Radio Broadcast

RADIO BROADCAST

WILLIS KINGSLEY WING, Editor OCTOBER, 1927 KEITH HENNEY EDGAR H. FELIX Vol. XI, No. 6 Director of the Laboratory Contributing Editor

AMO7S[G OTHER THINGS. . .

- - - - Cover Design From a Design by Harvey Hopkins Dunn MUCH is now being accomplished in the complete set SOfield that beginning with this issue, RADIO BROADCAST Station the Frontispiece The Most Powerful Broadcasting in World 340 will devote much of its space to reflecting the technical and other advances being made. The policy of this magazine remains as Now You Can Receive Radio Pictures - - Keith tienney 341 before, to present the news of radio surrounded by as much as of what the technical radio worker refers to as The March of Radio An Editorial possible "dope." Interpretation 344 And much "dope" there is in this complete set side of radio as Modern Radio Receivers are a Good Invest- The of Direct on the Danger Advertising Air articles which will in issues will ment The Month in Radio many appear following strikingly demonstrate. In all the other fields of radio endeavor Listening to World-Wide Broadcasting is Licenses and What They Mean which Near The Columbia Broadcasting Chain RADIO BROADCAST has covered heretofore the construction A Profound Study of Radio Law of radio receiving apparatus, laboratory experiments, short- - wave communication, from the technical and The 1928 "Hi'Q" Has an Extra R. F. Stage John B. Brennan 348 broadcasting program side, and many others which we have covered to Manufactured Receivers for the Coming Season - - - 351 the satisfaction of our readers, RADIO BROADCAST will be as active as before. The expansion in scope of our text pages is 1928 Radio Receivers of Beauty and Utility ------352 directly designed to keep our readers in close touch with all sides of radio. The Neutrodyne Group ,,.,,,, 354

Servants of Your Light Socket - - - - 356 A"\ /"HERE is the radio experimenter who has not read of the W rapid progress of the transmission of photographs by Radiolas for 1928 ,,,,,, j^g wire and radio and hoped that he would soon be able to share in the fascination of this new and intensely modern field? For for . Some New Offerings the 1928 Season 360 the past few years, RADIO BROADCAST has watched the progress of the art, hoping that devices would be developed within the New Tube - Millen A Regulator James 363 scope of the amateur laboratory and pocketbook. The leading article on page 341 describes the background of the Cooley The Receiver ------1928 "Equamatic" Julian Kay 364 "Rayfoto" system which in a very few weeks will be made available the of RADIO BROADCAST to the home A New Principle of R. F. Tuning David Grimes 367 through pages experimenter. To be able to construct a radio photograph re- Book Review - Car! Dreher 369 ceiver for less than $100 should appeal very strongly to the who are for new to do. Using Radio in Sales Promotion, by Edgar H. Felix experimental fraternity crying something Here, in a manner of speaking, it is. 1928 Loud Speakers - , , , . , j^o

Should the Small Station Exist? John Wallace 372 pages of this issue are devoted to showing the "The Listeners' Point of View" MANYofferings of the set makers for the coming season. Later issues of this magazine will describe in greater detail interesting Your A. C. Set - - H. Felix Edgar 374 technical features of these many receivers from many manufac? turers. As the Broadcaster Sees It - Carl Dreher 376 Transformers and Chokes for Home-Constructing Power-Supply r > T" HOSE of a technical turn of mind will read with great Devices - - Homer S. Davis 379 J. interest David Grimes' story on page 567 describing the theoretical features of a radio receiving system which is one cf "Radio Broadcast's" Laboratory Information Sheets - - - - - 388 the most interesting that has come to our attention in many No. The Glow Tube No. Care of Power Units 109 Type 874 133 Supply moons. Articles to follow by Mr. Grimes will describe the No. 130 Data on Honeycomb Coils No. 134 Loud Speaker Horns circuit constants and information about the No. 131 Resistance-Coupled Amplifier No. 135 Closely Coupled Circuits practical system. No. 132 Resistance-Coupled Amplifier Circuit No. 136 Carrier Telephony

Manufacturers' Booklets Available - - - - 394 Federal Radio Commission is making every effort to THEpopularize the use of the expression "frequency in kilo- Shall I - What Kit Buy? 396 cycles" instead of the familiar "wavelength in meters." It is hard for some, but one's in does to Recent Radio Articles going doing thinking kilocycles A Key .*<..>.. 398 remove serious from calculations. Ever since many complications - - its issue RADIO BROADCAST has "Radio Broadcast's" Directory of Manufactured Receivers 402 August, 1915, standardized the use of kilocycle designations, always printing at the same time, Making Radio Installations Safe Edgar H. Felix 410 the equivalent wavelength in meters. We are in sympathy with the wishes of the Radio Commission and invite the expression Book Review - 416 of our readers on this subject. Practical Radio Construction and Repairing, by Moyer and Wostrel WILLIS KINGSLEY WING.

Doubleday, Page & Co. Doubleday, Page & Co, Doubleday, Page & Co. Doubleday, Page & Co. MAGAZINES BOOK SHOPS OFFICES OFFICERS all COUNTRY LIFE (Books of Publishers) GARDEN CITY, N. Y F. N. DOUBLEDAY, President WORLD'S WORK I LORD & TAYLOR BOOK SHOP NEW YORK: 285 MADISON AVENUE NELSON DOUBLEDAY, Vice-President GARDEN & HOME BUILDER \ PENNSYLVANIA TERMINAL (2 Shops) RADIO BROADCAST NEW YORK: -/GRANT CENTRAL TERMINAL BOSTON: PARK SQUARE BUILDING S. A. EVERITT, Vice-President SHORT STORIES J 38 WALL ST. and 5^6 LEXINGTON AVE. ' CHICAGO: PEOPLES GAS BUILDING RUSSELL DOUBLEDAY, EDUCATIONAL REVIEW 848 MADISON AVE. and 166 WEST 32NDST. Secretary LE PETIT JOURNAL ST. Louis: 223 N. 8TH ST and 4914 MARYLAND AVE. SANTA BARBARA, CAL. JOHN J. HESSIAN, Treasurer EL Eco KANSAS CITY: GRAND AVE. and 206 W. ST. 920 47TH HEINEMANN LTD. A. Asst. FRONTIER STORIES CLEVELAND: HIGBEE Co. LONDON: WM. LILLIAN COMSTOCK, Secretary "WEST SPRINGFIELD, MASS.: MEEKINS. PACKARD & WHEAT TORONTO: OXFORD UNIVERSITY PRESS L. J. McNAUCHTON, Asst. Treasurer

OOUBLEDAT, PAGE & COMPACT, Garden Qity, X[ew

Copyright, 1927, in the United States, Newfoundland, Great Britain, Canada, and other countries by Doubleday, Page & Company. All rights reserved. TERMS: $4.00 a year; single copies 35 cents. 338 RADIO BROADCAST ADVERTISER 339

strides made in the thing available if we do not make use of it. It past few years by the can now be utilized very simply. Radio artists, THEbroadcasting stations in editors and many musicians have expressed both bettering the quality of their pleasure and amazement on hearing the tone transmission have been remark- portrayal of symphony orchestras, as well as jazz able. The same principles have bands which Nature's Sounding Board has made been applied to the phono- possible. graph, resulting in the new rec- Nature's Sounding Board is known as the Lata ords and machines which are Balsa Reproducer. It is more than a "loud miles in advance of the older speaker." It is science's latest contribution to type. the musical art. It will make any good radio re- These improvements are now ceiver sound much more natural and pleasing. Lata Balsa Reproducer available to every listener-in. Lata Balsa Reproducers are available in com- Model 150, Price $50 However, there are some radio pleted, artistically decorated models ranging in receivers which will not reproduce price from $30. to $50. Kits are the wonderful music being broad- also available in two sizes. The fa- cast by the improved stations. mous Lata Unit, or electrical driv- By applying the same principles ing mechanism is now ready for to radio receivers which have delivery and is ideal for use with proved so helpful in the broad- the Lata Balsa Reproducer Kits. casting and phonograph fields it The accompanying illustration is now possible to make the most will give you some idea of the at- out of the broadcasting. By utili- tractiveness of the reproducer the scientific aids now avail- Everything necessary for the building of a to realize its tone zing modern three-stage resistance coupled am- superior quality able old and new receivers be plifier which may be applied to any re- must hear it. may ceiver. 59.00 you made to produce music which in The Lata Balsa Kits are com- every way resembles the original, There is as plete and may be assembled in a very short time by much difference between this new form of repro- anyone. No mechanical skill or electrical knowl- duction and the old as there is between the new edge is required to follow the simple instructions. phonograph and the old scratchy, squawky Once you have cylinder machine of yesteryear. heard this won- Resistance coupling simplifies receiver amplifier derful repro- construction and greatly reduces the cost. It is ducer no other recognized by leaders in the search for the best will satisfy you. tone quality as being the ideal amplifying system. The coupon be- It permits the passage of the very low notes and low is for your the very high ones with the same ease. It brings convenience in to the loudspeaker a true but greatly amplified ordering. Use it picture of what is picked up from the broadcast- today and you The number 2 station. re- Lata Balsa Kit and Reproducer ing will never unit assembled. You can duplicate this as- in a short is little in sembly very time by using this kit There use having this wonderful gret it. and complete instructions RETURN THIS COUPON-

ARTHUR H. LYNCH, Inc. General Motors Bldg. 1775 Broadway BALSA ARTHUR H. LYNCH, inc. At 57th Street, New York City WOOD Gentlemen: General Motors Building REPRODUCER, Please send me the items checked, for which I enclose my Corp. 1775 Broadway money order or cash, also information on prices and sizes of NEW YORK CITY Art Models of Lata Balsa Reproducers. 331 Madison Avenue Lata Balsa Reproducer 13 JC 24 8.00 Kit," $ 21 X36 10.00 NEW YORK CITY Unit 8.00

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view of the transmitting panel of the 100-kilowatt transmitter at the South Schenectady laboratories of the General Electric Company. Experimental programs are sent out with this set, using the standard wavelength of WGY, from as midnight to one a. m., Eastern Time. The transmitter went on the air August 4th, marking the first time that power great as 100 kilowatts has been used in broadcasting. The three water-cooled 100-kilowatt tubes in the foreground have an attach- ment for clearing out the gas from the tube 'while it is on the panel RADIO BROADCAST

VOLUME XI NUMBER 6

OCTOBER, 1927 NOW-

You Can Build Your Receiver for Less Than One Hundred Dollars How It Works By KEITH HENNEY Director of the Laboratory

If II WERE is an undeniable thrill in witnessing when one considers the simplicity of the appara- worked under great odds, trying to send picture I an extraordinary scientific event, such as tus and the compromises which were necessary signals by short waves back to the United States. -^- receiving one's first broadcast program, or in order to obtain them, it must be remembered This background is necessary to understand the in talking across the Atlantic for the first time, that it is about seven years since the first small years of effort that have gone before the present or in seeing photographs that have been sent by group of amateurs heard the human voice, and development. This development has been slow, radio from England, or in talking via short-wave music, coming in by wireless. The early poor and full of disappointments but the final result amateur radio with a fellow "ham" on a steam- quality of reception must not be forgotten; nor has been that his system is workable, compara- ship a thousand miles up the Amazon river. In must we lose sight of the fact that it has taken tively simple to operate, and what is more im- fact, as the French astronomer, Camille Flam- since 1835, when S. F. B. Morse performed his portant in the eyes of the average experimenter marion says, "Unless one has a stone instead of epoch-making experiment of transmitting slow it is inexpensive. a heart and a lump of fat in the place of a brain, and uncertain telegraph signals via wires, to send THE LURE OF HOME EXPERIMENT it is difficult not to feel some emotion over the messages at the rate of several hundred characters achievements of science." per minute. should one want to receive pictures by The writer's first contact with Austin G. The Cooley pictures are better than most of WHYradio at home? As well ask: Why have Cooley, who has been responsible for the picture the static-laden ones that have come across the thousands of experimenters built receivers for transmission system to be described in RADIO the reception of music, or code? In this, there BROADCAST, produced one of those technical has been always the thrill of accomplishment; thrills. was down in the "shack" with one's Cooley working Radio pictures at home that's making something hands, something at 2 GY, the short-wave station of the RADIO that works: creation. there is the what the has been Secondly, hope BROADCAST Laboratory, a small place with Q experimenter in everyone's heart that television, the art of scarcely room enough to stow his extensive gear. waiting for. Now it is possible. transmitting scenes from life itself by wire or On one bench was a metal drum on which a shall become within his time. For less than $100, you can build radio, practical photograph of a young lady with a large and Before television shall be an accomplished fact, own receiver, connect floppy hat turned over and over. On the other yo'ur picture we must conquer the idiosyncrasies of the trans- side of the "shack" was another rotating drum it to your broadcast set and jump mission of still life pictures, an art known as covered with with a small of ex- photographic paper into a new and fascinating field of telephotography. By introducing legions spot of light playing on it, and filling the shack perimenters to the general problem of Exclusive articles in sending was an undefinable sound like that of a high experiment. and receiving pictures by radio or wire, Cooley speed motor whirring away with whining and RADIO BROADCAST in the Novem- may have a share in advancing the day when the somewhat obnoxious tone. In two or three min- more difficult task of ber number and infollowing issues committing moving pic- utes, Cooley stopped the motor, took the photo- tures to the ether shall be solved. The amateur will tell bow to build and graphic paper from the receiving drum, devel- you has been thanked by engineers for his persistence oped it in rather dim daylight, and there was the operate the receiver. in developing short-wave channels; many have young lady again, hat, white plumes and all. said that to him alone belongs the credit for ad- Between the transmitter and receiver was an vancing the art of communication by the use of artificial telephone line 300 miles long so that for Atlantic. Some of them are reproduced here. those very high frequencies. At any rate, he has all practical purposes the young lady's picture Improvement in detail and shading of the Cooley had his share in making possible communication had been sent to Garden City from, say, Wash- Rayfoto pictures will come. The important fact is by short waves across vast distances with inex- ington, D. C. that here is something the experimenter can have pensive apparatus. Who knows what his share Since that time, Cooley has produced several for his own and can have the sport of developing may be when the ultimate success of telephotog- picture systems, one of which is applicable to his experience as this apparatus is improved and raphy and television has been achieved? present wire telegraph channels so that facsimile refined. The transmission of a picture by the Cooley copies of original messages may be transmitted To know the Cooley apparatus is to know system differs from the transmission of music at a cost not exceeding present rates. Another Cooley, to visualize the young M. I. T. student in one important respect: it takes a single audio system the one in which we as radio experi- who preferred his own researches into the then frequency and performs tricks on it which at the menters are interested has been developed to unknown field of picture transmission to the pre- receiving end are translated from sounds to other the extent that with a not very expensive attach- scribed studies with the result that he was effects which influence a photographic paper. ment to the ordinary radio set, one can receive at dropped from the college register during hij For example, good broadcasting requires that a home photographs, letters, telegrams, pictures, fourth year; his long nights of work, sleeping band of frequencies 10,000 cycles wide shall be or text torn from newspapers. This system is when sleep was necessary beside his apparatus transmitted. These frequencies at the receiver are known as the Cooley "Rayfoto." on a laboratory bench. One should know of reconverted to sound waves. The picture system These radio-transmitted pictures are com- twenty-four-hour days in the Arctic on the takes a given frequency, say 1000 cycles, and paratively good reproductions, quite satisfactory MacMillan Expedition in 1926 when Cooley transmits its form of intelligence on it. In a way 342 RADIO BROADCAST OCTOBER, 1927

.-CORONA" COIL it is less complicated than broadcasting music; in AMPLIFIER other ways broadcasting pictures is more complex. AUDIO OSCILLATOR The station which elect broadcasting may WIRE FROM END Of NEEDLE to transmit pictures as well as music or speeches CORONA" COIL TO POINT will use its Since present equipment. pictures POINT according to the Cooley system are first translated into sound impulses and since the phono- REVOLVING DRUM graph record is a means of recording for future use such sound two impulses, thereby defeating [ PICTURE BEING RECEIVED ON time and broad- PIECE OF PHOTOGRAPHIC of nature's limitations, space,[the PAPER casting station that will invest in a phonograph turn-table needs no other equipment to fill the ether with pictures.

YOUR REGULAR RADIO RECEIVER IS USED

who will receive pictures will use THOSEtheir present broadcasting receiving set which should be equipped and operated so that overloading and severe distortion of other sorts do not occur. As in transmitting sounds, distortion at the receiving end produces an unintelligible or garbled The receiver must be within the reproduction. TO WIND "service area" of the transmitter that is, inside SPRING MOTOR the distance at which fading takes place; the op- RELAY TO era tor must be able to develop and fix ordinary de- RELEASE DRUM >--*' SPEED REGULATOR veloping-out paper, such as Azo, Velox, or other RADIO BROADCAST Photograph papers with which the amateur photographer is THE COOLEY "RAYFOTO" RECEIVER well familiar. Here is an for already opportunity Simplicity is the keynote of the Cooley picture transmission system. Signals in the form of an audio has his the radio enthusiast who dropped photo- frequency tone enter at the point marked on this photograph, are amplified in a single-stage trans- graphic hobby to bring developing trays from the former-coupled amplifier, after which they are placed on the oscillator circuit through a modulation in the oscillator circuit drive the corona circuit whose attic, and to renew his acquaintance with hydro- transformer not visible here. The signals output is conducted to the drum and the wire and needle point shown here. quinone, metol, HQ, and hyposulphite of soda! rotating photographic paper by The drum is rotated by the familiar spring motor which usually turns phonographic records. The The present simplified system transmits and milliammeter, which is essential, usually reads the oscillator current receives original photographs full of strong contrast, such as newspaper photographs, or those in which a loss of detail will not mar the recogniz- covered the entire picture, illuminating a small much as the plate of a vacuum tube is main- able features of the transmitted picture. The bit of it at a time. The light which is reflected by tained positive with respect to the filament by examples reproduced here will give an idea of the picture passes into a sensitive photo-electric the B batteries. When light shines on this po- the work that can be done. These limita- cell, another of modern science's marvels. When tassium plate, electrons, those omnipresent nega- are their tions are largely due to the simplification of the the beam of light falls on a black portion of the tive electrical charges, given off, passage are receiving equipment, and, as experimenters be- picture, most of the light will be absorbed and to the second electrode toward which they come more familiar with the present apparatus, little reflected and consequently what passes into attracted constituting an electric current. This more refinements will naturally follow, refine- the photo-electric cell will be small just as the minute current, usually of the order of a few ments which will make it possible to receive part that comes to the eye is small; which ex- millionths of an ampere is greatly amplified and greater detail, and naturally better pictures. plains what we mean by the word "black." interrupted by another current of looo-cycle The process of getting the picture into the This sensitive photo-electric cell, whose his- frequency. The result is that what were originally ether is not too complicated for anyone to under- tory dates back many years and touches the lives black and white visual images have been trans- are im- stand. The picture is wrapped around an alumi- of many famous scientists, consists of a potas- lated into sound impulses which then num drum which revolves in front of a very sium plate and a second metallic electrode which pressed on the radio transmitter, or a telephone it out like or music. strong light. As the drum revolves it moves along has a battery attached to it maintaining at a line, and are sent speech be re- a shaft, so that the beam of light eventually has potential positive with respect to the potassium, At the receiving end the process must versed, i. e. sound impulses must be translated into light impressions, back into those original black and white spots. Assuming that nothing happens in the intervening space, no static is no has lost the at the Picture to be sent picked up, fading signal, is wrapped around end the conventional broadcasting set " receiving this drum may be used, and if a loud speaker is attached to the output of the receiver in the normal manner we should hear this varying note which is about two octaves above middle C on the piano.

WHY LOCAL AMPLIFICATION IS NEEDED

Apieceof photographic MOST cases it will be necessary to boost this pa peris wrapped around this drum INwavering note to sufficient strength to operate the rest of the translating apparatus which consists of an oscillator, similar to that used in super- heterodyne receivers except that its wavelength is usually above the broadcasting band, and finally what Cooley calls a "corona" coil. It will remind old-time electrical experimenters of the Tesla coil, a device used to transform a.c. voltages into other voltages high enough to produce electrical discharges across intervening space, in L this case about a quarter of an inch. Under ordinary conditions, the carrier of the HOW THE COMPLETE SYSTEM WORKS transmitter tuned-in but no picture being on the air, the oscillator will be oscillating so feebly The owner of receiving apparatus need not worry about how the pictures get on the air, but in case he that no corona is taking place, but when the is interested, here is a layout of the complete system, transmitter, waves in the ether, receiver and all! arrives it to the oscillator The switch at the right of the receiving equipment and the trip magnet are part of the start-stop signal supplies power system that insures synchronism between transmitter and receiver so that a nice fat discharge is produced whose 343 OCTOBER, 1927 NOW YOU CAN RECEIVE RADIO PICTURES!

total cost of the apparatus, exclusive of batteries, tubes, and broadcast receiver will be less than $100. All of the electric apparatus can be made from material easily available to the experimenter. Complete descriptions by Mr. Cooley of this equipment and how to operate it will follow. A word about the availability of pictures. Inasmuch as the original equipment for a broadcasting station need involve no more than the expense of a phonograph, there is a certain source of these radio pictures in every broadcast station. Broadcast stations will find in the transmission of the Cooley "Rayfotos" a sensational extension of their activities and by the time this article is in the hands of experimenters, and by the time the receiving equipment is ready, pictures will be on the air. The Cooley system is being exhibited at the New York Radio Show this month. And there you are: Pictures by radio and in RADIO BROADCAST Photographs your own home. THE COMPLETE RECEIVING APPARATUS

Here is the entire receiving apparatus. The receiver in this case was a well known set operating from a 208 meters in another of the are SPECIAL MODULATION loop, picking up signals on which originated part Laboratory. They TRANSFORMER tuned-in and sent through the picture apparatus which is described in greater detail in the other photographs

CORONA DISCHARGE intensity varies with the shading of the trans- ing the receiver and trans- OCCURS AT THIS POINT mitted picture. mitter together has been The counterpart of the rotating drum of the employed. It is known as transmitter will be found at the receiver. Here, the "start-stop" system, instead of an electrical motor we use for sake of and is very simple and flexi- simplicity a phonograph turn-table which is ble. In operation the receiv- geared to a small aluminum drum around which ing drum revolves slightly the sensitive photographic paper is wrapped. faster than the transmitting The corona discharge sprays the paper from a drum and it therefore com- fine needle and in some way not well understood pletes a revolution in a affects the emulsion of the photographic paper. slightly shorter time. At Whether this is an electrical or chemical effect or the end of each revolution whether there is enough light from the corona to the receiver drum is held by expose the paper is not fully known. a trigger until the trans- But for Cooley's purpose it does not matter. mitting drum completes its When developed, the paper shows black spots revolution. A signal is trans- where the discharge was heavy; light spots where mitted then that releases the A CLOSE-UP the corona was weak. drum so the two receiving The modulation transformer, which was -hidden in the view on page Now in all picture systems, some means must start off The radio together. 342 by the corona coil is shown here. All of the parts for this appara- be to the receiver in exact are not provided keep syn- signals strong tus have been especially designed, and will be available soon. A good chronism with the sender; when the latter starts enough in most cases to idea of the gearing mechanism and of the width of the drum on which in is be from this The the receiver must start, and not the middle of operate the trip magnet that the picture received may had photograph. picture be as wide as the metal drum. The needle rides the picture which as anyone can see would have releases the receiving drum may point actually on the as is shown here certain disadvantages! A simple scheme for hold- at the beginning of each paper revolution so this magnet is operated through a more sensitive relay. Both the trip magnet and relay can be seen in the picture of the apparatus shown on this page. The single pole double throw switch S is really part of the trip magnet. When the arma- ture of the trip magnet is against the stop on the drum, terminals 2 and 3 on the switch are pushed together and therefore all of the energy from the audio amplifier passes into the relay. When the synchronizing impulse is received it activates the relay and the trip magnet thus releases the drum and also causes the switch S to make contact

between terminal I and 2 and then all of the energy passes into the oscillator. The present apparatus transmits 4x5 photographs at a rate of one and one-half inch per minute or a little over 3 minutes for a picture. The Cooley receiving apparatus consists of first of all one's broadcast receiver, then certain mechanical parts which will be on the market soon, and then certain electrical apparatus which any experimenter can build and operate. The

WHAT THE PICTURES LOOK LIKE These photographs have been transmitted by the Cooley Rayfoto system. Pictures may be five inches wide and about six inches long and a little over three minutes for each picture is required. These pictures have not been retouched Modern Radio Receivers Are a Good Investment

Radio World's Fair opens the has reached a standard of reproduction the better informed element of radio radio season for the broadcast far above that which satisfied the pho- listeners, we have analyzed this lack of listener. Fitting its significance, the nograph industry after twenty years of familiarity as attributable in part to the THEFair is held in mid-September at prosperity. This standard can be raised at experimenter's preoccupation with the the huge Madison Square Garden in New will with our present knowledge and facili- intricacies of set building and the failure of York. ties, although the cost of doing so is prohib- the radio set manufacturer to lay before No radio season has ever started more itive and the effect hardly noticeable to the this group, so invaluable to the building of auspiciously. Technical progress, repre- average listener. As to appearance, there is reputations, the real facts about the design sented by simple, easily operated and still room for some improvement by the and construction of his receiving set. Glit- maintained radio sets, many powered di- attainment of greater compactness in the tering generalities about performance do rectly from the electric light mains, with more powerful receivers, but models are not intrigue the radio experimenter who, broadened tonal range, bring the manu- available for which no apologies need be in past years, has successfully excelled in factured receiver to a standard so high that made even in the most exacting surround- these proclaimed qualities with his home- revolutionary change can no longer be ings. made contraptions. expected. Greater broadcasting programs Radio has certainly not reached its limit But a new day has dawned. The ex- and improved receiving conditions make of development. Improvements will con- perimenter cannot deny the superiority of the possession of these modern receivers all tinue always and this year's sets will always the better manufactured sets. Already he is the more desirable. be better than last. Two or three years turning his attention to new fields. While Every industry goes through the same ago, a radio receiver was but a one-year building radio receivers was still an experi- cycle of growth; first, it has a discouraging investment for those who would possess ment, the successful outcome of which de- struggle for recognition, then a boom the best available in the market. This year's pended upon skill, ingenuity and patience, period with almost day to day improve- standards are making the latest and best this hobby had no rival in the hearts of ment, and finally, stabilization, with slow, models perhaps a five-year investment in those who considered the soldering iron an continued and healthy progress, keen com- approximately the best radio reception instrument of conquest. The element of petition among leaders and the gradual attainable. mystery is disappearing. Set building has elimination of the less capable who thrived It is a strange paradox that the sub- become the following of a well established only during the boom period. stantial developments in manufactured formula. The thrill of accomplishment In stating that radio has reached a slower receiving sets are not more widely ap- still exists but the procedure is so well level of development and that the purchaser preciated by the technically minded radio charted that the joy of exploration and may now select his receiver with the enthusiast. From extensive contact with discovery is practically gone. These missing confidence that it will not be hope- elements, which satisfy the experi- lessly obsolete within a year or two, menter's insatiable desire to overcome or even four or five years, we draw obstacles and to conquer the unknown our conclusion from fairly simple and are being rapidly supplied by new lines indisputable premises. Improvement of endeavor. Telephotography and, of any device is a matter of rendering some day, television, international it so simple that no technical knowl- short-wave broadcast reception, mod- edge is required for its operation, so ern installations with remote control rugged and self-sustaining that but of the radio receiver, laboratory ex- little attention is needed to maintain periments, home motion pictures, it in good condition, and so pleasing aviation, mechanical models and a in appearance that it harmonizes with thousand one avenues of expression the most luxurious surroundings. beckon the experimentally inclined. High standards of simplicity have The pages which follow attempt to been attained in radio when we have reflect accurately the trends in the many receivers in which five circuits interests of our readers. The manu- are controlled one factured receiver deserves an increas- simultaneously by COLONEL LINDBERGH IN SCHENECTADY dial and calibrated so that stations " ing amount of attention, as do new Aviation and radio are twin sisters engaged in the joint enter- be The fields of like telepho- may promptly logged. only prise of overcoming time. Distances are no longer measured in development perishable elements in some receiv- miles, but in hours, minutes, and seconds. Colonel Lindbergh tography and short-wave reception. reduced the distance from New York to Paris from to ing sets now are the filaments of days We do not propose, in the least, to hours. Radio has brought all parts of the world into talking the vacuum tubes themselves which neglect the set builder, but rather distance of the United States," said Martin P. Rice of the need be to him in touch with the replaced perhaps only General Electric' Company. Above: Martin P. Rice, and at keep once a year. In tone quality, radio the extreme right Colonel Lindbergh latest developments of the art. We OCTOBER, 1927 SHORT-WAVE BROADCASTS YOU CAN HEAR 345

feel the broadened scope of our pages will number which may be accommodated tinction which will be recognized by the appeal to each of the three principal throughout the world. Receiving sets, legal profession as one of no small moment. elements of our reader audience, the ex- working on the high frequencies, are The book deals comprehensively with all perimental group; those professionally in- necessarily of the regenerative type and phases of radio communication and inter- terested in radio, ranging from dealer to consequently, at the present time at least, prets the Radio Act of 1927 in the light of engineer to manufacturer; and the radio no vast number of receiving sets can use precedents already established by the enthusiasts who follow these pages to keep these channels without causing destructive Courts. The book studies exhaustively the abreast of progress in radio. interference. Undoubtedly, the radiation complex problems raised by the existence problem will be overcome, but fading and of broadcasting stations, although the transmission will the author has been Listening to World-Wide Broad- irregularities prevent seriously handicapped use of short waves in the essential local and by lack of established legal and casting is Near precedents regional broadcasting services. decisions on most vital issues. Clearly, to the development of broad- Since short-wave stations practically many important legal questions which will casting, experimenters built receiving cover the earth with their signals, it is feas- harass the Courts during the next few PRIORsets having a wavelength range of ible to assign but one powerful short-wave months are yet to be settled. from 200 to 25,000 meters, so that they broadcaster to a frequency. Consequently, The preponderance of evidence and could eavesdrop on every available radio it is desirable to select a short-wave broad- precedents which Judge Davis cites leads channel. Experience has taught us to casting band at once and allot frequencies one to conclude that the question of build more efficient receivers for much so as to meet the needs of all the countries confiscation of property, involved in cancel- narrower ranges. Indeed the present of the earth. This matter should be con- lation of station licenses, is one which will broadcast band is the widest for which a sidered in the International Radio be decided against the regulatory power of high grade receiving set with easy control Telegraph Conference, convening in Wash- the Commission. On the other hand, can now be made. Many of the services ington in October, lest confusion and con- established stations, which find their ser- conducted on non-broadcasting channels gestion arise later. There is no need for a vice curtailed by interference from new- are gradually being rendered by radio great number of short-wave broadcasters comers, seem to have ample grounds for telephony rather than radio telegraphy. in any one country, and some means should securing restraining injunctions on the The objection that laborious study of the be devised for limiting their increase before grounds of prior rights. Reading these radio code is necessary to listen to them is the problem becomes as serious as the con- parts of the Judge's book leads us to regret thereby eliminated. gestion now obtaining on the conventional all the more that our suggestion that station Almost every day of the year, new radio wavelengths. priorities be recognized, was not embodied services open up. The possessor of a long- in the law. That was urged in these pages wave receiver his from before the Radio Act picks signals every A Profound Study of Radio Law long was finally section of the globe. A slight movement of drafted. the dials may transfer his attention from a F I THE Law of Radio Communication by The author considers federal jurisdiction station in Java to another in Iceland. There / Stephen Davis, former Solicitor of and its relation to state and local regulation are now nearly one hundred stations which the Department of Commerce, re- of radio communication, copyright ques- can be heard in any part of the world. cently published by McGraw-Hill, is tions, libel and slander, as well as the sig- Perhaps the most important develop- a valuable contribution to radio literature. nificance of every phase of the recent Act. ment of all, so far as the broadcast listener It has been is concerned, is the increasing interest in awarded the I. GENERAL BROADCAST ADVERTISING short-wave broadcasting. 2 XAF, the 32- Linthicum A. Basic Rates for periods between 7:00 P. M. to 11 :00 P. M. Local Time. meter (gijo-kc.) Schenectady transmitter Foundation RED NETWORK BLUE NETWORK Available only at a Group Available only at a Grant of the General Electric Company, is actually Prize by Charge Charge Charge CiltM Per Hr. Per K Hr. Cl^tOf Citift Plr Hr. Per tt "Hr. F,, IA Hr. Charge Che.,,, K'ew York $600.00 $375.00 $234.38 the world with radio the New York 75.00 supplying programs. faculty Boston . . 250.00 156.25 7.66 $600.00 $ $234.38

Hartford . 120.00 75.00 6.88 Benin . 25000 56.25 97.66 Its signals are frequently and regularly heard of law of 120.00 75.00 6.88 Worcester . . . 120.00 75.00 6.88 Springfield 210.00 .11.25 S2.03 in South South Northwest- Portland. Me. 120.00 75.00 6.88 England, Africa, America, Baltimore 190.00 18.75 74.22 Philadelphia . 310.00 193.75 1 1.10 Washinuton 190.00 1J8.75 4.22 New Zealand and Australia. An ern Univer- Rochester .' 200.00 25.00 78.13 increasing Schenectady . . 190.00 118.75 4.22 Buffalo .. .. 200.00 125.00 8.13 Pittsburgh 300.00 87.50 117.19 number of American stations, a dis- 250.00 156.25 7.66 broadcasting sity, Detroit 340.00 Cleveland ..'.'.'...... 250.00 156.25 7.66 212.50 126.56 Detroit 340.00 212.50 1 6.56 including WGY, KDKA, WRNY, WLW, WAAM, Cincinnati '.7T! 250.00 156.25 97.6* Cincinnati 250.00 156.25 7.66 WRAH and WHK are, or soon will be, broad- Chicago 460.00 287.50 179.69 Chicago 460.00 287.50 179.69

Total for Network. 11770.00 $2356.25 $1466.46 Total for Network. . .$2800.00 $1750.00 casting their programs on short wave- 11087.52 HOW MUCH SUPPLEMENTARY CITIES lengths. British, German, and Dutch IT COSTS TO Charae stations are within of range American short- CM,, Per 14 Hr. BROADCAST St. Lotiii .... (82.03 For me in conjvn, wave sets. Short-wave programs are readily Minn. St. Paul 82.03 the Rii or Bint Nttemk* Rate cards are heard at great distances during the summer used in " selling when the program range of most standard time"on the MIDWKSTKKN GROVP broadcast receivers is wavelength very air just as Davenport (190.00 18.75 use DCS Moinei : 190.00 18.75 limited. Several companies are already publishers Omaha 190.00 18.75 rate cards Kansas City 190.00 1875 preparing to meet the demand for short- Oklahoma City-Tuls 190.00 18.75 in selling Dallas Ft. Worth . . 190.00 18.75 wave receivers. "space." The Total for Croup $1140.00 $ 12.501 $445.32 The question may arise whether short- rates in these SOUTHERN OBO :p Louisville $180.00 ) 12.50 $70.31 tables 74.22 wave broadcasting will not replace our show Available only Nashville '... . 190.00 1875 For nte in conjunction witre what at group Mcmphii 190.00 1 18.75 74.22 the Red or Blue Network* present services. A short-wave transmitter exactly Atlanta 190.00 118.75 74.22 it costs to send is for Total for Croup $750.00 $468.75 $292.97 ideal long distance transmission but, a a m progr PACIFIC COAST NETWORK because of fading and the skip distance overtheentire San Francisco $300.00 $187.50 $117.19 at-a,laHt Los Angeles 300.00 187.50 117.19 effect, is of little or no local service. Within United States. Selectively Portland "150.00 3.7S 58.60 mtlh San Fnnfitco ' A Seattle 200.00 125.00 78.1 3 two hundred to six hundred miles of short- large part Spokane 150.00 93.75 58.60 of the charges Total for Network... $1100.00 $687.50 $429.71 wave stations, their signals are usually are consumed B. Basic Rates for other than between 7:00 P. M. 11:00 P. M. Local Time are inaudible but even moderate delivers in periods power the high one-half above rates. " of the counts on Basic of under contract not to exceed one year a strong signal for immense distances cost Rate* for number periods special tele- atton: beyond the dead area. Hence every high Less tkan 25 N phone wires 25 - 4 S* station an exclusive 50 . 99 IS frequency requires con necting 100 . Z99 100 and over channel, placing a definite limit on the the stations 346 RADIO BROADCAST OCTOBER, 192,7

