the usual shortcomings radio signal no matter what may be the dial in this direction. The 58 tubes, instead of being worked at position. 250 plate volts, take 200 volts at full -vol- setting the potentiometer, as Some of the resistor values in the r -f am- Incipient Motorboating ume of better plifier are a little unusual, otherwise the stability resulted that way. The screen volt- circuit does not depart from standard prac- A slight drumming sound when the set age was around 75 volts, actual. The 200 is first turned on, due the volt- tice. The suppressor grid is connected to to effectiveness volts may be measured with a standard cathode. The socket pins, looking at the of the capacities used for filtering not being meter, but the screen voltage may not ; a bottom, with the thick heater prongs to- instantaneous, is preliminary motorboating, vacuum tube voltmeter or other electro- ward yoß, reading in clockwise direction, and, if present, should be tolerated, as it sub- static type would be necessary. When the are: heater, heater, plate, screen, suppressor sides entirely before the heater tubes emit reading was taken with a voltmeter of 2,000- and sufficiently for the program to be audible. -volt about cathode. The control grid is the cap ohms- per resistance it was 50 of the tube. Six spring sockets used, If it is desired to get rid of this incipient volts 300 maximum deflection are on a -volt but these are now generally obtainable. So motorboating it may be done quite handily scale. such a meter draws 0.5 milli- Since are the new tubes, 55, 56 and 58, of by using a lower value of leak in any one full -scale deflection, at 50 volts which ampere at the 55 is the newest, just out. of the audio grid circuits. it draws 0.5/6, or a little more than 80 mi- The B supply choke is shown in the croamperes, but this is substantial com- Half -Wave Detection negative leg, as it is assumed that a dynamic pared to the screen current, therefore the speaker's field coil will be used. At 1800 error introduced by mere meter reading. The 55 is a tube that should be subjected ohms d -c resistance, with 60 ma flowing, a Also, the plate current does not run as to much experimental use by those highly little more than 100 volts will be dropped high as expected in the 58 tubes, duplicating interested in tone quality. You can have across this choke. Since the bias for the the situation obtaining with the '35, other- your choice of full -wave or half -wave de- '45 tube is taken from a division of this wise the 10,000 -ohm resistor would drop tection, using the diagram for full -wave, or, voltage drop, if the two equal resistors are entirely too much voltage. Also because of for half-wave, interconnecting the two diode used the bias will be equal to half the volt- the current being lower than expected. the plates, to which goes one side of L7, and age drop. Meters of the current- drawing biasing resistors (1,000 ohms) are higher returning the other side of L7 to one side type will not accurately read the voltage than expected. of the 0.5 meg. as resistor, ignoring the distribution across the resistors, as only 1 In this regard, however, allowing for dif- center tap. Even with full -wave detection ma is flowing, but the total voltage can be ferences in tubes, it should be stated that the small condenser across the 0.5 meg. read accurately, because of the choke coil these biasing resistors may be reduced in resistor should be retained, because of prac- carrying 60 ma, and the bias voltage will value until there is squealing at the higher tical difficulty in attaining perfect symmetry be proportionate to the resistance distribu- frequencies of the broadcasting stations, and in the detector handling varies radio fre- tion, e. g., 50,000 ohms, or other equal then increased just enough to stop the quencies of input, though full -wave, such values, will give a bias of half the drop. squealing. The operation may be performed lack of symmetry resulting in feedback, on the first tube circuit alone, as this is the which may be either positive or negative Higher Plate Voltage tube most likely to oscillate. The reason and in this instance happened to be positive, the higher values are given throughout is for the condenser got rid of some squealing. With the bias obtained in this way the that with these there was no sign of oscilla- Moreover, the output of the triode part of plate voltage is the voltage between B plus tion. the 55 was not entirely free of radio fre- and ground. Assume this is 250 volts, as Three 0.1 mfd. condensers in one shield quencies, and again a small condenser was shown on the diagram (voltage actually be- case are used for bypassing the first r-f used to detour the r -f from the plate circuit tween filament center and plate return). cathode, and the first and second r -f plate in which it is intended there shall be only Then the only remaining consideration is the and screen voltage supplies, and if there audio frequencies. voltage for negative bias of the '45. This is squealing trouble one Wáy of tending to The 55 takes a six -pin socket, the connec- is stated in the tube characteristic chart as reduce it is to increase the capacities by- tions for which, bottom view, large heater 50 volts. Another handy piece of informa- passing screen and plate voltages, particular- springs toward you, are, clockwise : heater, tion is that the plate current under these ly screen. This would not be necessary if heater, triode plate, diode anode, diode (Continued on next Page)

www.americanradiohistory.com July 30, 1932 RADIO WORLD Readin g A-C Voltages Diode and D -C Meter Are Used By Braley Thompson

MANY persons have sensitive cur - Another fact to consider is that the cal- rent meters, 0.1 or 0.5 milliampere, ibration will be made at audio frequency for instance, but these are d -c (60 cycles) and it would be difficult indeed instruments, and it is desired to measure to get hold of an r -f voltmeter, for it is a -c voltages. This can be done handily expensive and a person doesn't like to by using a tube as diode detector, thus INGOT lend (or borrow) it. However, the tube rectifying the a -c. The meter is put in rectifier is better than the copper oxide the cathode circuit, which consists of the type so far as permitting a wider range combined plate and cathode of a '27 or of frequencies, with smaller error, and 56 tube, it matters not which, except that radio frequencies may be measured on the heater current for the 56 is only about the basis of the audio frequency calibra- 0.6 that of the '27. The 2.5 volts for the 1MF0.uP tion. The accuracy will not be quite as heater may be a -c or d -c. good, as for a -f, but it will be passable. Thus a -c voltages of radio or audio FIG. 1 The tube capacity will detune the frequencies may be measured, except that measured r -f circuit in many instances, low voltages could not well be read, be- Very simple tube circuit, requiring also, but this could be compensated for by cause they would not produce sufficient no B voltage, but enabling reading putting a large coil, with a small tuning current. On the current score one would a -c voltages, audio or radio fre- condenser across it, in parallel with the have to select for the resistor R a value input points. It would have to be a coil that will give a good deflection for me- quencies, with the aid of a sensitive the impedance of which is suitable for the dium voltages, depending on the sensitivity d -c meter. frequencies handled, but as radio fre- of the meter. The less current drawn by quencies are at stake at the moment, a the meter at maximum deflection the 300 -turn honeycomb coil with a 0.0001 to more sensitive the meter. brate the meter in terms of current plot- 0.00015 mfd. condenser across it would Needs High Resistance ted against the known a -c input voltages. suffice. But the input a -c voltages are the very Why Compensation Results Like the diode used as detector in radio ones you desire to obtain. True, but you receivers, this one will need a high re- will have to borrow an a -c meter, and by The parallel coil reduces the inductance, sistance for R, because we have to limit using a resistor across the 110-volt line, but the parallel condenser increases the the current. Disregarding the low resis- with an a -c meter as check, take off vari- capacity, so that resonance may be estab- tance of the tube itself, the resistor R ous voltages and run a curve wherein the lished, whereas without this or some other may be around 100,000 ohms, to enable other variable is the current. similar arrangement there'd be some de- putting the a -c line voltage across the By selecting just the right value of re- tuning, which would make the voltage read connecting points, for approximate full - sistance the calibration can be made to less than it actually is in the set without scale deflection. Assuming the line volt- come out fairly even, so that even num- the tester connected. age to be 110 volts, the resistance that bers of voltages will fall on even numbers As audio frequencies are to be read, the gives full -scale deflection is the one that of the meter scale. bypass condenser across the load resistor limits the maximum reading to 110 volts, must be at least 1 mfd., and if you have whereas the other extreme depends on Approximate Linearity an 8 mfd. electrolytic condenser, or any how closely the low current readings may other capacity more than 1 mfd., you may be taken. The number of meter divisions The series resistance is so high com- use that. While the condenser -resistor likely will be 20 or 30, so, roughly, around pared to the sum of the resistances of the circuit has different impedances to differ- 5 volts would be the lowest reading. To meter itself and of the tube, that the volt- ent frequencies, this applies to audio fre- read lower voltages use a lower value of ages are substantially proportional to the quencies only, and the larger the con- resistor, but of course then the whole current, or the resistance of the total is denser, the smaller the difference. Be- scale is shifted, in a sense, and the maxi- approximately steady. A limiting factor sides, if notation is made of various audi- mum reading will be lower, too. If the is the varying resistance of the tube when ence frequencies, calibration for the usual resistance is halved the voltage reading too much current is drawn, so that if the selection of test frequencies may be car- possible is approximately halved. current is limited to 0.5 ma, even though ried out. These frequencies are 60 cycles Thus you may select the desired range. you have a 0 -1 ma, the result will be (due to easy access to the line), 200, 400, When that is done it is necessary to cali- closer to linearity. 800, 1000 and 5000 cycles. Voltage Options for T-R -F Set (Continued from preceding page) input, and also because of the much better the rule in practice should be to use all care conditions should be 34 ma, so, knowing the quality obtainable, for the second harmonic in shielding even in a set like this, for the plate voltage, the bias may be adjusted, if distortion is under 5 per cent. and the third sensitivity easily may rise to the squealing desired, to produce a flow of 34 ma in the harmonic distortion virtually absent, though point. Therefore commercial coil and other '45 plate circuit alone. it abounds in pentodes (mu of 95). There conditions taken into consideration, the volt- is little use in designing a circuit to take ages at the r -f end should be derived through Shielding Precautions the 55 tube and then use a pentode output resistors approximately as stated. If the voltage actually is more than 250 tube. Then you would be building up quality Twins for 0.00035 Mfd. to destroy it. volts, up to 275 volts, the bias should be The coil data are as follows : For Ll, increased, a little, for instance, for 275 volts Coil Information 12 and L3L4, wind secondaries 12 and IA the bias should be 56 volts negative, and the on 1 inch diameters, 127 turns of No. 32 plate current then 36 ma. No matter if the Three coils are used and they must be enamel wire. Put on three layers of insulat- plate voltage is higher, the plate current shielded. Also the tuning condenser, a three - ing fabric, or wrapping paper if you can't should not exceed 36 ma, as it is the current gang, should be shielded. Besides, there are do better, then wind the primaries, consist- limitation that is important, rather than the special tube shields for the 58, and these ing of 30 turns of any kind of insulated fine plate voltage. Higher voltages than 250, up should be used. The shields for the 58 have wire, say No. 40 silk. L5L6 is wound the to nearly 300 volts, may be treated on this a removable cap that fits over the top of same way, but inside this form, and finally basis, but no alteration need be made in any the tube dome as a companion to the shield attached to it by means of nut and machine other part of the circuit on this account, for built inside the tube. Also, the 55 should screws, a 44-inch diameter form is wound instance r -f pate, screen and biasing re- have a tube shield, though this may be of the with 150 turns or more of No. 32 enamel sistors, or audio load or biasing resistors. general type, whereas the use of a shield for wire, center tapped. It has been said that the sensitivity is the 56 is optional. The '45 and the '80 The data are for condensers of 0.00035 about the same as that of the previously should not be shielded. All shields must mfd. capacity. standard t -r -f set. This is true despite the be grounded. Automatic volume control can not well be use of the '45 power tube (mu of 3.5), Careful shielding is recommended for the used with a receiver of this type but is re- chosen for its standing of a greater signal 58 in circuits that are very sensitive, but served principally for superheterodynes.

www.americanradiohistory.com RADIO WORLD July 30, 1932 DEVICE GIVES ACCESS TO SET CAN TAKE By Paul Diagram of a GRID device for ren- GRID NOT USED CLOSED CIRCUITS CAP Il'1rlAgl CLIP dering the cur- 111 i THAT OPEN AT rents and volt- ,r 1 SWITCH SETTING ages of a re- ceiver accessi- ble by plugging in. The meter Gs Po .G OG OS is external and P6PQKo its connections UX P . UY a-j- F OF- thus may be 0 o \F-O OF+J reversed if cir- cumstances re- quire. The dif- ferent readings 50 are obtained by switching l BOTTOM VIEW OF THREE SOCKETS ON ACCESSOR OPEN CIRCUITS SET TESTERS of various kinds in- THAT CLOSE AT clude meters, but many radio experi- 5W. SETTING menters have the meters, and what they want is some device that will render access to receiver currents and voltages Accessor panel, with the length of wire for measurement. Lacking such a device from the panel just long enough to reach it is necessary when using one's own the tallest tube's cap ('24, '35, etc.). The meters for current measurements, almost newer screen grid tubes are not quite so RECEIVER SOCKET or always to break the line, actually cut high as the '24 or '35. The clip goes on of leads is six, then we need at least five unsolder, and that is no nuisance to have the cap, but then a lead is continued from different positions, for filament or heater to tolerate. clip, under the Accessor panel, to between need not be duplicated, but as we desire Therefore consideration was given to a the next two sockets, where emerges a also to measure voltage we must include device that would render the currents very long lead with a grid cap to reach a sixth position on is the principal diffi- the switch to enable accessible, as that over to the grid clip of the set for con- the meter to be thrown off the current - culty, the voltage access being simple nection. This lead may be 4 feet. reading points to a voltage- point. enough, for one would have merely to reading turn the chassis upside down. Yet when Adapters at Plug End Operation Tabulated volt- the currents are readable so are the The warning has been given that only Now let us obtain access to the cur- ages, with slight extra provision, there- for the Accessor panel are adapters rents. fore present device, called the Ac- the varieties The : plug into omitted, and sockets of three operation is as follows cessor, requires only that you used to take their place. However, at the (1) -A plugged six -lead cable is used, the receiver socket to read both currents receiver we don't know just what kind as previously stated, being inserted in the and voltages. of a socket we shall have to plug into, so receiver socket from which the tube One Avoidance of Adapters we provide a six -lead cable with a six -pin whose circuit is to be tested has been plug, which will take care of six -pin tubes, removed. The tube is put in an accessor Since the six -pin tubes carne on the with or without grid cap, but will take socket. market, with sockets to fit, quite a few care of no other tubes. Therefore we (2) -The free ends of the six -lead cable changes became necessary so that existing need adapters here for a certainty. are connected to the corresponding testers would meet the most modern re- The advent of the six -pin tube has springs of the six -pin socket in the quirements. The easiest method perhaps brought on the market adapters that, Accessor, through the points of the switch is to use the six -pin socket as a starter, when used with the six -pin plug of the that have closed circuits except when at but of course adapters may be used in- cable, will render access to UY and UX a particular switch setting the circuit is stead. For the Accessor instead of adapt- sockets, also to sockets for 11, 12, UX -199 opened. Across the five positions of this ers being used on its panel it was deemed and UV -199 and special types of tubes, switch are connected equivalent points, preferable to include three sockets -UX, as found generally in old sets made by representing identical switch pointer po- UY and six -pin -which would take care the smaller manufacturers. Other than UX sitions, of switches that are open circuits of virtually all the tubes that are taken and UY these adapters would have to be until closed by the switch point setting. from set sockets to be put into the Ac- duplicated at Accessor and receiver points. The open- circuit switch consists simply cessor. Exceptions are the WD -11, WD- However, we are stressing the general use of two tabs or lugs with contact positions 12, UX -199 and UV -199, but these are not of the Accessor for sets with the most which are met by two sliders, one for each often encountered, and any who desire to popular and prevalent types of tubes. tab. To these sliders the meter is con- provide for testing them may obtain the Now, let us see how we accomplish the nected, at the binding posts on the Ac- adapters. very thing we set out to do. cessor panel. Remember that we are talking about In the first place, we wanted to obtain (3) -Now the current flows through all only the panel of the Accessor, and are access to the current -carrying lines, so the circuits, without interruption, except excluding adapters, save for the special a meter could be slipped in series, for for the one instance of a particular switch purpose of the few uncommonly used measurement of the current. Obviously setting for current reading, when the tubes. The three sockets on the Accessor we must create a condition whereby when closed- circuit switch is opened and the panel suffice, therefore, but one extra pro- the meter is in circuit the current flows meter is put in between the open points, vision has to be made. Two of the sockets through it, but when the meter is out of thus closing the circuit in fact, but with may on occasion (one at a time) contain circuit the circuit is closed and the cur- the meter as the closing element. In this a screen grid tube that has grid cap on rent flows through the .Circuit but not way by turning the switch to any one top. When a tube is taken from the re- through the meter -at least not that par- of five positions the currents may be read, ceiver it is placed in the appropriate ticular current. although the precaution must be taken socket of the Accessor. Therefore a grid We shall use a switch, so it must be to have the right meter, or right deflec- clip would be left unconnected, and yet one that has closed circuits, except as one tion option where there is a multiple - its destination must be the cap of the circuit at a time is opened by particular purpose meter, so that a 0 -1 milliammeter tube. Thus a grid clip is provided on the switch settings. If the greatest number will not be at 0 -1 position for reading

www.americanradiohistory.com July 30, 1932 RADIO. WORLD SO YOU READINGS WITH OWN METER Erwin

power tube plate current, or indeed that present issue. As new tubes are brought a current -reading meter should not he out detailed information concerning them used when voltages are to he read. will be published in these columns. Code Explained Some Pointers on Tubes The switch,. shown at left on the panel The 82 and 83 are mercury vapor rec- diagram, bears numerical markings actu- tifiers, and their connections are the same ally, but if you want to engrave the panel as those for the familiar '80 rectifier. you may do so as shown. Irk means fila- The 56 and the '27 have identical con- ment or heater current ; Ik means cathode nections. current ; Igk means current in the grid The 58 has six pins and a\ grid cap. adjacent to cathode ; Igo means current in The heater pins are at the familiar po- the grid adjacent to plate; In means plate sition, and next to heaters are cathode current and E means voltage. Thus for and plate, on either side, the Suppressor voltage readings the current switch must grid being next to cathode and the screen be turned to E, which accounts for the grid next ,to plate.

sixth position. The 57 + has the same connections as Socket pin adjacency, not tube geom- the 58. etry, is meant. The 46 is a power tube, with UY base, At right is another switch, separate and but only four connections used electric- distinct, for obtaining the voltage readings ally, as for pne type of service (Class A) when the current switch is turned to E. Three are on the panel of the extra grid is tied to plate, while for These voltages are Er, for half the fila- sockets the other type (Class B) the two grids the Accessor, to receive different are tied together. The unchanged grid 2 type tubes, while grid cap and clip is the one equivalent to G post of the ment voltage ; Ek for cathode voltage ; Egk connections also are provided. The '27 and 56 type tubes. The grid at the for voltage of grid adjacent to cathode; code is explained in the text. cathode position as found in the '27 and Ek for cathode voltage and EP for plate 56 is connected either to plate (Class A) voltage. or to control grid (Class B). Since the neutral point is the center of The 55 has the usual heater connection, the filament or heater the total voltage distribution includes plate and cathode cathode is as in the '27 and 56, plate is across the filament of a battery -operated voltages as read for Ep, and if we sub- as in other tubes, while the two anodes tube, filament or heater of an a -c type tract the cathode voltage Ek from the are the remaining pins, in line with the tube, can not be read, but the half reading plate voltage reading we have the effec- heaters. must be multiplied by two to ,obtain the tive plate voltage. It will be the true The 85 is the automotive tube equiva- total. When a -c is used the meter has effective plate voltage, too, except for lent to the 55 and the connections are the to be of the a -c type. error due to the current drawn by the same as for the 55. Correct Interpretation meter, which is of no importance what- The 89 triple grid heater type power ever, except where there is a plate load amplifier has a six-pin base, heater, The reason for selecting the midpoint resistor. As the meter is no part of the cathode and plate standard, with the two of filament or heater is that in most a -c Accessor, it is up to the user to provide grids in line with the heater. The three circuits, and such circuits are in the pre- a meter of sufficient sensitivity if he de- grids are (1) cap of tube, (2) grid that ponderance, the center is grounded and is sires accuracy even in the case of re- adjoins plate, and (3) grid that adjoins B minus. This is an easy and good way sistance- coupled amplifiers. Voltmeters of cathode. These grid numbers are stand- to pick up grounded B minus, otherwise the 1,000- ohms -per -volt type are not ard. The complete exposition of this tube hard to establish through plug -in devices nearly sensitive enough for real accuracy in last week's issue should be studied. The and requiring a separate lead to chassis. in such cases, as the error may be as tube may be used as a Class A power am- The method, however, introduces the pos- much as 50 per cent. At least use the plifier triode, a Class A power output sibility of erroneous interpretation of highest voltage scale possible, as this re- pentode or a Class B power output triode, readings, and therefore the correct basis duces the percentage of error, because less depending on the connections of grids, of application will be explained. current is drawn by the meter for the as outlined last week. In battery- operated tubes the reference reading of the voltage. The three posts on the Accessor repre- point is the negative filament, and the The switch used is a commercial prod- sent one extra for safety, so that there reading is always taken from center to uct. It has five thick insulators stacked will be less likelihood of meter injury. negative filament, that is, half the fila- up, one for the detent, for preventing play ment voltage is read. Therefore a plate at switch points, two for the open circuit voltage reading would give, say, 135 volts, switch and two on the closed circuit on the meter, but we know this has been switch. The slider connections are to two 1,103,548 Receivers taken from the center of the filament, lugs non -symmetrically placed. The other which is positive in respect to filament lugs, four to a position, or 24 lugs, are Are minus by half the filament voltage. If the symmetrically disposed. The Trade Edi- in Use in Japan tube has a 2 -volt filament voltage and the tor of RADIO WORLD will answer questions Washington plate voltage reading is 135 volts, the concerning commercial products. The total number of receiving sets in op- actual plate voltage is the sum of half Radioists are familiar enough with the eration in Japan at the end of April was the filament voltage reading and all the old tubes to be able to obtain definite 1,103,548, according to a report to the De- plate voltage reading, or 136 volts. guidance from the symbols given, but as partment of Commerce from Assistant Com- With heater type tubes the voltage to the new tubes there may be some con- mercial Attache William S. Dowd, Tokyo. on the plate, screen grid or other posi- fusion, due to lack of familiarity. At pres- In that month alone 58,951 permits were ap- tively or neutrally biased grid, as the sup- ent not enough such new sets are in use proved, although all sets in private hands pressor, is the difference between the to make this important, and they prob- pay a monthly fee of 25 cents. cathode and the B voltages. Here we ably won't require servicing for six Increasing interest in short -wave interna- have no method of directly measuring that months or so. Meanwhile the service man tional broadcasts, according to Mr. Dowd, difference, for one side of the voltmeter and experimenter should familiarize him- seems to indicate that the Japanese govern- goes not to cathode but to heater center, self with the connections, characteristics ment will eventually modify the ban on which is nearly always grounded B minus, and other pointers about the new tubes, short waves to permit the public to use and the voltage we read is that between and keep posted on still newer ones as short-wave sets. Such action would un- the set's B minus and the effective plate they come along. The full information doubtedly increase the imports from the voltage. of the 46, 56, 57, 58 and 82 will be found United States, for a while, at least, be- Meter Error in the April 30th, 1932, issue of RADIO cause at present Japanese manufacturers WORLD, that on the 55 in the July 16th, make only long wave sets. At the present However, we can read the cathode 1932, issue, that on the 89 in the July 23rd, time these sets are supplied almost exclu- voltage itself. Therefore the B voltage 1932, issue, and that on the 83 in the sively by home manufacturers.

www.americanradiohistory.com 8 RADIO WORLD July 30, 1932 85 DUPLEX DIODE- TRIODE FO OFFICIAL DATA

4 FINS.I25 ±.003 DIA.

PIN I -DIODE PLATE PIN PIN 4- HEATER' 2- TRIODE PLATE PIN 5- CATHODE PIN 3- HEATER PING -DIODE PLATE CAP -GRID 60 °ALL PINS

2 P INS .15C ±.003

BOTTOM VIEW_DF BASE_

The current flowing between plate and which is common to the triode unit. Each cathode through a low resistance current diode plate has its own base pin. measuring device depends not only on the Rating Conditions and Characteristics: applied signal voltage (at a fixed cathode With an applied d -c plate voltage of 10 temperature), but also on the tube resist- volts, the space current per plate with no ance and follows approximately the rela- external load should exceed 0.5 milli- tionship i = k times the 3/2 power of the ampere. signal voltage. If the load resistance is Installation made sufficiently high the effect of the tube resistance is negligible and the dy- Th'e base of the 85 is of the small 6 -pin namic characteristic becomes linear. Since type. Its pins require the use of a stand- the diode resistance is low, the load re- ard six- contact socket which may be in- sistance required to produce approximate stalled to operate the tube either in a linearity is conveniently obtainable. Un- vertical or in a horizontal position. For der these conditions the diode as a means horizonal operation, the socket should be of rectifying the incoming signal is par- positioned with its heater pin openings ticularly suitable because of its freedom one vertically above the other. Base con- from distortion. nections and external dimensions of the Since the diode is a simple rectifier, it 85 are given in the drawing. The control - does not amplify. If increased voltage grid connection is made to the cap on top The 85, actual size output is desired, an auxiliary amplifier of the tube. stage is necessary. The bulb surface temperature on the Following are data from RCA Radiotron Two diodes may be used for full -wave hottest part of the bulb under operating Co., Inc., and E. I. Cunningham, Inc.: rectification or their plates may be con- conditions should not exceed 150° F. as nected in parallel (with decreased tube measured by a small thermo -couple. THE 85 is a heater type of tube con - resistance) for half -wave rectification. Shield -cans, if used, should provide suf- sisting of two diodes and a triode With full -wave rectification, the circuit ficient ventilation to prevent the bulb in a single bulb. It is recommended may be balanced for carrier input so that temperature from rising above the recom- for automobile service as a combined de- no carrier frequency is supplied to the mended maximum value. tector, amplifier and automatic volume grid of the following amplifier and no The heater is designed to operate under control tube. carrier -frequency filtering is theoretically the normal conditions of voltage variation In operation, the two diodes and the necessary. Half -wave rectification as com- of a 6 -volt automobile battery. Due to triode are independent of each other, ex- pared with full -wave rectification provides cept for the the heater - cathode design, the heater common cathode sleeve which approximately twice the signal output but voltage may range between 5.5 and 7.5 has one emitting surface for the diodes requires carrier -frequency filtering. volts during the charge and discharge and another for the triode. This inde- cycles of the battery without affecting to pendence of operation permits of unusual Tentative Characteristics 85 any great extent the performance or flexibility in circuit arrangement and de- of ser- sign. For example, the diodes of this tube viceability of this tube. The heater should can perform at the same time the func- Heater Voltage 6.3 Volts be connected directly across a 6 -volt bat- 0.3 : leads to have as tions of detection and of automatic vol- Heater Current Ampere tery the battery should ume control, with sensitivity control and Overall Length 4 9/32 "-4 17/32" low resistance as practicable. time delay action Maximum Diameter 1 9/16" The cathode circuit in most d -c re- confined to the avc cir- Bulb ST -12 cuit, while at the same time the shielding Cap Small Metal incorporated in the design between the Base (Refer to diodes and triode makes possible opera- Drawing tion of the triode as an amplifier under No. its own optimum conditions. 92S -4190) Small 6 -Pin 85 Designed Especially The design of the 85 is characterized TRIODE UNIT physically by the small overall size, the for Mobile Services dome -top bulb, the rigidity of electrode Operating Conditions and Characteristics : assembly, the symmetrical arrangement of (Class A Amplifier) Designed especially for all types of is in diode plates, and the separate terminals Heater Voltage 6.3 Volts mobile service, the 85 reality three for each electrpde. Plate Voltage 250 Volts Maximum tubes in one -two diodes and one triode Grid Voltage -20 Volts employing a common cathode sleeve, but Diode Detector Considerations Amplification each operating independently of the other. Factor The 85 is capable of performing simul- The simplest form of tube detector is 8.3 taneously the functions of detection, am- the diode. Its action depends on the uni- Plate Resistance 8300 Ohms Mutual Conduct- plification, and automatic volume control directional passage of current between of the input signal. plate and cathode. In the direction op- ance 1000 Micromhos Plate Current The design features of the 85 permit of posite to that producing current, the re- 7 Milliamperes unusual flexibility in its application to re- sistance of the diode is extremely high DIODE ceiver circuit design. Numerous compact while in the other direction its resistance UNITS designs with excellent performance capa- is quite low. This means high rectifying Two diode plates are placed symmetri- bilities are thus made possible by this new efficiency. cally around a cathode, the sleeve of type.

www.americanradiohistory.com (.) July 30, 1932 RADIO WORLD R AUTO SETS; ON THAT AND THE NEW 83

ceivers is usually tied in either directly or through biasing resistors to the nega- FULL-WAVE DETECTOR - DIODE-BIASED AMPLIFIER tive side of the heater circuit. The po- tential difference thus introduced between heater and cathode should preferably be kept as much as possible below the recom- 1 mended maximum of 45 volts. R3 of detector circuits --11- Complete shielding RI C4 employing the 85 is generally necessary to prevent r -f or i -f coupling between the R2 diode circuits and the circuits of other stages. AVC In the case of full -wave detection, with =C3 C1 circuits balanced to ground, shielding and FIG. 1 250V i -f by -pass filters are not theoretically re- quired. However, due to the practical FULL-WAVE DETECTOR - FIXED- BIAS AMPLIFIER difficulties of circuit balancing, their use is desirable. In the case of half -wave de- L. tTh tector circuits, their use is always neces-

sary. 111 Application 1 r} The 85 is recommended for performing A V.0 the simultaneous functions of automatic 4 volume control, detection, and amplifica- C 2 tion. This three -in -one feature is of de- ICI 1----111I1 cided practical importance to the set de- C signer. -- R4 FIG. 2 250V The application of this tube to receiver circuit design gives the engineer wide lati- HALF -WAVE DETECTOR - DIODE- BIASED AMPLIFIER tude in possible tube -unit connections. Since the 85 really consists of two diodes and a triode, each of these tube -units may be used in a circuit just as though it were I in a separate bulb. _ RI R3 For detection, the diodes may be util- ized in a full -wave circuit or in a half - wave circuit. In the latter case, one plate only or the two plates in parallel may R2 CI C4 be employed. The use of the half -wave C3 arrangement will provide approximately FIG. twice the a.v.c. voltage as compared with 3 2S0V the full -wave arrangement. For automatic volume control the con- HALF-WAVE DETECTOR - FIXED- BIAS AMPLIF ER trolling bias voltage may be obtained by either of two general methods. In one case, the required voltage is obtained from T r the detector circuit by utilizing the volt- R 1 ) III age drop caused by the rectified current vw^, flowing through a resistor in the detector circuit. In the other case, the required R2 -11-c R4 voltage is obtained by utilizing one diode A.VC. C3 for the sole purpose of automatic volume 250v control. This latter method is of particu- .w.--.- lar interest since it confines the sensitiv- - B+_ ity and time delay function to the a.v.c. FIG 4 circuit. Time delay action is, of course, determined by the use of a resistance and - SEPARATE AVC. FIXED-BIAS AMPLIFIER condenser combination having the de- HALF-WAVE DETECTOR sired time constant. The sensitivity con- ,-1 trol action is determined by applying a 8 negative voltage to the a.v.c. diode plate T RI C,. III of such a value as to accomplish the de- sired reduction. C6 _ +C4 be C1 For amplification, the triode may R4 employed in conventional circuit arrange- ments. Grid bias for the triode, depend- 250V ing upon circuit design, may be obtained from a fixed voltage tap on the d -c power A.V.C. supply or may be obtained by utilizing the R2/ C3 FIG.5 ÉIIIr variable voltage drop caused by the rec- tified current flowing through a resistor in the detector circuit. In this connec- tion, it should be noted that the accom- latter the order of 0.5 megohm shunted by a grams are of the same order of magni- panying diagrams designate this condenser Cl of approximately 150 mmfd. tude. arrangement as "Diode- Biased Amplifier." for broadcast frequencies or approxi- Fig. 2 shows a full -wave detection and The diagrams of Figs. 1 to 5 illustrate mately 600 mmfd. for usual intermediate automatic volume control arrangement the application of the 85 to typical cir- frequencies. The load resistance R3 is not with a fixed -bias triode. R4 and C2 are cuits. Fig. 1 shows Full -Wave Detection critical and may be about 100,000 ohms. approximately 0.5 megohm and 0.01 mfd. and Automatic Volume Control with the The values of resistors and condensers respectively. triode "diode- biased." R1 is a resistor of having the same subscripts on all dia- (Continued on next page)