For the time being, it is the only authority tions," says "one of the best known of these four and a half hours of broadcasting time to available to the lawyer handling cases for nuisance stations reported, the first week transmit. One of the important features of the radio was that an broadcasting stations. We hope, for the in February, that it had in a month sold gas company's campaign amount equal to fifty per cent, of the broad- good of radio, that Judge Davis will soon about 45,000 pieces of dress goods, amount- casting expense was spent in newspaper adver- find it necessary to write a revised edition ing to approximately 175,000 yards. tising to call the attention of radio listeners to occasioned by court decisions to the un- Figuring the mileage, this amounts to 99 the feature. It is an excellent example of success- answered questions which he so ably raises. -jV miles of dress the goods." Continuing, ful commercial broadcasting which won its His book establishes article comments on the thoroughly Judge competition which return by the real value of its service, I I I Davis as the American author- this outstanding direct advertising offers to the small The Bureau of Standards is prepared to calibrate ity on the law of radio communication. local merchant. crystal oscillators used in maintaining broadcast- One of the claims made to the Federal ing stations on their assigned frequencies, for a The of Direct Danger Advertising Radio Commission by one of these stations nominal fee. Stations contemplating taking ad- on the Air vantage of this service should first to the was that it lowered the price of goods to the apply Bureau, giving call letters, assigned United States Radio Society has farmer. Refuting this claim, the St. Joseph frequency, type, make and description of the oscillator to sent us its literature, including a newspaper says: be calibrated. This information is required be- THEcode of and for regulations by-laws One of the best cause the Bureau will for known stations , not far from St. not accept calibration local affiliated of the chapters society. By Joseph, recently put on an active sale of cans of instruments which are not so constructed that these local radio following regulations, any smoked salt for use in butchering on the farm. It they will remain in adjustment permanently. organization may become affiliated in the offered two cans of a good quality of smoked salt Ill WHAM, Rochester, New York, which national group, and means are provided for for $2.50, postage prepaid. Orders were accepted will soon have a 5Ooo-watt equipment of the for not less than two latest Milwaukee representation of each chapter in the cans. One Iowa farmer who type, WTMJ, and WJAX, Jack- fell for this national deliberations. In absence of local great bargain was shown the identical sonville, Fla., have been added to one or the product by his local merchant for only a dollar a other of the N. B. C. giving still chapters, a membership can be secured chains_,_ greater can. Another radio was ten of coverage to its J I I The Na- individuals who write Paul A. bargain pounds programs. by may tional prunes for $3.50, of a quality purchasable locally Electric Manufacturers' Association re- Greene, Managing Director of the Society, in one pound packages for twenty-eight cents. cently completed a study of the question at the Bar in Cincinnati Temple Building of the number of hours a week the listener Ohio. uses his radio set. This information has an im- The forwarded the portant on the sale of tubes and main- Society recently The Month In Radio bearing returns from a questionnaire to the Federal tenance accessories. According to the NEMA Radio Commission which emphasized the figures one listener out of a thousand uses his radio about hours out of unpopularity of certain broadcasters per- twenty-two twenty- OBERMEYER of the Consoli- one out blatant four; of a hundred, twenty hours out of mitting advertising, particularly dated Gas of Company New York in- twenty-four; one-tenth of the total more than two well known nuisances in Shenandoah, HENRYforms us that his received company more seven hours a day and four out of five in excess Iowa. The St. Missouri Commercial than letters from its Joseph, 31,000 customers as a result of thirty hours a week, which means five hours a of these sta- of a radio course on which News, writing "advertising homemaking required night, six nights out of seven. The statistics were evidently obtained by making a record of the listening habits of a handful of A TRANSCONTINENTAL the most rabid enthusiasts who could CANADIAN BROADCAST be found. We would particularly like to meet the person who uses his radio For the first time in history, twenty-three receiver hours out of Canadian stations from Halifax to Vancouver twenty-two were hooked up in the Diamond twenty-four. It is quite apparent that broadcasting Mark Jubilee Celebrations of the Dominion. A fea- Twain was right about statis- ture of the broadcast was the program of tics. Editor's Note: Mark Twain said: carillon music from the Peace Tower in the "There are lies, damn lies and statis- Parliament Buildings at Ottawa (in insert, tics." Ill The Canadian radio left). The illustration below shows the con- industry is developing rapidly. There trol room in the Parliament with Buildings are now at least a dozen first class telephones leading to the and tele- telegraph Canadian-made broadcast phone offices. Commander C. P. Edwards, receivers, head of and several factories engaged in the Canadian radio, is at the extreme right manufacture of radio tubes and batteries. Broadcasting has prospered with the backing of such powerful concerns as the Canadian National Railways and the Northern Electric Company. A patent pool, similar to that of the Radio Corporation of America, is licensing a number of first class manu-

facturers. On April i, licensed broadcast receiving stations numbered 134,486, as compared with 92,000 at the end of the previous year. The fees collected from the listener are applied to the elimination of interference and the proper administration of commercial radio telegraphy. Ill Dan-

ish statistics inform us that, on April I, 1927, there were 130,805 radio receivers in that country, almost equally divided between crystal and vacuum tube sets, and an increase of 50,000 over the previous year. I. i I There is a great increase in thedemand for radio receiving sets in Brazil and broadcast enthusiasm is spreading throughout the country with great rapidity. Most of the stations are OCTOBER, 1927 NEWS OF THE PATENT SITUATION 347

A. Victoreen the Radio suit resulted in a decision in favor of the latter. along the seaboard and long range receivers secured by John against the latter The R. C. A. has $200,000 for are consequently in special demand. American Art Company and others; developed already paid rights from that under the which will an receivers are making the greatest headway in the a substantially different device previ- Hopkins patents, prove unless are sustained market. ously judged to infringe. An action was brought unnecessary investment they * West- requesting that Radio Art be adjudged guilty of before the Supreme Court. The LICENSES AND WHAT THEY MEAN contempt but, upon submission of a brief that the inghouse Company secured an injunction against most important patent decision rendered new device was substantially different from that the Kenwood Radio Company in connection with THEduring recent months, which is, however, on which the earlier decree had been granted, the Armstrong's radio patent 1,113,149. still to future was that of Judge Court ordered the to file a new suit. The subject appeal, plaintiff THE COLUMBIA BROADCASTING CHAIN Thacher, favorable to the Radio Corporation case is cited in the interests of those who have Atwater Kent t t t United of against E. J. Edmond & Co., yielded to consent decrees, The ""THE Independent Broadcasters, and an- 1 Andrew jobbers. The decision establishes the validity Eisler Engineering Company of Newark which Major J. White, pioneer has scope of the Alexanderson patent 1,173,079, gen- nounces that it successfully defended itself sports announcer, is a leading official, given out a list of stations which will form its new net- erally known as the tuned radio frequency against the General Electric's suit which sought to work. The station is which is the third patent. The result of this decision has been to prevent it from manufacturing tipless tubes. key WOR, in New exceeded place all concerns making multi-tube sets, not The case was started in October, 1924, and the most popular station York, holding R. C. A. licenses in considerable jeo- final decision is of interest to all vacuum tube only by WEAF and wjz in number of listeners. ? f filed other stations are WEAM and WNAC in New pardy. About twenty-four important concerns manufacturers, f A suit has been The have already secured Radio Corporation licenses by the Balsa Wood Company, Inc against the England; WFBL, WMAK, western New York; and those outside the pale are making strenuous Balsa Laboratories Company, Inc. in connection WCAU and WJAS, Pennsylvania; WADC, WAIU, efforts to secure licenses. So far, no set company with their patent 1,492,982, describing dia- WKRC, Ohio; WCHP, Michigan; WMAQ, Chicago; in of licenses have been granted which do not guaran- phragms for sound reproducing devices. It i i and KMOX, St. Louis. Although, point com- tee a minimum royalty to the R. C. A. of One claim of V. K. Zwory kin's patent 1,634,390, numbers and station standing, the stations the chain are not in the lead, $100,000 a year. Just what the future holds for covering a secrecy system of transmission was prising everywhere doubtful. Alexander- it would not take for small companies is, at the moment, denied because of an earlier patent, long, given good programs, a of the radio Radio dealers are universally demanding ap- son's 1,426,944. Iff The Brandes Prod- such a chain to corner good part audience. paratus which is duly licensed and the position ucts Corporation has petitioned for a writ of of those who cannot, because of small produc- certiorari which may bring the dispute regarding Nothing will help the broadcasting situation is so much as real to the N. B. C. tion, guarantee such substantial royalties the Hopkins patent before the Supreme Court. competition most doubtful. The Radio Corporation could not Originally the Lektophone Corporation of Jersey chains, so that both organizations will conduct and tuck battle for long withstand the adverse criticism which would City sued the Western Electric Company, which a nip program supremacy. result were they to force smaller manufacturers out of business. The object of the patent law is to protect the rights of inventors so that they may derive just compensation for their inventive efforts. The use of patents for restraint of competition, even though patents themselves are an intentional and desirable monopoly, is not supported by public opinion. So long as a concern is willing to recognize inventors' rights and pay royalties it should not be prevented from engaging in competitive business. Dealers are justified in insisting upon licensed apparatus and it appears that the Radio Corporation and its licensees are the only ones who may legally make efficient, high grade radio receivers under present conditions. However, if patents are used in a coercive way to strangle smaller concerns, we doubt that it will result ultimately to the benefit of the patent holders. No one questions that the recent decisions have established definite supremacy of the R. C. A. in the patent situation, but the advantage should not, and probably will not, be used to force independents out of busi-

ness. I if f The Hazeltine Corporation won a vitally important decision against A. H. Grebe & Co. sustaining the Hazeltine patents 1,489,228 and 1,533,858. The distinction between the Rice and Hartley disclosures, upon which Grebe placed principal reliance, and that of Hazeltine, is clearly set forth in the decision. Although it is granted that both Rice and Hartley disclosed principles of neutralization, the superiority of the Hazeltine method, utilizing a capacity feed back of a voltage to neutralize the regenerative effect, is established as an improvement of great im- art. portance to the radio Professor | H. More- croft appeared as an expert for Grebe The Court, in its opinion, quoted an item from the "March of Radio," which Professor Morecroft formerly prepared for RADIO BROADCAST, acknowledging the importance of the Hazeltine disclosure. * I I A decision handed down in the Federal District Court at Baltimore sustained THE RADIO EQUIPMENT ABOARD THE MORRISSEY IN THE FAR NORTH Messrs. Willoughby and Lowell over James Edward Manley, of Marietta, Ohio, is shown before the radio apparatus aboard the Putnam-Baffin Harris Rogers in their patent for a submarine Island expedition. The Morissey, known to the short-wave code world as VOQ has a generator-powered reception system. Rogers claimed prior concep- short-wave transmitter, a battery-powered transmitter using a ux-852 tube (on the top shelf), a short- tion, but and Lowell an- Willoughby clearly and long-wave receiver, and a portable battery-operated transmitter. Signals from VOQ have been him in reduction to ticipated practice. clearly heard at the short-wave laboratory of RADIO BROADCAST and occasional radio dispatches f I f After yielding to a decree pro confesso from the expedition have appeared in the New York Times f ill I -if iC\^t he 192 s an Extra R* F* Stage By JOHN B. BRENNAN

Cascaded Stages Result in STATIONS Variable Interstage Coupling ^,- Carrier, Frequency-^ Sharpness of Tuning but Avoid Provides for EqualAmplification the Cutting Off of Side-Bands Throughout Broadcasting Band

-ANY discussion centering upon the pre- is slightly regenerative and which is set for res- INdominant requirements of a modern receiver, onance with the incoming signal of station B. it will generally be admitted that there are It will be observed that, while a section of the two outstanding things to strive for good qual- curve falls in that part of the space taken up by ity and a high degree of selectivity. Strangely stations A and C, the amplification of the signals enough, these two coveted qualities are diametri- from thest two stations is much below the am- cally opposed to one another difficult of attain- plification of the signal to which the circuit is ment in the combination. tuned. Maximum amplification of signal A is Nowadays, a receiver is judged by its ability to represented by X, the peak of the curve b. It faithfully reproduce music and speech, and this may be said of this circuit that it is highly selec- critical attitude on the part of the listener has tive but it will also be observed that the quality resulted in the setting up of a remarkably high of the signal is impaired due to the fact that all standard so far as the audio channel of the mod- the side-band frequencies, e to f, within the ten- ern receiver is concerned. kilocycle band of the station to which the circuit The other outstanding requirement, that of is tuned, are not amplified equally. The shaded selectivity, represents a problem which did not portion shows how unequal this amplification is exist in the early days of radio. To-day the and indicates the rapid cutting off of the side United States has over six-hundred broadcasting bands. A highly desirable curve would be one stations whereas there were barely a hundred where equal amplification of all the frequencies five years ago. within the band, e to f, is obtained, and where It needs no stretch of the imagination to real- there will be no response obtained to stations in ize that there is no receiver which, in a given adjacent frequency bands. location, can tune-in all six-hundred of these Now, going to the other extreme, in circuits stations. With an exceptionally good receiver, wherein there is no inherent regeneration, and however, listeners may tune-in more stations where the characteristic curve indicates broad- not merely the far-distant stations than with ness of tuning, as in Fig. 2, it will be noted that just a fairly good receiver. Yet, in spite of this, the shaded portion has become greatly reduced there is no advantage gained in such a case unless and therefoie practically an equal amplification the reception is of good enough quality reproduc- of frequencies within the band to which the cir- tion to warrant listening to it. cuit is tuned, is obtained. It will also be noted, To illustrate briefly the difficulties involved, however, that in such a circuit the amplification reference to Fig. i will prove helpful. Here a of signals obtained from adjacent stations, even suppositional case is presented where the vertical though the circuit is not tuned to them, is suffi- rectangular sections represent the ten-kilocycle cient to cause them being heard as a background ------bands several stations whose carrier to the desired It has been determined that occupied by 10 Kc. 10 Kc. 10 Kc. 10 Kc. 10 Kc. signal. are a of where a number of tuned frequencies equally separated by space FREQUENCY slightly broadly stages twenty kilocycles. The curve b represents the are arranged in cascade, each successive stage of a tuning characteristic selective circuit which FIG. I filtering the output of the preceding stage, and OCTOBER, 1927 THE 1928 "HI-Q" 349

.-Carrier Frequency-. production into a practical receiver. It is well known that a three-stage radio- frequency amplifier can be built to give a high degree of amplification and smooth operating characteristics; that is, it will have freedom from self oscillation, etc., if it is desired to work at a single wavelength, say, five- hundred meters. However, where, under these conditions, the circuits are re-tuned to, say, two hundred meters, they will go into violent oscillation and destroy the stability which they formerly possessed. Explained in another way, this means that, due to the fact that radio-frequency amplifier circuits have the tendency to oscillate, this oscillation becoming more pronounced as the wavelength is decreased, a circuit satisfactory for operation at five hundred meters is wholly unsatisfactory for operation at two hundred meters, due to inherent oscillation, unless, of course, some corrective feature, either mechanical or electrical, is incorporated in the circuit to prevent this oscillation and yet at the same time maintain the circuit at its high degree of amplification. It has been recognized that some system of securing uniform amplification at all broadcast frequencies is greatly to be desired and various methods for attaining this end have come into prominence during the last year. These systems in the main can be divided into two classes: (i) The mechanical control of coupling, such as is used in the King "Equamatic," "Hi-Q," and Lord systems and, (2) electrical systems, such as those relying on the function of combinations of capacity, inductance, and resistance the Loftin-White and "Phasatrol" methods, for example. A little calculation will readily show that these systems can be designed to produce a curve approaching the desired straight line indicating uniform amplification shown in Fig. 4. Since the resultant curve from the use of a and is so far removed from a FREQUENCY fixed coupling between primary secondary straight line characteristic, as will be seen by Fig. 4, even remedial systems, FIG. 2 where precautions have been taken to guard against inherent regeneration in the several stages, that the ideal response curve is approximately attained. This is graphically shown in

Fig- 3- From Fig. 2 we have observed that the response curve for a single stage is quite broad. It is reproduced again in Fig. 3 as curve No. i. However, when a second tuned stage, having the same characteristics, is added, the curve obtained is somewhat altered in form. The top of the curve has practically remained the same but its sides have taken a deeper slope, as shown by curve No. 2. In adding a third stage, the curve obtained is similar to the curve No. 3, wherein there is a further constriction of the sides of the curve. The fourth stage confines the curve within limits which very nearly approach the ideal. For those who desire a highly technical discussion on the points just outlined, it is recommended that reference be made to Professor L. A. Hazeltine's paper on the subject, which is contained in the June, 1926, issue of the Proceedings of The Institute of Radio Engineers.

THE NEW "HI-Q" RECEIVER FROM BEHIND THE PANEL The shield walls have been removed for this photograph so THE new Hammarlund "Hi-Q" Six receiver, that it may be clearly seen how all the parts are disposed INfour tuned stages are employed and the final response curve obtained from their use is similar to No. 4 of Fig. 3. In order to secure this result it was necessary to take

I precautions in setting up the four tuned stages to prevent the desired signal 1 being received by any other way than through the antenna into the first tuned stage, and so on, up to the detector stage. Therefore, the necessity for completely shielding each of the stages arose. Also, each of the several tuned stages had to be completely filtered by the use of radio-frequency chokes and bypass condensers so that there were not present any intercoupling effects which would cause unstableness in operation and thereby defeat the purpose of the use of these several stages. Were not the radio-frequency currents confined to their own individual stages by means of chokes and bypass condensers, and also by the individual stage shields, intercoupling effects would undoubtedly be caused either by capacitative coupling from the wiring of the circuits, inductive coupling between the coils of the various tuned circuits, or resistance coupling in the batteries, since one set of batteries is employed to furnish the B potential and its impedance is common to all the tubes. It was realized that all this must be achieved without sacrificing the sensitivity of the circuits, or in other words, their ability to bring in weak signals. This means that the various interstage transformers employed in the tuned circuits must be efficient enough so that weak antenna signals are built up to a strength sufficient to give a good response in the loud speaker considering that two stages of audio-frequency amplification are employed. 10 Kc. 10 Kc It is this desire for sensitivity that complicates the problem of combining these principal featuresof a high degree of selectivity and a high degree of re- 350 RADIO BROADCAST OCTOBER, 1927 though not absolutely perfect, are undoubtedly a step in the right direction. In the Hammarlund "Hi-Q" Six the results obtained by the use of four well designed tuned stages depended not only upon complete isolation of each of the four stages by means of shielding but by a combination of mechanical and electrical systems which, in the end, produced as near as possible the desired straight line of amplification. The mechanical feature consisted of automatically varying the coupling between the several primary and secondary coils by means of a cam located on the shaft of the condensers, so that a variable degree of coupling was obtained to give an equal transfer of energy between primary and secondary regardless of whether the circuits were tuned to two hundred or five hundred meters. By the use of the cam method it is possible to secure the correct degree of coupling at any dial setting due to the fact that the shape of the cam can be predetermined to provide the desired coupling. Since all precautions are taken to prevent feedback by isolating the several tuned stages, through the use of READY FOR THE BATTERIES radio-frequency chokes, bypass condensers, and This illustration shows the condenser employed in the new Six individual stage shields, only the tube capacity clearly gauged arrangement "Hi-Q" of the tubes employed in these stages remains to Uncontrollable new "Hi-Q" Six receiver, it will be noted that cause undesired coup- directly behind the panel there are two metal ling. The electrical means boxes located at either end, between which is a referred to above is ob- central space in which is located the drum dials Equally Good on All Wavelengths-^ tained by the use of "grid controlling the several tuning condensers. The " " - V suppressors r e s i s left-hand box shield is divided into two com- tance units located in partments housing the first and second radio- the grid circuits of these frequency amplifier stages with their associated m condensers. tubes. These "sup- Fixed Variable chokes and bypass In the right-hand grid - pressors" will cancel the Primary Primary box shield, also divided by means of a central Coupling tendency of the tube ca- Coupling wall, are located the third radio-frequency am- pacity to act as a coup- plifier and the detector stages. The two tuning ling agent and to cause condensers in each of these box shields are lo- feed-back. V cated on common shafts which terminate at From the detector grid 200 WAVELENGTH 600 the central space in the drum dials. These dials to the loud is a arc insulated from the shafts by means of insu- speaker FIG. fixed circuit with con- 4 lated coupling units. The following parts are stant audio amplifica- used in building the "Hi-Q" Six: tion. The volume control, situated in the radio- frequency amplification are employed, good tone i Samson Symphonic Transformer $10.00 circuit, regulation of of signals being maintained by the use of high- frequency amplifier permits i Samson Type HW-A} Transformer that the correct transformers. To secure its overall amplification so quality audio-frequency (3-1 Ratio) 5.00 amount of signal can be fed to the detector grid perfect amplification it is necessary that the ad- 4 Hammarlund o.oooj-Mfd. Midline Condensers to produce a volume of signal from the loud vantageous results to be obtained by the use of Hammarlund Six Auto- speaker which is satisfactory t6 the listener. The expensive transformers be not offset by the un- 4 "Hi-Q" Coils control, a filament rheostat which regulates the intelligent use of tubes in the audio amplifier. Couple 4 Hammarlund Type RFC-Sj Radio- voltage applied to the first three radio-frequency In the last or power audio stage either a ux-i 12 Frequency Chokes 8.00 tube filaments, prevents the overload- (cx-i 12) or ux-iyi (cx-3yi) type of tube should amplifier i Hammarlund Illuminated Drum B batteries. ing of the detector, especially during reception be employed with the correct and C Dial 6.00 local stations. Two of audio From the of the from powerful stages accompanying photographs i Sangamo o.ooo25~Mfd. Mica Fixed Condenser .40 i Sangamo o.ooi-Mfd. Mica Fixed Condenser .50 i Pr. of Sangamo Grid Leak Clips .10 i Carter IR-6 "Imp" Rheostat, 6 Ohms 1. 00

i Carter "Imp" Battery Switch . 75

i Durham Metallized Resistor, 2 Megohms .50 3 Parvolt o.5~Mfd. Series A Condenser 3.00 6 Benjamin No. 9040 Sockets . 4.50 3 Eby Engraved Binding Posts 45 2 Amperites No. i-A 2. 2O i Amperite No. 112 I.1O i Yaxley No. 660 Cable Connector and Cable 3.0O

i Hammarlund-Roberts "Hi-Q" Six Foundation Unit (containing drilled and engraved Westing- house Bakelite Micarta panel, completely finished Van Doom steel chassis, four complete heavy aluminum shields extension shafts, screws, cams, rocker arms, all hard- -ClOSj B45*B * wire, nuts and special 2nd. Del. 90 157 ware, required to complete re- A. F. &R.F. V. V- ceiver) CIRCUIT DIAGRAM THE HI-Q SIX Total The wor\ of the artist and interior decorator as well as harmonizing technical receiver design with the decorative the labors of the radio engineer are evident in 1927-28 demands of the home. Modern receivers are not one-year in' radio receivers. This Splitdorf "Abbey" set, designed by vestments because the receiver bought to-day will be up-to- T^oel S. Dunbdr after an o/d-u;or/d jewel case is a six-tube date for some time to come; for this, the engineer is responsi- receiver, priced at $100. This page and those which follow ble and in later issues of this magazine we shall report strikingly demonstrate how the manufacturer is successfully much of his fascinating wor\. 352 OCTOBER, 1927

7yZO l\aaio r\eceiuers

OFTEN it is said that a radio to be FRESHMAN G-4 receiver, fully appreciated by the feminine half of the domestic must be encased Here is a new electrically republic, in operated Freshman receiv- housings which are esthetically as well as technically satis- er, complete and ready to factory. It is natural and that, as radio has operate as delivered. The right become price is $225.00, which in- more an accepted part of the equipment of every home, cludes new RCA a. c. tubes women have had an increasing voice in the selection of the radio receiver. What, then, do the radio manufacturers offer to the prospective purchaser? To be brief, the radio receiver of 1927-28 is a thing of beauty as well as of utility. On these two pages, and on others in this issue, are grouped illustrations of the sets which have come from the manufacturers' THE STEWART- designing laboratories. Vari- WARNER 520 ous makers have grappled The tendency to- with the wards single-control important pro- is again manifest in blem of appearance, this six- lube re- and, as these illus- cei ver. Two tuned and one untuned trations show, stages of r. f., have met it detector, and two transformer-coupled in widely audio stages, com- different prise the circuit. The cabinet is of dull polished walnut veneer. The price, $125.00

BOSCH 66 Another single-control receiver employing six tubes, this one being priced under a hundred dollars. The beauty of the cabinet is a feature but the efficiency of tbe circuit itself has in no way been neglected. The illuminated dial is graduated into both GREBE'S "SYNCHROPHASE" SEVEN kilocycles and arbitrary The five tuned stapes (four r. f. and detector) are numbers tuned by means of a single dial and vernier, the rigidity of the tuning condenser assembly insuring ]>ermanency of the accurate factory ucl j tistment. The receiver has been carefully shielded, while the special coils employed enhance the selectivity and permit maximum amplification. These coils are of the binocular type and are wound with Litz wire

"COMMANDER" Here is a King six- tube completely shielded t. r. f. receiver which makes use of single control tuning. There are three r. f. stages. The loop may be folded into the cabi- This is a six-tube, non oscillating, t. r. f. set, balanced and shielded. net. Price $220.00 "Inductance tuning" is employed, a system which requires no variable condensers and which permits equal amplification throughout the frequency spectrum covered. The price of the receiver is $190.00 OCTOBER, 1927 353 ofneaviiy and CiuUn/

ways. Some of these models achieve their decorative effect through WORKRITE the dignity of utter simplicity; others are notable for the use of This eight-tube receiver has ornament in the treatment of the control elements. The metal all-metal chassis, and complete copper shielding. tuning and control escutcheon is supplied with some There is a single illuminated drum dial control. decoration, slightly reminiscent of that simplicity to be type Price, $160.00 without table found in the grouping of instruments on present day automobile dashboards. Illumination of the control escutcheon is also a feature which has much in common with the instrument panel on the modern motorcar. From the representative models shown on these pages, the house- wife can gain an excellent idea of the appearance of moderate priced radio receivers which are offered to suit her taste as well as that of her husband. Herideasof the necessary limitations of her domestic decorative scheme should b le n d with her husband's technical BELOW opinions. The Kolster 6H consists of a six-tube receiver power cone reproducer, and B socket power unit. Space is provided for either an A socket power device or a storage battery, which is extra. Price, $265.00

THE "WARWICK" In a cabinet of Tudor period. A six- tube SpUtdorf receiver, similar to that shown on page 351. is built in. Price, $275.00 with cone and power-supply unit

ZENITH The Model 17E electric. A single-tube 400- mA. unit supplies the necessary power. The receiver itself employs six tubes. The price is $350.00. Spinet base, $20.00 extra

THE "NAVAJO" Six tubes, shielded, single - control these words describe this new Mo- hawk receiver just

MS I hoy do other prominent receivers of the season, for lliis circuit combination pn'2 models. " The Navajo" sells for $67.50. Equip- ment to adapt it for a. c. operation is obtainable at additional cost

MU-RAD Two t. r. f. stages, detector, and three audio stages are included in tins receiver. The audio stages, all of the doublc-iinpcdmit'c fnrni, give uniform response between 30 and 5000 cycles, according to the manufacturers. Single-control tuning is featured. Price $48.00. In a console, equipped for complete a. c. operation, the receiver sells for $265 354 RADIO BROADCAST OCTOBER, 1927

THE 'BANDBOX'* This is a recent presentation of the Crosley Corporation. It is a six-tube neutrodyne made in two models, for battery or lump- socket operation, is shielded, and has one- dial tuning. The prices are $55 and $65, for battery and a. c. operation respectively

The Neutrodyne Group

A LOOP NEUTRODYNE It is a Freed -Eisemann eight- tube single-control receiver, retailing for $395.00 with a cone loud speaker, as illustrated

THE RADIO- PHONOGRAPH This Stromberg-Carlson mas- terpiece consists of a complete a. c. operated seven-lube single tuning control receiver combined with a modern electric phonograph. A concealed loop obviates the use of outdoor antenna. Price is $1245 completely equipped with cone loud speaker OCTOBER, 1927 THE NEUTRODYNE GROUP 355

FA DA

Three r. f. Hinges, two tuning controls, one-niece steel chassis, aud equalized amplification, are features of the Fada "Special," retail ing at $93.00

f II 1O THE lay radio reader the term "Neutro- dyne" means a type of receiver only a "| well-known type of long standing merit. To the engineer the term signifies much more. It recalls the researches of Professor Louis Hazel- tine of Stevens Institute of Technology; it brings the patent office to his mind; it indicates one of the present group of radio set manufacturers who have availed themselves of Professor Hazeltine's FOR THE "BANDBOX" inventions. This console has been specially For four years, the neutrodyne group, now con- designed for the Crosley "Band- box," illustrated on the left-hand sisting of Amrad, Fada, Freed-Eisemann, Cros- page. The "Bandbox." the chassis ley, Murdock, Workrite, Gilfillan, Howard, of which is completely shielded, be removed from its and have built re- may quickly Garod, Stromberg-Carlson metal cabinet and inserted in the ceivers that were representative of the best work more pretentious console of the best engineers. These receivers have become known for their reliability, their sensitivity, simplicity, and generally excellent service. They need no introduction to the American radio public. Of late, those who read the foreign radio press have noted the large number of times the French, English, Spanish, and German papers have described the neutrodyne, indicating that

Europe is following advances in American radio with great interest. For the coming radio season, the neutrodyne group has been more than busy, as the accompanying photographs will show. In common with other well receiver manufacturers, the THE FADA 7 organized has and time in research for It is optional whether loop group spent money or antenna i.s used with this better radio components, for even greater sim- receiver, which has four of and for greater of stages of r. f. An improve- plicity operation, fidelity ment in the detector circuit reproduction. A glance will show cabinet work reduces the of possibilities that cannot but amuse those who remember overloading. This seven- help tube receiver sells for $185.00 the early days of radio, when a conglomeration of wires and roughly assembled apparatus, frequently boasting no kind of housing whatever, was principally useful in collecting dust.

AMR AD'S "THE WINDSOR" This artistic cabinet houses a very efficient seven-tube neutrodyne chassis. Tuning is accomplished by a single dial and a further adjustment is provided for volume control. Either an antenna or loop may be used and all parts are copper shielded. A tone tiller is incorporated. The price is $195 OCTOBER, 356 RADIO BROADCAST 1927

A MARTI RECEIVER Another electric receiver, this one employing six tubes, three of which constitute the audio channel, resistance coupling being featured. Tuning is ac- THE "MAYFLOWER" complished by means of two dials Here is a five-tube completely a. c. operated receiver by Cleartone, of Cincinnati. Complete with a. c. tubes, loud speaker, and built-in power unit, the "Mayflower" lists at $250.00 ewamror ^^ & J **UOUT&* ^^^^i

The Radio Receiver Powered Directly from the Light Socket is like the Automobile with a Self-Starter Pushing the Button Starts the Machine Models on This Page are Repre- sentative of the Season's A. C. Set Offerings.

TO THE LEFT The well-known Lnftin-White circuit, s x tubes, is employed in the Arbor- 253 receiver. is I lone Model Tuning of a dial , Tomplishccl by means single ilibrated in wavelengths. A Peerless me loud speaker is included, and the ceiver may he used with either bat- eries or socket-power devices. The cabinet is of matched walnut, curly maple and rosewood veneers, and gum- wood. Price. $250.00

A NEW DEPARTURE IN POWER SUPPLY The Day-Fan Electric Company, of Dayton, Ohio, has placed on the market receivers which are powered by motor A. C. RECEIVER generators, all batteries being elimin- AN ECONOMICAL ated. The efficiency of the motor The manufacturers of this receiver, the generator principle of ^transforming Argus Radio Corporation, of New York alternating current to direct current City, state that the cost of operating this has long been recognized, but its appli- receiver is no more than one fifth of a cent cation t the powering of a radio per hour. The receiver is completely a. c. hitherto been 110 batteries or receiver has neglected, Operated, and employs three of so far as receivers commercially avail- chargers. There are six tubes in all. concerned of tuned and able are which are r. f . in a combination untuned stages. The final audio stage em- of ploys a 210 type tube, a plate potential 400 volts being applied to it. Provision is made so that the audio amplifier may be used in conjunction with a phonograph and pick-up device. Price $195.00, less tubes loud speaker OCTOBER, 1927 SERVANTS OF YOUR LIGHT SOCKET 357

LEFT This is a Freed - Eisemann electrically operated receiver, listing at AN ALL-AMERICAN HIBOY $295.00. A neutro- The receiver six tubes, and dyne circuit is used, employs may be obtained either to use the new a. c. and extraordinary tubes or for tubes, batteries or selectivity is claimed ordinary by the manufac- power unite being required in the latter turers case

SPARTON MODEL 62 Everything, with the exception of the loud speaker, is self-contained in this new electee receiver by Sparks- Withington. No batteries are required. The price, $188.00

BUCKINGHAM Here is a receiver which may be used with either batteries or power units. It employs six tubes, three of which are r. f. stages. The single-dial control system employed is a special Buck- ingham patent. The dial is THE CASE CONSOLE illuminated and calibrated An enclosed controlled from the in both kilocycles and de- .oop, front panel, obviates the necessity for an outdoor antenna. The receiver employs grees nine tubes and tuning is accomplished by means of a single dial. It is equipped with a Newcombe-Hawley loud speaker, which has an air column of seventy-two inches. The price of the console is $350.00, less accessories. The receiver is also obtainable for use with a. c. tubes, in which case the list price is $475.00 complete with tubes and ready to operate

ELKAY "SENIOR" Complete a. c. opera- lion with every necessary piece of equipment built in, unified tuning control, "Truphouic audio amplification, to- al copper shielding, six ulx^s thus can this lew Elkay receiver be lescribed. The list price s $195.00. Six McCul- lough a. c. tubes, and one Raytheon BH rectifier, are required as TO THE LEFT extras The electric receiver drawer of McMillan. Chicago. This drawer forms the nucleus of several attractive receivers by McMillan, ranging in price from $260.00 to $325.00. A table cabinet model lists at $170.00 THE NEW RADIOLA 17 A receiver which makes use of the new a. c. tubes in the first five stages and a 171 type tube in the final (second) audio stage. The receiver may therefore be supplied with A jtower from the house lighting circuit without the use of additional equipment. B and C batteries are also eliminated by the useof a suitable power device which is built in. Price $130.00

A NEW CONE The new 100-A cone ? If 'HE super-heterodyne and the tuned radio-frequency circuit, loud speaker priced with or without continue as the foundations at $35.00 regenerative action, ^ of the 1927-28 line of receivers offered by the Radio Corporation of America. A parchment cone, with properly balanced drive for the moderate power of the battery set or again the high power of the socket-power set, likewise continues as the basis of the Radiola loud speaker offerings. Alternating-current operation, with certain refinements particularly by way of rectifier tubes of increased output and better voltage regulation, makes a bid for favor in the higher priced combinations. The Radio Corporation has also added the new a. c. tubes as a means of electrifying even the moderate-priced Radiolas, the ux-227 heater type for the detector socket and the rugged filament ux-226 for all other positions. Starting out with the requirements of the modest home, there is the new Radiola 16, which fulfills the most rigid requirements of sensitivity, selectivity, ample volume, simplified operation, and excellent tone quality when used in combination with the new Radiola loo-A loud speaker. The Radiola 16 is a new uni-control six-tube receiver, embodying the well-known and perfected tuned radio-frequency circuit with three stages of radio-frequency amplification, a detector, and two stages of audio-frequency amplification, and utilizing five ux-aoi-A and one ux-112 tubes. The power tube in the last stage spells ample volume without possibility of distortion due to overloading. The internal construction of this Radiola is extremely rugged. The operation is reduced to one tuning control which can be logged for the station call letters. There is also a volume control, and a filament switch which starts and stops the reception of programs. To simplify the operation still further, the filament rheostats have been dispensed with. Radiola 16 may be operated from batteries or from a socket-power device. The cabinet of this receiver is of mahogany finish, and measures 165" long, 8j" high, and yj" deep. The weight is 145 pounds, and the price, $69.50 less accessories. Next comes the Radiola 17, aimed to produce, fora moderate price, a receiver completely operated from the a. c. house lighting mains. Simplicity of operation and maintenance are the main features of Radiola 17. It has three stages of radio-frequency amplification, a detector, and two stages of audio-frequency amplification. The new ux-226 a. c. tubes are used in the radio-frequency stages and in the first audio-frequency stage, while the new uv-22- a. c. tube is used as a detector. The last audio-frequency stage employs 3171 power tube. The B and C voltages are obtained from a power supply unit built into the set and employing the new high-power ux-28o full-wave rectifier. There are only three controls on this set, one knob for tuning, one for volume control to regulate the output of the receiver, and a power control switch to turn the receiver on or off. Inside this new Radiola 17 is located a switch whereby adjustment may be made for any variation in local line voltages between 105 to 125 volts. The size of the mahogany cabinet is 25^" long, jl" A CUSTOM-HUILT RADIO RECEIVER deep, and 8|" high. The receiver weighs 36^ pounds, and retails for The Radiola 32 combines the well-known RCA and a eight-tube super-heterodyne $ 130.00 without accessories. baflleboard loud speaker in a single cabinet. Since a loop, directionally variable, is built in this receiver, it may be used where facilities for outdoor antenna erection The well-known Radiola 20, with its two stages of radio-frequency are not available although are for antenna and if binding posts provided ground amplification, its regenerative detector, and two stages of audio such are used. All current is obtained into the house by plugging lighting supply. ux-120 The model is obtainable for either a. c. or d. c. operation. Price $895.00 complete frequency, employing the economical ux-igg and dry-cell UK