www.americanradiohistory.com 10 RADIO WORLD July 30, 1932 (Continued from preceding page) may be necessary to enclose completely The secondary windings of the power Fig. 3 shows a half -wave detection and the mercury vapor rectifier tube with per- transformer should be adequately insu- automatic volume control arrangement forated metal or wire screen shielding to lated from each other to withstand the with the triode "diode- biased." eliminate objectionable noise. The shield- full peak voltage of the high voltage wind- Fig. 4 shows a half -wave detection and ing must be designed to provide sufficient ing. Under recommended maximum oper- automatic volume control arrangement ventilation to prevent overheating of the ating conditions, the full peak voltage will with a fixed -bias triode. tube. It is usually necessary to place be about 1,400 volts. The resistance of Fig. 5 shows an arrangement whereby within the shield, small radio -frequency the transformer windings should of course one diode serves as half -wave detector, choke coils of low distributed capacity in be low if full advantage of the excellent the other diode as automatic volume con- series with each plate lead of the rectifier regulation capabilities of this mercury va- trol tube, and the triode as an amplifier so that the slope of the current wave por rectifier is to be obtained. with fixed bias. The use of a voltage Eb front to the filter is reduced sufficiently Shielding this tube, particularly in sen- for sensitivity control is also illustrated. to eliminate impact excitation. sitive receivers, may be necessary to elim- Diode plate 1 serves as demodulator (de- A further consideration in the opera- inate objectionable noise. tector), while diode plate 2 is used for tion of this mercury vapor tube is that Radio -frequency choke coils, connected a -v -c purposes. the full plate load must not be applied in series with each plate lead and placed In the diagrams with fixed -bias applied until its filaments have reached their nor- within the shielding if used, are usually to the triode, transformer coupling has mal operating temperature. Under normal necessary however, in receivers having high sen- been shown. This arrangement, conditions of operation, they heat quickly sitivity. The inductance of the chokes is not recommended for the "diode - when the set is "turned on" and are ready should be of the order of one millihenry biased" circuits. to supply the full load current before the or more. tubes in the receiver require it. A fuse having a rating approximately 50% in excess of normal lead require- TENTATIVE RATING AND CHAR- ments should be inserted in the primary ACTERISTICS of the power transformer. This fuse is necessary to prevent damage to the power 83 Filament Voltage 5.0 Volts transformer in case of excessive current Filament Current 3.0 Amperes which may flow under abnormal con- HE 83 is a full -wave, mercury vapor Maximum A -C Volt- ditions. rectifier tube of the hot -cathode type age per Plate . 500 Volts (RMS) T for use in suitable rectifying devices Maximum Peak In- Application designed to supply d -c power from an a -c verse Voltage 1,400 Volts power line. It is particularly recommend- Maximum D -C Output The 83 is recommended for supplying ed for supplying power of uniform voltage Current, continuous. 250 Milliamperes d -c power to receivers, particularly those to receivers in which the direct current Maximum Peak Plate employing Class B amplification in the requirements are subject to considerable Current 800 Milliamperes audio output stage. The direct current variation. Typical of such receivers are Tube Voltage Drop requirements of such receivers are such those employing Class B power ampli- (approx.) 15 Volts as to cause considerable variation in the fiers. Maximum Overall load impressed on the rectifier tube. Un- The excellent voltage regulation char- Length 5 3/8" less the tube and its associated circuit acteristics of the 83 is due to its low and Maximum Diameter 2 1/16" can take care of the load demand with practically constant voltage drop for any Bulb . ST -16 good regulation, unsatisfactory receiver current drain up to the full emission of Base Medium 4 -Pin performance fill be obtained. To meet this the filaments. Under normal operating operating requirement for extremely good conditions, the tube voltage drop is only Installation regulation even though the load current about 15 volts. This desirable feature is subject to considerable variation de- makes it possible to attain very high over- pending on the signal, the 83 is especial- all operating efficiency. The base of the 83 is of the medium ly suited. The coated filaments employed in this 4 -pin type. Its pins fit the standard four - contact In order to take full advantage of the tube provides an efficient source of elec- socket which should be installed regulation capabilities of this mercury tron emission, and reach their dull red to operate the tube in a vertical position vapor with the rectifier, the resistance of the trans- operating temperature quickly. base down. Only a socket mak- former windings (refer to "Installation ") Under operating conditions, the 83 has ing very good filament contact and ca- pable and the filter choke windings should be a bluish -white glow filling the space with- of carrying 3 amperes continuously as low as practicable. Since the drop in the plates and extending to some degree should be used with the 83. Unless this precaution through the tube is practically constant, into the surrounding space. This glow, is followed, poor contact at any reduction in rectified voltage when caused by the mercury vapor, is an in- the filament pins will cause overheating the load is increased, at pins is due to the drop herent operating characteristic of the 83. the and socket, lowered filament in the transformer and /or the filter wind- The effect of the mercury vapor in the voltage, and also high internal tube drop ings. 83 is to neutralize the space -charge volt- with consequent injury to the tube. Base connections If is it impracticable to use a transform- age drop so that it amounts to only about and external dimensions of er with sufficiently low resistance to give 15 volts at normal operating tempera- the 83 are given in a drawing. the desired regulation, improved regula- tures. This drop remains practically con- The bulb becomes hot during continu- tion of the ouput voltage may be obtained stant with any current drain up to the ous operation. Provision should be made, by employing a bleeder across the filter full emission of the filaments. It is ap- therefore, for adequate natural ventila- circuit. parent therefore that this tube under tion to prevent overheating. This point Filter circuits of the condenser input or operating conditions has very low inter- must be given proper consideration if the choke input type may be employed nal resistance, and that the current it shielding is employed around the tube. provided that the maximum voltages and delivers depends on the resistance of the The filament is intended for a -c opera- currents tabulated under "Rating and load and the regulation of the power tion from one of the secondary windings and Characteristics" are not exceeded. transformer. Sufficient protective resist- of a power transformer. This winding If the condenser input type of filter is ance or reactance must always be used provided with a center -tap or center -tap- used, consideration must be given to the with this tube to limit its current to the resistor should supply at the filament ter- instantaenous peak value of the a -c input recommended maximum value. minals the rated operating voltage of 5.0 voltage which is about 1.4 times the RMS If current in excess of the total effec- volts when average rated voltage is ap- value measured from plate to filament tive emission of the filaments is drawn, plied to the primary. with an a -c voltmeter. It is important, the tube voltage drop increases rapidly The high current taken by the filament therefore, that the filter condensers (es- with current and thus causes harmful and the danger of damage to the tube pecially the input one) having a sufficient- positive ion bombardment of the fila- caused by applying plate voltage to the ly high break -down rating to withstand ments. This bombardment may be so tube with its filament insufficiently heat- this instananeous peak value. It should great as to cause permanent damage to ed, make it imperative that all connec- be noted that with condenser input to the the coating on the filaments in a short tions in the filament circuit be of low re- filter, the peak plate current of the tube time. sistance and of adequate current -carrying is considerably higher than the load cur- It is characteristic of mercury vapor capacity. All wire connections should be rent. With a large condenser in the filter rectifiers that no appreciable plate current carefully soldered. circuit next to the rectifier tube, the peak will flow until the plate voltage reaches The plate supply is obtained from a current is often as much as four times a certain critical positive value. At this center -tapped high voltage winding on the load current. point the plate current rises steeply to a the power transformer. This winding When, however, Choke input to the fil- high value in a small fraction of a second. should be designed so that the maximum ter is used, the peak plate current is con- This surge of current reoccuring each a -c input voltage per plate will not ex- siderably reduced. This type of circuit, time either plate becomes positive, may ceed 500 volts RMS under varying con- therefore, is to be preferred from the excite circuits in the vicinity of the tube ditions of supply line voltage. The re- standpoint of obtaining the maximum to damped oscillation and result in noisy turn lead from the plate, i.e. the positive continuous d -c output current from the 83 radio receiver operation. In receivers of bus of the filter ánd load circuit, should under the most favorable conditions. low sensitivity, this noise may not be ap- be connected to the center -point of the [Illustrations regarding the 83 were pub- parent but in very sensitive receivers it filament transformer. lished last week.]

www.americanradiohistory.com July 30, 1932 RADIO WORLD ll The 55 for R -F and Detector One -Tube Set May Work Speaker By Caswell Henry REMEMBER the old one -tube set V use a ballast of 1.5 ohms. If we use 'a that operated a loudspeaker? The 6 -volt storage battery the ballast must be 3.5 ohms, for we have to drop 3.5 volts. set that used one regenerative tube, it is a detector, and a magnetic speak- If a storage battery is fully charged, crystal on a single . not a great possible to operate the tube er? While this set did give less deal of volume it did bring in signals cell, but the current will be a little low -power local stations in vogue than normal. In that case, of course, we from the any resistance at all. at the time. The set had one very dis- O.000í should not use ballast agreeable feature, and that was the in- MFO. constancy of the crystal rectifier. It Plate Voltage make adjust- was forever necessary to on of whisker. (Quaint, old The plate voltage to use depends ments the cat The higher the vo' - word, is it not ?) the volume desired. There is a certain reviving interest in age the greater will be the amplification and the and the possible output. The tube twill the one -tube set, but the crystal giving cat whisker must be left out. We have stand up to 250 volts. If a rectifier returning to this voltage is available it can be used, in the 55 tube a means for will the one -tube regenerative set without the but if batteries are to be employed it of continuous adjustment, for not be practical to provide this high nuisance Results will be obtained from the 55 can be used as a regenerative am- voltage. about 22.5 volts up. plifier and as half -wave rectifier. Bt. A circuit of this type is shown in Fig. It is not to be supposed that this of a regular three - FIG. 1. single -tube circuit will perform like in 1. First, it consists even like circuit tuner comprising a primary, a The diagram of a one -tube set eight -tube superheterodyne, nor This coil a five -tube midget. tuned winding, and a tickler. utilizing a 55 duplex triode in should not be like the modern midget diode Extremely small loudspeaker units áre coils if loud signals are to be expected for a regenerative and a rectifier circuit. available for small portable sets, and one they are only suitable in multitude sets of them would fit the circuit nicely. One utilizing screen grid tubes. No, the coil cathode lead. This is not by- passed in measuring 6.25 inches in diameter is of should he one of those low -loss coils order to make it more effective. the magnetic type and utilizes the wll- which at one time were so popular in Of course, if the three -circuit tuner has known push -pull action, but it is not or radio. Such coils are still available in a good rotatable tickler, this can be used a push -pull amplifier. radio stores, if they are not in the ex- as the main control, but even so, it is well perimenter's radio morgue. It should not to have the variable resistance because Good Near Big Stations sometimes the tickler is too critical. By be shielded. the method illustrated a fixed tickler The proper place for a one -tube set like this is in the immediate vicinity of high could be used. field Aperiodic Coupling filament supply may be either a -c power broadcast stations where the The is course, imme- In a is 2.5 strength high. Of "the In the plate circuit, coupling the am- or d -c. case -c used a volt diate vicinity" of a station depends on the plifier to the rectifier, is an untuned radio winding is required, one capable of de- from that station. For livering one ampere. If d -c is used, the radiated power frequency transformer. This is an old - some the radius might be 25 miles, For too, and there is best supply is a storage battery, one that time piece of apparatus, others, only half a mile. . evidence that it will come into wide use gives either 4 or 6 volts. If dry cells are The distance at which results may be requires used, enough of them should be connected again. An untuned transformer expected also depends on the kind ; of tight coupling between the two windings, in parallel to give the one ampere re- 4n- quired. If the cells are No. 6, not less antenna circuit used. An outdoor just about as tight as possible, provided 75 high, or long, should be 3 in used, tenna feet that there is not too much capacity be- than parallel should be because used. There should also be a good ground tween the windings. Coils of this type one cell is not supposed to deliver more provided. It will not do to use the have been made by winding two wires at than 0.25 ampere. This rating requires makeshift antennas and grounds often the same time, using one of them for that four of them be used, and that will used for modern multitube sets. The im- primary and the other for secondary. be more economical. The tube requires a terminal voltage plication, even with maximum regenera- It is possible that due to the high im- tion, is so low that we cannot afford to pedance of the primary of the untuned of 2.5 volts. Hence when we use batteries of different voltages we have to use a throw away pick-up like we can when winding the regeneration will not be sat- a multitube is used. The very best an- isfactory. This can be remedied with a different ballast resistor. In case we have cells, two them in series will give tenna, and the very best ground, should small variable condenser across the prim- dry of and the very best ground is a 3 volts, and we have to drop the excess be used, ary, such as a trimmer. cold water pipe. The detector circuit consists of the sec- half volt. Since the current is one am- ondary of this transformer, a magnetic pere, the ballast resistor must be 0.5 loudspeaker unit by- passed with a 0.0001 ohm. This is indicated on Fig. 1. If we mfd. condenser, and two diode plates tied use a 4 -volt storage battery we have to Tube List Prices together. The loudspeaker is the load drop 1.5 volts, and therefore we have to Type Price Type Price impedance in this case. The variable rec- List Liss tified current will flow through the speaker 11 $3.00 '38 2.80 and the radio component will flow LIST OF PARTS 12 3.00 '39 2.80 through the by -pass condenser. A some- One three circuit tuning coil for a 350 112 -A 1.55 '40 .3.00 what greater output is obtained when a mmfd. tuning condenser '20 3.00 '45 1.15 little larger condenser is used. It is per- One untuned radio frequency transformer '71 -A .95 46 1.55 missible to use as high a value as 1,000 One 350 mmfd. variable condenser UV -'99 2.75 47 160 mmfd. (0.001 mfd.) because it is con- One 0.0001 mfd. fixed condenser, or one UX-'99 2.55 '50 6.20 nected across a relatively low impedance. up to 0.001 mfd. '100 -A 4.00 55 1.60 That statement applies even if the im- One 0.002 mfd. by -pass condenser '01 -A 80 56 1.30 of speaker unit is as high 5,000 fixed '10 7.27 57 1.55 pedance the One ohm resistor '22 as 20,000 ohms. One 25,000 ohm variable resistor 3.15 58 L55 One ballast resistor to carry one ampere, '24 -A 1.65 '80 1.05 Control of Regeneration resistance to be one ohm for each volt '26 .85 '81 5.20 to be dropped '27 1.05 82 L30 In the cathode lead of the tube is a bias One six -contact socket '30 1.65 '74 4.90 resistor of 5,000 ohms shunted with a One grid clip '31 L65 '76 6.70 0.002 mfd. It is permissible diode '32 2.35 '41 10;40 condenser of One 55 type duplex triode ,33 ,68 to reduce this bias resistance to 2,500 One dial and one knob for tickler 2.80 7:50 ohms, but with the larger value the oscil- One small magnetic type loudspeaker ,34 2.80 '64 2:10 be controlled a little better. '35 1.65 '52 28.00 lation can One good antenna and ground lead ,36 The regeneration control is a 25,000 ohm One small wooden sub -panel 2.80 '65 15.00 variable resistance, also placed in the '37 1.80 '66 10:50

www.americanradiohistory.com 12 RADIO WORLD July 30, 1932 THE 55 AS A GRID VOL TA G STEADY i By J. E IT IS WELL KNOWN that when self bias is used on audio amplifiers there is a reverse feed back reducing the amplification. This reduction is consider- ably decreased by putting a condenser across the bias resistor, but this leads to frequency discrimination because the con- denser is not as effective on the low audio frequencies as it is on the high. It often happens that the high frequency response is already excessive, relatively, and the by- passed self bias resistor makes the dis- crimination still greater. The remedy, of course, is to use a very large condenser, but even with the largest practical con- denser there is some suppression of the low notes. AVC When a Class B amplifier is used self B+ bias is not possible because there is vir- tually no steady current in either tube. Therefore in these circuits the bias either FIG. 1 FIG. 2 must be obtained from a voltage drop in In this circuit the voltage divider or tubes must be used a duplex diode triode In this circuit the oscillator in Fig. which can be operated without bias. But tube is used as oscillator and as a 1 is used as a half -wave rectifier for such tubes require a driver stage due to C battery eliminator. The oscillator the grid bias and also as a half -wave the high power dissipation in the grid may be the same one used in a rectifier for automatic volume con- circuit when the bias is considerably posi- tive, and it will be positive all the time superheterodyne. trol. the circuit is working. There are other cases where self bias as usual. A center -tapped winding is put This possible use raises the question as cannot be used without encountering ob- on the oscillator coil and this winding is to the constancy of the voltage across R. stacles. Hence it is desirable to have a connected to the diode plates of the tube. Will that voltage be the same at all set- means for obtaining a steady bias which The tap on the winding goes to a high tings of the tuning condenser, or will it is not subject to the objections of self resistance R, the other end of which is vary over a wide range? If it varies con- bias, or even of bias obtained from a drop connected to the cathode. What is the " siderably the rectifier could probably not in the voltage divider. Batteries cannot action of the circuit ? As the power is be used for biasing the power tubes. But be considered because of room they take first turned on the circuit begins to oscil- this is a matter of design of the oscilla- and the necessity of frequent renewal. late. A voltage is applied to the coil L, tor. No doubt, an oscillator can be de- in the diode circuit. Rectification takes signed that will generate a steady oscil- A C Battery Eliminator place and a steady voltage develops across lating current. Indeed, such an oscillator the load resistance R. It is steady because should be used in every superheterodyne Using a small tube as a diode rectifier the voltage applied is not modulated and for it is just as important that the volt - and getting its voltage from the power the ripple, being of very high frequency, tage in LI be constant as it is that that line has been successful and quite advan- is taken out by condenser C across R. in L should be constant. tageous in circuits requiring a high nega- The ground end of R is positive and the Incidentally, the arrangement in Fig. 1 tive voltage. These work well with fila- left end is negative. Hence we can use offers a simple means for testing the con- ment tubes provided the output of the the voltage developed across R for bias stancy of the amplitude generated by the rectifier is well filtered. It is much easier on any tubes we wish, particularly the oscillator. If a d -c vacuum tube volt- to take out the hum from the output of audio amplifiers. meter, such as that described in the July a C battery eliminator than from a regu- There is one disadvantage in the ar- 16 issue, for example, is connected across lar power supply because the current rangement, and this is the time delay R and measurements are taken at differ- drawn need not exceed one milliampere. before the voltage builds up across R. ent settings of the variable condenser, And with a heater type tube it will work It takes some time for the oscillator tube the measured voltage would indicate the even better because no hum can come to warm up to the point of oscillation intensity of the oscillation, for it would from the heater. Incidentally, both the and some time in addition for the volt- be directly proportional to it. This would heater and the cathode of the tube can age to build up. The time constant of be better than to make the same study be grounded. the rectifier can be made small enough of the oscillator without the rectifier at- Since the introduction of the 55 and to be negligible without sacrificing filter- tached to it, because, without doubt, the the 85 tubes we have means for construct- ing, so the only appreciable time delay rectifier alters the characteristics of the ing simple and effective C battery elim- is that of the heater circuit. If all the oscillator. That takes a little power from inators because they are of the heater tubes in the receiver are of the heater it. Since this is a damper we might as- type and they can be used in either full - type there would be no serious effects, sume that the variation in the intensity wave or half -wave circuits. If they are but if the biased tubes are of the filament is less when the rectifier is attached than used in a half -wave circuit we still have type, like the 245 or the 250, they would when it is not. one of the elements for automatic volume be operating a zero or a very low bias for a moment. control or for detection. Power from the There would be a rush Combining A. V. C. line may be used for the grid bias supply. of high plate current for a moment. But One of the best points about these tubes with quick heater tubes even this time The duplex diode triode would tube can be is that they are versatile. be short. used as oscillator and C battery eliminator It is not necessary, though, to use power as in Fig. 1 and as an automatic volume from the line for supplying the grid bias Use in Superheterodyne control besides. How this may be done rectifier, at legst not directly. We can is shown in Fig. 2. The oscillator is just just as well take it from a high frequency This type of C battery eliminator does the same as it was before but one of the oscillator. And this offers possibilities for not necessarily require an extra tube in diode plates only is used the for grid bias many different circuit arrangements. circuit, especially in a superhetero- development and the other is used for dyne. We need an oscillator in that type automatic volume control A higher grid High Frequency Rectifier of circuit, and it might as well be a du- bias voltage can readily plex be obtained with diode triode tube. In addition to the this circuit since the entire winding L is Consider Fig. 1. Here we have a 55 oscillator and rectifier windings we can tube used for rectification. For the same wind- operating .first as a regular high fre- put on the regular pick -up winding, which ing the voltage across R would quency oscillator. Its cathode is grounded, be double. is indicated by Ll in the figure. The second diode plate is used for au-

www.americanradiohistory.com July 30, 1932 RADIO WORLD 13 : SUPPLY; í -F CURRENT IS RECTIFIED Anderson

ing a power tube. Lower voltages can catrode of the 55 is grounded. When the then be obtained by tapping R3. Tapping circuits shown in Figs. 1 and 2 are a grid leak of high resistances is done used the only type of oscillator that can by connecting resistors of lower and suit- be used is one in which the cathode is able values in series. connected to ground, except that a grid In some circuits the leads from coil L bias resistor may be put in the cathode to the rectifier will be long but they run lead above the grid return. But this re- in the direction of the intermediate ampli- sistor should be well by- passed and it fier so there is little danger of causing should not have an excessively high value. serious coupling, and they can always be An oscillator in which the cathode is con- placed so they will not interfere. The bias nected to a tap on the coil is excluded. voltage developed across R3 should not The reason for this is that the cathode be used for any of the r -f or i -f tubes must be at ground potential as far as unless the filtering is thorough because the high frequency is concerned. there may be strong undesired feedback. Even this possibility is not so serious be- cause the oscillation frequency is far re- moved from any signal frequency as well Third of Farms Have as from the intermediate frequency. FIG. 3 The use of the second detector for Sets in Pennsylvania obtaining a steady bias does not exclude In this circuit the duplex diode tri- its use for automatic volume control. The Washington ode is used as half -wave rectifier d -c drop in Rl is often used for that pur- The Department of Agriculture reports for detection, pose and there is no reason why it should that almost one out of every three farm and grid battery elimi- not be used in this arrangement. First homes in Pennsylvania is equipped with ra- nator, and also as an automatic a high resistance of about 0.5 megohm is dio receivers. Latest estimates show that volume control. connected to the negative end of R1 and of the 172,500 farms in the state, 55,330 have then the grid returns of the controlled radio sets. tubes are connected to this resistor. This Every year since information was first tomatic volume control in the same type is the usual of rectifier way. A limiting self bias re- available in 1924 has shown an increase over circuit. The coil IA is sup- sistor may be used for each of the con- the preceding year. The estimated sets for posed to be coupled to a coil in which trolled tubes, the or one may be used for each year are: 1924, 10,378; 1925, 18,225; signal current is flowing, for example, all of them without any complications. 1926, 21,630; 1927, 27,860; 1928, the last intermediate frequency 35,460; trans- Indeed, the ; ; former. There usual manual volume control 1929, 42,050 1930, 48,560 1931, 52,900 ; should be no coupling be- in which the potentiometer is connected 1932, 55,330. The rate of increase was tween L4 and the windings of the oscil- between the lator. antenna and the cathode re- lower for the last two years but despite the turns of the controlled tubes, with the depression there was a decided trend of radio The automatic volume control voltage slider to ground, can also be develops across resistance used with- toward the rural sections. The most rapid R2 and it out complications. This is because the increase occured between 1926 and 1927. filtered with condenser C2. The lead marked AVC is negative and is to be con- nected to the grid returns of the tubes to be controlled, through the usual filter resistors and condensers to prevent feed- Better Tone Possible back. Since the positive ends of the two load resistors R and R2 are grounded, it is clear that the tube cannot be used to apply both a steady and an automatically with Class B Negative varying voltage to the same tube. It A separate rectifier for C could be done, of course, but the desired bias supply ceiver tubes, and the secondary connected may be applied to all the tubes in a re- to the C bias rectifier tube. results would not be obtained. The two ceiver that require resistors would be in parallel. negative bias. The The situation that obtains is simply the circuit is so arranged that its positive reverse of what exists when the filament side is to the negative side of the heavy - transformer is used in customary fashion. Using Second Detector for Bias duty rectifier circuit of the receiver, so Instead of 110 volts a -c line voltage being all points on the C bias supply are "more dropped to 2.5 volts, 2.5 volts are raised to The second detector of a superhetero- negative" than B minus or chassis. 110 volts. Naturally the transformation dyne can be used for biasing some of So very little of the signal travels ratio is the same in either case, but the the tubes in the circuit, including the through the separate grid voltage supply method of connection changes the direc- triode part of the tube. How this may that it becomes much easier to produce tion of the transformation. be done is shown in Fig. 3. One of the audio circuits of excellent tone without In Class B amplifiers, as at present in diode plates is used for detection in the danger of crossing the forbidden threshold vogue in a -c sets, tubes are used that have usual way. The other plate is connected beyond which distortion of the worst type a very high mu, resulting in substantially to a coil L which is coupled to the oscil- is met, i.e., motorboating. no plate current flow when there is no lator. The detector part of the circuit Of course, since no current is drawn signal input. The entire operation de- develops a signal voltage across R1 and from the C voltage source it is not neces- pends on the signal casting the grids this signal voltage is applied to the grid sary to attain any real power, but only positive, hence grid current flows, and of the tube through a stopping condenser enough to run a small rectifier. This may might reach 60 microamperes or more. C2 and a grid leak R2. The other diode be any type of tube hooked up for use as Thus a special transformer is needed, and the coil L develop a steady voltage a rectifier. working out of a driver stage, so that the across R3, the ripple being removed by C3. While it would be necessary to supply secondary resistance will be low. Never- The grid leak of the amplifier part of a relatively high voltage to the C bias theless there is power consumption in the the 55 is connected to the negative end of supply, if the high negative bias required grid circuit and this really accounts for R3 and therefore the bias on the tube is for Class B operation of low mu output the need of a driver. the drop in R3. Other grids to be biased tubes is to be furnished, even that pre- The first presentation of Class B am- can also be connected to the negative sents no special problems. While a power plifiers concerned battery- operated sets, end. If the bias developed across R3 is transformer likely will not have the extra for low current drain and for high output too high for the grid of the 55, the low winding for high voltage (say, 110 volts). values from small tubes. For a -c sets the end of R2 may be connected to a tap certainly there are enough 2.5 -volt fila- same system -high negative bias, rather on R3. It is possible to adjust L, or its ment transformers obtainable and the 2.5- than zero bias with grid current-is ap- coupling to the oscillator coil, so that the volt side may be connected across a 2.5- plicable when the C voltage supply is a voltage drop in R3 is just right for bias- volt winding supplying the heaters of re- separate rectifier -filter circuit.

www.americanradiohistory.com 14 RADIO WORLD July 30, 1932 How Much on 5 Tubes? Diode and A -V-C in Experimental Set By Carter Wallingford

is 1.0987. At 5,000 cycles the attenuation is 3.47. This shows that even a condenser as small as 100 mmfd. when across a half megohm resistance will cut the higher audio frequencies considerably. For this reason it is allowable to use an even smaller by -pass condenser, especially if the detector circuit is full -wave. The lack of complete filtering is not serious because a condenser of 250 mmfd. can be put across the triode load resist- ance to remove some more ripple before it has attained much amplitude. There is little attenuation by the 250 mmfd. con- denser because it is connected across two comparatively low resistances, the load re- sistance of 20,000 ohms and the plate cir- cuit resistance, which is also rated at 20,000 ohms. Thus the condenser is across only 10,000 ohms, the two being in parallel. Hence at 10,000 cycles the attenuation amounts to only about 2.5 per cent. If the resistance were increased to 0.5 meg- FIG. 1 ohm the same condenser would cause an attenuation of 63.5. A five -tube midget receiver incorporating automatic volume control, diode detection, and two stages of resistance coupled audio amplification. Bias on Audio Tubes The bias on the audio tubes is obtained CAN A FIVE -TUBE midget receiver of output according to mood or the nature from a drop in a 300 ohm resistor placed be built with the new tubes, includ- of the program. in the B minus lead. The filter choke, ing the 55 and automatic volume The manual control can take the form which may be the field coil of the loud- control? Of course it can, but just how of a potentiometer in the antenna circuit speaker, is also placed in the B minus good a receiver of this kind will be that or of a potentiometer in the input to the lead, and the bias resistor is put between is a question to be answered by experi- audio amplifier. If the antenna potenti- the choke and ground. The same bias is menting. Just now the circuit in Fig. 1 ometer is used, 10,000 ohms will do, and used on the power tube and on the triode is being studied with the object of getting the resistance should be connected be- part of the detector. This is all right if a a five -tube midget which meets the speci- tween the antenna and cathode returns of 47 type power tube is used for the 55 fications and which at the same time will the two r -f amplifiers. Of course, it triode will work on the bias required by be more sensitive than the ordinary type would be necessary to disconnect the the power tube. The bias resistor is by- of midget receiver, using the old type cathode returns from ground. The slider passed with an 8 mfd. condenser to re- tubes. of this potentiometer should be connected duce degenerative coupling between the But how does it differ from any other to ground instead. two grid circuits. midget receiver, other than in the tubes If the manual volume control is put in The first twor -f coils used in the cir- used? For one thing, it has automatic the audio amplifier a good place for it is cuit are standard shielded midget type volume control, and the controlling volt- in the grid circuit of the 55 triode. The coils but the third is different in that it age is applied to the suppressor grids. It grid leak takes the form of a 0.5 megohm has an extra winding for the automatic also has a manual volume control asso- potentiometer, and the grid of the triode volume control circuit. This winding ciated with the automatic. This is a par- should be connected to the slider. This should be about the same as the tuned ticularly noteworthy feature. It is well arrangement is shown in Fig. 1. secondary as to number of turns but it known that automatic volume controls re- should be wound with finer wire near the duce the sensitivity of a receiver some- Detector Design ground end of the coil, over the primary what. But it is not necessary to connect Note that the by -pass condenser across winding. There should be an insulating the circuit so that this reduction must be the load resistance of the detector diode layer of about 1/32 inch between the In this case the manual control windings so that stray capacity will be tolerated. circuit is only 100 mmfd. The reason for low. allows adjustment for full automatic vol- using such a low value is to prevent high Of course, T3 should be shielded like ume control, none at all, or any degree of frequency suppression. We can easily the other two coils. control between these extremes. The load estimate what the suppression will be. Let The sensitivity of this receiver will not resistor volume control be quite as great as it would be if a on the automatic the load resistance be R and the capacity screen grid tube were for rectifier is a 0.5 meg. potentiometer, the C. is %, used detection Then the impedance R/(1 +C2w2R2) with grid bias. But the quality will be slider of which goes to the controlled where w is 6.2832 times the frequency in much tubes. By moving the slider to the nega- cycles. We are interested in the relative superior, and then we have the tive end of the resistance the full range values of this impedance at low and at automatic volume control feature in addi- is and by tion. The loss of sensitivity is due en- of automatic control obtained high frequencies. tirely to the detector. The triode ampli- moving it to the positive or grounded end, For the purpose of comparison we fier, there is no automatic control at all. can take zero frequency and compare the which has a gain of about 6, does not impedances at other frequencies with the quite compensate for the decreased sensi- impedance zero frequency. Well, at tivity of the diode rectifier. Yet the dif- Additional Control Needed at ference is slight. It is more sensitive than zero frequency the impédance is just R. it In any position of the slider the circuit Hence we get the relative suppression by would be with old type tubes. is always at its most sensitive adjustment dividing the expression for impedance by Type of Automatic Volume Control as long as there is no signal coming in. R. If we compare powers we square the A weak signal will cause a low bias and a expression, and if we tip the expression The application of the automatic volume strong signal a high bias and the ampli- upside down we get the attenuation in control voltage to the suppressor grids fication will be less the greater the bias. relative units, not in decibels. rather than the controls grids is not often Therefore most signals will come in with The expression for power attenuation done, but it is a method recommended by about the same intensity. This is particu- becomes (1 +C2w2R2). In Fig. 1 the value the manufacturers of the tubes as a means larly true if the full range of the control of C is 100 mmfd. and the value of R is for varying the selectivity so that it will is utilized. Of course, we cannot expect 0.5 megohm. Hence the expression be- be greatest on weak signals and least on the leveling to be good enough to justify comes 1+0.0987f2, in which f is the audio strong. When the voltage is applied in the omission of the manual control. frequency measured in kilocycles. At the control grid circuit the variation is Even if the signals from all stations came 10,000 cycles the value of f is 10 and the in the opposite direction, which is not so in at the same intensity we should still attenuation becomes 10.87. At 1000 cycles desirable. However, the effect of a change want a manual control to vary the amount the value of f is unity and the attenuation (Continued on next page)