SIX TUBES AND SINGLE CONTROL The new $69.50 Hadiola 16. This receiver, like the 17 illustrated atop the previous page, also employs three r. f. stages, detector, and two transformer- coupled audio stages, but the tubes are not of the a. c. type. The output audio tube is of the 112 type as opposed to the 171 in the Radiola 17. Tuning is accomplished by means of a single control knob, but there are also a volume-control knob and a filament switch

tubes, continues to occupy its place in the RCA line. This Radiola has proved a popular favorite, and for that reason it has been retained the It now lists for among present offerings. $78.00 less accessories. Likewise with Radiola 26, the six-tube portable super-heterodyne with its self-contained loop, loud speaker, and dry batteries, which has provided vacationists and travelers with satisfactory and convenient radio service, and which retails at 1225.00 complete. Radiola 25, a six-tube super-heterodyne priced at $165.00 with tubes, is also being retained for 1928 offering. Turning to the higher-priced there remain the well-known offerings, THE RADIOLA 20 Radiola 28, or eight-tube and the Radiola loud super-heterodyne, 104 This is not a new season's model but it has been carried over on account in of its speaker, which, combination, provide an exceptionally sensitive popularity. It is a flve-tube t. r. f. receiver with knurled-dial tun- set which be ing. Its price is $78.00 and it may readily be adapted for a. c. operation may completely powered from the a. c. house lighting system. The price of the Radiola 28 is $260.00 with tubes. The 104 loud speaker units cost $275.00 or 1310.00, for a.c. or d.c. operation respectively. Radiola 32, a newcomer to the Radio Corporation's line, with its handsome walnut grained cabinet in period design, consists of an eight-tube super-heterodyne, loop, Radiola 104 loud speaker, and is operated from the house lighting system. It provides maximum radio results in the most compact and attractive form. Certain refinements in design have permitted the inclusion of the powerful 104 loud speaker actually in the same cabinet as the super-heterodyne. The new receiver has a 32 self-contained loop which is turned by means of a knurled dial mounted near the loud speaker grille. Another feature is the small electric light bulb which is concealed in the top of the operating compartment to illuminate the dials and also to serve as a warning indicator when the current is turned on. The power is automatically switched off when the set is closed. The cabinet measures 52" high, 72" wide, and 17!" deep. The list price is 895.00, which is inclusive of all accessories. somewhat A lower-priced model, but likewise characterized by a distinctive cabinet and entirely self-contained equipment, is the Radiola 3O-A, comprising the eight-tube super-heterodyne with the new loo-A loud speaker and an arrangement whereby the set may be powered from the house lighting supply. The Radiola 3O-A measures 42^" high, 29" wide, and and its list is 17!" deep, price $495.00, all the including necessary accessories. Unlike the more expensive Radiola no is 32, loop contained in the cabinet of the 3O-A, antenna and ground connections being provided on the rear. A short indoor antenna is recommended for use with this receiver. Both of the latter, Radiolas, 32 and 3O-A, may be had for alternating current or direct-current operation. Furthermore, the 104 loud speaker unit is now available in a direct-current model, as mentioned above. The new Radiola loo-A loud speaker referred to above is the im- loud proved speaker for use with all receivers, whether they are operating on batteries or with socket-power equipment. The cone itself is of smaller diameter than the well-known 100 type, which it in RADIOLA 30-A replaces and, addition, embodies a newly designed drive that pro- The .-ircuit employed in this new receiver is identically the same as that of the vides increased response with even better tone than its quality prede- "Kudiola" 36, i. e., an eight-tube super-heterodyne and it is operated from the cessor. socket. The The cone is enclosed in an attractive metal case, suggestive of light 30-A retails for considerably less than the 32, however, its list price being $495.00 complete. The differentiating features of the less a mantelpiece clock, with silk screen bezel, the whole finished in expensive being model are: (1) The 100-A cone is employed instead of the more powerful and more dull bronze. This new cone loud speaker measures approximately 15" expensive bailleboard loud speaker, and (2) no loop is supplied. Antenna and ground connections are provided, and for average reception an indoor antenna will x n" and retails for ^35. ordinary be satisfactory 360 OCTOBER, 1927

FOR B AND C VOLTAGES Grebe offers an attractive socket power unit for radio receiving sets of from five to seven tubes. There are three B taps, 180, 90, and 22 volts, and two C values, 40 and 4 volts. Special design features have been applied to obviate "motor boating"

Lond Speakers, Cabinets and Accessories offered by Varioiis A POWER CONE REPRODUCER In addition to the cone loud speaker, this Kolster power assembly comprises Makers Show Definite New a B power device to furnish the necessary voltages to operate any commercial receiver. It is operated from the 60-cycle 110-volt a. c. house supply The price is $150.00 without tubes. Two rectifier tubes (CX-316-B or Trends UX-216-B), a regulator tube, and a power tube (CX-310 or UX-210). are necessary

VALLEYTONE MODEL 52 A Gve-tube receiver to suit the average pocket, its list price being $85.00, less accessories. Tuning is accomplished by means of two dials. A simple switching arrangement built into the set makes the use of a power tube optional

LEFT " The Spinet," a seven- tube balanced receiver by Colin B. Kennedy, Incorporated. There are four r. f. stages but just OIK- tuning control. The linish is of two-tone antique mahogany, and there is ample storage space for power acces- cessories. Price, $195.00

FOR THE SET CONSTRUCTOR Keeping apace with the commercial set manufacturer, the home constructor

of the Radio Master Corporation, Bay City, Michigan OCTOBER, 1927 361

THE BOSCH "NOBATTRY" This attractive unit is designed to tlcliver three B voltages, the taps being labelled ''low." "medium," and "high." The list pries of the device is $ 18.00. Taps on the transformer provide for three separate voltage ranges

All, while Serviceable and of Inter- esting Technical Design Are Made to Harmonize with Their Eventual THE "MINSTREL" A successful antenna receiver is this the Home. operated " seven-tube, single-control. Setting set. Apex The circuit employed is of the Technidyne" variety, one that has become increasingly popular lately, and which makes use of a new form of neutralization. Less accessories, the "Minstrel" lists for $225.00

ABOVE This is the Pfanstiehl Model 30 six-tube receiver. Its chassis is carefully shielded and equipped with flexible cable connections. Price, $105.00

RIGHT The "Baby Grand," by Audiola, Chicago, comes with either an eight-tube or six-tube chassis, the former listing at $275.00 and the latter at $225.00. There are two knobs on each model, one for tuning, and the second for volume control. Individual stage shielding adds to the general efli- ciency of the set. A .-pecinl long air-column loud speaker is built in

DESIGNED FOH A RADIO SET Here is another example of the cabinet makers' efforts to produce a radio cabinet which is in every respect equally as beautiful as the furniture sur- rounding !t. The finish of this particular cabinet is in walnut and maple and it is with a Farrand equipped cone loud speaker. 1 1 is designed to accom- modate all standard makes of radio receivers, and is a product of the M usical Products Distributing Company, New York City. Price $95 00 362 OCTOBER, 1927

B POWER The Kellogg B power unit has the usual three taps, for defector," "medium," and "high," but additional flexibility is obtainable by means of the knobs on the front panel. The detector voltage may be adjusted to any value up to 45, while the medium voltage tap may be set for anything up to 90 volts. The high-voltage tap is for a 171 type tube. Forty dollars is the price of the unit

AN ELLIPTICAL CONE The frame and base of this new Splitdorf cone is of rich antique walnut finish, deeply carved, the result, being a loud speaker which will enhance almost any setting. The elliptical shape of the cone makes possible deep richly resonant tones, the short diameter of the ellipse favoring the high notes, and the long diameter sustaining the deep tones. A combination of design features enables the loud speaker to handle great power. The list price is $35.00

A UNIT THAT SUPPLIES BOTH A AND B CURRENT Unlike many other units designed to supply both A and B current, this one does not use a storage battery in conjunction with a trickle charger. A rectifier and electrolytic filter condenser, combined in one cell, constitute the A unit. There are no tubes to burn out, the only attention necessary being the addition of water every three or four months. This Halktte "AB" is obtainable in two patterns, both with an output of 6 volts, 2 amperes, for the A supply, but one has a B output of 40 mA., 135 volts, while the second gives 55 mA., 180 volts. The prices are $59.50 and $67.50 respectively AN AUTOMATIC CHARGER A charging unit developed by the Westinghpuse Company iis incorporated m this useful Apco device. Full-wave rectification is accomplished by means of a series of special analysis copper discs in the transformer circuit. An automatic relay is combined with the Westinghouse unit so that, -once connected to the set, the charger is spontaneously set in operation when the receiver is not being used. The list price of this Apco unit is $16.50

THREE LOUD SPEAKERS IN DISGUISE first is less than a loud in concealment. A The group of books, in the place, nothing speaker " forty-inch A AND B POWER FROM ONE UNIT serpentine tone chamber winds behind the embossed leather book bindings. This Choral Cabinet" lists Acme, of Cleveland, is responsible for this useful power combin- at $50.00, or $75.00 if the equestrienne bronzes are included. The lamp too, in addition to serving its ation. Included in the unit is a B socket-power device, a 40 obvious purpose, hides an air-column loud speaker. Depending upon the finish, it lists at $35, $50.00, ampere-hour storage battery, trickle charger, and automatic or $60.00. The carved picture frame to the left also conceals a loud speaker, the tone chamber of which control switch. The unit may be obtained for 25- or 60-cycle is a thirty-inch serpentine winding. The hand carved black walnut model lists at $35.00, but other liouse supply, and for sets with varying amounts of tubes, the models are less expensive even as low as $20.00. Manufactured by Frank R. Porter, Washington, prices being between $95.00 and $108.50 District of Columbia Why It Is Desirable to Employ a tails of a New Qlow Tube Which Regulator Tube in B Devices De- Involves Some Novel Features

voltage-regulator tube received its Its small size and low cost permit its ready rather descriptive nickname, "glow tube," use in many cases where the older form of tube THEfrom the performance of some of the early was out of the question. Its silent non-oscillating models which, having an open top cathode, per- operation, its long life, its close control of voltage mitted an observer to see the ionized gas or (a variation of but 3 volts between a condition "glow" in the space between the anode and ca- of no load and full load being allowed), and thode. the use of a third or "keep-alive" element, are This tube is a device which, when connected all features which make it one of the most in- across the go-volt output of a B power-supply teresting developments in the B power-supply unit, will maintain that voltage at a constant field since the introduction of the filamentless value, regardless of any variations in load, full-wave gaseous conduction rectifiers. within reasonable limits, applied to the power The "keep alive" circuit is a most unique ar- unit. Without the use of such a regulator, the rangement of what really amounts to a tube voltage supplied by the device will fall off rapidly within a tube. The inner, or secondary tube, as the current drain is increased. operates without load from a high-voltage point By using a regulator tube, it is possible to of the filter circuit and keeps the gas within the construct a B power unit, the go-volt tap of glass tube ionized at all times. Thus, should the which will, for all practical purposes, deliver voltage across the operating electrodes at any volts to radio receiver whether it time fall below the value to maintain just 90 any RADIO BROADCAST Photograph required has 3 or 10 tubes. In the case of the majority INNER CONSTRUCTION the gas in an ionized state, the potential of the of radio receivers the go-volt tap supplies the third element will be sufficient to maintain The bulb has been removed to show B power for the radio-frequency and first audio ionization. In order to minimize the extra drain the electrodes of the "R" tube stages. In the case of a super-heterodyne, how on the rectifier and filter, a forty-thousand ohm ever, the go-volt tap will also have to supply resistor is employed to limit this parasitic cur- the B power for the intermediate-frequency By JAMES MILLEN rent to approximately three milliamperes. amplifier. Incidentally, as the load drawn by the As a result of the third element and its as- detector tube, in most sets, is substantially the sociated "keep alive" circuit, the high starting same, a suitable resistor with mid-tap may be lower voltage and thus less expensive bypass voltage required by former types of regulator connected across the voltage regulator tube condensers at the various voltage taps. tubes is eliminated. terminals to provide a fixed 45-volt tap. Now, it The first type of voltage regulator tube to The base contacts on the new "R" tube, as also happens that, when the regulator tube is appear on the market was of the two-element it has been named by the manufacturers, the used, variations in load on the 90- and 45-volt type and, like the prototype of most things, had Raytheon Company, are so arranged as to per- taps will have no effect upon the maximum its disadvantages. Different tubes varied con- mit its use in B units and combination power voltage tap of the power unit. The voltage at this siderably in characteristics, some having a amplifier B units designed originally for the ux- point will, however, vary with the load at the working voltage of as low as 70, while others had 874 (cx-374) the original voltage regulator high-voltage tap; but as we know that the usual over 100. Then, the voltage across individual tube placed on the market. When so used, the load to be applied to the high-voltage tap is a tubes would vary quite a bit between conditions third element does not operate. ux-171 or cx-371 type power tube, and that at of no load and full load. Another fault was that, While the tube may be added, along with suit- 180 volts this tube will draw a plate current of should the power unit be heavily loaded for any able resistors, to some of the heavy-duty type 20 mA., we can so design our power unit to reason, the tube would cease to glow and, before B power units now on the market which have supply exactly 20 mA. at 180 volts. again becoming operative, the voltage across it not been specially designed for use with a glow The result is a fixed-voltage power device would have to rise to a rather high value, which tube, it cannot be used with the average run which will supply 45, 90, and 180 volts to almost eliminated the possibility of partially providing of socket power-supply units due to the extra any standard radio receiver. Fixed-voltage con- for the initial cost of the tube by the use of low- load it imposes upon the rectifier and filter trol, however, is but one of the many points of voltage bypass condensers. chokes. Likewise, in home constructing a power merit of a "glow-tube" equipped power-supply But perhaps the most serious objection to unit employing the "R" tube, chokes capable unit. former voltage regulator tubes was the tendency of handling at least 85 milliamperes of direct The action of the tube in holding the voltage of many of them to oscillate and introduce noise current without core saturation must be selected. of the output circuit constant serves also to into the output circuit of the power unit. The At this time we are familiar with only two use eliminate the small ripples which may be pres- of a power unit equipped with such a tube chokes on the market that meet this condition often ent as a result of incomplete filtering, and thus would introduce sufficient noise into the the National and the Amertran. The rectifier makes possible a reduction in the capacity, and loud speaker to interfere with satisfactory re- tube should be of the 85- and not the 6o-mA. therefore the expense, of the final filter conden- ception. But now, after several years of research type. The power transformer should have a and ser. In fact, the tube, when in operation, has experimental work, a new form of voltage double high-voltage secondary with a voltage many properties in common with a large fixed regulator has been perfected. of 300 across each side. condenser. One of these properties is extremely low a.c. impedance which, when combined with its instantaneous response as a voltage regulator, entirely eliminates the annoying "motor- boating" effect which generally results when an attempt is made to use one of the ordinary B power units with many forms of amplifiers. A further advantage accruing from the construction of a B power unit employing a voltage regulator tube is an economical one. With its many electrical advantages, it need cost no more than that of a high-grade power unit of the conventional type. In the first place, the use of the "glow tube" results in a saving of OB- the number of high-voltage filter condensers required usually an expensive item. In the A B-DEVICE WITH THE NEW "R" TUBE second it the use of fewer and place, permits The new Raytheon tube has five leads, the fifth connecting to the metal pin in the tube base KAR/\5 5UAMATIC

RADIO BROADCAST Photograph A SYMMETRICAL FRONT PANEL REWARDS THE CONSTRUCTOR OF THE 1928 "EQUAMATIC" RECEIVER

Automatic Variation of Coupling between Primaries and Secondaries of Coil Units Provides for Equal Amplification Throughout Broadcasting Band Simplicity of Control Is Marked Improvement over Earlier Model By JULIAN KAY

NE of the most difficult disad- The Facts About This Receive constant amplification over the entire vantages to overcome in ampli- r broadcasting frequency band. fying high frequencies by means Type of CircuitI Tuned radio-frequency. The "Equamatic" system is not new 1 tubes. Five. of r. f. ioi-A of successive tuned stages is the apparent Dumber of Two stages with to the readers of RADIO BROADCAST, for tubes; detector, discrimination of the amplifier against (JOI-A) using special it was described in several issues of this detector tube; first audio stage, IOI-A the lower radio frequencies. The longer- magazine in 1926 by Zeh Bouck. The (JOI-A); second audio stage, 112 (311) wave stations on the average tuned r.f. receiver itself differs somewhat in vari- or other semi-power tube. set come in comparatively poorly, while ous ways from the set of last year; in Features Maximum r. f. gain obtained by use | there is no end of on the each of these several it is better amplification of special automatic variable coupling | respects shorter-wave stations. Any one who has arrangement. Only two tuning con- than last year's set. In the first place, it will trols there are three tuned operated one of these sets vouch for although ( is a two-dialed receiver, an obvious ad- Switch for one or two a. f. this fact, and any service man who must stages. I vantage over the three-dial receiver pre- answer questions from his clients will stages. viously described. The change is accom- 1500 kc. to 500 kc. (200-600 meters). agree that his main difficulty is in ex- plished by means of a lever pantograph plaining why such-and-such a set will arrangement which permanently con- not get KSD or KYW, longer-wave sta- nects together the variable tuning capac- tions, while it will get less powerful and often above. It is the outgrowth of a popular receiver ities of the second radio-frequency amplifier and " more distant shorter wavelength stations. of last year, the Karas Equamatic," and em- the detector circuits. Additional means have been Now the reason for this lack of pep on the ploys a mechanical means of maintaining "con- taken to insure maximum amplification and longer waves is not difficult to explain. When- stant coupling" between the output of one tuned complete stability, partly by filtering the radio- ever a tube has inductance in its plate and grid radio-frequency stage and the input of the next frequency circuits with chokes and condensers circuits, that tube does its best to regenerate, stage. This "constant coupling" means that and also by a new means of partially neutralizing and if a certain balance between these in- the plate circuit of the preceding tube will have the inter-electrode capacity of the tube the ductances is maintained, this regeneration will just enough inductance in it to transfer maximum capacity that causes regeneration. In addition, break into open oscillation. Squeals, howls, and energy at each frequency to which the circuit is an output filter has been added to the layout general instability result. This inductance is, tuned, but not enough inductance to make it so that a power tube can be used without the d.c. however, necessary to transfer energy from one oscillate. As the condensers are varied, the coup- plate current of this tube going through the wind- circuit to another. The tendency to oscillate in- ling is varied simultaneously, and in the proper ings of the loud speaker. creases as the frequency increases and as the proportion, to prevent troublesome oscillations, The receiver, then, consists of a two-stage amount of inductance increases, and more in- but at the same time to maintain more or less radio-frequency amplifierwith constant gain over ductance is needed to transfer the entire broadcasting band, a energy on the lower frequencies grid leak and condenser detec- than on the high; but with this tor, a conventional two-stage maximum amount of inductance transformer-coupled amplifier, the set will probably be uncon- and an output filter. The antenna trollable on shorter waves. or first-stage amplifier is tuned Thus, sets that get the longer- with the left-hand dial, while the wave stations with maximum r.f. second dial takes care of the other amplification cannot be held down two tuned circuits, which are on the shorter waves; those that made to tune exactly alike. Ease are especially stable on short of adjustment is secured by waves are as quiet as the pro- means of the ganged condenser verbial grave for DX on the longer arrangement without apparent waves. loss in either selectivity or sensi- The receiver shown in the pho- tivity over the three-dial model tographs in this article does not FIG. I described in RADIO BROADCAST suffer from the faults enumerated Circuit diagram of the new "Equamatic" receiver for October, 1926. OCTOBER, 1927 THE 1928 "EQUAMATIC" RECEIVER 365

Left. When the condenser is tuned for maximum wavelength, the coil should be coupled in this manner, allowing the largest transfer- ence of energy. Right. Minimum coupling, for shortest wavelength

RADIO BRUADCASI Phutograph RADIO BROADCAST Photograph FIG. 2 FIG. 3

Cushion Sockets . . A special Yaxley interstage and filament Five Benjamin 3.75 The receiver can now be connected to its A, B,

C 5 , Cr, Samson Mica switch is employed to cut out the final audio Neutralizing and C batteries. The diagram shows that the Condensers ..."... 3.50 amplifier when desired, automatically shutting r.f. tubes are run with 90 volts on the plate. A CT, Cs Sangamo o.oooi-Mfd. Fixed off the filament current to the tube in this circuit. bias of about one volt is placed on the Condensers .80 negative Thus the loud can be on local of the r.f. tubes, and is obtained through speaker operated Cs Sangamo o.oo6-Mfd. Fixed Con- grid stations from the first audio and when the across the filament rheostat. The C bias amplifier, denser .85 drop more is the second for the audio tubes is fixed in the receiver, volume desired, amplifier Cio, CH Sangamo o.ooi-Mfd. Fixed battery set shows. may be thrown into the circuit. Condensers i .00 as the photograph of the complete The final audio tube should be a ux-i 12 (cx-3 12), A list of parts for the receiver follows: The circuit diagram of the receiver is shown in with about 135 to 150 volts on the plate and a Karas 28 Trans- wire Ti, T2 , Type Audio Fig. i, and panel and sub-panel layouts are grid bias of negative 9. A separate ground formers $16.00 also given in this article. Attention is called to can be run to the set, or the A battery may be Le Karas Filter 8.00 Output .... the two neutralizing condensers connected from grounded instead. Either method of getting the Ci, Q>, C3 Karas Type 17 0.00037- the plate of each radio-frequency tube to the receiver grounded will be satisfactory. Mfd. Variable Condensers . . . 15-75 lower end of each input inductance, providing an This receiver is inherently easier to adjust LI, Li, LS Karas "Equamatic" Coils. 12.00 additional means of stabilizing the receiver at for a non-oscillating condition than a bridge Two Karas Micrometric Dials o-ioo . 7.00 The show how where an accurate and exact balance is. Three Karas Sub-Panel Brackets . .70 high frequencies. photographs circuit, Karas Control System, Including Com- simply the receiver goes together. The sub-panel, necessary. The three tuning condensers are plete Hardware 3.00 provided by the Formica Company, has three turned to the longest wave setting, or 100 on 1-4, Ls Karas or Samson loo-Milli- white lines engraved in it to show the position dial, and then, as the wavelength is slowly de- henry R. F. Chokes 5.00 of the three tuning coils, which can be easily creased again, with both the dials being turned Formica 7" X24" Engraved Front Panel 5.68 adjusted since they are attached to the sub-panel in synchronism, a point will be found where the Formica 9" x 23" Drilled Sub-Panel . 6.00 means of machine screws. set breaks into oscillation. Then the neutralizing Ri Carter lo-Ohm Rheostat (Gold by After the receiver is wired, the next condensers should be screwed down slightly until . properly Arrow) i oo Rj Carter zo-Ohm Rheostat (Gold step is to adjust the variable primary coils, which oscillation stops, and the wavelength decreased Arrow) i.oo are rotated when the condensers are turned. The again by rotating the condenser dial. This proc- Sw. Yaxley No. 69-8 Interstage condensers should be turned until the plates ess should be repeated until the shortest-wave- Switch (Gold) 1.25 completely interleave, and in this position the length adjustment, zero on the dials, is reached. J Carter No. 10 . . . .20 Tip Jacks primary coils should be parallel to the larger In actual practice, it will be found that no oscil- Ct Sangamo o.ooo25-Mfd. Fixed Con- secondary inductance, as shown in Fig. 2. They lation will occur if the condensers are adjusted denser with Clips .50 should be fixed in this position. Under these con- properly, and at the same time it will be dis- Ra Durham 2-Meg. Grid Leak . . .45 the loosest will exist between covered that the stations will not R< lA Amperite i.io ditions, coupling longer-wave and at the have lost of their a Rt 112 Amperite 1 . 10 primary secondary highest frequencies, any original strength, pheno- Yaxley Cable Plug 3.00 as shown in Fig. 3. menon that few balanced receivers possess.

Hole No. 1 No, 18 Or Holes No. 2 to 6 Tapped 8-32 Holes 74. 8V Drill 9 to 14 No. 26 Drill & C's'k. fof 6 32 Screw

& white filled LinesJ A,B,&C Engraved A

A SUB-PANEL TEMPLATE FOR THE 1Q28 "EQUAMATIC" RECEIVER 366 RADIO BROADCAST OCTOBER, 1927

The builder of this new "Equamatic" receiver should have no difficulty in making a No. li2-VD,.;i Holes No. 344- VDrill Hole No. 7 one hundred cent, workable set at the first Holes -VC per - Holes No. 5,6.4 8 No. 26 Drill 4 Csk. (or 632 Screw trial. The parts have been so placed that inter- action between circuits, which ordinarily is a 1 __t _._Aj difficult problem with which to cope, is minim- ized, and the progressively increasing coupling between circuits at the longer wavelengths provides the proper interstage energy transfer. The

first "Equamatic" coil, which transfers energy Volume 1st Slage Detktor 1 Off 2nd. S from the antenna circuit to the receiver proper, -Q-

be to have a different U . may arranged slightly I- %J~ 2W- 6^- ** i*-.*!--" 4- k 24' -W'l'Wj rate of change of coupling if desired if the user wishes somewhat greater selectivity for exam- FRONT PANEL DRILLING INSTRUCTIONS ple. In this case, the coupling at the lowest frequency may be decreased by making the prim- cation factor will have an actual advantage ground potential. The output filter, which is new ary and secondary not parallel, but turned at a over the 171 type, and louder signals will be in this year's model, consists of a conventional slight angle. In general, however, the greatest obtained. Thus weaker stations will operate a choke and condenser combination and, as may be coupling should be used at all times, and a loud speaker. seen in an accompanying photograph, is built somewhat smaller antenna used if greater selec- Now that we have outlined the electrical fea- into a round metal box similar to the audio trans- " tivity is desired. tures of this new Equamatic" circuit, there are formers. The latter, incidentally, have exception- The condensers which tune this receiver, if several mechanical notes which should be ally high primary inductance, which is necessary those specified are used, have a straight fre- brought to the attention of the home construc- for full reproduction of low audio frequencies. quency-line character- Their turns ratio is istic, a decided advan- about 2.5 to i. tage now that trans- In all receivers em- mitting stations are ploying two or more again operating on tuned circuits, tuning ten-kilocycle separa- is inherently sharp, tions. If it is desired making necessary to use a 171 type some form of fine ad- tube, somewhat differ- justment. In this re- ent connections must ceiver the designers be made to the last have used the famil- two tubes and their iar Karas dials which, plate circuits. As wired with their 63 to i according to Fig. I, RADIO BROADCAST Photograph reduction, and their the last two tubes get exceptionally smooth Here is the which is now Note the three-dial the same B voltage, 1927 "Equamatic" improved. tuning action, make tuning this being necessary a joy. The writer on account of the interstage switch. Additional tor. The condensers, for instance, are new, in found that the receiver tuned with great ease prongs would be necessary if the two audio that they are equipped with removable shafts although it was sharp enough to please a criti- tubes needed different B voltages. In the so that insulated ones may be substituted for cal fan. vicinity of broadcasting stations, however, the metal ones, and complete insulation from All in all, the home constructor should find the field strength is sufficient to give all the hand capacity thereby realized. In some circuits this receiver a well designed, simple-to-con- volume one can desire by using a semi-power this is important; in the present receiver, hand struct, high-quality set, and in building one, he tube of the 112 type. At some distance from capacity will not be apparent owing] to the fact will be equipping himself with a receiver of stations, the 112 tube with its greater amplifi- that the rotor plates of the condensers are at which he can be deservedly proud.

RADIO BROADCAST Photograph

LOOKING DOWN ON THE 1928 "EQUAMATIC" The arrangement of parts is neat and efficient. Note the lever pantograph arrangement which makes possible simultaneous adjustment of the second and third tuned circuits A New Principle R Tutiitii

The "Octa-Monic" System Resonates the Second Harmonic In-

stead of the More Usual Fundamental Increasing the Selectivity By DAVID GRIMES

TO the present time there have been plification to the high-pitched tones in an effort impedance exists in the plate circuit. This curved just three fundamental radio circuits, to provide for the reduction in side-bands. characteristic leads to distortion which is an- UPand of radio receiver has em- The came into use other name for the every type super-heterodyne general generation of harmonics. In variation of these three because of its selective its ployed some arrange- mainly properties and the plate circuit of the average r. f. amplifier is ments. First, there was the regenerative system; extreme sensitivity, permitting loop operation. only a small impedance, therefore in this circuit next radio-frequency amplification was devel- But the side-band limitation so characteristic exist the second harmonic as well as the funda- the and of a selective tuned set oped; and last, War Major Armstrong really radio-frequency mental image of what occurs in the grid circuit. produced the super-heterodyne. became very noticeable in super-heterodyne It is from this second harmonic that the "Octa- is a which increased circuits intermediate Regeneration principle by employing low-frequency Monic" gets its name. The idea of securing be transformers. Here the and minus signals may obtained by a properly phased plus jooo-cycle increased selectivity, not through the use of feed-back variation or reenforcement of the incoming which must pass through to insure additional circuits, but by the use of an inherent signals. When radio broadcasting first became good tone quality is a very large percentage of tube characteristic, is believed to be new. in the of circuit the intermediate carrier wave of or popular 1922, regenerative type 30,000 50,000 Reference to Fig. i shows the familiar grid- was generally used. The feed-back action made cycles. The resonant curve must therefore be voltage plate-current characteristic of a standard the receiver sensitive for distant which somewhat offsets the very reception quite broad, very vacuum tube. The curve follows a square law, and selective at the very particular frequency and in doing such, causes some interesting re- for which receiver the was tuned. As the number sults. 1 1 is desirable when using such a tube for an of stations and two or more increased, powerful amplifier to operate the grid voltage on a rela- local stations became established in of many tively straight part the curve so that fairly the receiver ceased communities, regenerative undistorted amplification will result. For perfect to satisfaction because of its broadness of give amplification, this curve should be a straight line. tuning. Near-by locals could not, therefore, be The very fact that it is not, however, makes the tuned out. The necessity for extra selectivity was vacuum tube a valuable device, as the non-linear met sets with tuned by radio-frequency amplifi- performance permits its use as a modulator, cation. But the standard two-stage tuned radio- oscillator, detector, and a harmonic generator. sets soon became frequency inadequate because It is its use in this last capacity that is least inherent resistances in the vacuum tubes and understood and least employed. associated circuits limited the ultimate select- Now, if a special negative C bias is placed on to be obtained therefrom. to off- ivity Attempts such a vacuum tube so that the grid variations set these resistances feed-back circuits take about such by place some point as A in Fig. i, have been somewhat successful in the increasing the conditions will be favorable for the genera- selectivity but in nearly every case the audio tion of second harmonics. Such harmonics are has suffered. The Inverse quality RGS Duplex, always the result of unequal amplification in the described in the and January, February, March, two halves of a carrier wave. By operating at issues of RADIO a 1927 BROADCAST, employed point A it will be seen that each positive half tuned circuit with an automatic radio-frequency of the carrier wave is amplified to a greater negative resistance circuit which greatly in- extent than each negative half. Such an unbal- creased the selectivity at all wavelengths. The anced carried wave may be resolved into a limiting factor was the tone quality, however, as balanced carrier wave of the same fundamental tends to cut the side-bands a super-selectivity on frequency plus another carrier wave of twice the carrier wave, thus the sacrificing high pitch frequency. This is graphically illustrated in Fig. audio tones. The selectivity of the RGS Inverse 2 and is known as Fourier's DAVID GRIMES Theorem. Briefly carried to such a Duplex was point that a special stated, it is as follows: audio circuit was employed to give extra am- If have advantage which the super-heterodyne possesses. we any single valued periodic curve, that one one value Recently, super-heterodynes using higher inter- is, having only of the ordinate to one value of the abscissa, and itself mediate carriers than the broadcast frequencies repeating at intervals, no matter how have been introduced to overcome the above regular then, irregular the curve be, provided it does not exhibit detriment. may

It is easy to see from this discussion that there I , is a real need for a new type of super-selective circuit that overcomes the side band limitation. With this thought in n ind, a series of tests has been conducted during the last few months, which has resulted in the development of the "Octa-Monic" principle. This is a new system for obtaining a higher degree of selectivity and follows from the considerations below. It had long been realized that selectivity was a geometric function and that placing one tuning circuit after another created the geometric conditions. Naturally, every geometric function occurring in radio was then investigated with a view to employing that feature for selectivity. One of the most promising was the generation of second harmonics and it is this that forms the basis of the new RGS "Octa-Monic" receiver. It is well known that a vacuum tube has a FIG. I curved characteristic unless a verv high externil FIG. 2 368 RADIO BROADCAST OCTOBER, 1927 discontinuities, it is always possible to roughly drawn, no attempt has been imitate this curve exactly by adding made to show relative amplitude the ordinates of superimposed simple only relative sharpness. In fact, quite periodic or sine curves of suitable amp- a bit of energy is sacrificed in securing litude and phase difference, having the second harmonic component. This wavelengths which are in the integer sacrifice is more than because relation to each other. justified of the real selectivity obtained, and Curve C in Fig. 2 shows the un- after all, amplification can always be balanced carrier wave in the plate cir- added to a receiver. The additional cuit of the tube operated at point A on amplification is easily added by the the characteristic curve in Fig. i. arrangements shown in Fig. 5, where Curve C is the equivalent of Curves one stage of radio frequency is placed A and B in Fig. 2. Curve A is the ahead of the harmonic generator tube. fundamental carrier wave similar to This additional stage does not need the one impressed on the grid of the to be particularly selective as the tube. Curve B is the second harmonic second harmonic principle gives all of wave. this necessary. For this reason, the None of the graphic representations additional tube has been called a coup-

1 pertaining to the second harmonic re- ling or amplifying stage the cir- veal the secret of selectivity. They cuits being designed primarily for am- merely indicate that such a second plification and not for selectivity. Its harmonic is The mathemat- circuit is to the present. FTC. 3 input closely coupled ical equation outlining the perform- antenna to give maximum energy pick- ance of the tube, however, does tell up with which to start. In order to car- is shown in Here the antenna some idea real offered the story. The equation for the unbalanced attempt Fig. 4. gain of the improvement by is is to the tuned of the the rier wave shown by Curve C in Fig. 2 as coupled directly input "Octa-Monic" as compared with tuned radio follows: harmonic generating tube. The grid is tuned to frequency, reference is made to Fig. 6. This shows the fundamental frequency of the broadcast the schematic arrangement of a standard two- ? station to be received. The second harmonics tuned receiver with the C = 2d ( + Eg + e ) e sin pt + cos (2 pt + X) stage radio-frequency are set up in the plate circuit where there is a resonant curves of the various parts of the circuit

tuned whose condenser beneath and numbered to Curve I The first part of the equation represents curve transformer, tuning correspond. resonates the at the second harmonic shows the of in the of the A in Fig. 2 the fundamental carrier. The second secondary sharpness tuning grid are to audio fre- first tube. Curve 2 indicates that the fundamen- part of the equation represents Curve B in Fig. 2 frequency. Signals changed the second harmonic component. Now it will be noted that this second harmonic cemponent is proportional to the square of the Detector Tube input voltage, e, and it is this squared function which gives the geometric requirement for selectivity. Reference is here made to Fig. 3, which shows a harmonic generator tube with the grid circuit tuned to some frequency, F, in the broadcast band. The resonant curve of this tuned input circuit is shown at A. Now the second harmonic currents, 2F, in the plate circuit of this tube, are proportional to the square of the input voltages on the grid. As the incoming frequencies are varied, slightly, from the true resonant value of the circuit, the voltages on the grid fall off to curve A. As the has de- according voltage To Audio creased from its maximum, y, to the half way point at x, due to a change in frequency, a, the second harmonic current decrease is much more rapid and abrupt than in the case of the funda- quencies in the standard detector tube in the tal currents in the plate circuit of the first tube mental current, resulting in a very sharp resonant same manner as any other circuit. Selectivity follow the same resonant curve. Of course, the curve in the plate circuit of the harmonic generat- superior to that obtained by a two-stage tuned energy is greater in the plate circuit but the ing tube. In these figures the fundamental and radio-frequency system was noted, although the curves have been drawn to the same scale for the second harmonic have been plotted so that they sensitivity of the arrangement was much less. purposes of comparison. Curve 3 shows a gain have equal maximum amplitudes to show the This would obviously be so because no ampli- in selectivity through the addition of the second relative sharpness of resonance. fication is present in Fig. 4, and because the tuned circuit, while Curve 5 shows the final The next step was to incorporate such a prin- amplitude of the harmonic is less than that of the gain in selectivity through the employment of ciple into a working receiving circuit. The first fundamental. In all of these diagrams, which are the 3rd tuned circuit. It can be seen that only