www.americanradiohistory.com July 30, 1932 RADIO WORLD lä A Portable Amplifier Suitable for Phonograph, Microphone or Radio By Louis Moses Try-Mo Radio Co. THE LOFTIN - WHITE amplifier lends itself admirably to the use of the 235 and the 247, or to a 58 and the 247. Such an amplifier has been built in a treasure -chest cabinet and is giving excellent results. We show the circuit diagram of it in Fig. 1, including the values of resistances and capacities used. The circuit is primarily intended for the amplification of signals from phonograph records but it may be used just as well for the amplification of signals from a radio detector or a microphone. At the input side we have an audio frequency transformer which may be coupled to any signal source we wish. The transformer actually used was one that matched the plate impedance of a FIG. 1. FIG. 2. three -element vacuum tube. Hence the amplifier may be connected to the output The circuit of a Loftin -White type The layout of parts of the Loftin - of a detector. The terminals of a pick -up amplifier utilizing a 235 and a 247 White amplifier diagrammed in Fig. unit can also be connected across the tubes. It may be used for the 1. The large circle represents the primary without change. If a low imped- amplification of any audio signals. loudspeaker. ance microphone is to be used, however, a matching transformer should be used between the microphone and the trans- A comparatively low screen voltage is to give the power tube the right voltage. former, or else a special microphone -to- used on the tube, which is necessary by If the half megohm coupling resistor grid transformer should be substituted. the fact that a very high resistance, were connected to the cathode, that is, This substitution is advisable if the circuit 500,000 ohms, is used in the plate circuit. the filament, the grid would be greatly is to be used primarily in conjunction If the screen voltage were high the plate overbiased by the steady drop in the with a microphone. voltage might be less than the screen coupling resistor. For this reason the voltage during part of the signal cycle, cathode is connected to a point on the The First Amplifier and then nothing but distortion would voltage divider lower than the line. The result. The screen voltage must always actual bias on the pentode power tube is The first amplifier is a 235 tube. It is be less than the effective voltage on the the difference between the drops in the biased by a combination of cathode drop plate. coupling resistor and in the 100,000 ohm and drop in the voltage divider. First we resistor between the filament and the have two resistors in parallel, one of 0.5 Hum Bucker coupling resistor connections to the volt- megohm and another of 100,000 ohms. Of age divider. Normally, this difference is course, these act as one resistor of value Connected between the cathode of the 16.5 volts. The next 100,000 ohm resistor 91,000 ohms. A single resistor of this first tube and the slider of a 250 ohm is used to establish a current in the por- value could be put in, if such a resistor potentiometer in the voltage divider is a tion of the voltage divider to the right of can be found. The 91,000 -ohm resistance one microfarad condenser. This is used the filament connection. provides the self-bias. There is also a for balancing out hum. A point can be A full -wave rectifier giving out a high 300 -ohm resistor in the cathode circuit, found on the potentiometer where the voltage is used. This is typical except if we consider the cathode circuit to ex- hum introduced in the plate circuit is ex- that the speaker field is used for filter tend to B minus. Through this 300 -ohm actly balanced out by a hum introduced choke. unit the bleeder current also flows so it in the grid circuit. This point must be Two separate filament windings are adds considerably to the. bias. There is found by trial. used for the two amplifier tubes. This is little danger of overbiasing the tube since The second amplifier tube is coupled done to eliminate the high voltage that it is of the remote cut -off type. The self - to the first by the direct method without would exist between the cathode and the bias portion of the cathode resistance is the use of a stopping condenser. This heater of the 235 if a single winding were more for stability than for bias. requires certain manipulation of the leads used. Suppressor Grids Tied to A -V-C (Continued from preceding page) The two controlled tubes are supposed the circuit with a metal screen which will in the selectivity with a change in the to be 58s, the detector a 55, and the power allow ventilation. sensitivity is relatively small, and the tube a 47. The rectifier tube should be reason the voltage is applied in the sup- a 280, but if an 82 is to be used it is only Detector Arrangement pressor grid circuits is that it simplifies necessary to make the heater winding for Attention is called to the arrangement the connections and avoids complications. the filament 2.5 volts instead of 5 volts of the detector rectifier circuit. The load It will be noticed that both the coil and and to put an r -f choke of one or two resistance and the 100 mmfd. by -pass the condenser in each of the tuned cir- millihenries in each lead to the plates. condenser are put above the tuned circuit. cuits inputting the controlled tubes are The gain in the 58 tubes is much This is done to permit grounding the tun- grounded. If the automatic volume con- greater than that in tubes like the 235. ing condenser. Incidentally, exactly this trol voltages were applied in the control For this reason more thorough shielding is done in the ordinary grid leak and con- grid circuits the coils could not be is essential. Special shields are available denser detector, and this circuit differs in grounded directly. for the tubes, which fit snugly over the no respect from such a detector except Necessity for Shielding tubes and still allow natural circulation of that the amplifier part is operated at its air for cooling the tubes. But using optimum adjustment as an amplifier. But The suppressor grids behave in about shielded coils and shielded tubes may not the arrangement has one undesirable fea- the same way as the control grids in re- be sufficient. Box shielding of stages is ture, which, however, is not enough to spect to changes in the negative voltage. recommended, in so far as this can be offset the advantage of grounding the The gain decreases with increased nega- done. Of course, it is not necessary to condensers, and that is that a consider- tive voltage. The suppressor grid, being separate the tuning condensers in order able r -f signal is impressed on the ampli- near the plate and negative, prevents elec- to put these also in the box shields with fier grid. The 250 mmfd. by -pass con- trons from reaching the plate, and the the tubes and coils with which they be- denser is necessary in the plate circuit. more negative it is the more it reduces long. If an 82 rectifier is used that tube This condenser eliminates the signal the plate current. must be well shielded from the rest of ripple with little audio suppression.

www.americanradiohistory.com 1H, RADIO W O x L D July 30, 1932 is greatest when the signal is absent en- tirely, would not a suitable corrective be the lifting of the bias on the controlled tubes, so that even at no signal there would be the recommended bias for maxi- mum amplification ?-G. R., Roanoke, Va. Radio is a University The method you outline helpful one, tending to correct for the noise between e QUESTION and Answer Department. Only questions from Radio Uni- stations on the dial, in that the noise is versity members are answered. Such membership is obtained bg reduced, especially if the limiting bias is sending subscription order direct to RADIO WORLD for one year (52 issues) raised sufficiently, probably to more than at $6, without any other premium. the minimum but the improvement is merely one of degree. The fact still re- RADIO WORLD, 145 WEST 45th STREET, NEW YORK, N. Y. mains that sensitivity is greatest when there is no signal, hence tube and circuit noises are amplified most under that con- dition. If the starting bias is raised high enough so that the noise is unobjection- able at no signal input, then of course the solution you propose is satisfactory, pro- vided, however, that you are willing to stand the sacrifice of sensitivity involved. * * * FIG. 1021 I -F Oscillator A simple os- KINDLY let me have the diagram of cillator, f o r a simple intermediate frequency oscilla- battery or a -c tor, of good frequency stability, for either operation. battery or a -c operation, preferably bat - tery.-K. J., Bangor, Me. Fig. 1021 shows the diagram A '27 or the new 56 tube is used, preferably the 56, if operation is to be from batteries, as the heater current is 1 ampere at 2.5 volts, compared to 1.75 amperes for the '27. Bypass for Diode to the current to screens through the re- L1L2, C1C2, may be a commercial inter- sistor), and you should increase the volt- mediate frequency transformer. Indeed, WHEN THE 55 TUBE is used it is age. Then more current will flow through it may be practical to take a transformer recommended that there be a condenser the biasing resistor. You should get a you intend to use in building a set, use it across the load resistor (the resistor be- starting bias of around 5 volts if you re- in this hookup for adjusting two other tween coil return and cathode), but dif- duce the 0.25 meg. resistor, in series with transformers in the set, then use the in- ferent values are prescribed, not only for the plate feed and screen, to 0.05 meg. termediate frequency in the set for lining different purposes but also different values (50,000 ohms). Then the voltage actually up the transformer taken out of the oscil- for the same purpose. Please clarify. - will be around 100 or a little more, which lator. This would be all right if you are J. C. N., Dubuque, Ia. is satisfactory from an operating view- to have two stages of i -f (three coils). There has been no discrepancy as to the point. Also the sensitivity will increase Aside from this, if you want to use 300 - 55. The load resistor you refer to is rec- materially when you have done this. Be turn commercial honeycomb coils, closely ommended at 0.5 meg., and the condenser sure that a good -sized bypass condenser coupled, Cl and C2 may be 0.00035 mfd., across it as 0.00015 mfd. for t -r -f and 0.006 is from screen voltage feed line to B and the circuit would have to be cali- for intermediate frequencies of the popu- minus, also from cathode of r -f tubes to brated. C3 is 0.00025 mfd., Rl is 0.1 meg. lar types. However, as to the 85, the B minus. About 0.1 mfd. is the usual value. or higher, while C4 is 1 mfd. or higher. counterpart for the automotive series, the If the sensitivity rises so high that squeal- * * * value of the condenser for superhetero- ing results, the 600 -ohm limiting resistor Is It a Cure for Fading? dynes has been specified as 0.01 mfd. The may be increased tc such value as stops only reason there is any difference at all squealing at the highest broadcast fre- IS IT TRUE that automatic volume between capacities for t -r -f and super- quency. Another remedy, not changing control cures fading? Does it help a heterodyne purposes is that the smaller the resistor, is to increase the capacity of great deal of short waves, where ordinarily t -r -f capacity is not sufficient of an r -f the bypass condenser from screen to there may be considerable fading ? -H. R., bypass condenser or filter for the popular ground. Tappan, N. Y. intermediate frequencies. However, the * * * It does not cure fading, but it does re- specification of 0.01 mfd. for superhetero- Problem of D -C Line Set duce the fading effect quite considerably. dyne frequencies, for the 85, may be an Fading is due to the arrival of the trans- indication that 0.006 was found in practice IS THERE ANY WAY of building a mitted wave by two paths, one the ground not to be quite high enough, since the 85 set for operation on the d -c house line wave, so- called because earth -bound, the was announced after the 55. It has been without using the heavy resistor to drop other the sky wave, so- called because it found in practice that for t -r -f 0.0015 mfd. the line voltage to the sum of the voltages rises skyward until it strikes the Kennelly - should not be exceeded, which does not across the series filaments or heaters? - Heaviside layer, when it is reflected back mean it can not be less, as less than half P. C., Brooklyn, N. Y. to earth. Since the two components take that capacity has been used successfully. There is no practical way of solving paths considerably different in geographi- * * * the problem except by using a reducing cal distance, despite the tremendous speed Screen Voltage Trouble resistor, whether filaments or heaters are of travel (around 186,000 miles per second) in series or parallel. If you use 2 -volt there is a sufficient difference in time be- IN THE T -R -F that I built, using tubes, since the filament current is small tween the arrival of the two components screen grid tubes, I do not get the bias (usually 60 ma), the resistor will not have to be measured without difficulty, or, if that I should get on the r -f amplifiers, as to be as "heavy" as if you use the auto- detected, to be distinguished by ear. The it is around 1.5 volts negative at minimum, motive series tubes. However, since the time difference is equivalent to a phase though the common limiting biasing re- automotive series tubes are of the heater shift, so the signal strengths 4f the two sistor for two tubes is 600 ohms. I thought construction, the plate voltages available may add up at one instant and buck each that, at 200 volts and around 5 ma per are not reduced, the two circuits being other at another, the result being a wax- tube, I should get a minimum drop of 6 independent, and it is recommended that ing and waning familiarly identified as volts. The circuit consists of the usual the automotive series tubes be used. A fading. Since automatic volume control t -r -f hookup, the plate B voltage be- theoretical solution would be to institute tends to keep the signal supply voltage ing dropped through a fixed resistor of a high frequency oscillator, rectify the to the second detector relatively constant 5000 ohms, and the screen voltage through oscillation current, and feed the filaments despite original differences, the quantity a fixed resistor, from the plate feed line, or heaters with this, using the line voltage of sound otherwise heard when receiving of 0.25 meg. Sensitivity is not what it for plate. However, there would have to fading stations is almost equalized. There should be, either. The screen voltage be considerable power available from the is no absolute levelling because the effect reads around 50 volts on a 1000- ohms -per- oscillator, and it would have to be of of bias variation on amplification is not volt voltmeter. -D. B., Ames, Ia. husky enough construction to permit this linear. We, too, have found that the variable power rating. * * * mu tubes, which seem to be what you are * * * Needs a Sensitive Set using, do not draw as much plate current A -V -C "Silent Spot" Hiss . as the average characteristics chart would FORMERLY I LIVED IN DETROIT indicate. However, in your case you have WHEN HISS and other noise are heard and my t -r -f set was satisfactory. I an actual screen voltage of around 80 (for on a set between stations (when no sta- listened to locals, but the chains were rep- the meter reads low, due to the consider- tion is coming in), due to the automatic resented and I was satisfied. Since then able current through die meter compared volume control, whereby the amplification I have moved to Reading, Pa., and the

www.americanradiohistory.com July 30, 1932 RADIO WORLD 17

FIG. 1022 A t -r-f set, push -pull output, using automotive tubes for battery operation in the home. set that was O. K. in Detroit is O. K. here, Wonders if Rug's to Blame set, is a preferable solution, but the re- too, for local reception, but there is not duced leak method is simpler and cheaper. enough in local reception to interest me. MY T -R -F SET BEHAVES peculiarly. * * * I want to get New York stations direct. It worked fine for a long time, so long Leak as Multiplier The receiver will not do that -isn't selec- as it was kept in one place, which was true tive or sensitive enough. I tried out a before we got a large rug for the living FOR USE with a 0 -1 milliammeter six -tube superheterodyne midget, and room. Now the front feet of the console would it be satisfactory for 1,000 -volt full - while that was more sensitive, it did not are on the rug, and as the rug is taken scale deflection to use a leak of 1 meg., do the trick. New York stations could be up to be cleaned the console is naturally as the wire -wound type of resistor of heard faintly, if the volume control was moved, and may be rolled about the room such high value costs more than I can advanced all the way, but then there was for other cleaning purposes. I just hap- afford at present ?-D. A. C., Paris, France. a racket, like static, that would make pened to put two and two together and Just in a pinch, and until you can get listening unbearable. Have you any sug- assume there was a connection between enough money to buy a wire -wound re- gestions ? -S. A. E., Reading, Pa. the consequences of the rug and the poor sistor of an accuracy of 1 per cent. or The situation in Reading is reported by reception. This reception consists of dis- better, the leak may be used, but first you our trade correspondent to be one re- torted, thin, weak, tinny results, compared must measure various leaks supposed to quiring a highly sensitive receiver to bring to the former full, rich, loud tones. The be 1 meg. or so, until you find one that in New York stations direct. There are volume control is not nearly as effective has a resistance value close enough. The many localities in the United States where as before. In fact, the only time reception commercial variation may be 10 Per cent., especially sensitive receivers are necessary can be heard is when the control is full - so you'll have to test until you find one to make distant reception possible. There- on. Meanwhile results are unbearable. temporarily suitable. After that you can fore as yours seems to be one of them, There is some improvement when aerial feel certain of temporary good use even to cure the situation you would have to is connected to cap of the second r -f from the leak, but as its resistance value get a "big" receiver. There are several screen grid tube, instead of to antenna will change with age and use, you had available that will render satisfactory post of set. -C. S. R., Toledo, O. better expedite as best you can the happy service. They are superheterodynes using Evidently the first r -f tube was sprung day when you get the wire -wound resis- 10 tubes or more. The racket you corn - out of the socket sufficiently to disestab- tor. plain of may be due to local disturbances, lish contact. Stray coupling gives enough * * * called man -made static, or simply to the input to the second r -f tube to permit The T -R -F Set, Auto Tubes fact that when you made the test on the some sort of reception, but the tone is midget super there was a storm in your bad, and WHAT ARE DESIRED are two stages the result weak, because absence of t -r -f, one resistance coupled audio, with locality or near it, with its accompanying of the first r -f tube from its socket puts static. Go to one of the radio stores and false voltages push -pull pentode output, for battery op- on the second r -f tube, and eration. Choose your own tubes. B., listen to a very powerful set actually perhaps at other points, too, because there -K. bringing in New York stations direct. isn't enough Wilmington, Del. current through limiting re- The diagram, Fig. 1022, uses two 234 Thus you can verify the existence of ade- sistors to drop the required voltage. For quate sensitivity and selectivity, and also instance, tubes for r-f, 232 detector, 230 first audio the bias may be far too low for and 238 push -pull output. The values of note the amount of background noise an abnormally high plate voltage on the constants are : Cl, C2, C3, three -gang normally to be expected. It should not second r -f tube, if a common bias is used 0.00035 mfd. ; C4, 0.0001 ; be so high as to be objectionable. for both, and if mfd. C5, 0.01 the volume control is in mfd.; C6, C7, 0.1 mfd.; C8, 1.0 the bias circuit it then would have little C9, mfd.; C10, C11, 2 mfd. ; Rl, 400 ohms ; P, 25,000 * * * effect. Push down the tube. If the socket ohms ; R2, 0.05 m -r. ; R3, 0.1 meg. ; R4, 025 is too defective to hold the tube in place meg. ; R5, 1 meg. ; R6, 2,000 ohms ; R7, Use of Cheap Meter despite slight jars, surely put in a new 600 ohms, 25 socket. See front-cover illustration. watts. The coils have 30- IN BUILDING a certain type of testing turn primaries (any insulated fine wire) equipment I shall not be able to use an * * * over secondaries of 127 turns of No. 32 expensive meter, and I am wondering if enamel wire on 1 inch diameter. it would be all right to use an inexpensive Incipient Motorboating * * * one (250 ohms per volt) provided the cir- Confidential cuit is so arranged that the meter is in MY RECEIVER STARTS to motor- IS IT PERMISSIBLE to disclose the it all the time ? -H. E. F., Montreal, P. boat when it is turned on, but the motor - contents of a talk between amateurs, Q., Canada. boating ceases about the time that a pro- overheard on the air? I understand that The reason why high resistance volt- gram becomes audible (heater tubes emit messages in general must be kept secret, meters are necessary, for general use, is sufficiently). Should I correct this, and but as to the amateur talks, as they are that they are applied only for short in- if so how ? -R. W., Madison, Wis. informal, I wondered if there is any re- tervals across potential sources and there This may be corrected by putting some striction-K. S. W., Altoona, Pa. must be very little current in the meter more capacity at the output of the recti- The amateurs are bound by law not compared to the current through the fier filter (assuming you have an a -c set), to reveal the subject or contents of any measured circuit, otherwise the accuracy or you may reduce the value of an audio talk or message heard, and importance of the reading will not be nearly enough. grid circuit resistor until the trouble dis- of the subject-matter of the talk or mes- But if the meter is to be left in the same appears, no matter what type of set you sage is in no way controlling. Likewise, circuit all the time the one you propose have. Extra capacity from the maximum listeners who are not licensed as operat- to use will be fully adequate. B voltage source to B minus. for any type ors are also bound by this rule of secrecy.

www.americanradiohistory.com 18 RADIO WORLD July 30, 1932 A THOUGHT FOR THE WEEK for hill -climbing. The sharp lines separ- ON'T smile coldly, or at all, when some ating capital and labor are largely ficti- D television concern goes up the financial tious when the lines prove, as in the pres- flue. Perhaps everybody connected with the ent depression, to have merged into a PECK IMPROVES did his level best to the enter- common plight. concern put * * prise on it feet. The time might have been too early or the money structure too wabbly Air Vogues or the goods offered not appealing enough to LENS SCANNER the public. Remember the many failures THE crooner's perch has been threat - early in the automobile, motion picture and ened these many months, first by he- A new television scanning wheel, only radio gamest Television is on its way - man baritones, now by comedians. 5g inches in diameter, yet projecting a about that. Millions more The singers, either type, have the easier 5x6 -foot picture which he says retains full make no mistake job, will be lost before television becomes a pay- for with their voice and personality brilliance and definition to the very edge as natural endowments, albeit improved of the screen has been produced by ing commercial proposition. Since the be- by experience, just ginning of time it has always been a case of they can rely largely on William Hoyt Peck. The new wheel is That holds the songwriters. The comedians do not similar in design to one he recently dem- the survival of the fittest. truism find a great industry turning out material good in connection with television. onstrated in the Hotel St. Moritz, New for them, and as they have particular York City, but gives a much clearer, methods for drawing laughs, or a "line" brighter image. of their own, as they call it, they fre- The spot of light, which the disc quently resort to their own devices. This projects from the crater tube to the works out all right when they have a screen by means of reflecting lenses, re- audeville act or are in a show, for the mains perfectly square at all parts of the same material is used perhaps for forty screen. The results are much more per- weeks. But on the air it must be some- fect detail and shading, sharper contrasts thing different each time, and that is and better definition. where the comedians are having their To secure this improvement, Mr. Peck troubles. has fabricated a special optical glass ac- The First and Only National Radio Weekly Most of them are backed up by script cording to a new formula which he has Eleventh Year men who write their stuff, but if it is still been working out during the past two Owned and published by Hennessy Radio Publications a general rule of the show business that months, with which he has been closeted Corporation, 145 West 45th Street, New York, N. Y puns aren't bought but made, it seems, Boland Burke Henoeuy, president and treasurer. 145 West in his laboratory. 45th Street, New York, N. Y.; M. B. Hennessy, rice - from the frequent pun11kig, that the Although thousands of dollars have been president. 145 West 45th Street. New York, N. Y.; Herman comedians economizing, Bernard, secretary, 145 West 45th Street, New York, N. Y. are too, and turn- expended in research, the new glass can Roland Burke Hennessy, editor; Herman Bernard, man- ing to "original" humorous thought. Thus now be so cheaply that a aging editor and businees manager; J. E. Anderson, tech- manufactured steal editor; J. Murray Barren. advertising manager. enjoyment of many a good meal or pal- dollar's worth of it will be sufficient pitating sociable is menaced when the for 225 lenses. puns spout from the console. The new wheel has an optical axis of Meeting the Tax * 2 inches (center of wheel to center of lenses). Each lens measures 4 inch in HE usual difficulty in getting the Tubes Expected diameter before being cut. A segment is radio industry to agree on anything HE choice of tubes for receivers is then cut from each side, leaving the lens T was absent in regard to the new tax certainly a wide one now, and one inch wide. The lenses are mounted in that includes some radio products. Trade T may expect that only few more tubes a perfect circle, rather than in the cus- conferences resulted in the increase of list will be announced presently, There is no tomary spiral, thus making use of all prices, really to make the consumer meet triple grid tube for the 2 -volt battery - the light projected from the crater tube. the extra burden by the amount of the operated series of tubes, equivalent to the As the lenses are arranged in a perfect tax on the manufacturer. This has the 46 and 89, nor a separate suppressor type, circle, there is no need to let the light advantage of not upsetting trade dis- equivalent to the 58, in 2 -volt battery spot spread, as in ordinary lens type scan- counts. series or 6.3 -volt automotive series, nor a ning discs. Instead the spot is concen- The tax is 5 per cent. on the manufac- duplex diode triode for these the 2 -volt trated through a condenser lens system, turer's selling price, and that is the series. So one may expect that five more and all the light is used, instead of 80% amount that is to be passed on, if the con- tubes will come along in due time. being wasted, as in other lens disc sumer is to absorb the entirety. However, The new tubes certainly produce im- systems. there is no law against raising list prices, provements, and the sets including them so the addition may be twice the amount are better performers than their predeces- of the tax, to net the manufacturer ap- sors. It has not always been true that Audience Split Over proximately the amount of the tax. one season's crop of sets was essentially In the case of tubes the general price better than the previous season's. Indeed, readjustment, in view of the tax, is one of with the pentode popularity of last sea- Anonymous Announcers reduction, since out of 44 tubes the prices son's sets it may be said that the oppo- WOR, Newark, N. J., recently made its of 9 are unchanged, and as to two others site was true in that very example. announcers identify themselves by call let- the prices are reduced 5 cents. whereas This time the command is forward. ters rather than by name. Typical of the seeming increases of list prices, by 5 * * hundreds of letters which have been re- per cent. approximately, indicates that the ceived by the station are the following tube manufacturers are absorbing half or A Quiet Revolution excerpts. more of the tax. HE 50 -cycle rule went into effect "I am at a loss to express my horror The radio industry has met the situation late last month and has worked at the system of designating your an- fairly, particularly since it is losing money T smoothly, with scarcely any criti- nouncers by code letters." in virtually all its branches, including sets cism. not "I wish to commend you for taking the There is no on sets as Some stations could get their and tubes. tax monitors on time, and were granted a initiative in abolishing the custom of such, but there is a tax on the chassis, as announcing phonograph respite. Aside from that we have found the announcer's name. They well as on speakers, tubes, an entirely new degree of accuracy- in fre- are just mouthpieces, so why annoy pickups and some other articles sold with quency transmissions by broadcasting sta- listeners with incidental names ?" or intended to be used with a set that tions, accomplished easily, despite early "I have always enjoyed knowing the is sold. By the certificate plan the actual misgivings that such accuracy could not name of the announcer. I am an ardent manufacturer may not have to pay the be well achieved. radio fan and I think that this is unfair tax. For instance, if he makes speakers not to the announcer. I know that I speak for a manufacturer, he may obtain the Now stations must vary from their set assigned frequencies by more than 50 for many other listeners." set manufacturer's certificate, and the set "Just why none of the other stations pays cycles in either direction, whereas the rule manufacturer the tax. formerly permitted 500 -cycle deviation. have had this thought I cannot see. Who No doubt the radio industry feels, like cares who the announcer is, long to Considerable reduction in interference as as he other industries, that it can ill afford was expected, for it was the very reason gives the information? I think the other pay taxes or raise prices. But it should for the rule, and for once the promised stations will follow suit." take into account that it can not con- land has become inhabited. "What, may I ask, is the big idea of tinue indefinitely the policy of manufac- eliminating the announcers' names ?" turing giveaways. The best sign of im- FADA HIRES 200 MORE "The personality of the announcer has provement of business conditions will nothing to do with the grogram. A good come when the markups are sufficient to Frank A. D. Andrea, President of the nameless voice is ideal." render a profit to manufacturers and sell- Fada Radio and Electric Corporation, ers. The number of employees is reduced, Long Island City, N. Y., announced that and the salaries of retained employees are during two days approximately 200 em- DID YOU KNOW THIS? reduced, because businesses are losing ployees were added to the payroll and RADIO WORLD has been first to reveal new moriey. So the general public, no less than that with continued evidence of increased tubes about to be announced officially, and business big or small, should be inter- buying power as recently experienced by first and occasionally the only magazine to ested in the restoration of conditions that the corporation, that between 1200 and print the complete official data, in the in- guarantee a fair return on manufactur- 1500 workmen may be added to the FADA stances of the 46, 56, 57, 58, 82, 55, 89, 85 ing and selling. Confiscation is no fuel payroll by Fall. and 83.

www.americanradiohistory.com July 30, 1932 RADIO WORLD 19

has a sister who is a psychologist. . . GEORGIE PRICE has a secret ambition to be a jockey.... DOROTHEA JAMES STATION SPARKS first achieved fame by playing the femi- nine lead opposite Wesley Barry in the film, "School Days." ... ENRIC MAD - By Alice Remsen RIGUERA is a personal friend of Ex- King Alfonso of Spain.... MARIA CAR - DINALE has a very beautiful home in is taking on a new lease of life, at least Rockville Center ... so has PHIL NAPO- around the Columbia studios. LEON; in fact, PHIL lives right opposite The Long Trek * * * MARIA. CLAUDE MÒARTHUR For "Death Valley Days" NBC lives in New Rochelle, N. Y.... SAMMY WJZ, Mondays, 8:30 P. M. Paul Whiteman is one of the busiest of HERMANN lives in Rye, N. Y. . . . band leaders. In addition to his daily and JIMMY HAUPT is summering at Green- We set out with Life un an ardent quest, weekly broadcasts and his recording ac- wood Lake.... so is PAUL SIMMONS. And goad ourselves onward without a rest; tivities and numerous comings and goings * * * With never a spell to pause and think, in the music realm of New York, the ANSWERS TO CORRESPONDENTS With time but to go-sleep, eat and drink. Dean of Modern Music has announced MARK CHASE, Erie, Penn. -Write to We struggle along to the bitter end, that he will hold open house each Wednes- the Columbia Broadcasting Company, at Believing ourselves on an upward trend; day for music publishers and will also con- 485 Madison Avenue, New York, N. Y., But the higher we go, the harder the pull; tinue his search for promising radio talent. before you come to New York. They It's a heavier load when the knapsack's So, all ye would -be radio singers, go to will send you passes for Chesterfield and full. see Paul Whiteman any Wednesday morn- Stoopnagle and Budd programs. All pro- ing between 10:00 a. m. and noon, at the grams emanating from New York studios And just as we're reaching a ledge above, Cascades atop the Hotel Biltmore. If he are on Eastern Daylight Saving time Life may give us a downward shove; thinks you have unusual radio possibilities basis. We hold up our head though our back is he will present you over the NBC net- * * * bowed, spirit's proud. works. MOLLY PRAGER, Brooklyn, N. Y.- And refuse to whine -for our * * * As far as I know, Lew Conrad is still in Oh, Life is a beggar we cannot trust, Ed Wynn has changed his mind and Boston. We rarely publish portraits. Traveling along in the heat and dust; will continue to broadcast all summer. Write to the Boswell Sisters in care of And little we know and less we reck, His original contract expired on July 19th, the Chesterfield program. They will send Life barters with Death on our long, lone but the sponsors of the program, the you their picture. Will send you an auto- trek. Texas Company, liked his work so much graphed picture this week. Thank you for -A. R. and the audience response was so great your kind words. * * * that Ed decided to stay. He is very wel- * * * come ; good air comedians are scarce l Death Valley Days is a dramatic pro- * * * C. WHITTLE, Del Monte, Cal.- Sorry; gram well worth the listener's ear. Spon- we have no space for detailed programs. sored by the Pacific Coast Borax Co., it WOR Look in your local daily paper for an- tells the story of the long trek through Tommy Weir, the sweet Irish . singer, nouncements. They are more up to date Death Valley by our pioneer forefathers. now has three programs on WOR. He than any programs we could publish. Such sterling artists as Virginia Gardiner, may be heard with Lee Cronican, pianist, * * * Edwin William Jack on Sundays at 11 :15 a. m. ; on Mondays Whitney, Shelley, R. McBride, Vernon Radcliffe, Joseph Bell with an orchestra, at 5 :45 p. m. ; and on MUDIE, New York, N. Y. -Mabel comprise the cast, with Fridays, also with orchestra, at 7 :45 p. m. Jackson is now broadcasting over WLW and Tucker Battle in John White doing the singing. Tune in ; you'll like him! Cincinnati. She has three commercial * * * * * * and two sustaining programs. You can One of the most interesting periods on reach her at that address. News of the Studios WOR is the "Unwritten History" series; * * * Mondays at 10:30 p. m. Cosmo Hamilton, WABC English novelist and lecturer, is the star Biographical Brevities "Lefty" Flynn, Yale football star of yes- of this program. He has a fine personal- AS TO DONALD NOVIS teryear, and his wife, the former Nora ity, an interesting background and talks Langhorne, youngest of the five daughters well. Donald Novis, the golden- voiced tenor, of a famous Southern family, have been * * * is from sunny California, and is the latest signed to appear as the regular featured of the sun -kissed folk to achieve popu- soloists on the Gerardine "Midsummer larity on the NBC networks. He was Nights" broadcasts over the WABC- Sidelights born on March 3rd, 1906, in Hastings, Columbia network; Thursdays at 8:30 LOUIS DEAN once clerked in his England. M the age of two years he was p. m., EDST. Their success as singers grandfather's general store at Valleyhead, brought to Canada by his parents. After on the program July 7th resulted in their Alabama-his remuneration being all the a short stay in Canada the family moved engagement for the entire series. In addi- candy he could take without being seen. to Pasadena, California, where Donald tion to Mr. and Mrs. Flynn, the broadcast MARK WARNOW once taught was raised and educated and where he will include an orchestra under the direc- English to emigrants.... BEN ALLEY first achieved fame. tion of Jack Berger and different guest worked with a Virginia road gang. . . . Donald attended Whittier College and entertainers each week. DON BALL played the ukulele and per- was the featured soloist of the college small glee club. He won first place in the Cali- * * * formed as master of ceremonies on a time vaudeville circuit. . SANDRA fornia State Eisteddfod. which, in case If you miss the name of Freddie Rich PHILLIPS earned her first pay playing you don't know, is really a Welsh singing from the Columbia air -waves during the for dancing classes. . . EARL SMITH, festival. Novis is his name, but he is very next two weeks, don't be alarmed ; he is one of the FOUR ETON BOYS, set up evidently no novice as a singer, for he only on a two -week working- vacation to type in a printing establishment. . . . has been a vocalist since childhood, and California, where he will serve as musical ALICE REMSEN once owned her own even in high school walked off with all director for the screening of Bing Crosby's tent show.... WILLIAM HALL once the singing honors. motion picture based on radio activities sold newspapers.... VERA EAKIN was At the Pasadena Community Playhouse and to be known as "The Big Broadcast." a piano teacher.... HELEN NUGENT the lad sang the leading tenor role in the During his absence his conducting will be was a school teacher. . HOWARD opera, "The Duenna," and created a sen- turned over to Mark Warnow, Andre BARLOW once was a stoker, tending sation. In 1928 he won the Atwater Kent Kostelanetz and Johnny Augustine, the the boiler in his father's furniture factory. Audition prize of $5000. latter the first violinist in Freddie's en- ... EDDY BROWN was born in Poland. He sang with the Coconut Grove or- semble. MURIEL POLLOCK, WILLIAM chestra at the Ambassador Hotel in Los * * * WIRGES, WILL DONALDSON, and Angeles, and came from there to New Studios are now being commandeered JESSE CRAWFORD are among the York, where he is now duplicating his at all hours of the day for commercial NBC musicians who boast of thirteen Western success and is the sensation of auditions. Hopeful artists are receiving letters in thier names ; they're not a bit the season on the NBC network. calls from agents and casting directors. superstitious.... DONALD NOVIS was Has a fine tenor voice and uses it in Sponsors are all praying for something born in Hastings, England.... BOBBE marked contrast to the mooing style of different to lure the listening public to DEANE, NBC actress, has a beautiful crooning delivery. It is to be hoped that their section of the dial. Radio scribes white Russian wolfhound named Czarina, he has started a new vogue in radio sing- are frantically writing comedy, old gags and a Great Dane named Eric.... MONA ing, although I must in justice say that are being resurrected, new wisecracks are LOWE, NBC contralto, has doubled for Lanny Ross did that some time ago, but being thought out with concentration two well -known actresses in pictures Lanny was not fortunate enough to be worthy of a better cause. Orchestra lead- which required vocal from a vocal -less "spotted" for a big build -up by NBC. ers are trying out new arrangers, hoping leading lady. . . . BERT LAHR once Donald Novis is being "built up" and will to get the almost impossible new angle in worked in burlesque for thirty -five dol- do NBC more credit than a great many harmony ; all of which proves thàt radio lars per week.... VIRGINIA ARNOLD of their former proteges.