R.F. Coupling Tube Harmonic Generator Detector

To Audio

FIG. 5 369 OCTOBER, 1927 BOOK REVIEW

band of the carrier frequency plus and minus 5000 cycles to- insure good tone quality and 10,000 cycles variation is a much smaller percentage of the second harmonic currents than of the broadcast frequencies. For example, at 1000 kc. a io,ooo-band represents i per cent, while in the second harmonic circuit this 10 kc. band is only 0.5 per cent, of 2000 kc. In this unique way a high degree of selectivity has been secured with Audio To a faithfulness of tone quality that is remarkable. This RGS "Octa-Monic" arrangement is a fundamentally new development. The existence and generation of second harmonics has long been known, but the application of these currents to the selectivity problem is a new feature. It has created a fourth and distinct of radio FIG. 6 type circuit. The next article in the series will discuss this be and will contain the tuning circuits offer any selectivity whatso- circuit the resonant peak may much sharper interesting development plenty than at broadcast without of information in connection with the ever. Fig. 7 shows the schematic sketch of the frequencies harming building "Octa-Monic" system and the associated re- quality. A tuned circuit must be able to pass a of the RGS receiver. sonant curves beneath the several circuits involved. Curve i indicates the sharpness of tuning in the grid circuit of the harmonic generator. This has the same shape as the first tuning circuit in the system. In the plate circuit the second harmonic currents follow the resonant

Curve 2, and the harmonic tuning circuit in the input to the detector still further sharpen this up to resonant Curve 3. This resonant curve is similar in shape to the tuning curve No. 5, in the system. The resonant curves in Fig. 7 are drawn on the same scale for the sake of comparison. It must be remembered that Curve 2 representing To Audio the second harmonic selectivity has much less energy in it than Curve i. It would seem, offhand, that this excessive selectivity in the "Octa-Monic" would raise havoc with the side-bands, as is the case in tuned radio-frequency circuits. The very harmonic currents themselves, however, offer the solution. At the high existing in the harmonic frequencies FIG. 7

merchan- The reason for the fundamental of Selling It by Radio been a broadcaster, advertising man, similarity dising consultant, and writer; and incidentally station programs is shrewdly analyzed in the Using Radio in Sales Promotion: By Ed- he is, among other things, a Contributing Editor second chapter. Almost all of them are planned gar H. Felix. Published by McGraw- of RADIO BROADCAST. to appeal to all tastes, thus including the largest Hill Book Co., Inc., New York City. 386 The author starts with a resume of the seven- possible audience. Artistic standards, not fun- pages. Price, $5.00. year history of the broadcasting art, and in his damental program appeal, are the variable first chapter he sounds a note which recurs quantity. Almost all the stations are shooting IS not without a touch of embarrassment throughout the book; broadcasting is a medium, at the same target, but with guns of different IT calibre. that I prepare to review this pioneer work on not for forthright advertising, but for securing the subject of broadcasting as an aid to mer- the good will of the consuming public. Radio re- In the chapter on "Building a Broadcasting chandising. The author has written in kindly ceivers are purchased for entertainment and Station" and that on "The Broadcasting Sta- terms of my own masterpieces on various occa- instruction. A trade name, a brief slogan, a very tion" near the end of the work, Felix discusses sions, and transported me over the highways in few words of product description, may be mixed technical aspects of the broadcast situation, such his private fleet of Minerva sedans. In finding with the entertainment and instruction, but Fe- as wavelength congestion, station organization, his work good, therefore, I lay myself open to lix always has his eye fixed on a psychological operation, and the like. He does not attempt to the charge of log-rolling. To preserve my honor, dividing line which cannot be crossed with either tell the reader how to build a station, and in I should like to pan the author and his treatise, propriety or safety. Broadcasting is primarily fact advises him against trying it. What he does but he has done too effective a job. The book is for the advertiser who can afford to wait, who is to outline the formidable problems which original, informing, and vigorous. Its blemishes has the resources to build up public good will, must be faced, and the general economics of the are slight and will probably be visible only to who is not too short either in his bank account situation. In discussing operation he describes the reviewers. or his patience. As for the little fellow who de- the functions of the various members of the Using Radio in Sales Promotion is written mands sales tomorrow morning Felix advises staff and the principles underlying their work. primarily for advertisers; it aims to instruct the him to take his money to the local newspaper. In many other chapters, as in those on "Po- man who contemplates spending a part of his The Midwestern broadcasting station which I tential Audiences of Broadcasting Stations" and advertising appropriation for time on the air. am reliably informed at this writing, is selling "Selecting a Commercial Broadcasting Feature," Throughout it names names, gives examples over the air by direct description, gasoline, Felix enters the engineering branch, and, deal- drawn from experience, and answers the ques- mattresses, gloves, overalls, radio apparatus, ing with field strengths and microphone char- tions which must occur to the man who signs cancer and rupture cures, and a 5O-cent chicken acteristics, he exhibits only minor lapses from " the checks. What interests the client interests dinner, is outside of Felix's pale. He (the broad- accuracy. the professional broadcaster equally, whether caster) does not earn the right to inflict selling Using Radio in Sales Promotion is written in he (or she) owns, manages, operates, sells time, propaganda in the midst of a broadcasting enter- a business-like, straightforward style, but it is writes publicity, or performs in the studio. tainment any more than an agreeable week-end not devoid of sharp hits and epigrams. I quote a Professional advertising men are in a similar guest may suddenly launch into an insurance few: "An expert is usually one who has not yet position. So there is Felix's potential audience solicitation at Sunday dinner," is the attitude learned enough of a subject to be aware of his " in these groups and their fringes. He is quali- expressed and implied on every other page of ignorance." Broadcasting is free and there- fied to speak to all of them, for he has himself Using Radio in Sales Promotion. fore freely criticised." CARL DREHER. 370 RADIO BROADCAST OCTOBER, 1927

THE A. K. CONE The new Atwater Kent Model E employs a novel method of cone suspension, permitting satisfactory re- spouse to minute vibra- tions. Price $30.00 AN "ACME" OFFERING THE CROSLEY This novel loud speaker makes use MUSICONE of a double cone arrangement, good A baflfleboard effect is ob- amplification of the low notes being tained the use of the tilt- possible on account of the free edge by table surface. Price 50 A DEPARTURE IN LOUD SPEAKERS cones. The manufacturers state $27. The Rola Model 20 combines a baffleboard loud that an output device is not necessary with this loud Price speaker of remarkable efficiency with floor speaker. $25.00 screen measuring three feet high by two feel wide. The price is $85

THE BOSCH 'LIBRARY AMBATONE"

TRIMM " CONCERTO' A $10.00 cone, fourteen inches in diameter. The seven teen -inch cone retails for $16.00 OPERADIO The "* Junior" model has a 30-inch exponential air column while the "Senior" has one of 54-inches, The prices are $15.00 and $25.00

IN GOTHIC DESIGN A beautiful and well- proportioned free-edge periphery cone. The reproduction from the ** Peerless" is in keeping with its appearance. Price A NEW MAGNAVOX $35.00 Loud speaker and B supply in one unit, a. c. operated. A 210 type power tube should be used. The loud speaker is of the dynamic type. Price for the unit, $110.00

FAD A "PEDESTAL* This is a twenty-two inch free floating cone of attractive Grecian design. The overall height ic fifty five inches. Price $50.00

THE "CASTLE" A two-tone bronze relief pattern enhances the appearance of this Tower seven teen-inch cone. Price $9.50 OCTOBER, 1927 1928 LOUD SPEAKERS 371

ALGONQUIN A full floating cone of a moisture proof impregnated fabric. The Algonquin BALDWIN Electric Company A special unit is re- GREBE "20-20" retails this cone at $15.00 sponsible for the good The numerals denoting tone of the Baldwin this model refer to the "99." This instrument cone diameter and the sells for $28.50 fact that it is constructed at an angle of twenty degrees. Price $35.00 ANOTHER ROLA ART MODEL A large and effective baffle surface is responsible foi- excellent tone Quality. Rola manufactures less expensive models, from $28.50 up. The one illustrated is priced at $45.00

UTAH This $30.00 instrument is of 5-ply a t u r a 1 finished walnut

A 22-INCH CONE The new Sparton loud speaker, a product of the Sparks-Withington Com- AN INNOVATION pany, retails at $30.00 An up-to-date post-war map of the world surrounds the Symphonic Globe loud a $35.00 product raker,the Symphonic Sales Corporation

IN DISGUISE A cone loud speaker in tin- table form the Teletone Model 70. Price $40.00

THE MOHAWK "PYRAMONIC." The pyramidal construction in the diaphragm is responsible for very excellent quality from this $25.00 instrument

ANOTHER PEDESTAL

The Haldwin loud s|H*:

case for the small broadcaster is seldom ourselves on good quality. KDLR has a studio THE SMALL STATION HAS NO PLACE IN CITIES 18 built ourselves Sabine's heard, because he is small, possibly and by 25 by following formulas. For band concerts we have a band THEbecause the public through habit and for D UT we are all in favor of abolishing the small shell, the only in the state of North Dakota, ^ other reasons, directs its attention to the larger station from the metropolitan areas. If the that will seat a loo-piece band, built so that the and better-known stations. Has the small Park district of Chicago, say, wants to focal point is 50 feet from the front of the shell Hyde broadcaster a Does he serve a local need? a little to retail place? and here we pick up every instrument with but publish four-page newspaper How can the small station better serve its pub- one "mike." The shell so built that a speaker in the local gossip to the provincial minded of its lic? An interesting letter from a reader in the shell can talk in a whisper and the "mike" will neighborhood, and to advertise the wares of its Devils Lake, North Dakota, discussing this pick it up and put it through an amplifier at local drug stores and meat markets, well and volume desired without its overridden topic follows: any being good. Nobody outside that section has to buy by hiss. the paper, nor need even know that it exists. 1 have been reading with a great deal of in- You, living in a city with the choice of a score But when that same Neighborhood Association terest your department in RADIO BROADCAST of fine stations at your command, find cause to starts to operate a radio station to afford op- and obtained very much enjoyment out of it. kick and kick loud, long, and lustily at what to the of the Numerous things that you say however lead me you hear. Come out here once and hear one sta- portunity piano pupils neighbor- to believe that you are about as biased an indi- tion or possibly two, both in the same state, hood and to peddle the aforementioned meat vidual as ever wrote. and after you are here awhile I guarantee you market's wares, it becomes, however low its cause will what hear. The particular thing that seems to you go back home and enjoy you power, somewhat of a public nuisance. Even the amount of is the small sta- Then after are home a to the greatest worry you give thought where it doesn't actually interfere with the first- tion. I own and operate a small station, as far rest of the world and try to do a little boosting class stations it needlessly clutters up the dials as power output goes. Some of the things you and cease knocking that about which you ap- and is an unpleasant distraction while tuning. say get under my hide. Picture yourself out here parently know so little. This complaint holds also for stations in suburbs in North Dakota, living in a small town or on a I hope that you have not been bored by the and in small towns within a hundred miles or farm vainly twisting the dials looking for en- length of this thing but allow me to say another tertainment. None to be had. Then, "This is thing, you have a wonderful magazine, but do so of some large city. KEJM The University of North Dakota" or WDAY use a little judgment. We have never heard our correspondent's the case be. or KFYR or KDLR as might A program BERT WICK Operator, KDLR. station KDLR; we hope to hear it when DX is again of entertainment for an hour or two comes good possible. Certainly the program he describes on the air. You listen, you are pleased, you Mr. Wick's point is well taken even if he sounds like a very creditable one. Mere magni- swear by the small station, you pick up a paper does take us to task at the same time. In our tude and wealth are not the only requisites for and note the many excellent programs being own let us that he overestimates our a station. While large financial sent out from a multitude of stations, none of defense, say good broadcasting not said resources must allow a station to which are heard here, except a few months in dislike of the small station. We have necessarily winter. Would you favor the abolishing of many harsh words about it. More than likely present more varied and elaborate offerings they the small station? Would you dismantle your he reaches this conclusion because of the fact do not guarantee artistry in that station's mode radio set in and not use it un- February again that we ignore the small station in these col- of presentation. til November? Would you if you turned on umns. If we do neglect it too much, there are It is perfectly possible for some small station, your set night after night and listen for sta- two reasons. First, the small local stations, being somewhere, to achieve a reputation equal, or tions that cannot be heard? Would you? low are difficult to "get" often enough even superior, to the large city stations. Whether Or would you listen to the very excellent pro- powered, to enable fair comment. local stations or not like the "Little Theater" there is no grams from our local small station? Secondly, you fact some Little Theater The programs sent out here are not the high are of especial interest only to the persons within denying the that pro- type of the big Eastern stations but they fill their limited range and hence do not logically ductions, financed on a shoe string, are superior the bill. An example of our type of program, demand space in an article that considers radio in artistry and in manifestation of good taste at the Oriental Monday evening 9:30-10:00 nationally. to many of the costly Broadway productions. Trio, the pianist a graduate of one of the largest Our correspondent asks us: "Would you favor The same opportunity presents itself in the schools in the country, a student of a noted the abolishing of the small station?" Our answer operating of a small radio station. An individual teacher in Berlin, the soloist a former member is and no. For small stations situated as are with good taste and a certain sort of genius of the Minneapolis Symphony, the violinist a yes gifted mentions in his letter he an ex- which we shall not to label could, con- former member of the Detroit Symphony all those he gives attempt doing their best. At 10:00 P. M. an hour of dance cellent vindication. There are long periods dur- ceivably, operate a station in time which listen- music played by an 8-piece organization coming which it is impossible for isolated communi- ers the country over would labor with flattened posed of men who have been playing together ties to receive the distant stations, even though ears to pick up. He would have to be an in- for three and who know and understand years powerful, with any sort of satisfactory recep- dividual of extraordinary personality and that music. At 1 1 :oo p. M. fifteen minutes of the finest tion. They are entitled to local stations, of low personality would have to manifest itself in kind of pipe organ music. And on a Wednesday power, to fill in these hiatuses. Moreover the every detail of the programs he offered. He would evening a program of band music played by a fact that the is local must give it have to have complete supervision over every band of sixty boys, "The Governor's Boy Con- very program to those in the hinterlands item he broadcasts do all his cert Band of Devils Lake" an organization of a certain interest and, essentially, six years standing under the leadership of the who take a keen interest in local things, in con- own announcing. In contrast to the impersonal, finest bandmaster in this section of the country trast to the city dwellers who don't know their routine, and frequently "high hat" manner and of the playing overtures and marches high- alderman's name nor the people in the apart- affected by the metropolitan stations, his mode est class. The soloist with the band is a who lady ment below. The farmers and other dwellers in of presentation would have to be decidedly per- has recently returned from that famous music the Centerville area are just as likely to prefer sonal and intimate. He would have to establish school in Philadelphia where you must have the wares of Centerville's lo-watt broadcasting a very real bond between himself and his au- talent to get in. That was our program last week. station to those of wcco as are to dience. The musical he offered would Daily we run the noon hour program playing they likely programs the Centerville to the have to his own as would the finest available recordings of symphony prefer Bugle Minneapolis express tastes, every orchestra and famous singers, played through Tribune. Probably they are personally ac- other sort of program he offered from time to an electric pick up. Daily we broadcast the wea- quainted with most of the performers who appear time. And if he were a big enough man, his tastes ther and market information reports and the before the Centerville station's microphone, or would be broad, and he would, in consequence, station is listened to. eagerly at least they know the announcer's cousin attract a big enough audience. He would not You may wonder at our quality. We have the Nellie or their nephew goes to the same Dis- have to have a lot of artists, but the few he had finest and newest type microphones, the best trict school as the Staff Organist's son. Hence would have to be good, and show, in all their amplifying equipment that we can buy, tested their interest in the local is natural work, his fine Italian hand. and balanced pick uplines, a monitoring opera- program since it are His as "editor" of all that his station tor at each end, every piece of equipment enough, and they enjoy they entitled position meter-checked at both ends and we pride to it. offered would very closely parallel that famous OCTOBER, 1927 THUMB-NAIL PROGRAM REVIEWS 373

instance in the history of American journalism advertising. If the bonds of a common father- lone, When You're in Love, Listening, Honolulu wherein an editor of unusual genius, though at- land hold these people close enough together to Moon, and Selections from the "Red Mill" tached to an unimportant newspaper in an un- make a newspaper self supporting, it would following each other in sentimental succession. important Mid-Western town, gathered to him- seem, by analogy, that an unpretentious broad- But Erva Giles has a beautiful soprano voice for self such fame that his editorials were quoted casting station would not be an impossibility. these songs and the Radiotron's much featured the country over and his newspaper even en- The value lo those, like ourself, who do their Vaughn De Leath always delights us with her joyed a scattered circulation over many remote best talking and listening in the American pa- mellow alto and throaty half-spoken passages. states. tois, would be, perhaps, not large. But it would I PAN A TROUBADOURS (Red Network) continue And finally his reward would be considered be a great thing for students of foreign languages to be one of the most reliable orchestras that are in the form of dross dollars about as great as to have a station they could tune-in on, on oc- to be heard weekly. Their plucked instrument, is the financial reward of the operator of a Little casions, to supplement their reading and writing section (they have another section strings) Theater. work. Moreover it would give a pleasant cos- continues to lead in its field, which is probably mopolitan tang to the air. And picture the de- to be expected considering all the practice it Why Not a Station Operated by a light of a listener out in Kansas tuning through has had over the past two and a half years. to some Italian station in New York and imagin- Foreign Language Group? ELK'S MALE QUARTET (Blue Network) The ing he had got Rome! quartet is an unfailing radio standby. Mayhap are several broadcasting stations, our interest in the quartet springs from the mostly among the smaller ones, devoted Thumb-Hail Reviews fact that every one of us is a potential singer in THEREto some special group of listeners. For ,.,,: a and stands to contribute his instance there are the two labor stations which quartet ready services thereat under proper stimulus, such as aim their output especially at the man in over- >E WRITE in themiddleof the summer, a shower room, a clam bake, or a couple of stiff alls; and then the stations operated by some at a time when DX conditions are at snorts. Be that as it may, the Elks' is an excel- religious group, as the Roman Catholic and their worst, so instead of trying to re- lent quartet. Christian Scientist. It has puzzled us, from time view some static-mingled distant squawks we to time, that no station has ever come into exis- shall confine ourself to considering some of the CONTINENTALS (Blue Network) The Conti- tence operated by a foreign born, or foreign chain features which are received over a wide area. nentals is a very able organization made up of a descended, group for the benefit of its fellows The summer season, may we say, has been chorus and soloists under the direction of Cesare in this country who cling to the mother tongue. better than any previous summer in radio's Sodero and specializing in opera selections. The While we have no statistics at hand to soloists include Astrid Ejelde, soprano and lend weight to this proposal, isn't it said an excellent one; Elizabeth Lennox, con- that there are as many Italian speaking tralto; Julian Oliver, tenor, and Frederic people in New York as in the city of Naples, Baer, baritone. The program is well selected and more Swedes in Chicago than in the and does not stick too exclusively to the city of Stockholm? If these statements be threadbare arias. Tuesday evenings at nine exaggerated at least the "foreign-language" Eastern time. populations of these cities do run into large STROMBERC-CARLSON ORCHESTRA (Blue figures. Chicago, besides its vast area around This is Olson's Belmont Avenue where one can examine Network) George band, playing under a trade name, and a first rate the store signs for blocks without seeing a band it is, as others than ourself will assure name that does not end in -son, has popu- you. Perhaps much of the credit for the lous settlements of persons of Polish de- smooth and beguiling manner in which it scent, Italian and German. These people plays is due to its orchestrator, one Eddie particularly the older generation, have re- Kilfeather, who specially arranges many of course among themselves almost exclusively its numbers. to their former native tongue. Their sons and daughters though they prefer the STADIUM CONCERT (Blue Network) The American idiom, have, nevertheless been Stadium concerts occupied, as last year, acquainted with the second since language first place on the list of summer offerings. childhood. It seems to us they should be We were afforded mingled emotions in hear- interested in hearing programs conducted ing our M r. Stock as guest conductor of the entirely in their own language, featuring Philharmonic musicians, what with the cur- artists and of their and in speakers race, rent prospects of having no Chicago Sym- devoted to their racial general interests. phony Orchestra this coming season, due to The Great War is remote now so enough wage disputes. (We wonder why the Or- that no idiot would be to call likely the AN ESKIMO LULLABY AT WGY chestral Association didn't offer to sell manoeuvre unAmerican. to meet the in- In the Schenectady studio, Trixie Ahkla, Eskimo, sings a good broadcasting privileges Ihere have been foreign creased language pro- night lullaby for her two sons Miles and Billy. Up North, where demand for funds). To quibble from various stations in the United grams the night is long, this domestic duty need be discharged only about minor points: we saw no reason why States, but Some once a only intermittently. year the announcer should descend from his pon- French were broadcast a programs by New derous and dignified perch at intervals to York station, wiuo in has for two Chicago nearly history. Many features quite up to winter time refer to one of his fellow workers as "Jimmy." If broadcast a in Swedish Sun- years program every standards were heard. The stations supported they will be high-hat let them be consistent. from day morning 8:35 to 10:00. Inquiry at WIBO the annual vociferous protestation that "there reveals the fact this CITIES SERVICE CONCERT (Red Network) An that program has been en- is no summer slump in radio!" So many dif- received Swedish orchestra under the direction of Rosario Bour- thusiastically by people, not ferent agencies are engaged in re-iterating this in but distance don and a chorus called the Cavaliers. But what only Chicago by long experts in phrase every year, particularly radio manu- Wisconsin and Minnesota both of which shall we say about them? we have exhausted our states facturers, that it occurs to us that they do pro- have a Swedish critical imagination. At any rate are con- large population. The same sta- test too much, and that a slump none the less they tion sistently good. in the recently inaugurated a program in German exists. If it does exist it is because radio listen- They specialize lighter on afternoons from composers, Herbert, Friml, Straus, and so forth, Sunday 2:30 to 3:30. ers have been able to discover other doings more 1 here is no doubt at all that a with other occasional novelties. foreign language intriguing than sitting in the front parlor of a station, properly situated, would a warm summer's and enjoy large evening, not because the sta- ROYAL HOUR (Blue Network) After having enough audience to make its efforts worth while. tions have not an effort to made please. distributed roses the length of this column it is Nor does there seem to be much doubt that it now our privilege to get mad. The Royal Hour's could artists; an Italian station get suppose THE RADIOTRONS (Blue Network) These art- thirty-minute broadcast is a throw-back to sent out a call for Italian But there ists in their singers! may program of alternated orchestra radio's worst days. Advertising is jammed in be some question as to how well it could and voice strike a mood that support nicely ties the so thickly that the musical part hardly has a itself. here is the rub and the reason that whole In the Perhaps shebang together. case of the pro- chance to stick its nose out before it is drowned none has so far appeared. However the foreign gram we have in mind the flavor in persisting further advertising. Every number on the pro- communities in the cities to large manage support throughout was a decidedly saccharine one; gram is introduced with a labored reference to flourishing which are with such numbers as Tumble Shack in newspapers, packed Down Ath- the sponsoring company and its product. YourA* C. Set

How to Search for Defects When Your A. C. Oper- ated Receiver Qoes Dead

EDGAR H. FELIX

CALL THE SERVICE MAN

"Shut off the power, call for a trained professional service expert, and leave the set alone" the advice to perplexed owners of a. c. sets in time of trouble by the head of the service department of one of the largest radio manufacturing concerns

head of the service department of one cipally because of inadequate knowledge of tion but one, if you have opportunity to look at THEof the largest radio manufacturing concerns power engineering. the output condenser in the power supply of a in the country was asked at a meeting re- The excessive service grief which attended Stromberg-Carlson a. c. receiver, you will ob- cently what advice he would give to the owner some 1925 and 1926 a. c. sets has been largely serve that its size compares with that of condens- of an a.c. operated set which has suddenly gone cured by the application of the principles of ers used in receivers of a year or two ago almost out of order. power engineering to radio. These pioneer models as does a match box with a steamer trunk! Ex- "Shut off the power, call for a trained pro- taught us the stresses and surges to which the pensive as these improvements are, they are an fessional service expert, and leave the set alone," filter condensers are subject with the consequence economy because they approach the ideal was his answer. "The troubles that arise with that the latest receivers have condensers of con- "plug the set into the light socket and the re- a.c. receivers are few and easily remedied by ex- siderably greater voltage-carrying power than ceiver is ready to operate for a period of years perts, but an experimentally inclined novice those of past seasons. New rectifier tubes of without attention." who doesn't know what he is doing can actually greatly increased capacity have solved voltage TWO TYPES OF A. C. SETS do great damage if he starts to tinker aimlessly. regulation and life problems, while such refine- When a person gets sick, he calls on his doctor; ments as ballast tubes and regulator tubes give IN GENERAL, there are two outstanding types A when his automobile goes out of order, he brings the designer wide latitude in his work. Also we of alternating-current sets first, those in it to the service station; but when a radio set have new types of tubes which avoid the use of a which the alternating current of the line is con- goes wrong, three out of five listeners proceed rectifier by using alternating current for the A verted into direct current by rectifiers, smoothed boldly with soldering irons to change wires, to supply. All of these advances have brought us by filters and then used to power filaments of the short-circuit transformers, to reverse connec- to the threshold of a new era in radio set design more familiar type of vacuum tubes and, second, tions, and to apply high voltages here and there, and the elimination of the burden of maintenance those with tubes utilizing raw alternating cur- just to find out what happens. A competent attention. Given capable engineering and ade- rent, either of the rugged filament or heater ele- man, familiar with the functioning of radio sets quate quality of materials, the modern alternat- ment type. Already considerable experience has and their associated power supply, makes an ing-current set, whether it be of one type or been gained with the first type of set and its inspection, analyzes the difficulty, and replaces another, is reasonably reliable and a marked im- service and engineering difficulties are quite whatever is necessary in a few minutes at a min- provement in convenience over its less advanced well known. With the second, there is less ex- imum of expense; a venturesome experimenter predecessor. perience, and which of the two kinds will prove usually tinkers until he has done serious damage, Certain parts of the alternating-current re- the ultimate winner is hard to say at this writing. then calls in an expert and, when he gets the bill, ceiver, however, depreciate with long use. It is Tubes using raw a. c. for their A supply never- wonders why radio repairs are expensive. There no more possible to design a wear-proof radio theless need d.c. for B and C power, and therefore is nothing mysterious or really troublesome receiver than it is to design a wear-proof automo- a rectifier of some kind is necessary unless A and about modern a. c. sets, and servicing them is bile. Vacuum tubes lose their emission and con- C batteries are employed. The use of these tubes usually a matter of the utmost simplicity." densers, unless of tremendously greater voltage requires the introduction of an appreciable 60- Careless tinkering may prove an unhealthy capacity than their service requirements de- cycle a. c. current right into the radio receiver, for the would-be pastime radio expert who is mand, eventually break down. 1 1 is only a matter in and near the radio-frequency elements, intro- accustomed to learn his radio by practical ex- of time, however, when the service attention ducing hum difficulties, and the life of the tubes perience. Large condensers of several microfarads required by a.c. sets will be reduced to a matter under ordinary service conditions is yet to be capacity, charged to 500 volts, may impress their of annual inspection to replace rundown tubes. determined. Considering that RCA, Cunning- effectiveness upon him with such force that he Indeed, some of the latest sets have actually ham, McCullough, Van Home, and others are will find himself involuntarily, violently, and un- reached that stage. making a.c. tubes, it is certain that there has controllably seated on the floor several feet from But we cannot expect a radio receiver to re- been much fruitful development work done since the radio set. if But, he temper his examination quire no attention whatever. Filter condensers the first of this- type' of tube was introduced sev- with of the c. knowledge, most likely faults of a. are really moving parts. They are constantly sub- eral years ago. sets can be identified operated readily by their jected to considerable voltages, and are charged As to the first type of receiver, that is, those us- symptoms and, in some cases, the necessary and discharged rapidly and continuously. The ing conventional tubes, usually of the 199 type, measures for repair taken. atomic structure of their components is con- with filaments in series and powered by a rectifier Servicing the a. c. set has brought a new dig- stantly strained so that in time they become less system, there is a wealth of practical experience to the of it nity job repairing radio sets because capable of resisting these rapidly changing volt- in servicing them, gained during the last two has converted the receiver to an electric power age strains. The experience of the last two years seasons. The largest sellers in this class have been device of considerable magnitude. Indeed, so has resulted in the widespread use of bypass and the Radiola super-heterodyne outfits used in marked is the change involved in the engineer- filter condensers which will, under ordinary con- connection with the 104 loud speaker and an ing design of a. c. sets that some of the earlier ditions, serve for a period of years, rather than a.c. rectifier power unit; the Garod, and the models, designed by radio engineers, failed prin- months, as was the standard heretofore. To men- Zenith. By consulting not only manufacturers OCTOBER, 1927 YOUR A. C. SET 375

but the service heads of dealer responsible organ- the filament-type rectifier tubes. In most cases, which has previously been quiet, may be due to izations, it has been possible to learn what the if the rectifier tube or tubes show a blue or purple the breaking down of a bypass condenser, a service in connection with the sets are. it problems glow, means that they have begun to leak. If change in the load conditions of the power line, The author is particularly indebted to the R. T. so, place the set out of service at once, as there or reversed line connections. The latter is some- M. Service and to Mr. H. T. Cervantes of is Haynes no other repair possible than replacement of times correctable by pulling out the plug, giving Griffin Service for of the informa- Radio much the rectifier tubes. it half a turn, and re-inserting it. The power-line tion which follows, based on their experience with When there are two rectifier tubes, it may noise may require the attention of the power thousands of these sets in the New York area. happen that the plates of one of them turns company as, quite frequently, it is the result of The for the procedure locating trouble, sig- bright red while the other remains its normal using an appliance in the immediate vicinity nificance of symptoms, and the remedies, are color. Usually, this is a direct and simple indi- which sets up power surges in the line. These can described with a view to aiding the set owner cation that the tube which looks normal has lost be cured by installing an interference preventor in determining whether his set requires the serv- its emission and the entire load of the set is being at the device. ices of an expert service man or whether a drawn from the other tube, which becomes red From the foregoing, it is obvious that there is simple adjustment will put it back in service. as a consequence of this overloading. The remedy nothing unusual or startling about the service Breakdowns with a.c. sets generally impose a is obviously replacement of the rectifier tube requirements of a.c. sets. They introduce new strain on the rest of the outfit and, consequently, which does not overload. problems but, once these problems have become a certain amount of knowledge of possible diffi- On the other hand, when both rectifier tubes familiar, they will not cause any serious modifica- culties may avoid more serious damage. become bright red, it is due to an unusual load tions in radio servicing. The radio trade is learn- When the set goes dead, either shut off the upon them, usually a broken-down bypass or ing that it must take its service responsibilities until the power service man takes charge, or else filter condenser. Should this occur, the set seriously while the consumer is recognizing that determine immediately whether the rectifier should be placed out of service at once because service is something which he should pay for, tubes if light and, the set has them, note also if this places an extreme overload on the rectifier just as he does when he has his watch or automo- the ballast and the regulator tubes glow. If these tubes and the only remedy is replacement of the bile repaired. Free service has worked as much tubes appear to be functioning, reduce the fila- defective condensers. This is a job for an ex- harm for the consumer as it has for the industry ment voltages by means of the filament rheostat. perienced service technician. itself, because dealers giving extensive free serv- Sets with filament rectifiers do not, of course, With those sets using regulator tubes, the sim- ice ultimately fail in business. And there can visual indication give of their condition and in- plest check which a service man is usually in a be no redress when the dealer has gone out of is of no avail. spection The usual procedure, with position to apply at once is the substitution of a business. Amateur servicing with power sets, such is to test a rectifiers, with rectifier tube good regulator tube to check the condition cf the also, may result in more serious damage, just as known to be good. tube in service. When the regulator tube does not does inexpert tinkering with an automobile. Next check the condition of the radio, detector, give a colored glow, either violet or pink, it is Just why there is hesitancy in admitting these and audio set. tubes of the This is easy, if you not receiving its necessary voltage supply, due simple facts is a little hard to understand, since, can in in plug phones the detector and audio to the shorting of a bypass condenser, failure of with a little consideration, anyone will under- A in the indicates stages. signal phones that all one or both of the rectifier tubes, a failing ballast stand that free service, inexpert service, and the tubes supplying them, including radio- tube or a radio or audio tube, the elements of promises of perfect reliability do not promote frequency and detector stages, and sometimes which are short-circuited. It is the purpose of satisfaction to the radio user. the first audio stage, are in good working order, the regulator tube to keep the voltage supply It is premature to set up rules for the selection as is the power supply for all but the final output constant. A prolonged loud signal or continued of a. c. sets at this stage because the relative tube. strong static may increase the brilliancy of its merits of the various a. c. systems have not yet

1 n absence of this convenient test, examine the glow. But, if the antenna is disconnected any been fully proved by user experience. One of the tubes in the radio receiver. If necessary, darken flashing of the regulator tube which occurs indi- safest guides is to consider the engineering repu- the room to do so because tubes of the dry-cell cates that it is defective. tation and stability of the manufacturer and the type do not generally light very brightly. With This completes the only frequent troubles en- service reputation of the dealer from whom the some series filament receivers, all the tubes go countered with a. c. sets. It is needless to go into set is bought. A manufacturer who has a reputa- out one filament fails. when With others, a re- the usual defects loose connections, defective tion worth losing will not skimp by using a sistor is used in parallel with each filament as a plug or flexible cord to power line, lost emission cheaper filter condenser in the hope that it will protective measure and it will pass enough cur- of power tubes, dirty contacts with socket, in- not break down prematurely, nor will a dealer of rent to light the remaining tubes in the receiver correct adjustment of reproducer, and other established standing in his community jeopard- one or filaments are when two burned out. difficulties which are not specifically assignable ize his standing by taking on a line without ade- If you do not locate the tube out of order by to the a. c. set. They are the kind of difficulties quate test and engineering examination. The day substitute inspection, a good tube for each one which occur with increasing rareness as the of the a. c. set is here. It means simplified radio in the receiver, one at a time, remembering, of mechanical and electrical design of receiving and adequate power, essential to beauty of re- course, the first instruction to keep the filament sets improve. production. It means a broader market for radio rheostats low. It may be worth while, however, to mention receivers, with the inevitable consequences of In the case of sets without the filament resist- that a sudden increase of hum in the reproducer, larger production and more radio for the money. ors in parallel, an even more serious strain is impressed upon the filter condensers when one radio tube goes out, unless a regulator tube is employed. In some cases, when the filament load is removed from the rectifier system, the voltage builds up greatly, sometimes sufficiently, in fact, to cause the breakdown of filter condensers. The capable service man who, from a brief inspection of the receiver, decides that one of the radio or audio tubes may be dead, tests the tubes with a tube tester rather than placing his reliance upon the power supply of the set to do so. This avoids undue overload of the rectifier condensers. The manufacturer's instruction book often explains the best course to follow when the receiver goes dead and, understanding the reasons for it, the reader will not leave his power supply turned on if his tube filaments do not light, should the manufacturer advise him not to do so.