www.americanradiohistory.com 20 RADIO WORLD July 30, 1932

SECRECY PLAN Engineer's Ring W8XK HAS NEW Heated by Wave DISFAVORED IN National Broadcasting Company engineers SCHEDULE AND recently found their most carefully designed microphones acting in a strange manner. The technical men immediately suspected in- POLICE TRAFFIC terference was caused by broadcasts from the NBC experimental television studio. A TRANSMITTER Washington right and that the clender metal rod which check-up proved that the engineers were Pittsburgh The Federal Radio Commission collated supports the microphone formed a perfect New short -wave broadcasting facilities statistics on police radio stations showing antenna for the television waves. have been installed at Westinghouse station the average time required to transmit a call In another case an engineer working near W8XK, Saxonburg, Pa., approximately 30 is 1 minute, 2 seconds, the number of arrests the NBC television transmitter atop the miles from here. was 12,676, amount of property recovered Empire State Building, N. Y. City, felt one The National Broadcasting Company and $386,953 (260 stolen cars not included), of his fingers grow suddenly hot. Investi- local programs broadcast through this number of autos equipped 2,255, service area gation showed that a ring on that finger American station are daily received by in- 28,190 square miles, population 32,585,000. acted as a coil and could dissipate the power habitants of the remote plains of Argentina, The statistics covered last April for cities only as heat. dwellers in the teeming cities of distant In- of 100,000 or more. Smaller cities reported dia, residents throughout hurope as well as 453 arrests, $34,860 recovered. Total mes- those of the Arctic who have been shut off sages for both classes was 160,668. from civilization. During the hours that the "The majority of stations transmit each short -wave unit is on the air is broadcasts three times, and the consensus is that with a view to transmitting the maximum call amount of information with the minimum the programs of KDKA. the number is sufficient, says the Commission. number "Six cities did not report the number of of words is much more divided. At Uses Four Waves radio. least one city reports the use of a very com- arrests made as the direct result of plete code numerical in Only about fifty per cent of the cities had based on a system Since the installation of the short -wave information available as to the amount of which the type and gravity of the crime is equipment both KDKA and W8XK pro- property recovered. indicated by the size of the number, such as grams go on the air from that site. New Number 1 murder, Number 2 "A number of cases of interference was indicating a equipment for broadcasting on 15,210 kilo- an armed holdup, et cetera. Other cities are meters) 21,540 kilocycles reported and in only one case was the do not cycles (19 and source of interference within the same zone experimenting with a code system but (13 meters) has been installed. The equip- city. In this case it ap- feel that hey are as yet in a position to re- ment for short -wave frequencies of 6,140 as the reporting port on its feasibility. A few cities have pears that the two adjacent çities involved A kilocycles (48 meters) and 11,870 kilocycles have established no means of co- operative tried code and discarded its use. large (24 meters) was moved to Saxonburg from gorup of licensees feels a code system use of the frequency and the city having an that its former location at the "hill" radio sta- is unnecessary if care is used by the dis- miles emergency announcement is unable to inter- of unneces- tion on the Greensburg Pike, about 28 rupt routine announcements being transmit- patcher to avoid the transmission from the present Saxonburg location. sary word and, therefore, do not recom- Radio has ted by the other city. It is believed that mend its The Federal Commission grant- proper co- operation such as in effect be- adoption. ed a license for W8XK to operate on power tween other cities sharing the use of a single Call Letters Enough up to 40 kilowatts. Not only are these short- frequency will completely eliminate this dif- wave programs of W8XK received direct ficulty. "The Commission's observers report that on short -wave sets but millions tune in on 9 to 10 P.M. Busiest some stations are transmitting an announce- them after the waves are picked up by re- ment periodically of call, frequency, wave, lay stations and rebroadcast on standard "A study of the cases of interzone inter- authorization, etc. wavelengths. ference indicates that the receiving equip- "This announcement is not required by The 19 -meter wavelength is used for ment furnished police cars is, in many cases, the regulations and occupies valuable time morning short -wave broadcasting. In the not up to modern engineering standards, as which may be needed by some other city for afternoon and early evening 25 meters are stations 16 kilocycles from the assigned fre- the transmission of an alarm with reference used. After sundown and at night the 48 In view of the lack of availability of fre- to an extdemely important message. It is meter wavelength is placed in operation. quency are reported as causing interference. recommended that this practice be discon- quencies it will not be possible to provide tinued, as the transmission of call letters Schedule of Sending for a greater separation between channels alone is sufficient. Certainl,, the transmis- of call letters, city, name, and correct The official daily broadcasting schedule in the near future. sion in "The busiest hour of the day appears to time should be the maximum material trans- of W8XK Eastern Daylight Savings time is as follows : be between 9 and 10 p. m. The four hours mitted for test purposes. prior to 10 p. m. are reported as busy hours 48 meters- 6,140 KC - 5 p. m. to sign -off by at least fifty per cent. of the cities, while 15 Persons Caught in Act 25 meters-11,870 KC - 4 p. m. to 10 p. m. 19 meters -15,210 KC - 7:30 a. m. to 5 p. m. the same number of cities report only two 14 meters -21,540 KC - 7:30 a. m. to noon busy hours after 10 p. m. "One city reports specifically that during "Metropolitan area police radio systems, the month of April fifteen persons were in which one city serves adjacent munici- caught in the actual commission of crime. Dorothy Lewis Dies; palities, are growing in favor. Twenty - Another city believes that police radio could eight cities have reported that they are reg- be better administered by the installation of ularly serving adjacent municipalities. Two cinct for the purpose of serving that pre - NBC Staff Contralto cities report the rendering of service on small, lower powered transmitter in each pre- has completely San Francisco special occasions. It is known that some of cinct alone, while another Dorothy Lewis, National Broadcasting the cities which have rendered no report are abolished all precinct stations and operates the entire system from the central head- Company contralto, died here. actually conducting service for the benefit of Miss Lewis had been a member of the surrounding municipalities. quarters. Still another reports that it con- nects the telephone system to the police staff of KPO, key station of the NBÇ -KPO transmitter during the reception of emer- network, for about two years. She was Word- Economy Code in gency calls in order that all cars may hear born Portland. While on a month's va- between the dis- cation at the home of her father, H. L "Many licensees believe that secrecy sys- the actual conversation Lewis, long illness. can be made patcher and the citizen reporting the emer- she died after a tems have possibilities if they As a concert singer she toured vaudeville mechanical, rather than of the code book gency. circuits of the West for seven years before type. The majority of licensees believe that Two -Way Talks turning to radio. Her first microphone ap- secrecy systems are unnecessary and that the pearances were at NBC station KGW, number of times that the transmissions are "It was suggested that a two -way com- Portland. used for improper purposes is far out- munication system should be provided to per- weighed by the salutary effect due to recep- mit patrolmen in cars to transmit back to REMOVAL REQUEST OPPOSED tion by the general public. One licensee, headquarters or to other cars information of with reference to a secrecy system, states crime. It Washington general imporance in combating Examiner Hyde, of the Federal Radio that it is his belief that any criminal organi- is recognized that a two -way system of com- zation having the ability to install and oper- munication has distinct advantages and Commission, has recommended that the ap- ate an intercept system for the protection of would permit greater flexibility in the plication of WJW, Mansfield, Ohio, to re- criminals against the police would be able to motorized police force. How- move to Akron be denied. The station is handling of a F. Weimer as the Mans- duplicate mechanical devices installed for ever, no consideration can be given to the operated by John secrecy purposes and render such a system of such a service until a suf- field Broadcasting Association on a frequen- authorization kc of 100 ineffective. ficient number of frequencies become avail- cy of 1,210 with a power watts and "Opinion with reference to code designed able." unlimited time.

www.americanradiohistory.com July 30, 1932 RADIO WORLD 21

RULES RELAXED Engineer's Wife EXPLOITATION Indorses the 55 While considerable technical compari- FOR ECONOMIES sons and contrasts, with illuminating RECOMMENDED curves, are published regarding detector tubes, sometimes a practical demonstration before non -technical listeners serves as BY BIG CHAINS good a purpose -especially as radios are TO EDUCATORS bought by non -technical folk, for the The two big chains, those of the National great part. Washington Broadcasting Company and the Columbia A radio engineer had a receiver oper- Dr. C. M. Koon, specialist in education Broadcasting system are making wide re- ating in his home for several weeks, '24 by radio at the United States Office of adjustments to meet conditions. Besides the detector. Along came the 55 tube and he Education, recommends that the methods reduction in number of employes and salary put that in. He commented to his wife, used by commercial nroadcasting corn - cuts for many of those retained, artists have who takes no particularly scientific in- panies in attracting the interest of listen- had their pay reduced; indeed, were the first terest in music, or the faithfulness of ers to their programs be studied by edu- effect of the economy wave, audio amplifiers and detectors, that the cators interested in educational broad- ones to feel the fine. and now other changes are being made. radio sounded She agreed. The casts. One of them, in the case of the National set played during two weeks. Then the If a broadcast is intended for instruc- to engineer put in a 57 tube, but the input purposes," he said, "the participa- Broadcasting Company, has been permit and tube overloaded tional mention of prices during certain was too great, that tion of listeners is of paramount im- the as had the '24. Next he used a 56 hours, on the that house- often, portance, and the methods used by com- morning theory as detector. The 56 is like the '27, and wives have an interest in them. However, mercial stations in sponsoring, announ- no particularly detection as afforded by these two types cing, and determining the success of their since night listeners have is what had been regarded as standard different interest it is expected that in time programs are the results of important ex- against mentioning of excellence. periences." there will be no barrier One night, with the 56 tube doing its price, provided it is done in an acceptable duty, the engineer's wife turned off the Will Publish Book manner. set, an unusual act, for she is a steady Done Indirectly Now listener. This is recognized by the Office of "Can't stand that racket," she com- Education in its preparation of a forth- At present price is mentioned indirectly, coming booklet on "How to Broadcast cost plained. - when expressible in terms of some unit The engineer replaced the 55 tube after the Art of Teaching by Radio," Dr. Koon of a commodity or a utility service. For in- the missus had fallen asleep and from then added. Many programs which have not stance, when the manufacturer of a tooth on the missus has been listening to the been set up primarily as educational paste wants you to know it costs only 15 set with great delight. nevertheless have been instructional in cents -whereas his competitors are charging many instances. The following additional a quarter -he says that his toothpaste, un- information was made available : like others, costs no more than a package Extensive publicity, aids to study, and of popular brand cigarettes. What cigarettes listener cooperation are important factors of this type cost is well known to nearly in broadcasts for instructional purposes. all listeners, so the effect of a direct state- A variety of ways is employed by the ment of price is achieved without offending NAMES SPELT broadcast stations to secure effective use the rule. of the broadcasts. Again, if something, like package candy obtainable at news -stands, cost a nickel the Field Scanned manufacturer can let you know fact by AS PROTECTION that A number of the methods has been stating, as he does, that the price is no more listed by the Office of Education in its than that of a local telephone call. The reason why the simplest names and study and are being analyzed as guides in However, the reason for admitting specific words are spelled over the radio is that un- mapping instructional programs. An- mention of price, a practice that is not taboo less this is done the listeners may get quite nouncements in newspapers in the form at small radio stations, is to attract more an erroneous idea of what was said. Even of feature articles, syndicated stories, sponsors. Just now the chains need busi- famous names of individuals -Floyd Gib- photographs of participants, letters from ness, and both have reduced their rates, at bons, Lowell Thomas, Graham McNamee, listeners, announcement programs, for least for certain periods, while one chain is etc. -don't "register" sufficiently, as the mail example, bring forcibly to public atten- offering a monthly payment to member sta- discloses. Letters addressed to Boyd Big- tion what to expect. tions, instead of so much per program gins, Roy Gilbert, Royal Gibson, Low Tom - Instruction by radio, it was said, will picked up. mers, Laurel Thompson, Gray Nanny, Re- not be successful without the mastery by Records Permitted gan McName and the like are many, alto- those who sponsor it of certain technique, gether too many. Therefore sponsors who equally as important in attracting listeners Phonograph record use has been taboo by desire to get a trade name across have it as the program itself is of educating NBC, but now the situation has changed, so spelled, and while most listeners will feel them. that the local station manager can suit him- they are being patronized, the sponsors want self about the use of recordings. Such use to feel that their own products will be has grown fast in radio, due to the large patronized, hence go to the pains of utter difference in cost between playing a record simplicity. Four Tenors Form and having the performers in the studio, or Whether the fault lies exclusively with receiving the program over telephone land those listeners who do make the mistake in Challenge Polo Team wires from some other station. In case of names, or whether the radio receivers must the wired program, the toll for wire use is share the blame, has not been determined. A polo team has been formed by four Broadcasting Com- paid by the originating station ; nevertheless The best minds of the country do not as a tenors of the National the price actually becomes a part of the bill rule write lettérs to stations. In fact, many pany Artists Service. Frank Parker, tenor rendered to the sponsor, if a sponsored pro- of the letters contain bad mistakes in Eng- of the A. & P. Gypsies and Cities Service gram is sent, and thus permission to use re- lish, both as to spelling of simple words and programs, is captain. cordings comes as a measure of economy. use of false syntax. This lends color to the Bob Simmons, tenor recently heard on The rule against them used to be so strict assertion that listeners are to blame, to a The Campbell Soup hour, will play Number that even birds were placed in a studio to large extent. But if one listens to an old - One position ; Henry Shope, tenor of The give atmosphere to an orchestra, rather than time regenerative receiver, with its badly Cavalliers Quartette, will play Number use a recording of the warbling of some cut sidebands, wretched audio amplification, Two ; Parker will play Number three, and canaries. and the climax- capping distortion of a 1926 Julian Oliver, Spanish tenor, will play The rule of the Federal Radio Commis- model horn, it is hard for the most literate Back. sion, requiring that recordings be announced to determine the niceties of proper names. All arrangements are handled by Parker as such, in words clearly disclosing that a at the NBC studios, 711 Fifth Avenue, New record is being played, remains in force. It the chains. The economies being instituted York City. was considerably modified for a while, but by the chains are to prevent a loss, and as than the modification was rescinded. the question of fees is to be decided largely OPPOSES ABILENE STATION The changes being wrought have an in- on existing conditions, the conferees have a direct effect on the negotiations between the great deal about which to talk. Washington American Society of Composers, Authors The truce between the two ends September Examiner Pratt, of the Federal Radio and Publishers, and the broadcasters. The 1st. a compromise is expected, so that copy- Commission, has recommended to the Com- society seeks a 300 per cent increase in fees right music can continue to be played, es- mission that the application of Bernard charged to big stations, lesser or no increases pecially as broadcasting depends so largely Hanks, Abilene, Texas, for a new broad- to smaller stations, and cites the profits of on the use of such music. casting station be denied.