The best test of radio and audio tubes is to use a tube tester or to replace the entire lot. Otherwise substitute a good tube in each socket, one at a time, leaving the remaining tubes in their sockets. Assuming that rectifier and ballast tubes MAKING TESTS ON AN A. C. UNIT light and that radio and audio tubes have The two-microfarad condensers on the RCA 104 loud speaker been proved good, the next thing to examine is power unit are here undergoing tests for possible defects AS THE BROADCASTER SEES IT

Going to Jail for Radio in Germany

THE United States, a good many, broadcast in the nearest zoo, thus relieving the tax-payers in such matters on the part of Messrs. Kendall listeners are in but not for to in two and Laurence M. IN jail, listening ways. Banning Cockaday. They run the programs. They went to prison first and Some of these penalties, I admit, appeal to me, altogether too good a magazine to permit such listened to the radio afterward, broadcasting and I have derived pleasure in contriving them. a high concentration of mistakes to the cubic being one of the inducements offered in all up- But, as I said, I disapprove the principle, since centimeter of printer's ink to pass unnoticed, to-date penitentiaries. In Germany, however, I am a broadcaster myself, and might be one of especially in reference to the Brahmins of the radio has been the direct instrumentality where- the first to be dragged to the hoosegow. I there- radio art. by one gentleman went behind the bars. It ap- fore appeal for moderation in this instance, and that he was a which means, shall to pears Scbwarfboerer, telegraph my Congressman requesting Memoirs of a Radio Engineer. XX literally, a black listener, i.e., one who neglects that our government make representations to to pay a fee and secure a license for his receiving the Reich on behalf of the imprisoned Scbwar^- FIRST assignment at the Aldene fac- set, as required by German law. The first time hoerer. tory was in the test shop. This was a this recalcitrant BCL was caught he was fined MYgood-sized room in the old stone build- his set confiscated. The second time the which later became an annex to the and Radio's "Aristocracy of Brains" ing, merely authorities, with due process of law, clapped him modern factory structure erected to fill the war- OFTEN reflect on the melancholy fact that into the jug for three weeks. If they catch him a time requirements of the Army and Navy. Along the men who really made radio, the Mar- third time presumably he will be tried by a court I one wall there was a switchboard controlling the riotts, Alexandersons, Fessendens, Hogans martial of studio managers and shot some Green- supply of a.c. and d.c. to various outlets. For the and the rest, are not as well known as the more wich Mean Time morning. rest the room was crowded with quenched spark popular announcers of fifty-watt stations. Com- As a practicing broadcaster, I regard this inci- transmitters of all sizes from one-quarter to five pared to the coruscating luminaries of the net- dent as a bad precedent, and am relieved that it kilowatts, miscellaneous apparatus in various works, like MacNamee and Cross, the engineers occurred in a foreign country. For, if a broadcast states of disarray, work tables, meters, and a do not shine at all. For this there are, of course, listener may be sent up for a little radio boot- few men: W. H. Howard, the Chief of Test; sufficient reasons, psychological and sociological; legging in this style, it is only a matter of time Baldwin Guild, now practicing patent law with one might as well lament that Dr. G. W. Crile is when the broadcasters themselves will spend Pennie, Davis, Marvin, and Edmonds; my pres- not as well known a man as Babe Ruth. I shall their week-ends behind stone walls with spikes ent colleague O. B. Hanson; a tall gentleman not waste my tears in this cause, yet I cannot and sentry boxes on top. A program impresario named Lieb; a more medium-dimensioned gen- refrain, coming down to cases, from pointing an permitting one of his flock of baritones to sing tleman named West, and myself. I may have accusing finger at our contemporary and friend, "Rolling Down to Rio" will be sent away for omitted someone, but I think this comprised the Popular Radio, which on Page 402 of its April, six months. The singer himself will merely re- list in May, 1917. 1927, number, prints a picture with the caption, ceive a black eye at the hands of one of the catch- The engineering staff of the Marconi Company "A Group of Radio's 'Aristocracy of Brains.' polls, for delicate psychological tests have proved had the privilege of using the facilities of the test The description which follows is reprinted ver- that all baritones are subject to an irresistible room for experiments when they could get in. batim: impulse to warble this tune. When one of the By experiments I do not mean research on elec- Dr. Bohn front of the is receiv- water-cooled tubes lies down in the middle of a Ralph (in desk) tron velocities or anything else at all recondite, the Liebman Memorial Prize of the Institute program, interrupting the festivities for a minute ing but merely such incidental tests and measure- of Radio Engineers from Mr. Donald McNicol, or so, the engineer of the station will be set to ments as the design of former President of the Institute. Dr. Bohn him- always accompany ap- breaking rock for one year. When the transmitter paratus. This work had to be sandwiched in be- self is the new president. At Mr. McNicol's left deviates from the the tween the routine test functions of the assigned frequency, jolly is Mr. John V. N. Hogan, Contributing Editor depart- technician will be separated from his wife and of Popular Radio. Next to him is Mr. R. H. ment. Inasmuch as I was known to possess some children one year for each kilocycle high or low Mariott. Behind Dr. Bohn are Professor Michael engineering training, I was assigned temporarily and if another station has been heterodyned the I. Pupin, of Columbia University, Mr. L. E. as a sort of assistant to engineers who required and Mr. E. F. W. owner thereof will be permitted to extract the Whittemore, Alexanderson, work to be done in the test room. My first job well-known inventor and radio engineer of the offending engineers' teeth. This may seem a was handed to me laconically by Mr. Woodhull, General Electric Company. cruel, unusual, and hence unconstitutional pun- one of the transmitter engineers. A five-kva ishment, but it is a sound maxim of law that a Children, what is wrong with this description? transformer was trundled into the test shop and statute may be constitutional in one age and un- In the first place, the President of the Institute dumped off. "Measure the iron losses," said Mr. constitutional under later circumstances, and of Radio Engineers is Dr. Ralph liown. The prize Woodhull, and disappeared. some judge may reverse the process and decide is awarded each year in memory of Colonel I gazed at the transformer. It contained plenty that, as broadcasting was not known to the Morris N. Liebmann. Mr. Hogan's middle initials of iron in the form of a shell core, and no doubt Founding Fathers, new and appropriate punish- are y. L. Robert Henry Marriott, the first Presi- there were losses. I could identify the primary ments may properly be devised for erring dent of the Institute, spells his name with two leads, which were to be fed at 1 10 volts a.c., and broadcasters. On this principle, announcers who "r's." Finally, the gentleman in the picture just the secondary terminals, which were expected to read telegrams of appreciation to the radio audi- behind Professor Pupin looks suspiciously like deliver juice at 10,000 volts or so to the quenched ence will be forced to eat a pound of coarsely Dr. J. H. Dellinger, and not at all like Mr. spark gap of the five-kilowatt transmitter. I ground Celotex. Announcers who read their own Whittemore. The total of errors appears to be had never measured the iron losses of a trans- from poetry over the air will be thrown to the tigers five. 1 call loudly for a more flattering vigilance former, but 1 had some vague recollection, OCTOBER, 1927 TECHNICAL PROBLEMS FOR BROADCASTERS 377

Section of the American Institute of Electrical place and time. But what is a good engineer? on Oct. One who has, in the course of practice, got rid Engineers 17, 1923. Reprinted May, 1924 Western Electric Inc. Tele- of a few thousand of such bonehead ideas. He by Company, (Bell phone Laboratories, Inc.). gets paid largely for the relatively accurate of judgment physical magnitudes (always THOUGH telephone wires used in con- checked by measurement) and economic results nection with broadcast transmission are checked the balance which lie (always by sheet) A in general not utilized for other communi- has been able to in their put place. cation services during program periods, technical ( / o Be Continued) broadcasters will find it instructive to learn some-

--f- E=960V. thing about the multiplication of channels on Technical Problems for Broad- expensive long distance circuits by the use of casters. IV separate frequency bands for different purposes. Doctor Jewett, who is himself responsible for feed of a FIG. I plate fifty-watt (oscillator much of this development, has outlined the main rating) tube used as a reactance-coupled features in this paper. THEamplifier in a broadcast transmitter is my studies, that the procedure was to put rated shown in Fig. i. Plate potential is supplied by a voltage across the primary, leave the secondary storage battery with an output voltage E of 960 open, and measure the power input with a watt- volts, the internal resistance being negligible. meter under this no-load condition. So I looked r\ r\ ~r The reactor in the plate circuit has 50 henrys around for a wattmeter. The only one I could \j inductance and the d.c. resistance RL is 1320 find had a full scale deflection of 7.5 kw., so I ohms. The resistance drop across it is designated the switch. rvrv. hooked it up and threw Nothing by VL, and this will necessarily depend on the happened. I disconnected the wattmeter and mean current plate current lp which is indicated tested it on another set which was under load. byamilliammeterAin the plate circuit. This plate n n ../ There was nothing obviously wrong with the current varies with the negative grid bias EG instrument; it read several kilowatts. I put it according to the upper characteristic curve of back in my circuit and tried again, still without rv.rv../ Fig. 2. The problem is, Given a safe plate dissi- results. After an hour or so Woodhull came back pation of 70 watts for the tube in question, what and wanted to know what the iron losses of his is the minimum allowable negative grid bias transformer were. With much embarrassment I n n under the conditions shown? confessed that I did not know, and showed him Solution my predicament. He looked over the circuit, n. and then glanced at the wattmeter. The scale We are told that 960 volts is the steady output losses are of the made him laugh. "The iron only potential of the storage battery under all con- order of a hundred watts," he told me. "You ditions, since its internal resistance may be neg- can't read that value on this scale. Get a o.;-kw lected. Hence, in order to find the actual voltage FIG. meter out of the storeroom and try again." VP on the plate of the tube, all that is required 3 Following these directions, 1 measured the iron is to find the voltage drop along the reactor for The first point which concerns us is the analy- losses of the 5-kva transformer at 70 watts, if various plate currents, and subtract these values sis of a square-topped wave, reproduced here as I remember the figure correctly. Then we went from 960. The plate dissipation Wp of an am- Fig. 3. Such a wave is produced in a direct cur- ahead with some other tests involving loads. of the type shown is the product of the plifier rent telegraph system which has neither capacity This incident illustrates what the engineering mean current and voltage, as indicated by plate nor inductance, as the circuit is made and broken student just out of school is up against. He d. c. instruments in the circuit. We may therefore by a key. It may be established mathematically usually has only a vague idea of magnitudes. 1 draw up the following table: and graphically that such a square-topped wave had studied under first-rate teachers and my EG IP Vi. VP WP is composed of a continuous direct current and preparation in some directions, was not at all Mill - Volts Walls a number of sine wave alternating currents, com- bad. But there were numerous other fields in Volts Amperes Volts 30 94 124 836 78.5 prising a fundamental frequency corresponding which I really did not know whether the answer 35 83 105 855 71.0 to the keying frequency, and, theoretically, an would out in millimeters or or watts 95.5 864.5 62.5 come meters, 40 72.5 shows 45 62 81.5 878.5 54.4 infinite number of odd harmonics. Fig. 3 or kilowatts. If that wattmeter had swung up to this d.c., and the a.c. to the elev- iron components up a of a kilowatt or two for the losses first are obtained from the reading The two columns enth harmonic, with the resultant wave form in of a small transformer, I should not have been characteristic. The plate current-grid voltage each case, and the ideal rectangular shape which surprised. A bonehead idea? Certainly, at that column follows when the value of cur- VL plate is secured when all the harmonics are preserved. rent in each case is into 1320, the d.c. multiplied Fig. 4 is a diagram showing the same components resistance in ohms of the the di- reactor, giving in their relative amplitudes. If the current at the rect across the Sub- voltage drop winding. receiver is to be a strict reproduction of that at tracted from these values individually 960 volts, the keying end, frequencies considerably higher the actual to yield plate potentials corresponding than the keying frequency must be transmitted. the various bias The grid figures. plate dissipa- With hand sending it may be necessary to pass tion is then calculated in each instance as the over the line frequencies as high as 40 cycles, of the Vp and Ip. As it the product happens, to preserve the wave shape. With a multiplex results are of about plate dissipation numerically printer the range is preferably extended to 100 the same order as the currents in milli- plate cycles per second. Even in telegraphy, we note, so that be in the form amperes, they may plotted accurate reproduction (what we call "good qual- of the lower curve of 2. is an accident, Fig. (This ity" in broadcasting) requires widening the from the fact that the resulting plate potentials frequency band. are near 1000 but of course an volts, independent Instead of keying a direct current for telegraph characteristic could be drawn in any case.) From this curve we note that 70 watts dissipation cor- responds to 35.5 volts negative grid bias. The answer to the problem is, therefore, that 35.5 volts is the minimum allowable bias to be used with the tube in question if the plate is not to be overheated.

Abstract of Technical Article. VI

i the Most of the Line A Statement "Making OF 3F 5F 7F 9F 11F 13F 50 ' Referring to the Utilization of Frequency 60 5fi 30 FREQUENCY Bands in Communication Engineering," by Dr. Frank B. Jewett. Presented before Philadelphia FIG. 4 378 RADIO BROADCAST OCTOBER, 1927 communication, we may make and break an alternating current carrier. The resulting wave is shown in Fig. 5, the carrier being assumed to obey a sine law, and the line to be without inductance or capacity. This wave may be resolved into a fundamental and harmonics, as shown in

Fig. 6. The difference between Fig. 4 and Fig. 6 is that in the former (d.c.) case the harmonics are grouped in ascending order on the positive side of the hoizontal axis, starting with the frequency O, which is the direct current component, while with an a.c. carrier the harmonics are grouped on either side of the carrier fre\ quency. In the latter method we employ a process of modulation and remodulation (now more

i Home^Constracting Transformers and

The Second of Two Articles Intended to Obviate Tricky Mathematical Calculations when Building These Units The Design of Choke Coils, and the Actual Construction of Both Chokes and Transformers, Is Discussed

By HOMER S. DAVIS

coils are used in radio work chiefly 50,000 lines per square inch, with a reasonable clear up any doubtful points remaining. Suppose to value CHOKEintroduce opposition to the flow of of G. This is relatively easy with small cur- a 2o-henry choke coil is desired, capable of alternating current, while at the same rents, but with the larger currents it is very carrying 85 milliamperes of direct current. direct time allowing current to pass easily. In difficult to maintain reasonable flux density. Where a choke is connected directly to the out- the lower the of the alternat- The value of increases with the size of the of a rectifier general, frequency G put without previous filtering, the the more the inches ing current, inductance required. choke, starting with about 0.03 as a maximum value of the rectified alternating cur- At radio frequencies, air-core chokes may minimum. rent may be as high as 1.57 times the value of sufficient but at To avoid the mathematical difficulties of provide opposition, audio fre- using the direct current. Since both the alternating quencies and for smoothing out the ripple in the above formulas, calculation charts have been and direct currents contribute to the flux in the iron power-supply units, an core is provided to devised to replace them, formula No. I being core, and only the direct current component has a make possible greater inductance in a more represented by Chart II and formula No. 1 by been used in the formulas, it is customary to compact unit, since the magnetic flux will flow Chart I. allow for the alternating current component by through iron more easily than through air. The first things to begin with in designing a modifying the value of flux density substituted A different situation exists in the core of the choke coil are the inductance and the current in the formulas. About 35,000 lines per square choke coil than in the transformer core. In the capacity. A reasonable length of air gap is then inch will be satisfactory. Assume an equivalent latter, the magnetic flux due to the alternating decided upon, and a flux density of about air gap of about 0.05 inches. The number of current has the core all to itself, while in the 50,000 lines per square inch assumed to start turns of wire to wind on the coil may be found case of the choke it with. has to share the core with the The number of turns can then be found from Chart I. The key at the bottom of the flux due to the direct current. from 2 or To make certain formula No. Chart I, after which the chart shows which scales to connect together. that the direct current flux size of does not saturate core may be figured from formula No. i Accordingly, draw a straight line from 0.085 the an air must be in or Chart II. Here it be on core, gap placed somewhere may found that either the current scale to 3 5,000 on the flux density the core. This greatly complicates the design, the amount of copper or the size of the core is scale. Through the point at which this line crosses and a reasonable of is difficult to excessive from the of the length gap standpoint economical and index line, draw a second line from 0.05 maintain. Too a will it great gap reduce the induc- compact design, in which case may be neces- on the equivalent gap scale until it meets the tance and therefore require a larger choke for sary to try again with a larger air gap or a smaller turns scale, at 6500 turns in this case. Next, the same amount of inductance, while too small flux density, or both. Several trials are often the size of core to use is obtained from Chart II. a gap will increase the harmonics, thus impairing necessary before a reasonable design is arrived Draw a line from 20 on the inductance scale to the filtering action. It is generally agreed that a at. Then with these vital factors settled, the 0.05 on the equivalent gap scale. Through the good value to use is one that uses up about next step is to choose the size of wire to handle point at which this line intersects the index ninety per cent, of the magnetizing force. For an the current, just as was done with the trans- line, draw a second line from 6500 on the turns ordinary silicon steel core this means a gap about former. scale until it meets the core area scale. This inches for each inch of core Here it 0.005 long length. again is convenient to lay out a full- point indicates a net area of 0.74 square inches, actual value to " The give best results can be size drawing of the choke coil, to see just how its which is approximately equivalent to a core determined only by trial with the other appara- proportions will work out. As with the trans- square. tus with which the choke coil is to work. the a Only former, compact arrangement should be As mentioned before, the design is not so core of construction will be striven for. type considered in Enameled wire is best for the choke, straightforward for the larger currents. It is this article, as was done in the case of the trans- as the voltage difference per turn is small and difficult to arrive at a compact, economical data for which were in thicker insulation former, design given last would make the choke un- design, and frequently it is necessary to make month's article. Allow necessarily bulky. for about iV of in- several trials. Sometimes a faulty design will The inductance of the choke coil is sulation between the proportional winding and the core. not be evident from the plain figures, but will to the cross section area of the to the core, square Insulating papers between layers are seldom show up when the full-size drawing is made. of the number of turns of and used with choke coils. If wire, inversely to the layout looks un- The only remedy is to try again. the length of the air gap. This is expressed mathe- wieldy with all the winding on one side of the Having settled on the number of turns and as: it be matically core, may split into two coils on opposite area of the core, the next step is the determina- this legs. Although requires less wire per turn, tion of the wire size. This is done in exactly the

. (i) about 10 per cent, more turns should be added same manner as with the transformer. Then to each coil to make up for the effect of leakage comes the full-size layout, estimation of where L is the in of flux inductance henries, A the net between them. With the drawing com- materials, and resistance calculation. If the area of the core cross section in the around the center square inches, N pleted, length line of the resistance proves excessive for the particular use the number of turns, and G the air core be measured and the to equivalent may theoretical which the coil is to be put) choose a larger in inches. The air is defined of air on the gap equivalent gap length gap computed basis of 0.005 size of wire and make a new layout. The design as the total reluctance of the core, including the inches per inch of core length, and compared is then complete. actual air gap, reduced to an air gap of the same with the value used in the design, to make sure CONSTRUCTION cross section^which will replace it. The value of that the latter was not assumed too small. The air to use in the choke amounts of wire and core equivalent gap designing material may be "IpHE preparation of the core of the trans- is uncertain. It is best figured from the formula: estimated in the same manner as with the trans- * former or choke coil should be undertaken former. The resistance of the Nl choke coil is an first. Several sources of the material are open to . factor, the total important and, knowing length the constructor. Oftentimes a junked pole of wire and looking up its resistance per thou- transformer may be obtained for a small sum in which N is the number of turns of I sand feet in wire, the wire table, on page 277 of the from the shops of the local power company or the current in and B the flux in it be amperes, density August article, may readily estimated. from a junk yard, the core of which may be lines per inch. The value of I If the resistance square being proves greater than desirable, removed, cleaned with kerosene or alcohol, and predetermined, the number of turns so as use a size of wire. adjust larger cut down to the required size. For use in a B to give a flux density of not more than about The solution of a should typical example socket power-supply device, the core of a toy 380 RADIO BROADCAST OCTOBER, 1927

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If the interleaving type of con- drive a spike in the center of one end of the struction is used, the building up mandrel, grind or file off the head, and secure the B of the core may be expedited by end of the spike in the chuck of a hand or breast providing some sort of square cor- drill which is clamped horizontally in a vise. j ner as a guide, such as a cigar box A lathe may also be used. A small geared emery with two adjacent sides removed. wheel is excellent for the purpose. Another com- Only three sides of the core should mon method is to fasten the mandrel to a wooden B be assembled at first, alternating disc which is clamped or wired to the flywheel of the layers as shown in Fig. i; the a sewing machine. If a geared emery wheel or fourth side is to be put in piece hand drill is used, the number of turns of wire by piece after the coils have been may be computed by determining the turns ratio Odd Layers Even Layers slipped into place. The partially between the crank and the spindle, and then completed core is carefully re- counting the turns of the crank. Another way is moved to a vise and clamped, -, Fourth leg to and the legs that receive the coils be added piece bound tightly with a layer of tape, by piece after B or with heavy string, which may windings are in be later unwound as the coils are place pushed onto the core. The joints should be carefully trued up, making sure that the pieces butt together well. A wooden mallet, or a rawhide or lead hammer be Transformer Core may used for this purpose. B FIG. I Preparing the coils is not difficult if done properly. They should transformer will often be found to be about the be evenly wound in layers, not only to All Layers right size without cutting. Ordinary stovepipe make for compactness, but to prevent the iron may be cut to size and used, but it will possibility of two turns of widely different increase the losses, resulting in excessive heating voltages coming together. Coils of small en- and waste of power unless a much larger core is ameled wire should have a layer of paper be- used. The use of regular transformer steel is tween each layer of wire, to keep the winding recommended wherever possible. Motor or arma- even and to improve the insulation. If special ture repair shops sometimes handle it. Supply insulating papers are not available, tracing paper houses that cater to transmitting amateurs such as used by draftsmen, will serve the purpose often stock it and will cut it to any desired size. nicely; ordinary wrapping paper can also be Their advertisements may be found in current used. These papers may be omitted with the amateur periodicals or their addresses obtained larger sizes of enameled wire, since they are from a neighboring "ham." This source lacking, easier to wind evenly and the voltage difference FIG. 2 purchase the best available grade of soft sheet between layers is less. They may be dispensed iron or steel from a local tin shop. It should be with entirely if cotton-covered wire is used. not more than 0.014" thick. It is best to cut the Windings of cotton-covered wire may be to insert the spindle of a revolution counter into a material to size with squaring shears, or to have a made moisture proof and more rigid by applying hole in the free end of the mandrel, as shown in tinsmith as accurate is a thin coat of each do it, work essential. shellac to layer as wound, and Fig- 4- Unless the pieces are square and of uniform size, baking the finished coil to dry it out. Enameled As the coils are to be taped when finished, wind poor joints at the corners will be inevitable and wire cannot be treated in this way, however, as a layer of heavy string around the mandrel and the resulting small air gaps will increase the core the shellac may soften the enamel. Small coils of fasten the ends. This is to be unraveled after the losses to reduction of effective due area. All enameled wire may be made rigid by dipping coils are wound, enabling them to be slipped off be in as a rough edges should removed and the pieces them melted wax, such mixture of beeswax easily and allowing room for the tape. A layer lie flat. and rosin. is should Ordinary paraffin not suitable, as it or two of fibre is then cut to size and squarely If an old core is used, the construction of the may soften if the transfor- transformer will of course depend upon whatever mer runs at all warm. Air r 1 conditions are encountered. But assuming that Large coils may be painted [) Gap-, the raw material is available, several types of with insulating varnish or core arrangement are possible. The one shown black asphaltum paint. in Fig. i, using interleaving joints, is most con- The windings may either venient for transformers. Two different sizes of be made self-supporting or are as pieces required, shown A and B, with wound on a fibre spool enough of each to stack twice as thick as the which is slipped over the completed core when tightly clamped. Another core. The former is the way of building up the core is indicated in Fig. 2, more common method. A but this type is not practical unless the pieces square wooden mandrel of the core are very accurately cut and closely the same size as the core butted This together. construction may be used cross section is first pre- for choke coils, however, since an air gap is re- pared, cut to the same quired somewhere in the core, its location being length that the winding is immaterial as long as the requisite total length is to be, and sanded smooth. provided. Fig. 3 illustrates a modified construc- For the larger core sizes it tion for chokes which has the advantage of being may have to be built up of easier to clamp. In this case the pieces are cut to several thicknesses of wood four different sizes, with enough of each to make glued together. Flanges a up the full thickness of the core. quarter of an inch thick Some sort of insulation between the lamina- are then screwed to each tions to should be provided, reduce the core end, as shown in Fig. 4; losses due to eddy currents. Commercial trans- these are later to be re- former steel usually comes with an oxide coat- moved in order that the ing for this purpose. Ordinary rust is often winding may be slipped off. sufficient when the oxide coating is not present, Some means of rotating but it is better to apply a thin coat of shellac the winding form must to one side of each piece, allowing it to dry be provided. A conveni- thoroughly before assembling. ent arrangement is to 382 RADIO BROADCAST OCTOBER, 1927

bent around the string-covered mandrel and should he covered with Flanged winding Mandrel glued in place. On high-voltage windings, empire cloth tape. The above about 500 volts, add a few layers of em- tape should not be al- pire cloth, which may be obtained at motor re- lowed to bunch at the pair shops. inside corners, or trouble will be experi- WINDING THE COIL enced in inserting the coil is now ready to be wound. Pass the core. The coils should THEfree end of the wire through a small hole not be taped too heav- Chuck drilled in the flange, leaving enough wire to ily, or they will not provide a lead to the panel. If fine wire is used, cool well. the lead and the first few turns should be of in- Small coils of en- sulated flexible wire, to avoid any possibility of ameled wire may be the lead breaking off. The fine wire is then conveniently made by soldered to this, carefully cleaned pf any excess winding them on Revolution Counter flux, and the joint covered with a bit of tape. spools made of pieces FIG. 4 The rest of this first layer is then wound. If the of fibre glued together. wire is cotton-covered, this layer, and each After being wound the succeeding layer as wound, may be given a thin wire may be covered with a layer or two of in each corner of the core for a small bolt, but the coat of shellac as a binder, or insulating papers heavy paper or one layer of friction tape. diameter of the hole should not exceed one- may be used as described above, for enameled The finished coils, after painting or moisture- fifth of the width of the core leg, otherwise the wire. The wire should be wound as tightly as its proofing, may now be placed on the core, un- effective area of the core will be reduced. A panel will It the on each as its coil is of strength permit. may be necessary here to winding string leg pushed bakelite or hard rubber may be provided to wear a glove on the guiding hand, or to pass the on. The fourth leg of the core is then put in, piece hold the terminals, which may be ordinary bind- wire over a piece of cloth held in the hand. by piece, hammering the corners up tightly. ing posts or soldering clips. The leads may be Guiding the wire will be made easier if the hand is If the winding fits too loosely, extra core pieces brought up to the back of the panel and soldered held as far away from the coil as is convenient. may be forced in, taking care not to damage the to the terminals. They should be kept well The turns should be kept close together and not insulation of the coil, or small wooden wedges separated from each other and insulated with allowed to overlap, and extreme care should be may be driven between the coil and the core. "spaghetti" or similar tubing. Flexible insulated exerted to avoid any possibility of shorted turns. hook-up wire makes good leads. The terminals A shorted turn acts as an independent short- of the transformer should be plainly and per- circuited secondary and will burn out as soon --Flexible manently labeled with their voltages. as the transformer is connected to the line. lead The transformer should be tested before being Where taps are brought out, the turns per layer connected to any other apparatus. First con- should be so arranged, if possible, that the taps nect the primary to the line without any load will come at the end of a layer. Be especially on the secondary, to detect any shorted turns, watchful here for shorted turns. In finishing which will show up as excessive heating or as an the winding, pass the end of the wire through actual burn-out. If after several hours the trans- another small hole in the flange and fasten the former is only slightly warm, it is probably all last few turns with a bit of sealing wax. With right. The terminal voltages may be checked fine wire the last few turns and the lead should with an a. c. voltmeter, if desired. be of flexible wire just as at the start. If another After the choke coil is completed the air gap winding is to be placed over the first, they should must be adjusted to the proper value. This can be separated by several layers of friction tape or only be done experimentally, by connecting the empire cloth. choke to its associated apparatus and changing Where a split secondary is used, the two coils the gap until the best filtering action is obtained. may be wound side by side, each covering half The gap should then be filled with cardboard or a the mandrel, rather than one on top of the other, cloth pad and the core permanently clamped, to to insure their having symmetrical characteris- prevent the gap being gradually closed by the tics. An end flange may be removed while a magnetic pull between the two parts of the core. fibre separator is slipped in place, and one side The inductance of the choke cannot be measured filled tightly with cloth strips while the other is directly. If the necessary meters are available, being wound, to prevent the separator being it may be found as follows. Connect the choke in crowded over. A split or center-tapped filament series with a battery and measure the voltage winding of only a few turns may be wound by across the coil and the current in amperes means of a of each it. Its then be calculated pair wires, comprising half of "--Tape half-lapped through resistance may the total number of turns, the end of one wire from Ohm's Law: being connected to the of externally beginning FIG. 5 the other so as to put them in series. The connection between the two is used as the center

tap. The whole assembly should be made rigid, to Then connect it across a source of a. c. voltage The finished be removed from the winding may reduce any audible hum when the transformer of known frequency, such as the no-volt line, form off .one of the and by taking flanges pulling is in use. and again measure the current and voltage. The out the of after which the coil can layer string, Methods of mounting the transformer or choke impedance is then: be off. It then be as in slipped may taped, Fig. 5, coil are shown in Fig. 6. Angle iron, strap iron, or using ordinary friction tape and advancing half square lengths of wood may be used for clamp- the width with each turn. High-voltage coils ing the core. Another method is to drill a hole The inductance, L, may then be calculated from the formula:

Z = T/R2+(2icfL)2

Or its equivalent:

The writer wishes to acknowledge his in- debtedness to Prof. F. S. Dellenbaugh, Jr., of the Massachusetts Institute of Technology, for the FIG. 6 design formulas applying to the choke coil. RADIO BROADCAST ADVERTISER 383

Not a Super-Heterodyne Not Tuned Radio Frequency Not Regenerative

AH models of the R. Q. S. "OCTA-MONIC" will be on display at the Radio World's Fair, New Mcdison Square Qarden, between the 19th & 24th of September inclusive at the booth of the R. Q. S. Mfg. Co., Inc.

BUILT FOR MODBRN BROADCAST CONDITIONS 384 RADIO BROADCAST ADVERTISER

New a

utstanding Contributions

The fundamentally new R. G. S. "Octa-Monic" Receiver developed by David Grimes is one of the four great radio developments of the past 10 years. The R. G. S. "Octa-Monic" principles are fully as important and represent as basic A. C. Tube Models a contribution to the Radio Art as did any of the discoveries of DeForest, Arm- strong, Alexanderson, etc., etc. R. G. S. "Octa-Monic" These new and revolutionary principles of tuning, or the radio frequency end A-C Tube Kit of the R. G. S. "Octa-Monic", produce results not only superior but, these of this Receiver far in advance of receiver developed including detailed instructions and graphic principles tuning place any to date. The R. G. S. "Octa-Monic" is fundamental and is as radically new as blue-prints; all necessary apparatus, power was the (A-C Tube) trans/ormer, four'Uiay line Super-Heterodyne. voltage switch, carefully tested and selected These highly efficient principles employed in the new R. G. S. "Octa-Monic" heavy duty wire, lamp socket connections cover not only the tuning or radio frequency end of this receiver but they cover and cable etc., etc., readv to build ,$114.60 the amplification end as well. The R. G. S. "Octa-Monic" amplifier (Power tube in the last stage,) gives, unquestionably, as perfect reproduction as it is possible to buy, regardless of cost. The R. G. S. "Octa-Monic" comes to you more heavily endorsed by able authorities than any other receiver ever presented to the Radio Public. The editor of one of the most important radio publications in America said that it was the only receiver he had ever seen in his career as an editor to which the terms "new and revolutionary" could be applied in good faith. to Selectivity superior to the super-heterodyne without cutting side bands. Selectivity enough that is R. G. S. "Octa-Monic" eliminate the heterodyne squeals of local stations, operating on a higher octave; selectivity to A-C Tube Chassis equal over the whole dial without being at all critical at any point; selectivity enough separate with ease the local jumble of Metropolitan (New York City, Chicago, San Francisco, etc.) stations; Completely assembled according to latest between stations and WNYC in a lo- selectivity enough to give five (5) degrees of silence WEAF laboratory methods, with instructions and cation 200 yards away from WNYC. blue-prints /or installation, ready to plug- Selectivity positive enough to make use of vernier control unnecessary. in your lamp socket and operate, $129.60 Sensitivity or Distance-Getting Ability. Can work right down to static level. This insures trans-continental or trans-oceanic reception on favorable occasions. R. G. S. "Octa-Monic" Volume sufficient to fill a hall that will seat 5500. A-C Tube Receiver Radio Art will Tonal Quality that is as nearly perfect as development in the permit. housed in an attractive, partitioned, wal- Straight Line Audio Amplification. nut table cabinet, $149.60 Stability Margin of 800 ohms. The average receiver has a stability margin of from 6 to S. "Octa-Monic" eliminates of ao ohms. This high stability margin of the R. G. any possibilities Batteries as low as howling from poor batteries or "motor-boating" from eliminators. registering NOTE: In A- C Tube Models of the 10 volts will deliver a clear tone, free from howling, in this receiver. R. G. S. "Octa-Monic", the perform- at all broadcast wavelengths. ance is practically as startlingly satisfac- Straight Line Radio Amplification insuring reception Volume and tone tory as the Battery models. Straight Line Volume Control that makes distorting of impossible. selectivity are about the same; the Tonal and from stations Automatic Wavetrap for prevention of heterodyning whistling resulting is better on local Duality slightly strong first octave beat. operating on one-half wave-length or on stations but on distant stations or stations Automatic Filament Control. of wea\ signal strength, a slight hum is 22 mils. noticeable. Employs 135 Volts or 180 Volts. Draws and under actual broad- Each R. G. S. "Octa-Monic" is carefully tested with scientific apparatus elaborate ex- To all intents and purposes, while of is just as thor- casting conditions before it leaves the laboratories; every piece apparatus periments have proved all A-C models oughly tested before it is built into this receiver. the new and revolutionary R. G. S. of co-ordinated Receiver built of apparatus. Careful "Octa-Monic" The R. G. S. "Octa-Monic" is a closely quality quite satisfactory. determine the merits tests are the basis for the choice of each piece of apparatus, tests that not only relation to the whole receiver. of each individual part, but more importantly its Price Notice in last and Western Standard Cunningham tubes (?CX joi-A's and iCX 371, Power tube stage) Electric Cone are recommended for best results. Above prices do not include Cunningham is built on A-C and Fewer Tubes nor the "B" Bat- The R. G. S. "Octa-Monic" is highly attractive in appearance. It five-ply, specially walnut twill x to which is mounted beautifully designed panel, finished, tery Eliminator. All A-C models shellaced sub-panel (oo| 9!) dials are in operate on any good eliminator. This, 7 x n. The panel and trimmed gold. instructions and therefore permits the use of your own "B" The R. G. S. "Octa-Monic" is unusually simple to construct. The blueprints It without are to follow and Battery Eliminator. goes say- are more comprehensive and complete than any issued to date. They <-ery easy that B Batteries will also which is one of the receivers ing, of course, come, attractively bound, with your R. G. S. "Octa-Monic," simplest perform perfectly satisfactorily. DEALERS: Write for Complete Merchandizing Plans

BUILT FOR MODERN BROADCAST CONDITIONS RADIO BROADCAST ADVERTISER 385

ff QCTA-MONIC of Ten Years of Radio Development

will to operate. There are but two dials, the nearest possible approach to tuning efficiency, and you find that stations actually "click" or "tumble-in" for you as you slowly rotate your dials. The customary need of wooden screw-drivers or involved balancing devices is entirely removed or "B" Elim- in the R. G. S. "Octa-Monic." Major or minor adjustments are unnecessary. The R. G. S. "Octa- Battery Monic" is free from ordinary service. Tuning condensers are the only moving parts, and as a conse- inator Models quence, there are no fussy mechanisms, either mechanical or electrical, to get out of order. R. G. S. "Octa-Monic" Kit The R. G. S. "Octa-Monic" operates satisfactorily on either a good "B" battery eliminator or all batteries without "motor-boating" or howling. of parts including required apparatus, transformers, rheostat, drilled and en- The R. G. S. "Octa-Monic" is so that it will fit cabinet or console. Write for designed any good graved panel, etc., etc., even the necessary literature. cabinet and console Acme Celatsite unre is enclosed in the attractive container; and Orders cannot be accepted for individual pieces of apparatus or blueprints. complete thorough instructions and blue-prints, ready to The R. G. S. "Octa-Monic" is sold as follows: i. R. G. S. "Octa-Monic" kit of parts including build, $79.60. all required apparatus, transformers, rheostats, drilled and engraved aluminum panel, etc. even the necessary Acme Celatsite wire is enclosed in the attractive container, complete instructions and blueprints, ready to build, $79.60 2. R. G. S. "Octa-Monic" chassis, completely assembled according to latest laboratory methods with complete thorough operational instructions, ready to operate, $89.60, 3. R. G. S. "Octa-Monic" Receiver housed in an attractive, well-designed, walnut table cabinet, $104.60, 4. R. G. S. "Octa-Monic" Tuning kit, including all necessary apparatus and complete blue-prints and instructions on how to build the radio frequency end of this Receiver and on how to hook-up to your favorite amplifier, $59.60 5. R. G. S. "Octa-Monic" Tuning Chassis, completely assembled according to latest laboratory methods with complete instructions and ready to wire to your amplifier, $66.60. All models of the R. G. S. "Octa-Monic" have been adapted to the Cunning- R. G. S. "Octa-Monic" Chasis ham A-C and Power Tubes CX one C and one CX 371. (Four (4) 326, (1) 327, (1) assembled to latest The "B" Eliminator and the Tubes are not included in completely according Battery Cunningham to the This eliminates an on laboratory methods, ready operate, following prices. unnecessary expenditure your part $89.60 because the A-C Tube models of the R. G. S. "Octa-Monic" have been designed to operate satisfactorily with any good "B" Eliminator. It is recommended if R. G. S. "Octa-Monic" Receiver "B" Eliminator has no "C" tap, that use the 40 volts your battery you regular housed in an attractive, of C well-designed.u'al- battery. nut table cabinet, $104.60 The A-C Tube models are sold as follows (i) The R. G. S. "Octa-Monic" A-C Tube kit, in- R. G. S. "Octa-Monic" all with and and instructions, ready to eluding necessary apparatus complete thorough blue-prints, Tuning Kit build, $114.60 (2) The R. G. S. "Octa-Monic" A-C Tube Chassis, completely assembled according to latest laboratory methods, with thorough operational blue-prints and instructions, ready to including all necessary apparatus and com- plug-in your light socket and operate, $129.60 (3) The R. G. S. "Octa-Monic" A-C Tube Re- plete blue-prints and instructions on how ceiver housed in an attractive, well-designed, walnut table cabinet, $149.60 to build the radio frequency end of this receiver and on how to hooff up to your fa- The R. G. S. "Four" employing the Inverse Duplex System (i) R. G. S. "Four" Kit, all parts, com- vorite amplifier, $59.60 plete instructions, $74.40. (2) Chassis, assembled according to latest laboratory methods, $84.40. R. G. S. All prices slightly higher west of Denver. Canadian and Export prices on request. "Octa-Monic" Tuning Chasis Go to your dealer to-day and insist on a demonstration. If he hasn't stocked the R. G. S. "Octa- completely assembled according to latest Monic" yet, tear off and mail to us the attached coupon with the required information. Every effort laboratory methods with complete instruc- will be made to arrange a demonstration for you. tions and ready to urire to your amplifier, Arrange for that demonstration now because you have a real radio thrill waiting for you. In the $66.60 R. G. S. "Octa-Monic" you will hear radio at its best. And when you hear the R. G. S. "Octa- Monic" you will know why it is: "The Synonym of Performance" R. G. S. MANFG. CO., Inc. All models of the R. G. S. and the R. G. S. "Octa-Monic" "Four" are fully protected by Staten Inland, New York Grimes Patents issued and pending. Gentlemen: I want to hear your R. G. S. "Octa-Monic." Please arrange with "Trade Mar^ Registered. my dealer, whose address I have printed below, for a demonstration. I am much interested in this receiver but this request for DEALERS: Write for Complete Plans a demonstration and literature, you understand, entails no obliga- Merchandizing tion on my part. My Name R-G'S Manfg. Co., Inc. Street City or State of the My Dealer's Name . Grimes Radio Engineering Company, Inc. His Address Staten Island New York

BUILT FOR A\ODERM BROADCAST CONDITIONS 386 RADIO BROADCAST ADVERTISER

Tireless Performance

These gulls fly and fly until we wonder how such stamina can be contained in so frail an object. Just so with CeCo Tubes. A strong combination of frail materials. Glass for- a covering; hair-like wires for filament; fine spun metal for grid. But so carefully engineered, so cleverly assembled so skill- fully exhausted, so thoroughly tested that their durability is astounding to the radio operator and fan who judges CeCo performance by ordinary standards. You expect MORE of CeCo Tubes and get more. A Type for Every Radio Need General Purpose Tubes, Special Purpose Tubes, Power Tubes, Filament Type Rectifiers, Gas Filled Rectifiers and A. C. Tubes. Ask your radio dealer for complete data sheet of CeCo Tubes.

C. E. MANUFACTURING CO., Inc., Providence, R. I.

Announcing Our New Gas Filled Rectifier (NO FILAMENT) TYPE D-G

Maximum Volts 300 Maximum Cur. 85 M-A

Long Life without decrease in output is assured if these values are not exceeded.

Easy Filtration. Less strain on Filter condensers and smoother output with less Hum or Ripple.

These tubes are tested in a Standard rectifying circuit using well designed parts. The unit is connected to a ripple test position, and tube checked both by phones and observed on an oscillo- graph, insuring a perfect tube which will give excellent results in well designed and constructed units. PRICE $5.00 Write for Data Sheet giving Makes a Good "B" Eliminator BETTER Characteristics of all CeCo Tubes RADIO BROADCAST ADVERTISER 387 Restored Enchantment

This is the kveready Layerbilt that gives you Battery Power for the longest time and the least money.

IHERE is no doubt of it- radio is better with Battery Power. And never was radio so worthy of the perfection of reception that batteries, and batteries alone, make possible. Today more than ever you need what batteries give pure DC, Di- rect Current, electricity that flows smoothly, quietly, noiselessly. When such is the current that operates your receiver, you are unconscious of its mechanism, for you do not hear it humming, buzzing, crackling. The enchantment of the program is complete. Batteries Radio is better with themselves have im- BatteryPower proved, as has radio. Today they are so perfect, and so long-lasting, At a turn of the dial a radio comes to It is clear. as to be equal to the demands of the program you. It is true. It is natural. You the modern receiver. Power your set thank powers of nature that have with the "B" Bat- once more to the distant Eveready Layerbilt brought quiet reaches of the radio-swept No. 486. This is the tery battery air. You are grateful to the broadcasters whose programs were whose unique, exclusive construction never so enjoyable, so enchanting. You call down makes it last longer than any other blessings upon the that has allotted to each station Eveready. Could more be said? In authority its proper place. And, if are most homes a set of Layerbilts lasts you radio-wise, you will be thankful that you bought a new an entire season. This is the battery set of "B" batteries to make the most out of radio's newest and that Power with brings you Battery most glorious season. all its advantages, conferring benefits and enjoyments that are really tre- NATIONAL CARBON CO., INC. Q] New York San Francisco mendous when compared with the Unit of Union Carbide and Carbon Corporation small cost and effort involved in re- placements at long intervals. For the best in use the radio, Eveready Tuesday night is Eveready Hour Night 8 P. M., Eastern Standard Time Layerbilt. WEAF A'eir York WGR Buffalo WON Chicago WRC Washington WJ A R Providence WCAE Pittsburgh WOC Davenport WGY Schenectady WKKI Huston WSAI Cincinnati Minneapolis'"""'"* WIIAS WDAF Kannu wcco( Louisville City WTAM Cleveland I St. Paul WSR WKI Atlanta Philadelphia WWJ Detroit KSD St. Louis WSM Hashville WMC Memphis

EVEKtADY Pacific Coast Stations 9 P. M., Pacific Standard Time KPO-KGO San Francisco KFI-tos Angeles idio Batteries KFOA-KOMO-Scattte KCW-Portfand heard the neu, flow you Tic-tor record by the Eveready Hour Group -orchestra --they last Middleton's and longer nngen m Down South Overture and Dvorak's Coin' II.,,,.,-:' 388 RADIO BROADCAST ADVERTISER

The Radio Broadcast

SHEETS

RADIO BROADCAST Laboratory Information Sheets are a regular feature of this THEmagazine and have appeared since our June, 1926, issue. They cover a wide range of information of value to the experimenter and to the technical radio man. It is not our purpose always to include new information but to present concise and accurate facts in the most convenient form. The sheets are arranged so that they may be cut from the magazine and preserved for constant reference, and we suggest that each sheet be cut out with a razor blade and pasted on 4" x 6" filing cards, or in a notebook. The cards should be arranged in numerical order. An index appears twice a year dealing with the sheets published during that year. The first index appeared on sheets Nos. 47 and 48, in No- vember, 1926. In July, an index to all sheets appearing since that time was printed. The June, October, November, and December, 1926, issues are out of print. A com- Variable Resist plete set of Sheets, Nos. I to 88, can be secured from the Circulation Department, Doubleday, Page & Company, Garden City, New York, for $ i.oo. Some readers have asked what provision is made to rectify possible errors in these Sheets. In the unfor- To carry plenty of power and withstand tunate event that any such errors do appear, a new Laboratory Sheet with the old high voltage this new unit provides number will outstanding advantages. A single turn appear. THE EDITOR. of the knob gives full resistance variation. Units are practically heat-proof, and will dissipate up to 20 watts through the entire resistance, without of out. Resistance danger burning No. 129 RADIO BROADCAST Laboratory Information Sheet October, 1927 remains constant at any knob setting. Used as improvement The Type 874 Glow Tube over present controls, or add to the "B" HOW IT FUNCTIONS that might be obtained from a B power unit not eliminator that has no using a glow tube. At no load the voltage is 123, /TXHE type 874 tube is a special voltage regulator while at a load of 10 mA. the voltage drops to 90- variable voltage. A * designed for use in B power units to maintain If, however, the receiver requires 20 milliamperes, 50,000 ohm unit at- the voltages, supplied by th^ unit, constant. An the actual voltage available would be only 60 volts. tached to high voltage ordinary B power unit operated without a glow tube has a comparatively poor regulation, i.e., the volt- terminal, a provides age changes considerably with changes in the tap adjustable to any amount of current being drawn from the unit. It would be of decided if this voltage. When replacing present con- obviously advantage voltage could be made to remain practically controls, use 100,000 ohms for detector stant at all loads. The power unit could then be used and ohms for intermediate vol- 50,000 with any receiver irrespective of the amount of current it reason) with the tage. Also 10,000 and 500,000 ohms. being drawn by (within knowledge that the actual voltages designated on Each ...... $2.00 the binding posts of the B device were being supplied. How the glow tube functions to maintain the EA-V~V voltage constant may be understood by reference H DUTV to the curve A. This curve is plotted by measuring the voltage across the glow tube with various load currents and it should be noted that the voltage PotentiomeleR across the tube is practically 90 at all loads up to more than 40 mA. In when Identical with above Re* ordinary operation, there is no current being drawn from the 90-volt a third sistor, plus ter- tap, the glow tube current is about 45 milliamperes. minal. Potentiometers Then, if current is drawn for a receiver from the 90-volt which would cause the volt- provide better tap, ordinarily voltage age to go down, the current through the glow tube regulation for "B" Elim- automatically decreases, providing for the current inators than the two- required by the set. The voltage thereby is maintained at 90. 10 20 30 40 50 60 70 80 90 100 terminal type and are exactly Curve B illustrates the curve of output voltage 1, LOAD CURRENT IN mA. economical because no fixed resistors are needed. Have ample current carrying capacity for any "B" power circuit. Try this improved regulation on your Elimina- tor. Resistances up to 10,000 ohms all wire wound. 1,000, 3,000, 10,000, 25,000, 50,000, RADIO BROADCAST Information Sheet loo.oooWIREohms, $2.00.WOUND No. 130 Laboratory October, 1927

Built for the heavy current of A 6? B power circuits. The wire is wound over asbestos, fixed with heat-proof cement. Ample area. Flat and thin, making them easy to mount. Resistance values for all ABC Power Circuits.

At your dealer's or C. O. D. Send for the new Centraiab A and B power circuit Literature. CENTRAL RADIO LABORATORIES 22 Keefe Ave. Milwaukee, Wis. RADIO BROADCAST ADVERTISER 389

- Dalkite has pioneered but not atpublic expense,

The great im- *rom trouble seldom equalled in . i any industry. Because the first in . provements radio n ltn ,, , Balkite B, purchased 5 years ago, have been power made is stiU in use and will be for years by Balkite. to come. Because to your radio dealer Balkite is a synonym for First noiseless battery charging, quality. Because the electrolytic Then successful socket "B" Balkite "A Contains no light rectification developed and used battery. The Then trickle ' power. charging. And same asBalkite"AB' below, but for by Balkite is so reliable that to- the "A" circuit only. Not a battery most of Bal- today, important all, it is standard on the and charger but a perfected light day signal socket "A" One of unit power supply. kite"AB,"a complete contain- of most American as well the most remarkable develop- systems ments in the entire radio field.Price no in ing battery any form, supply- as and Oriental rail- $32.50. European both "A" and "B" di- ing power roads. Because Balkite is per- from the rectly light socket, and manent equipment. Balkite has while set is in operating only use. pioneered but not at the ex- This pioneering has been pense of the public. important. Yet alone it would Today, whatever type of set never have made Balkite one of you own, whatever type of power the best known names in radio. equipment you want, whatever Balkite is Balkite "B' today the established you want to pay for it, Balkite life in radio. The accepted tried and proved leader because has it. And light socket "B" power supply. of Balkite 300,000 units in use show that it per- production is lasts longer than any device in radio. Three models: "B"-W, 67-90 formance ir* so enormous volts, $22.50; "B"-135,* 135 volts, the hands of $32.50; "B"-180, 180volts,$39.50. that prices Balkite now costs no more than its owners. are astonish- the ordinary "B" eliminator. Because with ingly low. 2,000,000* Your dealer units in the will recom- BALKITE "AB field Balkite mend the Bal- Contains no battery. A complete unit, replacing both has a record "A" and "B" batteries and supplying "A" and "B" kite equip- current directly from the light socket. Contains no of long life battery in any form. Operates only while the set is ment you need in use. Two models: "AB" 6-135,* 135 volts "B" Balkite and freedom current, $59.50: "AB" 180 Chargers 6-180, volts, $67.50. for your set. Standard for "A" batteries. Noise- less. Can be used during reception. FANSTEEL PRODUCTS Inc. Prices drastically reduced. Model COMPANY, s "J,"* rates 2.5 and .5 amperes, for Nprth Chicago, Illinois both rapid and trickle charging, $17.50. Model "N"* Trickle Charger, rate .5 and .8 amperes, ru^_L_>Tttl_ $9.50. Model "K" Trickle Charg- er, $7.50. *SpeciaI models for 25-40 oclej at slightly higher prices. Prices are slightly higher West of the Rockies and in Canada, Balkite Tower Units- 390 RADIO BROADCAST ADVERTISER

W.W.V.-.W.V No. 131 RADIO BROADCAST Laboratory Information Sheet October, 1927

Resistance-Coupled Amplifier

DATA ON CONSTANTS structed B power unit or batteries. No trouble what- soever should be experienced when operating the LABORATORY Sheet No. 132 is given a unit from new batteries, but it is possible that ONcircuit diagram of a resistance-coupled ampli- "motor-boating" troubles will develop when the Unaffected by temperature. fier using the new type 240 high-mu tube (Cunning- amplifier is used with some B power units. The moisture or atmospheric ham 340). To obtain satisfactory operation overall gain is comparatively and difficulties changes. Does not age type high from such an it is essential that several of this sort become more as the orchangein resistance. amplifier pronounced amplifi- points be given careful consideration. In the first place it is essential that excessive C bias is,not used on any of the high-mu tubes. The following values should be used in combination with the voltage shown in the circuit diagram to prevent overloading: 1 volt on the first 3 volts on the second and stage, stage, 3 1000 40.5 volts on the 171 power tube. The second consideration of great importance in the construction of such an amplifier is that the coupling condensers, Ci, Q, and Ca, be of the best quality that can be obtained. Even a small amount of leakage across the condenser, due to faulty insulation, will permit some of the plate potential to leak through it to the grid of the next tube and this will not only cause distortion but very frequently will make the amplifier absolutely inoperative. Use only the best of mica condensers. A solid-molded fixed re- It is, of course, also essential that the plate and sistor, baked under high grid resistance be noiseless in operation but it is not pressure, and accurately necessary that they be exactly of the values given calibrated. Can be soldered in the circuit. A variation of ten or twenty per cent, without affecting accuracy. in these values is quite unimportant. The plate supply for the amplifier may either be a well con- Two Remarkable Radio Resistors

Bradleyunit'A is an outstanding success! It is a fixed resistor for radio circuits of all kinds, and has a capacity of a watts. It is rugged and can be soldered easily, without affecting the rating of the unit. Bradleyohni'E is widely used by manufacturers ofB'Eliminators for plate voltage control. Its remarkably wide, noiseless range, accomplished with two columns of graphite discs, accounts for its tremendous popularity. Use Allen'Bradley resistors in your own hook-ups for superlative results. Follow the example of prominent radio manufacturers. They know!

Bradleyohm-E is available in several ranges and ratings. Sold in distinctive checkered cartons. Ask your dealer for Bradleyohm-E

ELECTRIC CONTROLLING APPARATUS RADIO BROADCAST ADVERTISER 391

Down BringsYou Either of These Guaranteed Eliminators

Super-Power Super-Power "A" Eliminator "B" Eliminator Here is a constant, unvarying, smooth, hnmless current Do away with "B"batteries their annoyance and the at 6 volts for radio receiver 201 any using -A and power constant expense of always getting new ones. The great tubes. Uncertain batteries with their storage changing "B"EIimintoroffered here replaces thempermanently. and other bothers are with. power, chargers done away Just attach this eliminator to your set plug it into an This eliminator "A" batteries. In completely replaces electric light socket and a steady flow of power is de- addition set current at all times it is your gets perfect livered to your set. Hum, noise, distortion and all other always to do its best. Stations come in and ready easily disturbances are gone. Built with heavy duty chokes, quickly. transformers and the finest of condensers in the filter system, it is 100% efficient at all times the most mod- Not a Battery-Charger ern and flexible"B"Eliminator in the world. Used with any good "A" Eliminator it completely electrifies Combination your set. This Super-power "A" Eliminator consists of a large capacity rectifier which changes the alternating house- Complete With Raytheon Tube lighting current into direct current. Then a highly effi- This Super-power "B" Eliminator can be used with cient filter of heavy duty system extremely high capac- any set up to 12 tubes. It comes complete with full ity the direct current from the wave changes pulsating rectifying 85 mil. Raytheon tube, making possible rectifier into even current for the fila- the smooth, lighting delivery of great current at a high voltage. This ments in the radio tubes. Anyone can install this Super- Raytheon tube has indefinite life as it has no filament Eliminator in a few minutes. Just it to power"A" attach burn out. Delivers up to 180 volts. to set and it your plug into an electric light socket. The case is beautifully finished in olive green Duco Your set is with the instantly supplied correct amount with black panel etched in gold. Equipped with rubber- of hum-free used current, only when set is in use. You covered cord and socket plug. High voltage and are of taps assured good current whenever you want it. This variable adjustments enable the use of new tubes "A" Eliminator works power perfectly whether used once or Operates fromllO-120A.C., 60-60 cycle current. Has thousands of times a tap year. It has no moving parts to for intermediate voltage on which 67^ to 90 volts wear out. from socket 110-120 Operates light volts, may be obtained. The detector tap will supply 22'^ to 60-60 cycle A.C., output 6 volts direct current for all 67J4 volts. Variable adjuster will deliver any desired sets to 12 tubes with tubes.There are up power no bat- detector voltage. On and off switch and high and low teries to be charged. It is fool-proof in operation. Once voltage switch are integral parts of the eliminator. No attached it is can permanent you forget you ever additional switches or cords are necessary. heard about "A" batteries. Test It for 30 Days Before Only $1.OO We make the same liberal offer on both the "B" and the You Buy "A" Eliminator. Fill out the coupon and mail it to us with a dollar Just fill out the coupon below and mail it to us with a indicating which eliminator you wish. If both are desired dollar bill. We will send you this "A" Eliminator to send $2.00. Each eliminator must then test. It must deliver satisfaction before After make good while you test it for 30 days before you you buy. another pay 30 days trial pay only $5.00 a month until have cent. After test the balance is due in easy install- you paid ments. $31.50. Only our great buying power enables us to make This "B"Eliminatorordinarily sells for as high as the cash this liberal offer and to also sell this Super-power "A" price of $42.50. This is Eliminator for easily }| less than is ordinarily asked. your oppor- to Take advantage of this offer today. tunity get it for Remember if you are disappointed only in any way we will re- $29.50 pay- able in fund your dollar and easy ay return postage. installments. Y'ou run no risk. Order Cotnpleteln- tractions now. with each unit (or wiring to set.

Alail This Coupon. ELLIOTT RADIO CORPORATION, DEPT. 172 709 West Lake Street, Chicago, Illinois Attached find $1.00 for which you asree to send me ( ) "A" Eliminator at $31.50. (_ ) "B" Eliminator at $29.50. (Send $2.00 if both are desired, as described in your ad.) Full particulars will be sent me by return mail and my money refunded if I do not accept your offer.

Name

Addrets

City Statt, 392 RADIO BROADCAST ADVERTISER

No. 134 RADIO BROADCAST Laboratory Information Sheet October, 192?

More Loud Speaker Horns

THE EXPONENTIAL TYPE sponding to the low frequency cut-off point pf the for your horn, the resonance in the horn will be negligible. CORRECTLY designed horn makes a very The wavelength in feet is determined by dividing A good type of loud speaker. The best horn is the velocity of sound in feet per second, which is in this one which radiates most uniformly over the re- 1 120, by the frequency. For example, a horn whose money quired range of frequency and it has been proved cut-off frequency is to be 32 cycles, corresponding mathematically that the exponentially shaped horn to a wavelength of 39 feet, should have a mouth of conforms closely to this requirement. A horn is of 39 divided by 4, or 9$ feet. These facts indicate the exponential type when its cross section area definitely that a horn, to be a good one, must be doubles at equal intervals along its length. For large. Small horns, whether they are or are not example, a horn would be of the exponential type exponential, cannot radiate the low frequencies. if at the orifice it had an area of { square inches The horn makes it possible for a comparatively and an area of \ square inches, 1 square inch, and small diaphragm to get a good grip on the air and 2 square inches, at distances of 1, 2, and 3 feet thereby produce a large volume of sound. The small respectively from the orifice. The rate of expansion diaphragm and the large horn may be replaced by determines the lowest frequency of which the horn a large diaphragm, as is done in a cone type loud will be a good sound producer. A horn which doubles speaker. in area every foot will reproduce down to about 64 The material of which the horn is made is im- cycles, and a horn which expands twice as rapidly portant. Although a horn may be well designed, will only reproduce well down to 128 cycles. and constructed to the correct size, total length and A properly designed horn should be free from expansion per unit length, it may still fail to give noticeable resonance, and to prevent this the mouth really good results because of resonant effects in the of the horn should be made large enough to trans- material used in the construction. The material mit the sounds coming from it without any great used should have no marked resonant frequency amount of back pressure. In the design of loud unless it is very low, where it might help to increase speaker horns it has been found that, if the mouth the low note radiation. is made comparable to \ of the wavelength corre-

No. 135 RADIO BROADCAST Laboratory Information Sheet October, 1927

Circuits -^^^ - Closely Coupled

*2850 is an amazingly RESONANCE CURVES curve. It is evident from the resultant curve that the low for this "B" Brwer combination of these two circuits produces a resul- price TF TWO circuits are coupled together by a con- tant characteristic curve which is quite broad and A Unit. Yet, in spite of price, denser, as shown in the sketch, and they are both flat on the top in comparison with the quite sharp adjusted so that they are tuned to slightly different peak of either circuit alone. This double peaked ef- Sterling quality is maintained frequencies, we will find that a resonance curve of fect is a characteristic of closely coupled circuits and has been used to some extent in radio receivers. throughout An ordinary resonance circuit consisting of a coil and condenser has a For life,in fact for single comparatively sharp efficiency, long resonance curve and therefore frequencies slightly permanent operation, only the above or below the resonant frequency are not amplified as well as the latter and, therefore, the rectifier genuine Raytheon BH tuned circuit tends to cut down the amplification of the side bands of the wave and this causes is used. For convenience there's incoming some loss of high frequencies. If a receiver is made an "on" and "off switch. up, however, with two coupled circuits, such as we have indicated, this cutting of the side bands will Current regulation? It's perfect! not take place because the flat top of the resonance curve can be made sufficiently broad so as to give Amplifier and detector voltages equal amplification over a band 10,000 cycles wide are variable. An additional FREQUENCY and therefore practically equal amplification can be obtained at all frequencies 5000 cycles above or be- primary control regulates all low the carrier frequency. The circuit has not been combination has the form shown the solid used in actual practice to any great extent because or small sets. the by voltages to suit large curve. The resonance curve of either separate circuit of the difficult tuning required and because of the alone would have the form indicated by the dotted careful adjustments necessary. No wonder the Sterling R-81 is found today on thousands of 3 to 8 tube sets, giving constant, dependable light socket service, Ask your dealer for a demonstration of the R-81. Sterling No. 136 RADIO BROADCAST Laboratory Information Sheet October, 192? THE STERLING MFG. Co. 283 1-53 Prospect Ave. ' Cleveland, Ohio The Sterling Mfg. Co.'i 21-year repu- Carrier Telephony tation stands behind every dealer who sells thcLtcrimg line. THEORY AND USES of being radiated into the air by means of an antenna, is coupled directly to the power line. The /T> HE use of power lines for the dissemination ot coupling between the transmitter and the power * intelligence is becoming increasingly common line is generally made through high-voltage coup- throughout the country. Large power companies ling condensers and special filter and protective have in many cases installed radio equipment for circuits. At the receiving end an ordinary radio inter-communication between various power plants; receiver can be used to detect the signals. It also these radio- frequency signals are transmitted over must, of course, be coupled in some way to the the power lines rather than through the air, and, in transmission line. The system is generally operated this way less interference is encountered. The sys- in duplex so that transmitting or receiving can be tem has also been used in some communities in accomplished at any of the various terminals of the order to make it possible to receive musical pro- system. grams at home by connecting a suitable device In carrier telephony it has generally been found directly to the power socket. best to use carrier frequencies somewhat above For commercial use, this system has certain 50,000 cycles. For comparatively low radio fre- advantages, such as lack of interference, which quencies, around 10,000 cycles, there is considerable make its use valuable, but it is unlikely that the loss in the various power transformers in the line, system will ever replace broadcasting. The number and at frequencies intermediate between about of different stations that can be "tuned-in" by a 10,000 and 50,000 cycles there will very likely be subscriber using the system is naturally limited, sharp resonance peaks causing excessive loss at and this is a definite disadvantage. particular frequencies. Above 50,000 cycles an The system actually differs very little from that ordinary transmission line is fairly satisfactory of ordinary broadcasting, the major difference as a transmitting medium. being that the power of the transmitter, instead RADIO BROADCAST ADVERTISER 393

VARIABLE LINE VOLTAGE CONSTANT OUTPUT REGARDLESS OF LOAD &AYTHEO*

Raytheon Voltage Regulator Tube

TT7XPERIENCE gained in seven years of ex- nounced effect in eliminating the last vestige of \-j haustive research, experiments and tests, ripple from the output, and when connected to have enabled the Raytheon Research Labora- an amplifier will completely eliminate tories to produce a new and fundamentally "motor-boating". improved Voltage Regulator Tube of marked A new feature the starting anode characteristics. incorporated in type R, maintains constantly a state of Raytheon Type R, when incorporated in the ionization in the tube to prevent any "going proper B Power circuits, maintains constant volt- out" regardless of the load fluctuation. on the 90 and lower and age voltage taps greatly Raytheon Type R, can be used in any improves the on the 180 and power voltage regulation unit circuit now on the market employing a glow 135 volt taps, regardless of variations in either tube with greatly improved results. Diagrams of the line voltage or load current. The variable an approved R tube installation, in con- controls can be thus eliminated the Type voltage and nection with the construction of the unit heavy duty Raytheon BH simplified. tube, can be had from the Raytheon Research Furthermore, this new tube has a very pro- Laboratories upon request.

Price Raytheon BH a Raytheon, Type R, 90 volts, 60 milliamperes $4.00 Raytheon BA a 125 milliampere 350 milliampere rectifying tube, rectifying tube becauseofitscon- for complete bat- stant heavy duty tery elimination. output, is espe- Watch for the cially designed for new ABC power use in conjunc- units employing tion with the Ray- Raytheon A the compact efficient recti* this rectifier. theon Type R new in and Tube ner, principle construction. Regulator For A battery chargers and A battery in light socket eliminator units. power units. RAYTHEON MANUFACTURING COMPANY CAMBRIDGE, MASS.

V THE HEART OF RELIABLE RADIO POWER < RADIO BROADCAST ADVERTISER

A Varied List of Books Pertaining to Radio and Allied Subjects Obtainable Free With the Accompanying Coupon

r> EADERS may obtain any of (be booklets listed below by us~ 80. FIVE-TUBE RECEIVER Data are given for the con- **- ing the coupon printed on Page 396 Order by number only. struction of a five-tube tuned radio-frequency receiver. Complete instructions, list of parts, circuit diagram, and \. FILAMENT CONTROL Problems of filament supply, template are given. ALL-AMERICAN RADIO CORPORATION. voltage regulation, and effect on various circuits. RADIALL 81. BETTER TUNING A booklet giving much general in- COMPANY. formation on the subject of radio reception with specific il- 2. HARD RUBBER PANELS Characteristics and proper- lustrations. Primarily for the non-technical home construc- ties of hard rubber as used in radio, with suggestions on tor. BREMER-TULLY MANUFACTURING COMPANY. how to "work" it. B. F. GOODRICH RUBBER COMPANY. 82. SIX-TUBE RECEIVER A booklet containing photo- 3. TRANSFORMERS A booklet giving data on input and graphs, instructions, and diagrams for building a six-tube output transformers. PACENT ELECTRIC COMPANY. shielded receiver. SILVER-MARSHALL, INCORPORATED. RESISTANCE-COUPLED AMPLIFIERS A dis- SOCKET POWER DEVICE A list of 4_. general 83. parts, diagrams, cussion of resistance coupling with curves and circuit dia- and templates for the construction and assembly of socket grams. COLE RADIO MANUFACTURING COMPANY. power devices. J EFFERSON ELECTRIC MANUFACTURING COM- 5. CARBORUNDUM IN RADIO A book giving pertinent PANY. data on the crystal as used for detection, with hook-ups, 84. FIVE-TUBE EQUAMATIC Panel layout, circuit dia- and a section giving information on the use of resistors. grams, and instructions for building a five-tube receiver, to- THE CARBORUNDUM COMPANY. gether with data on the operation of tuned radio-frequency 6. B-ELIMINATOR CONSTRUCTION Constructional data transformers of special design. KARAS ELECTRIC COMPANY. on how to build. AMERICAN ELECTRIC COMPANY. 85. FILTER Data on a high-capacity electrolytic con- TRANSFORMER AND CHOKE-COUPLED AMPLIFICA- denser used in filter circuits in connection with A socket New Transformers 7. TION Circuit diagrams and discussion. ALL-AMERICAN power supply units, are given in a pamphlet. THE ABOX RADIO CORPORATION. COMPANY. for A.C. 8. RESISTANCE UNITS A data sheet of resistance units 86. SHORT-WAVE RECEIVER A booklet containing data Power Supply and their application. WARD-LEONARD ELECTRIC COMPANY. on a short-wave receiver as constructed for experimental 9. VOLUME CONTROL A leaflet showing circuits for purposes. THE ALLEN D. CARDWELL MANUFACTURING distortionless control of volume. CENTRAL RADIO LABORA- CORPORATION. The AmerTran Power Transformer TORIES. 88. SUPER-HETERODYNE CONSTRUCTION A booklet giv- 10. VARIABLE RESISTANCE As used in various circuits. ing full instructions, together with a blue print and necessary Type PF-281, $25.00 each CENTRAL RADIO LABORATORIES. data, for building an eight-tube receiver. THE GEORGE W. 1 1. RESISTANCE COUPLING Resistors and their ap- WALKER COMPANY. to audio amplification, with circuit diagrams. 89. SHORT-WAVE TRANSMITTER Data and blue prints IN audio transformers, S'icationEJUR PRODUCTS COMPANY. are given on the construction of a short-wave transmitter, 12. DISTORTION AND WHAT CAUSES IT Hook-ups of together with operating instructions, methods of keying, and ASAmerTran stand with standard circuits. ALLEN- other data. RADIO ENGINEERING LABORATORIES. products resistance-coupled amplifiers pertinent first in the power transformer BRADLEY COMPANY. oo. IMPEDANCE AMPLIFICATION The theory and practice 15. B-EtlMINATOR AND POWER AMPLIFIER InStrUC- of a special type of dual-impedance audio amplification are field. They are up-to-date in de- tions for assembly and operation using Raytheon tube. given. AI.DEN MANUFACTURING COMPANY. GENERAL RADIO COMPANY. B-SOCKET POWER A booklet constructional well made and 93. giving sign, dependable. 1 53. B-ELIMINATOR AND POWER AMPLIFIER Instruc- details of a socket-power device using either the BH or 313 tions for assembly and operation using an R. C. A. rectifier. type rectifier. NATIONAL COMPANY, INCORPORATED. Type PF-28r, illustrated above, GENERAL RADIO COMPANY. 94. POWER AMPLIFIER Constructional data and wiring 16. VARIABLE CONDENSERS A of the func- of a combined with a an elim- description diagrams power amplifier B-supply becomes virtually A-B-C tions and characteristics of variable condensers with curves unit are given. NATIONAL COMPANY, INCORPORATED. inator when used with AC tubes and specifications for their application to complete receivers. ipo. A, B, AND C SOCKET-POWER SUPPLY A booklet ALLEN D. CARDWELL MANUFACTURING COMPANY. giving data on the construction and operation of a socket- and the proper filter circuit for 17. BAKELITE A description of various uses of bakelite power supply using the new high-current rectifier tube. in its and its BAKELITE THE R. S. Music COMPANY. of from to radio, manufacture, properties. Q. DC voltages 425 650 CORPORATION. 101. USING CHOKES A folder with circuit diagrams of POWER SUPPLY A discussion on with the more circuits wher^ choke coils volts, plate current no milliam- 19. power supply popular showing may particular reference to lamp-socket operation. Theory be placed to produce better results. SAMSON ELECTRIC peres. This unit is designed for and constructional data for building power supply devices. COMPANY. with the ACME APPARATUS COMPANY. use new UX-28i rectify- 20. AUDIO AMPLIFICATION A booklet containing data ACCESSORIES the ing tube, and has a 750 volt on audio amplification together with hints for construc- plate tor. ALL AMERICAN RADIO CORPORATION. 22. A PRIMER OF ELECTRICITY Fundamentals of winding which enables it to be 21. HIGH-FREQUENCY DRIVER AND SHORT-WAVE WAVE- electricity with special reference to the application of dry METER Constructional data and BURGESS cells to radio and other uses. Constructional data on with a or rec- application. buzzers, used UX-28i 2i6-B BATTERY COMPANY. automatic switches, alarms, etc. NATIONAL CARBON COM- CHOKES A PANY. tifying tube. In addition, there 46. AUDIO-FREQUENCY pamphlet showing positions in the circuit where audio-frequency chokes may 23. AUTOMATIC RELAY CONNECTIONS A data sheet are filament heating windings for be used. SAMSON ELECTRIC COMPANY. showing how a relay may be used to control A and B cir- CHOKES Circuit il- cuits. YAXLEY MANUFACTURING COMPANY. the new tubes. 47. RADIO-FREQUENCY diagrams AC Therefore, lustrating the use of chokes to keep out radio-frequency 25. ELECTROLYTIC RECTIFIER Technical data on a new currents from definite SAMSON ELECTRIC COMPANY. of rectifier with curves. KODEL RADIO this single unit will convert AC points. type operating 48. TRANSFORMER AND IMPEDANCE DATA Tables^iving CORPORATION. house current into filament and the mechanical and electrical characteristics of transformers 26. DRY CELLS FOR TRANSMITTERS Actual tests and with a short of their well illustrated with curves what and bias impedances, together description given, showing exactly plate current, grid poten- use in the circuit. SAMSON ELECTRIC COMPANY. may be expected of this type of B power. BURGESS BATTERY CONDENSERS A of the manu- tial. Used with types 709 and 854 49. BYPASS description COMPANY. facture of bypass and filter condensers. LESLIE F. MUTER 27. DRY-CELL BATTERY CAPACITIES FOR RADIO TRANS- AmerChokes in the filter circuit, a COMPANY. MITTERS Characteristic curves and data on discharge tests. AUDIO MANUAL which are often BURGESS BATTERY COMPANY. receiver be constructed to 50. Fifty questions may asked regarding audio amplification, and their answers. 28. B BATTERY LIFE Battery life curves with general AMERTRAN SALES INCORPORATED. curves on tube characteristics. BURGESS BATTERY COM- operate entirely from the house COMPANY, 51. SHORT-WAVE RECEIVER Constructional data on a PANY. lighting circuit. receiver which, by the substitution of various coils, may be 29. How TO MAKE YOUR SET WORK BETTER A non- made to tune from a frequency of 16,660 kc. (18 meters) to technical discussion of general radio subjects with hints on Type H-67 Heater Transformer is 1999 kc. (150 meters). SILVER-MARSHALL, INCORPORATED. how reception may be bettered by using the right tubes. 52. AUDIO QUALITY A booklet dealing with audio-fre- UNITED RADIO AND ELECTRIC CORPORATION. a new unit recommended for use quency amplification of various kinds and the application 30. TUBE CHARACTERISTICS A data sheet giving con- with the RCA UX-226 raw AC am- to well-known circuits. SILVER-MARSHALL, INCORPORATED. stants of tubes. C. E. MANUFACTURING COMPANY. VARIABLE CONDENSERS A bulletin an FUNCTIONS OF THE LOUD SPEAKER A non- tubes and the detector 56. giving 31. short, plifier UY-227 analysis of various condensers together with their charac- technical general article on loud speakers. AMPLION COR- tube. It also has a third filament teristics. GENERAL RADIO COMPANY. PORATION OF AMERICA. DATA Facts about the of direct METERS FOR RADIO A of meters used in of two UX- 57. FILTER filtering 32. catalogue winding capable handling current supplied by means of motor-generator outfits used radio, with connecting diagrams. BURTON-ROGERS COM- 171 tubes. In connection with the with transmitters. ELECTRIC SPECIALTY COMPANY. PANY. RESISTANCE COUPLING A booklet some SWITCHBOARD AND PORTABLE METERS A booklet new becomes 59. giving 33. AC tubes, type H-67 general information on the subject of radio and the applica- giving dimensions, specifications, and shunts used with the power source for the filament and tion of resistors to a circuit. DAVEN RADIO CORPORATION. various meters. BURTON-ROGERS COMPANY. 60. RESISTORS A pamphlet giving some technical data 34. COST OF B BATTERIES An interesting discussion is therefore a real "A" elim- battery on resistors which are capable of dissipating considerable of the relative merits of various sources of B supply, HART- inator. This transformer sells for energy; also data on the ordinary resistors used in resistance- FORD BATTERY MANUFACTURING COMPANY. coupled amplification. THE CRESCENT RADIO SUPPLY 35. STORAGE BATTERY OPERATION An illustrated $12.00. COMPANY. booklet on the care and operation of the storage battery. 62. RADIO-FREQUENCY AMPLIFICATION Constructional GENERAL LEAD BATTERIES COMPANY. Write for Booklet, "Improving the Audio details of a five-tube receiver using a special design of rad o- 36. CHARGING A AND B BATTERIES Vaiious ways of Amplifier," and data on Power Supply Unitt. frequency transformer. CAMFIEI.D RADIO MFG. COMPANY. connecting up batteries for charging purposes. WESTING- 63. FIVE-TUBE RECEIVER Constructional data on HOUSE UNION BATTERY COMPANY. AMERICAN TRANSFORMER CO. building a receiver. AERO PRODUCTS, INCORPORATED. 37. CHOOSING THE RIGHT RADIO BATTERY Advice on 64. AMPLIFICATION WITHOUT DISTORTION Data and what dry cell battery to use; their application to radio, 178 Emmet Street Newark, N. J. curves illustrating the use of various methods of amplifica- with wiring diagrams. NATIONAL CARBON COMPANY. tion. ACME APPARATUS COMPANY. 53. TUBE REACTIVATOR Information on the care of 66. ETERODYN E Constructional details of a with notes on how and when thev should be also make Audio SupER-H vacuum tubes, We Transformers seven-tube set. G. C. EVANS COMPANY. reactivated. THE STERLING MANUFACTURING COMPANY. Choke Coils and Resistors. 70. IMPROVING THE AUDIO AMPLIFIER Data on the 54. ARRESTERS Mechanical details and principlesof the characteristics of audio transformers, with a circuit diagram vacuum type of arrester. NATIONAL ELECTRIC SPECIALTY showing where chokes, resistors, and condensers can be used. COMPANY. AMERICAN TRANSFORMER COMPANY. CAPACITY CONNECTOR of a new device ' 55. Description Transformer Builders for 72. PLATE SUPPLY SYSTEM A wiring diagram and lay- for connecting up the various parts of a receiving set, and * Over Years out plan for a plate supply system to be used with a power at the same time providing bypass condensers between the Twenty-Six amplifier. Complete directions for wiring are given. AMER- leads. KURF-KASCH COMPANY. TRAN SALES COMPANY. (Continued on page $96) RADIO BROADCAST ADVERTISER 395

VITROHM RESISTORS and RHEOSTATS

cover every resistance requirement in current supply unit circuits

to build the power circuit you will this year and there CHOOSEis a dependable Vitrohm Resistor and Rheostat exactly engineered to meet your requirements.