www.americanradiohistory.com 22 w RADIO WORLD July 30, 1932

INTERFERENCE Tradiograms STANDARDS ON By J. Murray Barron Recording Radio Programs Lord & Thomas, advertising agency, which SLEUTHS CURE is said to place the largest volume of radio TUBES VOTED; advertising on the air, has purchased special phonograph disc recording and reproducing apparatus from the Record & Recording VARIOUS ILLS Division of the R. C. A. Victor Company. PARTS DEFINED It is understood that Lord & Thomas plans Two reports on cures for interference are to make disc records of programs with the New standards for radio adopted by the contained in "The Pacific Radio Trade As- new apparatus as an inexpensive means of American Standards Association follow: sociation News," July issue, as follows: preserving the program exactly as it goes Four -pin bases of the large and small type, out on the air. The recording apparatus is large BY PAUL E. CURRENT four -pin base without bayonet pin, simple, inexpensive and portable. It consists large five -pin base without bayonet pin, four- Interference investigations in the new ter- of a unit of two turntables, an amplifier and pin transmitting tube base, large transmit- ritory are progressing very nicely and the suitable volume control, a two -button studio ting tube base, four -pin sockets for receiv- dealers are all highly enthusiastic over this microphone and a loudspeaker for playing ing tubes, and five -pin sockets for receiving service. back the records after they are made. Pre - tubes. Many new problems have been encount- grooved records of a semi -flexible material The standard also specifies dimensions for ered and some of them require a great deal are used for recording and the records may terminal caps for both receiving and trans- of experimenting and tests to lower the noise be played back immediately after they are mitting tubes and for connections between level. These problems are especially hard made. the tube elements and the pins. when the complainant lives almost directly * * * The manufacturing standards applying to under some of the high voltage lines that Even today, with all the readjustments broadcast receivers establish a national network that country. called for by the business world, and the standard for the frequency range of receiv- The interference encountered there is not many persons who feel that they should ers from 550 kilocycles, or 545.1 meters, to the typical noise of power leaks of various mark time, we still find some who keep 1,500 kilocycles, or 199.9 meters. The rat- sorts, but appears to be a noise field that is ahead of the times. ing and design of socket -power devices and very similar to a magnetic field that sur- Leeds Radio Store, at 45 Vesey Street, electric radio receivers are to be standard- rounds a magnet. N. Y. City, caused customers entering the ized for operation on coltages from 105 to The noise is encountered suddenly and store to be greatly surprised to find that 125. stops very abruptly. Shield lead aerials and they automatically announced their arrival A standard test for quality of soldering filters helped in some cases and in others even though they entered through an open of cords tips or terminals to radio cards did absolutely no good. In one case, the door. A photo cell, with an electric bell in is also provided. This test is a straight pull antenna coupler system eliminated the noise the circuit, did the trick. Just this simple of 5 pounds applied to the tip or terminal. almost altogether, while in another place the arrangement caused a very great interest Other details for which standard dimensions filtered aerial did the trick. and naturally a lot of good publicity. It are established are cord tips, binding posts, We have taken several of the new deal- was an original idea applied to a retail store cable terminals, radio plugs and packs, and ers on trips with us and demonstrated to in a unique way. pilot lamps. There are also standard defini- them what we do and how we do it. Sev- Every day we find more and more new tions for the various parts of radio receivers. eral installations are sold each trip, and schemes for the phot ocells and they are we feel very confident that the membership finding their way into practically every busi- NBC MANAGES GOLDMAN as a result will increase more each month. ness. Edwin Franko Goldman has signed an ex- * * * clusive long -term management agreement BY FRED D. ROWE From indications in the retail radio field with the National Broadcasting Company. The remodeling of an apartment house in N. Y. City business must surely have with wire screen and plaster on the outside taken a turn for the better. Harvey's, the was responsible for several complaints of radio store formerly at 105 West Forty- NEW INCORPORATIONS radio interference. The set owners used in- third Street, has moved to 103, a much side antennas, resulting in a coupling with larger quarters. In addition to two large Furst Radio Corp., New York City -Atty., J. and very modern windows which house one Furst, 51 Chambers St., New York City. the nearby street cars. Loomis Refrigerating Corp., New York City - Radio interference covering an area of of the finest radio displays in mid- Manhat- Atty., L. E. Forman, 450 - 7th Ave., New York two miles was caused by two guy wires tan, we find upon entering the store a cheer- City. -laid Rotary Electric Co., Galesburg, Ill. -Attys.. Dela- fastened to a pole carrying 11,000 volts ful and well -out display. salon with about ware Registration Trust Co., Dover, Del. which were rubbing against a street light everything in 1932 radio receivers. To the Warner Acoustical Construction Corp., New York pole. left side in the rear is a fully -equipped serv- City-- Atty., J. W. A. Kelly, 170 Broadway, New York City. Dial telephones have been responsible for ice department. Executive offices are placed Phil Brill, New York City, electrical business- several recent interference calls. The in- on a large balcony in the back section of the Atty., A. N. Wolf, 162 W. 42nd St., New York stallation of condensers by the Pacific Tele- store. These quarters are the third this City Standard Appliance Corp., phone & Telegraph Co. eliminated the concern has occupied on Forty-third Street. Brooklyn, N. Y., re- frigerators-Attys., Oberlander & Oberlander, trouble. Each move has been into a bigger place. 32 Court St., Brooklyn, N. Y. * * * A defective aerial on an apartment rub- CORPORATE CHANGES bing against another caused noise in all the One of the finest and most elaborate tube Capital Reductions sets with aerials in close proximity to the displays to be seen in New York City is Edison General Electric Appliance Co., New York ones found rubbing together. now attracting attention at Walter H. Nuss- City, 85,227 to 58,725 shares, no par. Broken rail bonds and pitted trolley cir- baum, Inc., 61 Cortlandt Street. All details Name cuit breakers were responsible for several Change and most known advance information on Marquette Radio, New York City, to Radio recent complaints. We recommended a tubes is here for the benefit of the public Chassis. shield leadin with the flat top portion of who have need for such and a special corps the antenna at quite a distance to the feed- of men is on duty. ers, etc. * * * We are continually finding that loose Once again New Jersey folk will find a Literature Wanted fuses, switches and lamps in the building are radio shop handy as they rush to catch the Readers desiring radio literature from responsible for many interference calls. train. Modell has opened a radio booth manufacturers and jobbers concerning stand- Another source of trouble is often found store at the Cortlandt Street end of the ard parts and accessories, new products and be caused by the of aerial and new circuits, should send a request for pub- to reversing Hudson Terminal with a full supply of lication of their name and address. Send ground connections at the set. tubes, receivers and some parts. request to Literature Editor, RADIO WORLD, * * * 145 West 45th Street, New York, N. Y. M. B. SLEEPER IN NEW POST Last week saw the opening of another new radio store on Cortlandt Street, the M. B. Sleeper, following his resignation Cort -Wich, E. O. Cole, R. E.. Cole's Radio Service Co., 2714 as sales manager of Pilot Radio, has been northwest corner of Cortlandt Warren Blvd., Chicago, Ill. and Greenwich Streets. Clifford A. Case, National Electrical and Radio elected assistant vice -president of the United * # * School, Figueroa and Santa Barbara, Boston, Mass. Los States Capital Corporation, Blair Radio Labs. have Angeles, Calif. In this capacity, he will be in charge of sales moved to new and Wm. Dong, 106 Main Street, Salinas, Calif. enlarged quarters at 18 Warren Street, N. William McPhaill, 100 North 19th Street, Corsi- in three subsidiaries : Radio Television In- Y. City. Power amplifiers and public cana, Texas. dustries Corporation, at Reading, Mass.: ad- Geo. H. Foster dress systems, & Sonm, 1836 Hall Ave., Sharps - Globe Television & Phone Corporation, of together with special lab ville, Penna. New and Television Products, work, demanded the additional space. Hugh Bossiev, P. 0. Box 150, Alexandria, La. York City, Herbert T. Abfalter, 378 Harrison St., Marquette, Inc., which has purchased the equipment and SHORT WAVE CLUB Mich. patents of the Sleeper Research Corpora- E. O. Cole. R. E., Cole's Radio Service Co., 2714 E. C. Lawrence, Hotine Radio Service, 442 . 6th tion. Sales headouarters of the three com- Warren Blvd., Chicago, Ill. Ave., Brooklyn, N. Y. Fausto M. Donastorg, Yngenio "Angelina," S. P. Norman L. Raper, 601 E. Commercial St., panies are located at Reading. Mass. Macroris, Dom. Rep. Charleston, Mo.

www.americanradiohistory.com July 30, 1932 RADIO WORLD

Secondary Inductances Accurate Coils That Exceed to plus or minus 0.6 microhenry Your Requirements for Precision Tuned Radio Frequency Coils THESE coils are for two stages of screen grid radio frequency amplification, using any type screen grid tubes, including the newest ones, and any type of detector tube. There are three coils to a set. Each coil is wound on a 1 -inch diameter tubing and anchored to an aluminum shield base, to which base the shield proper makes a tight fit. The bases have punched openings through which four lugs protrude, and also are provided with rigid 6/32 machine screws for mounting. These screws protrude downward and are 1 11/16 inches apart. The coils may be mounted on chassis cut for the wafer type tube socket, or may be mounted by means of threaded bushings, elevated half an inch from a chassis top, requiring no cutout chassis. The shield has a small protected opening at top so the lead for the grid cap may be brought through. The opening is bevelled. This constitutes the protection against fraying the insulation of leadout wire to grid cap. The shield cover is 25fi inches outside diameter and 254 inches high. Inside the shield base are stamped designations as follows: P, B, G and ground symbol. These stampings are near openings through which the corresponding lugs protrude downward. Besides, there is a side lug, protruding outward near the bottom of the form. P and B are always the primary connections, P going to plate an B to B plus, except in the case of the coil used for antenna coupler, when P goes to aerial and B to ground. G is always the connection for grid cap of the r -f tubes, also grid cap of the detector if it is a screen grid tube, otherwise to G post of socket of the detector tube. The side lug is the grid return connection, usually grounded in circuits. The stamped ground symbol is not the ground connection but represents a tap on the secondary for tuning to 80 meters. The broadcast band is covered in full with the entire secondary -( and side lug -while from 200 to 80 meters are covered when the ground symbol tap is picked up by condenser stator. To accomplish 80.550 meter coverage, therefore, a three -deck switch, two positions for each deck, is required, and must be of the insulated type. The moving arms connect to condenser stators, and pick up either the full secondary or the tap, which is about one -quarter of the secondary, in number of turns. The full secondary is always in the grid circuit, wired as previously stated, but the tuned circuit is made to consist either of the full secondary of one -quarter of the secondary, CAT. NO. 1 -Three matched shielded t -r -f trans- by switching the condenser stator to either point. former:, for 0.00035 mfd., vvi h 80 -meter tap. The 80 -meter tap does not have to be used, but is advantageous to those desiring to tune in tele- $1.35 vision, amateurs, police calls, some relay broadcasting and other interesting transmissions in a band CAT. NO. 2-Three matched eh elded t -r -f trans- listener. formers, for 0.00046 mid. (Scovill condenser). of frequencies replete with novelties for the usual broadcast with SO-meter tap $1.35 High impedance primaries are used, the number of turns chosen so that the same coils may be CAT. NO. 3 -Three matched shielded t -r -f trans- used for antenna coupler and interstage couplers. formers. for 0.0005 mfd., with 80 -meter tap. All coils are guaranteed to cover the wave band when condensers of the specified capacity are used. $1.35 sold on a 5 -day money -back guarantee. We pay the postage on all coil orders, on Three -deck long switch for above All coils are coils, $2.50 basis of remittance with order. Precision Coils for Double Detection Circuits Tuner -Mixer Coils THE tuning coils for superheterodyne construction are for a stage of t -r -f, modulator and oscillator, with oscillator secondary inductance accurately chosen on the basis of specified capacity of padding condenser. These coils are for broadcast band coverage only. The coils are of the same type of mechanical construction as the t-r -f coils. Since there is no secondary tap, the code for connecting the t -r -f coils of the superheterodyne combination is different: P and B, primary; G and ground symbol, secondary. P would go to plate or antenna, G to grid cap, while B and ground symbol are the returns. The oscillator has a smaller inductance secondary, for padding, and moreover is a three -winding coil. The three windings are: pickup, secondary and tickler. Th_ pickup winding consists of 10 turns, and is brought out to two side lugs. The polarity of its connections unusually is of no importance. The secondary is represented by G and ground symbol, G going to grid and ground symbol to grid return, usually ground. The IÍÍ iiGlü'; tickler connections for oscillation require that the lug at B be connected not to B plus but to plate, hence the P lug goes to B plus. In any case, if no oscillation results, reverse connections. the tickler The intermediate frequency transformers are in an aluminum shield and consist of two loosely- coupled low r -t resistance honeycomb coils, with compression type Tuning Coils for 175 kc Receivers Hammerfund condensers that hold their setting. CAT. NO. 4 -Three shielded Bolls. two for modulator and r -f and one for oscillator, for 0.00035 mfd. three -gang condenser. Oscillator coil has pickup winding. Inter- mediate frequency intended, 175 kc. Price includes padding condenser, 705 -1000 mrd. Intermediate Transformers $1.80 CAT. NO. 5-Same as Cat. No. 4, except that this set to for 0.0005 mfd. $1.80 CAT. NO. 6 -Same as Cat. No. 4, except that this set is tor the 5.00048 mid. THE intermediate transformers consist of two honeycomb coils, &rill condenser $1.80 wound with low resistance wire, coils spaced 1 inch apart, and Tuning Coils for 365 -465 kc Receivers thus affording loose coupling, stability and high selectivity. The CAT. NO. 7 -Same as Cat. No. 4, except padding is for 365 -465 kc and padding con- coil assembly is enclosed in an aluminum shield, with open bottom. denser is 950 -450 mmfd $1.80 CAT. NO. 8 -Same as Cat. No. 6, except padding is for 365 -465 kc and padding con- The shields are 2q inches diameter, 2 inches high. At bottom are denser included is 350 -450 mmfd $1.80 two small rigid brackets, tapped for 6/32 machine screws. The taps are 1 11/16 inches apart. Four outleads, 6 inches long, are wired to the coils. Their colors are green, black, yellow and red. The primary consists of the yellow and red leads, yellow to plate, Short -Wave Plug -in Coils red to B plus. The secondary consists of the green and black leads. Green emerges through a protected small opening in the top of the WOUND on 1.25 inch diameter finest shield and goes to grid cap of a screen grid tube. Black bakelite forms, with flange for grip- is the return ping, these short-wave plug -in coils afford for the secondary, usually to ground. Both primary and secondary high efficiency. Tube sockets serve as are tuned, and thus the coils are for screen grid tubes exclusively, receptacles for these coils. The coverage except the second detector may be any type tube. The condensers for with four coils is 13 to 200 meters with 0.00014 mfd. capacity. Also 0.00015 tuning the coils are Hammarlund's compression type. on an Isolantite mfd. may be used without change. The base. The set -screws for adjusting these condensers with a screw- coils may be used for any of the popular driver are accessible from the top of the shield. short-wave circuits. CAT. FFI75- Shielded intermediate frequency transformer. 175 ke 81.1, CAT. SWA -Pour plug -in toils. ffZ base, primary and secondary; primary may be used roe feedback CAT. F F -450-Shielded intermediate frequency transformer, affording chelee by if condenser connecta aerial to grid $1.35 condenser adjustment of frequencies from 365 to 450 ke $1.3$ CAT. SWB -Four plug -In coils, 6 -pin base; I primary, secondary, fired tickler $1.70 Padding Condensers @ 4Sc Each UX wafer sockets or 6 -pin wafer sockets, lic. each CAT. PC- 710 -For 175 be Intermediate. Put In series with oscillator tuning condenser. Capacity 700 -1000 mmfd. Hammerfund, Isolantite base. CAT. PC- 3545 -Same a above, except 950 -450 mmfd. for 365 -400 be inter- mediate. Prompt SCREEN GRID COIL CO. We Pay Service 145 West 45th Street, N. Ye City Postage

www.americanradiohistory.com RADIO WORLD July 30, 1932 RADIO EQUIPMENT- SERVICE LEADERS

Thor's Bargain Basement Official National Headquarters for AUTO AERIAL Ham & 187 Greenwich St. New RADIO Servicemen's York CORP. THE GREATEST PARTS Brunswick NEW and STARTLING Headquarters STORE IN NEW YORK REPLACEMENT PARTS Improves Reception. Ad ass, a completeWave and npmlt- Pathfinder Superheterodyne Kit. Complete Stock of all Brunswick and Ready to Install. Andrepa, Short Wave and E10.50, with Speaker. Bremer -Tully Radio Parts and Pho- Mail orders filled. nograph Accessories Maintained at Sample complete. Dare in stock. Largest assortassort- - $1.00 BILL ment of Dynamic and Magnetic of sq. feet of floor All Times. Write for Free Manual. Speakers in Thousands Dealers write for Wholesale Prices the country. space devoted exclusively to BR-W. L RADIOS 142 -W. Liberty St. New York, N. Y. NETSON RADIO COMPANY TRY -MO RADIO CO. N. Y. CITY Serviceman. Amateur & Experimenter 78 Cortlandt Street New York 85 Cortlandt St. - 178 Greenwich St. Replacement ,C es1 P 78 LATHES POLO 7s AIR EX Used and reclaimed South Bend PRECISION PRODUCTS Power Transformers, Filter and By- Lathes. One 9 ", $127; 13 ", $278; T -R -F and Superheterodynes, Pass Condensers. Volume Controls, REPAIRING Voltage Dividers and Fixed Resistors. EXPERT 16 ", j33ß just a few left. Guar- short -wave converters PARTS anteed good as new. Terms, or and parts. SEND FOR OUR FREE 100 -PAGE REPLACEMENT for cash. South Bend SendSen for CatalogueC l Bue CATALOG Lathe Works, 312 E. Madison, Polo Engineering g, 78 Cortlandt St., N. Y. City South Bend, Insane. haler, /rte. 125 West 45th st nNea Yak N. Y eclerated 25 Park Pl. De . W. N. Y. ea ELECTRIC EYE! Experimental Radio World -Wide Reception SPEAKER BUILDERS (255 pages. 168 figures. and the various applications of this with SINCE 1921 slatrenle tube should be known to the 128 experiments.) the COMET "PRO" Short - radis man. Instruction By R. R. Ramsey, Prof. of Physics, Wave Superheterodyne. The most Offering you direct Speaker Service on included ln home study Ind. t- .;v. The experimenters manual: efficient ever desiga:d," say ex- Magnetic and Dynamic Speakers. s e h e e I Mean :emente, a '. and resident Testa, Calibrations, perts. Write Dept. h:W -1 for 16- We manufacture CONE and VOICE COIL 'f. a,' s o und amplification with ordinary radio and physical at/- p¢qe ASSEMBLIES for any Dynamic Speaker. Write for II. "Measure and Know "..$2.75 illustrated folder. I Í, I, courses. paratus. Special discount te `calera. / lustrated book. RCA HAMMARLUND -ROBERTS. INC. U Institutes, Dept. WR -7. RAMSEY PUBLISHING CO. LEOTONE RADIO CO. St.. N. Y. C. BLOOMINGTON. IND. 424 W. 33rd St. New teck \I1 75 Varick 63 Dey St.. N. Y. City LOOK OVER NEW RADIO HORI20NS 10 Meters" Service Men Need R.C.A. VICTOR SHORT- New 68 -page NATIONAL Manual SERVICE Ultra Short Wave Radio contains the his- the E L E C T R A D RESISTOR WAVE is fast becoming the leading publi- CONVERTERS cation for radio tory of Ultra Short Wave Development, HAND BOOK, for replacing re- Brand new, complete with eight coifs and -service men. If you articles about Ultra SW Quasi-Optical sistor5 and volume controls in all three tubes, $14.95. 3000 -ohm Frost wire keep rvCe de- and Infra -Red Bays, Commercial Applica- wound, potentiometer, velopmen0ete. you should be a aub- in Communications receivers. A real buy for $1. a manufacturers type. scriber for SERVICE. fion of Short Waves 4 30c. Four for $1.00. Baldwin double Work. 5 Meter Amateur Band, Ultra year,Y with supplements.pplements. See it at Tear Your dealer's. magnetic cone speaker chassis, new. $1.35. out this advertisement and at- Short Waves for Television. Over 120 il- We pay postage. tech a $1.00 bill for year's sub - lustrations. Send today for your nsv n

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