Resistance is the heart of power circuits. Assure yourself of quiet, permanent, and unfailing service by insisting upon Vitrohms for radio. Each of the 95 Vitrohm Radio Resistors and Rheostats is guaranteed unconditionally for continuous duty in any circuit where it operates within its watts-dissipation rating. And Vitrohms have the highest watts-dissipation rating without resistance change of all resistance units.

The Adjustat The Adjustat is a new Vitrohm Rheostat Like all Vitrohm Products, the resistive use in radio designed for current supply element, wire having a low temperature unit circuits. coefficient of resistivity, is embedded and Each Adjustat has 15 steps of resistance permanently protected by a fuse-on coating and is arranged for potentiometer connec- of vitreous enamel. tion. Its compact size, 2% inches in diameter, permits the use of several Adjustats 11 Types are available as listed below. in circuits where adjustable resistance is The Adjustat is priced at $3.00. desirable.

1 4 2 ohms, 3 amp. 507-72, 6 ohms, 1.5 507-73, 20 1.0 507-79, ohm, amp. 507-71, amp. ohms, amp. 507-74,^ 30 0.75 507-80, 50 ohms, 650 m.a. 507-81, 600 ohms, 180 m.a. 1000 m.a. ohms, amp. 507-75, ohms, 125 |j ' 507-76, 225O ohms, 90 m.a. 507-77, 10,000 ohms, 40 m.a. 507-78, 25,000 ohms, 10 m.a.

Raytheon and QRS ABC Units Vitrohm Grid Leaks for Transmitting Circuits

Three new Vitrolim Radio Products are immediately avail- Vitrohm Transmitting Grid Leaks are now available for the able tor use in the 350 m. a. and 400 m. a. Raytheon QRS R.C.A. UX 852 and De Forest P and H transmitting tubes. ABC Current Supply Units. Vitrohm Resistor 507-62, priced at $7.50, is tapped tor all voltages needed in the QRS Ward Leonard has developed a complete standard line of Circuits. transmitting grid leaks and rheostats covering all circuits Vitrohm Resistor 507-70, priced at $7.50, is officially ap- up to and including those of 1,000 watts If are proved by the Raytheon Laboratories for use with their input. you interested in this and radio rectifier. (Illustrated.) other apparatus, write for Radio Vitrohm Rheostat 507-59, priced at $5.50, is designed for Bulletin 507 (1927-1928). It will be sent witaout charge. series primary control in both circuits. Ward Leonard/rectric Company 31-41 SOUTH STREET ^^^X^ MOUNT VERNON, N. Y.

resistor specialists for more than 35 years 396 RADIO BROADCAST ADVERTISER

68. CHEMICAL RECTIFIER Details of assembly, with wiring diagrams, showing how to use a chemical rectifier for charging batteries. CLEVELAND ENGINEERING LABORA- TORIES COMPANY. 69. VACUUM TUBES A booklet giving the characteristics of the various tube types with a short description of where they may be used in the circuit. RADIO CORPORA- TION OF AMERICA. 77. TUBES A booklet for the beginner who is interested in vacuum tubes. A non-technical consideration of the various elements in the tube as well as their position in the receiver. CLEARTRON VACUUM TUBE COMPANY. 87. TUBE TESTER A complete description of how to build and how to operate a tube tester. BURTON-ROGERS COMPANY. 91. VACUUM TUBES A booklet giving the characteristics and uses of various types of tubes. This booklet may be obtained in English, Spanish, or Portuguese. DftFoMBT RADIO COMPANY. 92. RESISTORS FOR A. C. OPERATED RECEIVERS A booklet giving circuit suggestions for building a. c. operated receivers, together with a diagram of the circuit used with the new 4OO-mill ampere r ctifier tube. CARTER RADIO COMPANY. A folder in- ttft 97. HIGH-RESISTANCE VOLTMETERS giving formation on how to use a high-resistance voltmet r, special consideration being g'ven the voltage measurement of socket-power d- vices. WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY. 102. RADIO POWER BULLETINS Circuit diagrams, theory constants, and trouble-shooting hints for units employing th BH or B rectifier tubes. RAYTHEON MANUFACTURING COMPANY. 103. A. C. TUBES The design and operating character istics of a new a. c. tube. Five circuit diagrams show how to Convert well-known circuits. SOVREIGN ELECTRIC & MANUFACTURING COMPANY. APPROVED RADIO PRODUCTS MISCELLANEOUS 38. LOG SHEET A list of broadcasting stations with columns for marking down dial settings. U. S. L. RADIO, Modernize your radio set construc- INCORPORATED. BABY OF tion with these two great Yaxley 41. RADIO TRANSMITTER 9XH-9EK Descrip- tion and circuit diagrams of dry-cell operated transmitter. contributions to convenience, effi- BURGESS BATTERY COMPANY. 42. ARCTIC RADIO EQUIPMENT Description and circuit ciency and good appearance; details of short-wave receiver and transmitter used in 'Arctic exploration. BURGESS BATTERY COMPANY. 43. SHORT-WAVE RECEIVER OF 9XH-9EK Complete Automatic directions for assembly and operation of the receiver. BURGESS BATTERY COMPANY. Power Control 44. ALUMINUM FOR RADIO A booklet containing much radio information with hook-ups of basic circuits, with A new and better inductance-capacity tables and other pertinent data. ALUMINUM COMPANY OF AMERICA. control that power 45. SHIELDING A discussion of the application of cuts in the B elimi- shielding in radio circuits with special data on aluminum shields. ALUMINUM COMPANY OF AMERICA. nator and cuts out 58. How TO SELECT A RECEIVER A commonsense what a radio set and what should the trickle charger booklet describing is, you expect from it, in language that any one can understand. when the set is DAY-FAN ELECTRIC COMPANY. switched on. Cuts 67. WEATHER FOR RADIO A very interesting booklet on the relationship between weather and radio reception, out the B elimina- with maps and data on forecasting the probable results. tor and cuts in the TAYLOR INSTRUMENT COMPANIES. 73. RADIO SIMPLIFIED A non-technical booklet giving trickle charger pertinent data on various radio subjects. Of especial interest to the and set owner. CROSLEY RADIO COR- iwhen the set is beginner PORATION. "switched off, auto- 74. THE EXPERIMENTER A monthly publication which unfail- gives technical facts, valuable tables, and pertinent informa- matically, tion on various radio subjects. Interesting to the experi- No. Series menter and to the technical radio man. GENERAL RADIO ingly. 444 COMPANY. Type. With the exclusively Yaxley 75. FOR THE LisTENER-^-General suggestions for the feature that the selecting, and the care of radio receivers. VALLEY ELECTRIC kaeps voltage drop COMPANY. volts less than two-tenths (2-10) when 76. RADIO INSTRUMENTS A description of various used with sets having a current draw meters used in radio and electrical circuits together with a short discussion of their uses. JEWELL ELECTRICAL IN- equivalent to four 199 type tubes up STRUMENT COMPANY. TROUBLES A to eleven 201 type tubes $5.00 78. ELECTRICAL pamphlet describing the use of electrical testing instruments in automotive work combined with a description of the cadmium test for storage batteries. Of interest to the owner of storage batteries. Cable Connector BURTON ROGERS COMPANY. 95. RESISTANCE DATA Successive bulletins regarding Plug the use of resistors in various parts of the rad'o circuit. INTERNATIONAL RESISTANCE COMPANY. 96. VACUUM TUBE TESTING A booklet giving pertinent data on how to test vacuum tubes with special reference to a tube testing unit. JEWELL ELECTRICAL INSTRUMENT COMPANY. 98. COPPER SHIELDING A booklet giving information on the use of shielding in radio receivers, with notes and diagrams showing how it may be applied practi:ally. Of special interest to the home constructor. THE COPPER AND Preserve the neat appearance of your BRASS RESEARCH ASSOCIATION. 99. RADIO CONVENIENCE OUTLETS A folder giving all wires in set by centering battery diagrams and specifications for installing loud speakers in at some distanc: the set. one cable. Safe, various locations from receiving neat, compact simple YAXLEY MANUFACTURING COMPANY. and sure. Plug is of handsome Bake- lite construction. Contact springs of USE THIS BOOKLET COUPON phosphor bronze. Positive contact. U \nio BROADCAST SERVICE DEPARTMENT RADIO BROADCAST, Garden City, N. Y. No. 660 Cable Connector Plug, Please send me (at no expense) th following book- | Complete $3.00 No. 670 Cable Connector Plug for Binding Post Connections, Complete $3.50

At your dealer's. If he cannot supply you, send his name with your order to YAXLEY MFG. CO. Dept. B-9 So. Clinton Street CHICAGO, ILL. RADIO BROADCAST ADVERTISER 397

TJSF FOR THE FINEST ^OJJf JVnrVTU}KARAS .r/AJVIOPARTS POSSIBLE RESULTS

in building your 2-Dial Karas Equamatic or in building any other high grade receiver

)U must, of course, use Karas Parts when you build your NEW Karas 2-Dial Equamatic Receiver the powerful 5-tube completely balanced and perfectly neutralized radio frequency circuit with which Karas scores again in another sensational success for 1927-28. This new receiver was designed by Karas engineers to operate at maximum efficiency with Karas parts and will only do so when these parts are used exactly as specified. But ALL Karas parts are adapted for use in scores of other popular circuits are specified in the lead- PRODUCTS ing successes of 1927-28 by many leading radio publications and to get the maximum of efficiency the finest possible results you should be sure to use Karas pajrts when building ANY receiver. There is not a circuit in popular use which cannot be vastly improved through the use of these parts in place of less efficient ones.

Karas Engineering is Known All Over the World All over the world, wherever radio has penetrated, Karas parts are known for their precise, careful engineering. The reputation of the entire Karas line has been built upon sound radio engineering practice, allied with precision manufacturing methods, insuring positively and certainly that each Karas part will do exactly what we claim it will do. Other manufacturers do not bother to work within limits of accuracy as close as those established in the Karas factories. Yet we know of no other way to build radio apparatus and have it exactly right. Our standards are high, but they are essential to best results in radio performance. Sound engineering practice, scientific study of every problem presented, and the finding of the correct solution, are Karas essentials upon which we have built the remarkable reputation Karas Products enjoy. For example, in our new Type 28 Transformers we use her- metically spun-sealed steel clad cases in which the impregnated windings are sealed. Moisture cannot enter this case, nor can the insulating compound ever get out. Thus the delicate windings are forever protected from injury. The NEW Karas Type 28 In our new S. F. L. Condensers we work within such close limits that the shafts of any Karas Condenser may Audio Transformer be instantly removed and interchanged with the shaft of any other Karas Condenser of the same type. In the Price, ?8.0O Karas Micrometrie Vernier Dial we obtain a 63 to I gear ratio and you obtain i|ioooth of an inch tuning as a result. You will discover for yourself many other examples of Karas engineering as you use Karas parts in building your sets.

Use these Karas Parts for the 2-Dial Equamatic You will wish to build a Karas 2-Dial Equamatic right away when you know how mar- velously simple it is to operate how powerful and sweet-toned it is and what selectivity and volume it possesses. There is nothing else to equal it in a 5-tube receiver many 6 and 7 tube sets cannot rival the 2-Dial Equamatic. This new Karas receiver is extremely easy to build. Our Complete, detailed instructions make every step very clear and very easy to follow. You can build this receiver in a few hours and thus have one of the finest, most selective radio frequency sets you have ever owned. To build this receiver you will need, in addition to certain standard parts easily obtainable anywhere, the following Karas parts which your dealer has in stock for you: Karas Micrometric 3 Karas Equamatic R.F. Transformers, each $4 $12.00 Vernier Dials, The Karas NEW Output 3 Karas Equamatic Type 17 Removable Shaft S. F. L. Variable Condensers, each $5.25 15.75 Price 3.50 Filter, Price ?8.0O 2 Karas Micrometric Vernier Dials, each $3.50 7.00 2 Karas Type 28 Impregnated Audio Transformers, each $8.00 16.00 I Karas Output Filter 8.00 3 Karas Subpanel Brackets, set of 3 70 I Karas 2-Dial Control System, complete with three extra shafts and all necessary assembly hardware for set 3.00

Mail the coupon to-day for complete list of parts, and full information about this receiver. Then order the necessary Karas and other parts from your dealer so you can build this set without delay. You will be delighted with it -will find it a receiver of tremendous power, volume and tone, and the most satisfactory receiver you ever built. Be sure to mail coupon to us to-day. oAddress

The NEW Karas S.F.L. Condenser with Removable KARAS ELECTRIC CO. Shaft, Price: .O0025 mfd., 5; .O0037 mfd. 5.25; North Rockwell Street Karas Equamatic Inductance .0005 mfd. 5.50 4033-J Chicago Coils, Set of 3, #12.0O

KARAS ELECTRIC CO. 4033 J North Rockwell St. Chicago Please send me complete data on the new 2-Dial Karas Equa- matic Receiver, and also data on the Knickerbocker 4, as well as information about the new Karas parts.

Name .

Address

City . . .

State . . 398 RADIO BROADCAST ADVERTISER

R 375.3. ELECTROLYTIC RECTIFIERS. RECTIFIERS, WHAT KIT SHALL I BUY? (Continued) QST." April, 1927. Pp. 34-38. Dry Electrolytic. in R. 220. BROWNING-DRAKE Five tubes; one stage tuned Developments Dry Electrolytic Rectifiers," S. Kruse. radio frequency (Rice neutralization), regenerative detector of a combination of P - K sin ut sin wt sn of audio combination A new type rectifier, using copper, (jt + PI + (Ji j + ft (tickler control), three stages (special __ discs last mentioned of resistance- and audio). Two controls magnesium, and composition (the ' 1 impedance-coupled + K &,' sin wt -f si*3 ut + K consisting of zinc selenide and copper selenide, among other KB; one 221. LR4 ULTRADYNE Nine-tube super-heterodyne; things), has been perfected for A battery chargers up to I of tuned radio one modulator, one oscillator, %ftf'Sf/fo stage frequency, 3 amperes output, and also for A battery substitutes, as and two three intermediate-frequency stages, detector, stated. Complete details concerning mechanical and elec- transformer-coupled audio stages. trical characteristics of this new type of dry rectifier are 222. GREIFF MULTIPLEX Four tubes (equivalent to six given. tubes); one stage of tuned radio frequency, one stage oj UNITED STATES LAWS AND REGULATIONS. transformer-coupled radio frequency, crystal detector, two Roo7.i. LAWS, and one of QST. April, 1927. Pp. 39-44. Radio Act, 1917. stages of transformer-coupled audio, stage ' "The New Radio impedance-coupled audio. Two controls. Price complete Law, The text of the new Radio Law, as enacted by parts, $50.00. complete Congress in February, 1927, is printed for the benefit of the 223. PHONOGRAPH AMPLIFIER A five-tube amplifier de- readers of QST. vice having an oscillator, a detector, one stage of trans- of former-coupled audio, and two stages impedance-coupled Rii3-5. METEOROLOGICAL. METEOROLOGY, to modulate the audio. The phonograph signal is made 057" April, 1927. Pp. 45-46. Distance Calculations. oscillator in much the same manner as an incoming signal "How Far Is It?" C. C. Knight. Mfr fc- from an antenna. A method whereby distances on the earth's surface from 6 wr with is outlined place to place may be determined accuracy, the in terms of spherical trignometric formulas. As stated, plan is very simple and the average person may obtain very can't get away from "variables" USE THIS COUPON FOR KITS good results using these formulas. Distance on flat maps are YOUin the radio power unit. Line vol- very inaccurate ordinarily, since it is difficult to make RADIO BROADCAST SERVICE DEPARTMENT allowances for the curvature of the earth. tage fluctuations, changes in receiver Garden City, New York. tubes, differences in rectifier tubes, low- R26i. ELECTRON-TUBE VOLTMETERS. VOLTMETER, Please send me information about the kits infollowing Electron-Tube ered rectifier output with age, unequal dicated by number: QST. April, 1927, Pp. 47-53- "The Most Useful Meter," R. F. Shea. drain for different inter-related cir- yet A comparison made between ordinary types of meters cuits well, there are many "variables" used in radio measurements and the vacuum-tube voltmeter latter is when accurate present and for which you must com- shows how far superior the making and values. Five of with suitable resistance values. tests for small current voltage types pensate commercial vacuum-tube voltmeteis, their apparatus, and and their are outlined in Of course, if you are an expert mathe- circuit arrangement, operation, detail. The following are some of the many measurements matician and to engineer, preferring that can be made with this handy instrument : ( i ) Obtaining work the slide rule than to enjoy radio gain through a radio-frequency or audio-frequency ampli- wave form of an oscillator; Meas- programs, then by all means get the fun fier; (2) Checking the (3) Name. (4) Employing it as a wavemeter of out of the resistance uring high impedance; figuring necessary high precision. values. And don't forget to change the Address resistors from time to time to compensate (Number) (Street) R38i. CONDENSERS. CONDENSERS, QST. April, 1927. Pp. 55-57- Electrolytic. for the changing conditions. " " Electrolytic Filter Condensers, L. F. Lenck. if are the radio en- The operation of electrolytic filter condensers, employing But you just average (City) (State)ate) aluminum "pie-plates" and ammonium phosphate in their thusiast, the best results with Thisis seeking ORDER BY NUMBER ONLY. couponcoupo must I make-up in smoothing out the lectified a. c., is outlined. the least troubles, then use variable re- accompany each order. The method of forming plates and precautions to take in sistors to take care of all "variables." RBio27 getting good results are discussed in detail. And when you say variable resistor R344.4. SHORT-WAVE GENERATORS. TRANSMITTER, that means. RADIO BROADCAST. April, 1927. Pp. 57O-573- Slort-Wavt. "A 20 40 80 Meter Transmitter," K. Henney. Supplementing data given in the April, 1926, and Nov. 1926, RADIO BROADCAST, on the construction and operation of a short-wave transmitter, additional information is pre- CLAROSTAT sented concerning a similar set which operates from the A KEY TO RECENT power mains, using two 216-6 rectifiers and two ux-2lo oscillators. The circuit is of the well-known Hartley pattern. Considerable information on details of construction is pre- CAVTION! Clarostat is being imitated RADIO ARTICLES sented so that any one interested in transmitters may set Look for the name on the shell! the outfit. Data on DeForest transmitter tubes are also i stamped up By E. G. SHALKHAUSER given. GET THE FACTS! R35i. SIMPLE OSCILLATORS. OSCILLATOR, is the twenty-third installment of references QST. March, 1927. Pp. 23-27. Calibrator. Ask your local dealer regarding A. Crossley. Clarp- THISto articles which have appeared recently in var- "Quartz Crystal Calibrators, stats and how can them in Two circuits, in which the quartz crystal may be used to you apply ious radio Each Better periodicals. separate reference set up continuous oscillations, are discussed. These employ that new or old radio power unit. between should be cut out and pasted on 4" x 6" cards for either a crystal placed between plate and grid or still, send a quarter for our big 32-page of a vacuum the latter method being or in a scrap book either alphabet- grid and filament tube, filing, pasted and small in book "The Gateway to Better Radio," preferred, With large inductance capacity or numerically. An outline of the Dewey harmonics which contains a vast fund of informa- ically the phase adjusting circuit of the plate, many Decimal System (employed here) appeared last in are said to beobtainable. Thecrystal calibrator, as described, tion on radio in general. the January RADIO BROADCAST. may be used to measure accurately inductances, capacities, meters, transmitters, etc. AMERICAN MECHANICAL frequency MINING AND RADIO. LABORATORIES, Inc. R536 MINING. Radio. Feb., 1927. Pp. 28-ff. 285-87 North Sixth St. Brooklyn, N. Y. "Experiments in Radio Prospecting, "J. G. Alverson. The author gives some of his findings regarding the pro- the R344-4. SHORT-WAVE GENERATORS. TRANSMITTER, pagation of radio waves through the crust of earth, Tkt PIWEI CUROSTAI 15-16. Short-Wave. the wave-front of the electromagnetic wave Q5/. April, 1927. Pp. f showing how A husky for handling "A 15-Meter Commercial Station-2 XS." changes with a change in rock, earth, and minerals. Data In several i a small real power. The General Electric station 2 XS, operating on 5 meters, are presented of many observations made with turns of it covers knob, built for the purpose of transmitting to Buenos Aires 365 transmitter operating on a wavelength of looo meters (300 wide range. Handle! in the year, regardless of weather conditions, is de- and an receiver. up to 40 watts. In days kc.) using ordinary type set is rated at kw. and radiates its three ranges to scribed. The 7 energy 10 ohms. 25-500 from a horizontal doublet with reflector. SETS. SUPER-HETERODYNE, R343 5. SUPER-HETERODYNE ohms, 200-100.000 Radio. Feb., 1927. Pp. 25-ff. Best 1927 Model. ohms. Price S3 50. DETECTOR ACTION DETECTOR ACTION. Ri34. "The 1927 Model of Best's Super-Heterodyne," G. M. QST, April, 1927. Pp. 17-18. Best. "Which Is the Detector Tube?" L. W. Hatry. The improved model of Best's super-heterodyne receiver difference in of detectors and in The operation amplifiers is outlined foi the set builder. The set consists of nine tubes, standard radio circuits is discussed. Whether a tube func- with two tuning dials, and is completely shielded. tions as a detector as an amplifier, or both, depends upon various factors in the circuit, such as grid return, connection Ro84. MAPS AND CHARTS. CHART, of grid leak, etc. Radio. Feb., 1927. Pp. 140-141. L, C, f Data. "Chart for Radio Circuit Calculations," E. L. Hall. R330. ELECTRON TUBES. ELECTRON TUBES. A graphic chart, showing the relation between frequency, QST. April, 1927. Pp. 26-30. UX-240. inductance, and capacitance for values as used in radio "CX-340 UX-240," R- S. Kruse. The is diawn for of calculation. The STANDARD CLAROSTAT between the ux-2oi-A and the ciicuits, purposes rapid In making a comparison within several The ideal B-voltage tap accuracy of results obtainable may be per new ux-24O amplifier tube, the writer presents the details control, providing the cent, of the mathematical calculation, as stated. The range for upon which good amplification depends, namely: (i) The precise voltage each may be extended beyond those actually shown by a simple circuit and for any type amplification constant of the tube; (2) the plate impedance process. of tube. Universal resis- of the tube; (3) the impedance of the transformer. The tance of from range ux-240 is said to be excellent for c. w. and for resistance- to 5,000.000 practically broadcast sets. As a detector, this new tube is said R350. GENERATING APPARATUS; ohms, with a current car- coupled to eliminate considerable interference because of its peak TRANSMITTING SETS. ry ingcapacity of 20 watts. TRANSMITTER, Noiseless. characteristics. QST. March, 1927. Pp. 33-3?- nonpackinf*. Hexible. foolproof and indestruc- "A Flexible Transmitter," F. J. Marco. tible within its is described which uses the Armstrong working R25I.2. THERMO-ELEMENT. THERMO-COUPLE A transmitter capacity, Price S2.25 circuit. It is said to be capable of a QST. April, 1927. Pp. 31-32. DKVHIK. tuned-grid tuned-plate to either the 20-, the or the 8o-meter band "A Sensitive Thermo-Couple," B. J. Chromy. quick change 40-, or means of coils. A very inexpensive and useful thermo-couple, made of (1500-, 750-, 3750-kc. band) by plug-in an to watts be used tellurium and platinum wire, is described. The method of Tubes giving output power up 7.5 may circuit methods cf constructing the device and calibrating its range, together with the apparatus. Complete diagrams, data are with a wiring diagram and experimental data, are given. tuning, and operation given. RADIO BROADCAST ADVERTISER 399

Most popularB FWer Unit /or radio sets inthe^orld 7he Super B, illustrated above is only $29$?, complete with ^Cajesiic Super-Power -Rectifierliibe.

GRIJNOV^ HINDS " CO, 4572 ARMITAGE AVE, CHICAGO-ILL 400 RADIO BROADCAST ADVERTISER

Ri 13.5. METEOROLOGICAL. METEOROLOGY. R$$2. TRANSMISSION OF PHOTOGRAPHS. PHOTOGRAPH I. Radio Proc. R. E. Feb., 1927, Pp. 83-97. World. Feb., 26, 1927. Pp. 4-5. TRANSMISSION. "The Correlation of Radio Reception with Solar Activity "First Television Hookups Elucidate Alexanderson and and Terrestrial Magnetism," G. W. Pickard. Baird Plans," H. Wall. Atmospheric changes and the resulting magnetic storms The Alexanderson and the Baird systems of television affecting radio reception are discussed. Atmospheric changes are shown in schematic diagram. The two systems are com- are said to be due to radiations and emissions from the sun. pared and the advantages and disadvantages outlined. The author compares observed radio reception data, obtained over a continuous period, with meteorological data, Rii3.4. IONIZATION; HEAVISIDE LAYER. HEAVISIDE and finds a close correlation of sunspot disturbances and Radio World. Feb., 26, 1927. Pp. 8. LAYER. radio reception on the upper broadcast wave spectra. "Radio Ceiling Again Verified." Graphs drawn from observed data obtained from station Experiments conducted by the Carnegie Institute regard- WBB.M show that, when average results are compared with ing the existence and probable nature of the Kenelly- magnetic storms, both variations appear to be more or less Heaviside layer have established that such a layer actually ex- at in phase. ists an altitude varying between 50 and 1 30 miles. Whether the radio waves are 'reflected or refiacted from this upper Rim. GENERAL METHODS AND APPARATUS. MEASUREMENTS, layer is not definitely known. Fading may be explained Proc. /. R. E. Feb., 1 1. Receiver. on the that waves neutralize each " 1927. Pp. 90-1 assumption interfering Importance of Laboratory Measurements in the Design other. of Radio Receivers," W. A. MacDonald. A series of thirteen fundamental tests are outlined for de- Ro2o. TEXTBOOKS. TEXTBOOKS. termining individual and overall characteristics of com- The New York Sun. Radio Section. Nov. 6, 1926. Radio. mercial receivers. A series of graphs gives the results ob- "An Expert's 3-Foot Shelf of Radio Books, "S. R. Winter, tained from a typical circuit and depicts to what degree The following is a list of textbooks and published material a high precision standard may be used. selected by Doctor Dellmger, of the Bureau of Standards, for the radio man: Ri34. DETECTOR ACTION. DETECTOR, 1. "Signalling Through Space Without Wires," H. Proc. I. R. E. Feb., 1927. Pp. 113-153. Action. Hertz. The Moorish design Pacent Cabinet NEW "A Theoretical and Experimental Investigation of De- 2. "The Principles of Electric Wave Telegraphy and Tele- Cone in two-tone antique finish $o nn tection for Small Signals," E. L. Chaffee and G. H. J. A. mahogany ...... *jiJ' uv phony," Fleming. Browning. 3. "Electric Waves," H. Hertz. Data are given on the detecting properties of diode and 4. "The Principles Underlying Radio Communication," triode valves as used in radio circuits. The mathematical Bureau of Standards.

presentation is expressed in terms of the circuit impedances 5. "Radio Instruments and Measurements," Circular TONE and the first and second partial differential coefficients 74, Bureau of Standards. QUALITY^ of the static characteristic curves of the device, taken at 6. "Robinson's Manual of Radio Telegraphy," United the points on the curves determined by the steady polarizing States Navy. " It is then that the is so How to a Wireless is their voltages. assumed impressed signal 7. Become Operator," Chas. B. outstanding small that for these coefficients any given steady voltages " Hayward. can be assumed constant within the range of the variation 8. Direction and Position Finding," R. Keen, of feature due to the signal voltage. Sheffield, EnglancL 9. "I. C. S. Handbook for Radio Operators," Interna- three R430. INTERFERENCE ELIMINATION. INTERFERENCE, tional Correspondence Schools. new Pacent QST. March, 1927. Pp. 9-14. Elimination. to. "Radio Telephony for Amateurs," S. Ballantine. "Cures for 'Power Leaks,'" R. S. Kruse. n. "Radio for Everybody," A. C. Lescarboura. products bring a new and The article states that power leaks and other sources of 12. "Radio for All," H. Gernsback. be eliminated keener of radio high-frequency interference may by proper 13. "Elements of the Mathematical Theory of Electricity enjoyment by filtering. The '"Tobe," the "Dayfan," and other interference and Magnetism," J. J. Thompson. "Handbook of for the true eliminating devices are described. 14. Technical Instruction Wireless fidelity and realism Telegraphists," C. Hawkhead and H. M. Dowsett. TRANSFORMERS. "Wireless of their Ri42.3- INDUCTIVE COUPLED CIRCUITS. 15. Telegraphy and Telephony," H. M. Dow- reproduction. QST. March, 1927. Pp. 20-22. Tuned R.F, sett. "The Theory of a Tuned R. F. Transformer," G. H. 16. "The Thermionic Vacuum Tube and Its Application," Browning and F. H. Drake. H. J. Von der Bijl. A mathematical presentation, supplemented by experimen- 17. "The Radio Amateur's Handbook," F. E. Handy. tal curves of tuned radio-frequency transformers, is given. 18. "Yearbook of Wireless Telegraphy," Wireless Press, The results show that the secondary inductance should be Ltd. (Published annually). made as large as possible, the losses made very small, and 19. "Electromagnetic Oscillations in Oscillators and Radio the as low as Zenneck. primary-secondary capacity kept possible, Telegraphy,"- j. " in order to obtain maximum efficiency. 20. "Wireless Telegraphy and Telephony Chas. R. Gibson. Ri40. RADIO CIRCUITS. MASTER-OSC. 21. "Radio Laws and Regulations of the United States," QST, March, 1927. Pp. 38-fT. AND POWER-AMP. U.S. Department of Commerce. "How Our Tube Circuits Work. Part 4," CIRCUITS. 22. "The Realities of Modern Science," John Mills. R. S. Kruse. 23. "Electric Oscillations and Electric Waves," G. W. In this fourth of a series of articles on radio circuits the Pierce. writer takes up the many phases of oscillator circuits with 24. "Principles of Radio Communication," J. H. More- and without amplifier hook-ups. A variety of subjects deal- croft. ing with this of circuit are taken as for instance: of Radio Transmission and with " type up, 25. "Principles Reception Wobbulatipn," its causes and remedy; steadiness of wave Antenna and Coil Aerials," Bureau of Standards. with and without the use of a crystal; the characteristics 26. "Methods of Measurement of Properties of Electrical of the Armstrong circuit; single- and multi-stage amplifiers Insulating Materials," Bureau of Standards. and their use as wave-changers in order to prevent trouble- 27. "Handbook of Safety Rules for Radio Installations," some feedbacks. Bureau of Standards. 28. "Wireless Telegraphy and Telephony," W. H. Eccles. R9oo. MISCELLANEOUS. FUTURE 29. "Thermionic Tubes in Radio Telegraphy," John Popular Radio. March, 1927. Pp. 229-ff. OF RADIO. Scott-Taggart. "Radio in 1950 A. D.," Dr. Lee DeForest. 30. "Radio Broadcast's Knockout Receiver," Doubleday, The author enumerates some of the future possibilities Page and Company. found in the stored-up energy of waves as utilized for radio 31. "How to Build Your Radio Receiver," Popular Radio transmission and reception. The newly discovered cosmic Publishing Company. ray, having a wavelength of 0.0004 angstrom units, and 32. "The Radio Service Bulletin," United States De- The new 17-inch Pacent Balanced Cone es- traveling at a much greater speed than light waves, as partment of Commerce. (Monthly). tablishes a new standard in cone " stated by Millikan, is said to have many possibilities. 33. Introduction to Line Radio Communication," Signal speaker performance Corps Pamphlet. 11342.7. AUDIO-FREQUENCY AMPLIFIERS. AMPLIFIERS, 34. "Modern Radio Operation," J. O. Smith. Radio. March, Audio- "TheC. W. Manual," B. Dow. "Popular 1927. Pp. 253-ff. 35. J. Audio Amplifiers," E. L. Bowles. Frequency. 36. "Radio for Amateurs," A. H. Verrill. The underlying principles covering audio-frequency 37. "Circular No. 24," Bureau of Standards. reproduction and amplification are outlined in an elementary 38. "Copper Wire Tables,"- Bureau of Standards. discussion. Causes and effects of distortion, at either the 39. "The Radio Direction Finder and Its Application to transmitting or receiving end, may be corrected, it is said, Navigation," Bureau of Standards. by proper design and construction of the apparatus. 40. "Formulas and Tables for the Calculation of Mutual and Self-Inductance," Bureau of Standards. R2oi.s. SHIELDING AND GROUNDING. SHIELDING. 41. "The Outline of Radio," J. V. L. Hogan. in Radio Radio News. Feb., 1927. Pp. 988-fF. 42. "Qualitative Experiments Transmission," "Shielding in Radio Receivers," M. L. Hartmann and Bureau of Standards. J. R. Meagher. ACTION. REFLEX A brief and elementary discussion on the theory of shield- Ri34.8. REFLEX receivers is Some of the benefits of shield- Feb., 21-27. ACTION. ing of radio given. QST." 1927. Pp. ing are said to be increased amplification, increased selectiv- Developments in Tuned Inverse Duplex," David 2. ity, better neutralization, and decreased body-capacity Grimes. Part effects. In this second of two articles, the Inverse Duplex System of amplification in the radio and audio circuits, developed for are discussed. For the audio stage, a trans- R37S-17S- 3 ELECTROLYTIC RECTIFIERS.K.ECTIFIERS. RECTIFIERS,KECTIFIER: duplexing, former-resistance-transformer arrangement is said to be The Transmitter. Dec. 1927., Pp. lo-ff. Cbemicail. desirable and effective. In order to obtain "Practical Chemical Rectifiers," C. R. Stedman. the most equal over the entire broadcast band, a radio fre- In constructing a practical chemical rectifier, the writer amplification filter circuit, comprising a choke suggests that pure aluminum should be used. Both the lead quency-audio frequency The Pacent PHONOVOX (electric pickup) at- coil and a fixed condenser, is connected between and aluminum plates, however, should be of the same size. large tached to ami Circuit and are shown. your phonograph radio, repro- The solution recommended is either bicarbonate of soda stages. diagrams panel layouts duces records with the tone quality 4 ~* -j -Q or ammonium phosphate. Constructional details and wiring rivaling the electric ... iL' ALTERNATING CURRENT SUPPLY. A.C. FOR phonograph diagrams are given. R344-5. RADIO BROADCAST. Feb., 1927. Pp. 393-396- FILAMENTS. demonstration "A.C. As a Filament-Supply Source," B. F. Miessner. Ask your dealer for a R342.7. AUDIO-FREQUENCY AMPLIFIERS. AMPLIFIERS, The writer discusses the problems encountered in light- write dealer doesn't handle. Radio World. Feb., 19, Pp. 5. Audio-Frequency. or us if " 1927. the filaments of radio vacuum tubes from the regular More Volume from Lower Ratio in Audio Transformers, ing direct or current obtained from the light socket. a K. B. alternating Frequent Condition," Humphrey. to eliminate the in the a.c. Filter systems, devised hum In analyzing the importance of proper relation of audio line, which many varying characteristics, as shown transformer ratios to tube it is stated presents winding resistance, as to the in are given. The 1 1 2 type tube, compared that consideration should be given the various factors in- graphs, the 201-A type, and the wx- 12 type, is considered the volved from an engineering standpoint when selection is 199, RADIO CORPORATION best tube to use for radio-ami audio- frequency amplifica- made. Usually, it is said, more volume and less distortion tion in a.c. lighted filament circuits. 156 W. 16th Street, New York City is obtained from properly constructed low-ratio transformers than those of high ratio. RADIO BROADCAST ADVERTISER 401

87% At 30 Cycles!

CURVE SHOWS TRANSFORMATION OF SILVEP-MAR3HHLL TffANSFORMEKS WHEN OPERATING OUTA TUBE HAVING A PLATE RESISTANCE OF10.3OO OHMS.

IIP In this standardized Hack shielding case are housed the famous 220 audio and 121 output At an S-M 220 audio transformer in a standard transformers, 222 output, 230 push-pull input, jo cycles, amplifier 231 push-pull output, 325 filament. 329, j2pA circuit gives 87% of the amplification obtained at 1000 cycles, while its and Unichoke and 330 power transformers, 331 curve is substantially flat from 100 to 1000 cycles. Above 2000 cycles, the 332 condenser bank. And a new super-power curve for a single stage falls off gradually, while in a standard two stage full wave ABC supply transformer is on the way the curve is flat to above type 328, at $18.00, for one or two 2168 or amplifier circuit, substantially up 5000 cycles 281 tubes. which frequency it falls off rapidly to keep static, heterodyne squeals and "set noise" at a minimum.

The above paragraph sums up at once the desirable characteristics of an audio amplifier for realistic recreation of broadcast programs, and the actual performance of S-M audio transformers. It is just this fact that has made 22o's the choice of over half of the designers of the new 1927-1928 circuits, for engineers know that the short cut to the finest of quality is to use S-M audios. Experienced fans know this too, as is proven by the fact that 22o's have outsold every other transformer in their class by a wide margin for over a year. And S-M audios are signally favored by being used in more broadcasting stations than any other types. WCAE, WBBM, WEBH, KFCR, WTAQ, KGDJ, WLBF, and many others. WCFL, the "Voice of Labor" checks quality of all programs with them. Nathaniel Baldwin, Inc., famous speaker experts, test with 22o's and 22i's. Sillier- Marshall now two smaller size audio offers Your guarantee of quality is to use S-M 220' s and 22i's in every circuit you build, and transformers replacement in old sets, for worl^ you'll find that over half the popular 1927 and 1928 circuits will give you just this same wherever and size is a consideration. 240 price Type guarantee of quality. But S-M promises unconditionally that you can improve any set by audio is or to the ma- transformer equal superior using 22o's and 22i's, and back? the promise by the offer of your money back if 22o's and audio but does not jority of high-grade transformers, 22i's don't give you more satisfactory quality than you've ever heard before. below So cycles to the extent reproduce frequencies The 220 audio is the biggest value on the market, and its performance- measures up to that the 220 does. Its famous single stage amplifier its 4 pound size. It contains more steel and copper than any other transformer the mea- curve is shown above in two the stages, 243*5 af- sure of transformer merit. Price $8.00. the same 5000 as do ford practically cycle cut-ojf 221 output transformer not only protects loud speakers against power tube plate cur- 22o's, althought this is not evident in the single rents, but compensates low frequencies for all loud speakers. Price $7.50, or with cord curve above. 241 stage output transformer offers and tip jacks, No. 222, $8.00. the same low as 221 frequency compensation type 230 push-pull input and 231 push-pull output transformers are priced at $10.00 each. and 222. Due to their small size, these transformers will in almost the older and once fit any of receivers, The New Shielded Six Is installed, will wori^ wonders in tone qualitv im- Ready! their that provement, for performance nearly equals The Improved Shielded Six is ready, the very latest model of this excellent receiver of 22d's and 22i's. Size 3 f high, 2\" wide, V which has over a year of successful and satisfying performance to its credit. The Improved 2j" deep, weight 2 Ibs. 4 ozs. each. Price, 240 audio model has vastly increased selectivity, greater distance getting ability, and the same fine $6.00, 241 output $5.00. tone that has made almost every builder say of the original, "That's the finest set I've ever heard!" Laurence Coc^aday, for the preferred audio am- This the Six offers the additional of with 210 plifier for the LC-20 receiver uses t!*o 24o's and a year possibilities push-pull amplification tubes for the man who wants the utmost. All in the Six deserves the as 241 with an S-M power supply! all, reputation the finest tuned R. F. kit you can buy, equalled only by $200 to $400 factory built sets. Yet it's priced at but $95.00 for the complete kit, or $142.00 assembled, in cabinet, and guaranteed to satisfy you. S-M will be glad to tell owners how last year's model can be converted to the Improved Six, or push-pull 210 amplification installed with simple changes.

We can't tell you the whole story of new S-M ---_... developments, so if you'll just fill in the coupon, and SILVER-MARSHALL, Inc. mail it with ice to cover we'll send postage, you 838 West Jackson Blvd., Chicago, U. S. A. free more up-to-the-minute advance radio informa- Please send me information on new S-M tion than you could buy in a text book. developments, for which I enclose IDC.

Silver-Marshall Inc., Name 838 West Jackson Blvd. Chicago, U. S. A. Address. . 402 RADIO BROADCAST ADVERTISER "RADIO BROADCASTS" DIRECTORY OF MANUFACTURED RECEIVERS

d A coupon will be found on page 416. All readers who desire additional bers in the coupon, mail it to the Service Department of RADIO BROADCAST, information on the receivers listed below need only insert the proper num- and full details will be sent. New sets are listed in this space each month.

KEY TO TUBE ABBREVIATIONS NO. 484. BOSWORTH, B5 NO. 413. MARTI

99 60-mA. filament (dry cell) Five tubes; 2 t.r.f. (26), detector (99), 2 transformer Six tubes: 2 t.r.f., detector, 3 resistance audio. All 01-A Storage battery 0.25 amps, filament audio (special a.c. tubes). T.r.f. circuit. Two dials. tubes a.c. heater type. Two dials. Volume control: control: size: 23 x 7 12 Power tube (Storage battery) Volume potentiometer. Cabinet resistance in r.f. plate. Watts consumed : 38. Panel size 71 Power tube (Storage battery) x 8 inches. Output device included. Price $175. 7 x 21 inches. The built-in plate supply employs one 16-B Half-wave rectifier tube 16-B rectifier. The filaments are supplied by a small NO. 406. CLEARTONE 110 80 Full-wave, high current rectifier transformer. Prices: table, $235 including tubes and rectifier 81 Half-wave, high current Five tubes; 2 t.r.f., detector, 2 transformer audio. rectifier; console, $275 including tubes and rectifier; Hmu High-Mu tube for resistance-coupled audio All tubes a. c. heater type. One or two dials. Volume console, $325 including tubes, rectifier, and loud speaker. 20 Power tube (dry cell) control: resistance in r. f. plate. Watts consumed: 40. 10 Power Tube (Storage battery) Cabinet size- varies. The plate supply is built in the NO. 417 RADIOLA 28 00-A detector receiver and one rectifier tube. Filament Special requires sup- Eight tubes; five type 99 and one type 20. Drum 13 Full-wave rectifier tube down transformers. Prices from ply through step range control. Super-heterodyne circuit. C-battery connec- 26 a. c. tube $175 to which includes 5 a.c. tubes and one rectifier Low-voltage high-current $375 tions. Battery cable. Headphone connection. Antenna: 27 Heater type a. c. tube tube. loop. Set may be operated from batteries or from the NO. 407. COLONIAL 25 power mains when used in conjunction with the model 104 loud Prices: $260 with tubes, DIRECT CURRENT RECEIVERS Six tubes; 2 t. r. f. (01-A), detector (99), 2 resistance speaker. battery with model 104 loud a. c. audio (99). 1 transformer audio (10). Balanced t.r.f. operation; $570 speaker, NO. 424. COLONIAL 26 circuit. One or three dials. Volume control: Antenna operation. switch and on 1st audio. Watts con- Six tubes; 2 t. r. f. (01-A), detector (12), 2 trans- potentiometer NO. 540 RADIOLA 30-A sumed: 100. Console size: x x 18 inches. former audio (01-A and 71). Balanced t. r. f. One to 34 38 Output Receiver characteristics same as No. 417 except that three dials. Volume control: antenna switch and poten- device. All tube filaments are operated on a. c. except a.c. type 71 power tube is used. This model is designed to tiometer across first audio. Watts required: 120. Con- the detector which is supplied with rectified from operate on either a. c. or d. c. from the power mains. sole size: 34 x 38 x 18 inches. Headphone connections. the plate supply. The rectifier employs two 16-B tubes. Price built-in filament The combination rectifier power amplifier unit uses The filaments are connected in a series parallel arrange- $250 including plate and supply. two type 81 tubes. Model 100-A loud speaker is con- ment. Price $250 including power unit. NO. 507. CROSLEY 602 BANDBOX tained in lower part of cabinet. Either a short indoor or long outside antenna be used. Cabinet size: NO. 425. SUPERPOWER Six tubes; 3 t.r.f. (26), detector (27), 2 transformer may 42'/2 x 29 x 17% inches. Price: $495. Five tubes: All 01-A tubes. Multiplex circuit. Two audio (26 and 71). Neutrodyne circuit. One dial, Cabinet size: x x inches. heaters for the dials. Volume control: resistance in r. f. plate. Watts 17} 5} 7|- The a.c. tubes and the 71 filament are in NO. 541 RADIOLA 32 required: 30. Antenna: loop or outside. Cabinet sizes: supplied by windings B unit transformers available to either on or This model combines receiver No. 417 with the model table, 27 x 10 x 9 inches; console, 28 x 50 x 21. Prices: operate 25 60 is means of uses 81 table, $135 including power unit; console, $390 includ- cycles. The plate current supplied by 104 loud speaker. The power unit two type rectifier tube. Price for set unit tubes and a 10 is ing power unit and loud speaker. $65 alone, power $60. type power amplifier. Loop completely enclosed and is revolved by means of a dial on the panel. NO. 408. DAY-FAN "DE LUXE" Models for operation from a. c. or d. c. power mains. A. C. OPERATED RECEIVERS Cabinet size: 52 x 72 x inches. Price: $895. Six tubes; 3 t.r.f., detector, 2 transformer audio. All 17% 01-A tubes. One dial. Volume control: potentiometer NO. 508. ALL-AMERICAN 77, 88, AND 99 539 17 across r.f. tubes. Watts consumed: 300. Console size: NO. RADIOLA Six 3 t. r. f. detector 2 transformer tubes; (26), (27), 30 x 40 x 20 inches. The filaments are connected in Six tubes; 3 t. r. f. (26), detector (27), 2 transformer Rice neutralized t. r. f. drum audio (26 and 71). Single series and supplied with d.c. from a motor-generator audio (26 and 27). One control. Illuminated dial. tuning. Volume control: potentiometer in r. f. plate. set which also supplies B and C current. Output de- Built-in power supply using type 80 rectifier. Antenna: Cabinet sizes: No. 77, 21 x 10 x 8 inches; No. 88 Hiboy, vice. Price $350 including power unit. 100 feet. Cabinet size: 25A x 7% x 8'/8 . Price: $130 25 x 38 x 18 inches; No. 99 console, 27} x 43 x 20 inches. without accessories. Shielded. Output device. The filaments are supplied NO. 409. DAYCRAFT 5 by means of three small transformers. The plate supply NO. 421. SOVEREIGN 238 employs a gas-filled rectifier tube. Voltmeter in a. c. Five tubes; 2 t.r.f., detector, 2 transformer audio. Seven tubes of the a.c. heater Balanced t.r.f. supply line. Prices: No. 77, $150, including power unit; All a. c. heater tubes. Reflexed t.r.f. One dial. Volume type. Two dials. Volume control: resistance across 2nd audio. No. 88, $210 including power unit; No. 99, $285 in- control: potentiometers in r.f. plate and 1st audio. Watts consumed: 45. Console size: 37 x 52 x 15 inches. cluding power unit and loud speaker. Watts consumed: 135. Console size: 34 x 36 x 14 inches. The heaters are a small a. c. Output device. The heaters are supplied by means of supplied by transformer, while the is means of rectified a.c NO. 509. ALL-AMERICAN "DUET"; "SEXTET" a small transformer. A built-in rectifier supplies B plate supplied by and Price less tubes. The using a gaseous type rectifier. Price $325, including Six tubes; 2 t. r. f. (99), detector (99), 3 transformer C voltages. $170, following have one r.f. are not reflexed: power unit and tubes. audio (99 and 12). Rice neutralized t.r.f. Two dials. more stage and Day- craft All Volume control: resistance in r.f. plate. Cabinet sizes: 6, $195; Dayrole 6, $235; Dayfan 6, $110. NO. 517. AND 512 "Duet," 23x 56x16} inches; "Sextet," 22}x 13} x 15} prices less tubes. KELLOGG 510, 511, inches. Shielded. Output device. The 99 filaments are Seven tubes; 4 t.r.f., detector, 2 transformer audio. NO. 469. FREED-EISEMANN NR11 connected in series and supplied with rectified a.c., All Kellogg a.c. tubes. One control and special zone while 12 is supplied with raw a.c. The plate and fila- Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans- switch. Balanced. Volume control: special. Output de- ment supply uses gaseous rectifier tubes. Millammeter former audio (01-A and 71). Neutrodyne. One dial. vice. Shielded. Cable connection between power supply on power unit. Prices: "Duet," $160 including power Volume control: potentiometer. Watts consumed: 150. unit and receiver. Antenna: 25 to 100 feet. Panel 7|jj unit; "Sextet," $220 including power unit and loud Cabinet size: 19J x 10 x 10} inches. Shielded. Output x 27} inches. Prices: Model 510 and 512, consoles. $495 speaker. device. A special power unit is included employing a complete. Model 511, consolette, $365 without loud rectifier tube. Price $225 including NR-411 power unit. speaker. NO. 511. ALL-AMERICAN 80, 90, AND 115 Five tubes; 2 t.r.f. (99), detector (99), 2 transformer NO. 487. FRESHMAN 7F-AC NO. 496. SLEEPER ELECTRIC audio (99 and 12). Rice neutralized t.r.f. Two dials. Six tubes; 3 t.r.f. (26), detector (27), 2 transformer Five tubes; four 99 tubes and one 71. Two controls. Volume control: resistance in r.f. plate. Cabinet sizes: circuit. audio (26 and 71). Equaphase One dial. Volume Volume control: rheostat on r.f. Neutralized. Cable. No. 80, 231 x 12} x 15 inches; No. 90, 371 x 12 x 121 control: potentiometer across 1st audio. Console size: device. Power supply uses two 16-B tubes. inches; No. 115 Hiboy, 24 x 41 x 15 inches. Coils indi- Output 24} x 41} x 15 inches. Output device. The filaments and feet. Prices: for Antenna: 100 Type 64, table, $160; Type vidually shielded. Output device. See No. 509 and are all one unit. heaters B supply supplied by power 65, table, with built-in loud speaker, $175; Type 66, power supply. Prices: No. 80, $135 including power The one 80 rectifier tube. Price plate supply requires table, $175; 67, console, $235; Type 78, console, unit; No. 90, $145 including power unit and compart- Type $175 to $350, complete. $265. ment; No. 115, $170 including power unit, compartment, and loud speaker. NO. 536. SOUTH BEND NO. 522. CASE, 62 B AND 62 C Six tubes. One control. Sub-panel shielding. Binding NO. 510. ALL-AMERICAN 7 a.c. tubes. Drum control. Volume con- Posts. Antenna: outdoor. Prices: table, $130, Baby McCullough variable resistance in audio Seven tubes; 3 t.r.f. (26), 1 untuned r.f. (26), detector Grand console, $195. trol; high system. C-battery (27), 2 transformer audio (26 and 71). Rice neutralized connections. Semi-shielded. Cable. Antenna: 100 feet. t.r.f. One drum. Volume control: resistance in r.f. NO. 537. WALBERT 26 Panel size: 7 x 21 inches. Trices: Model 62 B, complete plate. Cabinet sizes: "Sovereign" console, 30} x 60} with a.c. equipment, $185; Model 62 C, complete with Six five a.c. tubes and one 71. Two x 19 inches; "Lorraine" Hiboy, 251 x 53j x 17} inches; tubes; Kellogg a.c. equipment, $235. controls. Volume control: variable resistance. "Forte" cabinet, 25} x 13} x 17} inches. For filament plate Isofarad circuit. device. cable. Semi- and plate supply: See No. 508. Prices: "Sovereign" Output Battery NO. 523. CASE, 92 A AND 92 C shielded. Antenna: 50 to 75 feet. Cabinet size: 10 x $460; "Lorraine" $360; "Forte" $270. All prices include J a.c. tubes. Drum control. Inductive unit. First two include loud 29} x 16} inches. Prices: $215; with tubes, $250. McCullough power speaker. volume control. Technidyne circuit. Shielded. Cable. NO. 403. ARGUS 250B NO. 538. NEUTROWOUND, MASTER ALLECTRIC C-battery connections. Model 92 C contains output device. Loop operated. Prices: Model 92 A, table, $350; Six 2 t.r.f. 1 untuned r.f. detector Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio tubes; (99), (99), Model 92 C, console, $475. (99), 2 transformer audio (99 and 12). Stabilized with (01-A and two 71 in push-pull amplifier). The 01-A grid resistances. Two dials. Volume control: resistance tubes are in series, and are supplied from a 400-mA. across 1st audio. Watts required: 100. Cabinet size: rectifier. Two drum controls. Volume control: variable BATTERY OPERATED RECEIVERS 35J x 14| x 10J inches. Output device. The 99 filaments plate resistance. Output device. Shielded. Antenna: are connected in series and supplied with rectified a.c., 50 to 100 feet. Price: $360. NO. 512. ALL-AMERICAN 44, 45, AND 66 while the 12 is run on raw a.c. The power unit requires Six t.r.f. 2 transformer two 16-B rectifier tubes. Milliammeter included in d.c. NO. 545. NEUTROWOUND, SUPER ALLECTRIC tubes; 3 (01-A, detector) 01-A, and Rice neutralized t.r.f. Drum Price $250.00 including self-contained power unit. audio (01-A 71). supply. Five tubes; 2 t.r.f. detector (99), 2 audio (99 models: No. console (99), control. Volume control: rheostat in r.f. Cabinet sizes: Other 125, $125.00; model, $375.00. The 99 are in series and are from and 71). tubes supplied No. 44, 21 x 10 x 8 inches; No. 55, 25 x 38 x 18 inches; an 85-mA. rectifier. Two drum controls. Volume con- NO. 401. AMRAD AC9 No. 66, 27} x 43 x 20 inches. C-battery connections. trol: variable resistance. device. Antenna: plate Output Battery cable. Antenna: 75 to 125 feet. Prices: No. 44, Six tubes; 3 t.r.f. (99), detector (99), 2 transformer 75 to 100 feet. Cabinet size: 9 x 24 x 11 inches. Price: No. $125 loud No. 66, $200 and Two dials. Volume control: $70; 55, including speaker; (99 12). Neutrodyne. $150. loud resistance across 1st audio. Watts consumed: 50. Cabi- including speaker. 490. net size: 27 x 9 x 11 inches. The 99 filaments are con- NO. MOHAWK J NO. 428. AMERICAN C6 nected in series and supplied with rectified a.c., while Six tubes; 2 t.r.f., detector, 2 transformer audio. All the 12 is run on raw a.c. The power unit, requiring two tubes a.c heater type except 71 in last stage. One dial. Five tubes; 2 t.r.f, detector, 2 transformer audio. 16-B rectifiers, is separate and supplies A, B, and C Volume control: rheostat on r.f. Watts consumed: 40. All 01-A tubes. Semi balanced t.r.f. Three dials. Plate current. Price $142 including power unit. Panel size: 12} x 8f inches. Output device. The heaters current 15 mA. Volume control: potentiometer. Cabinet for the a.c tubes and the 71 filament are supplied by sizes: table, 20 x 8} x 10 inches; console, 36 x 40 x 17 NO. 402. AMRAD ACS small transformers. The plate supply is of the built-in inches. Partially shielded. Battery cable. C-battery Five tubes. Same as No. 401 except one less r.f. type using a rectifier tube. Prices range from $65 to connections. Antenna: 125 feet. Prices: table, $30; stage. Price $125 including power unit. $245. console, $65 including loud speaker. RADIO BROADCAST ADVERTISER 403

is the Above master Ray-O-Vac 45-volt "B" battery, with the new construction, made especially for sets using four or more tubes. Improve Reception and reduce operating expense

engineers say that for new method of construction prevents EMINENTthe best radio reception the "B" internal short circuits and prolongs power supply should have as little in- the life of the battery from 10% to ternal resistance as possible. 15%. Otherwise signals are liable to be dis- There are twice as many radio owners torted in amplification, and natural, using Ray-O-Vacs today as there rounded tones cannot come out of the were a year ago. They know what loud speaker. low internal resistance and staying power in "B" batteries mean. The special formula used in making Ray-O-Vacs produces batteries that Ray-O-Vac batteries are sold by the have only from % to Vs the internal leading dealers in radio equipment resistance of ordinary sources of "B" and supplies. If you have any diffi- power supply. culty getting them write us for the name of a dealer who can At the same time, this special formula nearby sup- makes batteries that deliver a strong, ply you. steady voltage over an unusually long FRENCH BATTERY COMPANY time. It gives them staying power. MADISON, WISCONSIN

And the long-life of Ray-O-Vac bat- makers offlashlights and batteries teries is now still longer, because a and ignition batteries 404 RADIO BROADCAST ADVERTISER

NO. 485. BOSWORTH B6 NO. 441. FREED EISEMANN NR-77 NO. 543 RADIOLA 20 Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 Five tubes; 2 t. r. f. (99), detector (99), two transformer audio (01-A and 71). Two dials. Volume control: transformer audio (01-A and 71). Neutrodyne. One former audio (99 and 20) . detector. Two variable grid resistances. Battery cable. C battery dial. Plate current: 35 mA. Volume control: rheostat on Regenerative drum controls. C-battery connections. Battery cable. connections. Antenna: 25 feet or longer. Cabinet size r.f. Shielding. Battery cable. C-battery connections. Antenna: 100 feet. Price: $78 without accessories. 15 x 7 x 8 inches. Price $75. Antenna: outside or loop. Cabinet size: 23 x 10} x 13 inches. Price $175. NO. 480. NO. 513. COUNTERPHASE SIX PFANSTIEHL 30 AND 302 442. Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- NO. FREED-EISEMANN 800 AND 850 Six tubes; 3 t.r.f. (01-A), detector (01- 2A), transformer audio (01-A and 12). Counterphase t.r.f. Two former audio (01-A ind 71). One dial. Plate current: Eight tubes; 4 t.r.f. (01-A), detector (01-A), 1 trans- dials. Plate current: 32 mA. Volume control: rheostat 23 to 32 mA. Volume control: resistance in r.f. plate. former (01-A), 1 parallel audio (01-A or 71). Neutro- on 2nd and 3rd r.f. Coils shielded. cable. C- Shielded. Battery cable. connections. An- Battery dyne. One dial. Plate current: 35 mA. Volume control: C-battery battery connections. Antenna: 75 to 100 feet. Console tenna: outside. Panel size: 17J x 8} inches. Prices: No. rheostat on r.f. Shielded. Battery cable. C-battery size: 18} x 40} x 15} inches. Prices: Model 35, table, 30 cabinet, $105; No. 302 console, $185 including, connections. Output: two tubes in parallel or one power $110; Model 37, console, $175. loud speaker. tube may be used. Antenna: outside or loop. Cabinet sizes: No. 800, 34 x 15} x inches; No. 850, 36 x x NO. 514. 13} 65} NO. 515. 7-A COUNTERPHASE EIGHT 17}. Prices not available. BROWNING-DRAKE Eight tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- Seven tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio former audio (01-A and 12). Counterphase t.r.f. One NO. 444. GREBE MU-1 (Hmu, two 01-A, and 71). illuminated drum control. dial. Plate current: 40 mA. Volume control: rheostat in Volume control: rheostat on 1st r.f. Shielded. Neutral- Five 2 t.r.f. 1st r.f. Copper stage shielding. Battery cable. C-battery tubes; (01-A), detector (01-A), 2 trans- ized. C-battery connections. Battery Cable. Metal former audio connections. Antenna: 75 to 100 feet. Cabinet size: (01-A and 12 or 71). Balanced t.r.f. One, panel. Output device. Antenna: 50-75 feet. Cabinet, or three dials or 30 x 12} x 16 inches. Prices: Model 12, table, $225; two, (operate singly together). Plate 30 x 11 x 9 inches. Price, $145. current: Model 16, console, $335; Model 18, console, $365. 30mA. Volume control: rheostat on r.f. Bi- nocular coils. Binding posts. C-battery connections. NO. 516. BROWNING-DRAKE 6-A Antenna: 125 feet. Cabinet size: 22} x 91 x 13 inches. NO. 506. CROSLEY 601 BANDBOX Six tubes; 1 t.r.f. detector 3 audio Prices range from $95 to $320. (99), (00-A), Six tubes; 3 t.r.f., detector, 2 transformer audio. All (Hmu, two 01-A and 71). Drum control with auxiliary Volume control: rheostat on r.f. 01-A tubes. Neutrodyne. One dial. Plate current: NO. 426. HOMER adjustment. Regenera- 40 mA. Volume control: rheostat in r.f. Shielded. tive detector. Shielded. Neutralized. C-battery connec- Battery cable. C-battery connections. Antenna: 75 to Seven tubes; 4 t.r.f. (01-A); detector (01-A or OOA); tions. Battery cable. Antenna: 50-100 feet. Cabinet, 150 feet. Cabinet size: 17J x 5j x 7}. Price, $55. 2 audio (01-A and 12 or 71). One knob tuning control. 25 x 11 x9. Price $105.

Volume control : rotor control in antenna circuit. Plate

NO. 434. DAY-FAN 6 current : 22 to 25 mA. "Technidyne" circuit. Completely NO. 518. KELLOGG "WAVE MASTER," enclosed in aluminum box. cable. con- 504, 505, AND 506. Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 trans- Battery C-battery nections. Cabinet size, 8 x x inches. Chassis former audio (01-A and 12 or 71). One dial. Plate 19} 91 size, Five tubes; 2 t.r.f., detector, 2 transformer audio. 6f x 17 x 8 inches. Prices: Chassis $80. Table cabi- current: 12 to 15 mA. Volume control: rheostat on r.f. only, One control and special zone switch. Volume control: net, $95. Shielded. Battery cable, C battery connections. Output rheostat on r.f. C-battery connections. Binding posts. device. Antenna: 50 to 120 feet. Cabinet sizes: Daycraft Plate current: 25 to 35 mA. Antenna: 100 feet. Panel: NO. 502. KENNEDY ROYAL 7. CONSOLETTE 6, 32 x 30 x 34 inches; Day-Fan Jr., 15 x 7 x 7. 7} x 25} inches. Prices: Model 504, table, $75, less Prices: accessories. Model 505, table, $125 with loud Day-Fan 6, $110; Daycraft 6, $145 including Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- speaker. loud not available. Model 506, consolette, $135 with loud speaker; Day-Fan Jr. former audio (01-A and 71). One dial. Plate current: speaker. 42 mA. Volume control: rheostat on two r.f. Special NO. 519. 507 AND 508. NO. 435. DAY-FAN 7 r.f. coils. Battery cable. C-battery connections. Head- KELLOGG, connection. Antenna: outside or Six 3 2 transformer Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 resist- phone loop. Consolette tubes, t.r.f., detector, audio. One ance audio (01-A), 2 transformer audio (01-A and 12 size: 36} x 35} x 19 inches. Price $220. control and special zone switch. Volume control: rheo- or 71). Plate current: 15 mA. Antenna: outside. Same stat on r.f. C-battery connections. Balanced. Shielded. as No. 434. Price $115. NO. 498. KING "CRUSADER" Binding posts and battery cable. Antenna: 70 feet. Cabinet size: Model 507, table, 30 x 13J x 14 inches. Six tubes; 2 t.r.f. detector 3 trans- NO. 503. FADA SPECIAL (01-A), (00-A), Model 508, console, 34 x 18 x 54 inches. Prices: Model former audio and Balanced t.r.f. dial. (01-A 71). One 507, $190 less accessories. Model 508, $320 with loud t.r.f. Plate current: control: rheostat r.f. Six tubes; 3 (01-A), detector (01-A), 2 trans- 20 mA. Volume on speaker. former audio (01-A and 71). Neutrodyne. Two drum Coils shielded. Battery cable. C-battery connections. control. Plate current: 20 to 24mA. Volume control: Antenna: outside. Panel: 11 x 7 inches. Price, $115. NO. 427. MURDOCK 7 rheostat on r.f. Coils shielded. cable. Battery C-battery Seven tubes; 3 t.r.f. (01-A), detector (01-A), 1 trans- connections. connection. Antenna: outdoor. NO. 499. KING "COMMANDER" Headphone former and 2 resistance audio (two 01-A and 12 or 71)- Cabinet size: x x inches. Price 20} 13f 101 $95. One control. Volume control: rheostat r.f. Coils Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- on shielded. Neutralized. cable. con- former audio (01-A and 71). Balanced t.r.f. One dial. Battery C-battery NO. 504. FADA 7 nections. metal case. Plate current: 25 mA. Volume control: rheostat on r.f. Complete Antenna: 100 feet. Panel size: 9 x 23 inches. Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 trans- Completely shielded. Battery cable. C-battery con- Price, not available. former audio (01-A and 71). Neutrodyne. Two drum nections. Antenna: loop. Panel size: 12 x 8 inches. NO. 520. 57 control. Plate current: 43mA. Volume control: rheostat Price $220 including loop. BOSCH on r.f. Completely shielded. Battery cable. C-battery Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio connections. Headphone connections. Output device. NO. 429. KING COLE VII AND VIII (01-A and 71). One control calibrated in kc. Volume Antenna: outdoor or loop. Cabinet sizes: table, 25 i x control: rheostat on r.f. Shielded. cable. C- Seven tubes; 3 t.r.f., detector, 1 resistance audio, 2 Battery 13i x 11* inches; console, 29 x 50 x 17 inches. Prices: connections. Balanced. device. Built-in transformer audio. All 01-A tubes. Model VIII has one bcttery Output table, $185; console, $285. loud spea'.ier. Antenna: built-in loop or outside antenna, more stage t.r.f. (eight tubes). Model VII, two dials. ICO feet. Cabinet size: 46 x 16 x 30 inches. Price: Model VIII, one dial. Plate current: 15 to 50 mA. $3-10 NO. 436. FEDERAL including enclosed loop and loud speaker. Volume control: primary shunt in r.f. Steel shielding. Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 trans- Battery cable and binding posts. C-battery connections. NO. 521. BOSCH 66 76 former audio (01-A and 12 or 71). Balanced t.r.f. One Output devices on some consoles. Antenna: 10 to 100 "CRUISER," AND dial. Plate current: 20.7 mA. Volume control: rheostat feet. Cabinet size: varies. Prices: Model VII, $80 to Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio on r.f. Shielded. Battery cable. C-battery connections. $160; Model VIII, $100 to $300. (01-A and 71). One control. Volume control: rheostat Antenna: loop. Made in 6 models. Price varies from on r.f. Shielded. C-battery connections. Balanced. $250 to $1000 including loop. NO. 500. KING "BARONET" AND "VIKING" Battery cable. Antenna: 20 to 100 feet. Prices: Model 66, table, $99.50. Model 76, console, $175; with loud Six 2 t.r.f. detector 3 trans- NO. 505. FADA 8 tubes; (01-A), (00-A), speaker $195. former audio (01-A and 71). Balanced t.r.f. One dial. tubes. Same as No. 504 for one extra Plate current: 19 mA. Volume control: rheostat in r.f. Eight except NO. 524. CASE, 61 A AND 61 C stage of audio and different cabinet. Prices: table, $300; Battery cable. C-battery connections. Antenna: out- console, $400. side. Panel size: 18 x 7 inches. Prices: "Baronet," $70; T.r.f. Semi-shielded. Battery cable. Drum control. "Viking," $140 including loud speaker. Volume control: variable high resistance in audio sys- NO. 437. FERGUSON 10A tem. Plate current: 35 mA. Antenna: 100 feet. Prices: NO. 489. MOHAWK Model 61 A, $85; Model 61 C, console, $135. Seven tubes; 3 t.r.f. (01-A), detector (01-A), 3 audio and 12 or One dial. Plate (01-A 71). current: 18 to 25 Six tubes; 2 t.r.f. (01-A), detector (00-A), 3 audio NO. 525. CASE, 90 A AND 90 C mA. Volume control: rheostat on two r.f. Shielded. (01-A and 71). One dial. Plate current: 40 mA. Volume Drum control. Inductive volume control. Battery cable. C-battery connections. Antenna: 100 control: rheostat on r.f. Battery cable. C-battery con- Technidyne circuit. connections. cable. feet. Cabinet size: 21} x 12 x 15 inches. Price $150. nections. Output device. Antenna: 60 feet. Panel size: C-battery Battery Loop Model 90-C with 12} x 8j inches. Prices range from $65 to $245. operated. equipped output device. NO. 438. FERGUSON 14 Prices: Model 90 A, table, $225; Model 90 C, console, NO. 449. $350. Ten tubes; 3 untuned r.f., 3 t. r.f. (01-A), detector NORBERT "MIDGET" audio and or NO. 526. 25 (01-A), 3 (01-A 12 71). Special balanced One multivalve tube; detector, 2 transformer audio. ARBORPHONE t.r.f. One dial. Plate current: 30 to 35 con- mA. Volume Two dials. Plate current: 3 mA. Volume control: rheo- Six tubes; 3 t.r.f. (01-A), detector (01-A), 2 audio trol: rheostat in three r.f. Shielded. C- Battery cable, stat. Binding posts. C-battery connections. Headphone (01-A and 71). One control. Volume control: rheostat. connections. Antenna: size: battery loop. Cabinet connection. Antenna: 75 to 150 feet. Cabinet size: Shielded. Battery cable. Output device. C-battery con- 24 x 12 x 16 inches. Price $235, including loop. 12 x 8 x 9 inches. Price $12 including multivalve. nections. Loftin-White circuit. Antenna: 75 feet. Panel: 7} x 15 inches, metal. Prices: Model 25, table, $125; 439. 12 NO. FERGUSON NO. 450. NORBERT 2 Model 252, $185; Model 253, $250; Model 255, combin- Six tubes; 2 t.r.f. detector 1 trans- ation phonograph and radio, $600. (01-A), (01-A), Two tubes; 1 t.r.f., detector, 2 transformer audio. former audio 2 resistance audio (01-A), (01-A and 12 One multi-valve tube and one 01-A. Two dials. Plate or Two dials. Plate current: 18 to 25 mA. Volume NO. 527. ARBORPHONE 27 71). current: 8 mA. Volume control: special. Battery cable. control: rheostat on two r.f. shielded. Partially Battery Headphone connection. C-battery connections. An- Five tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio cable. connections. Antenna: 100 C-battery feet. tenna: 50 to 100 feet. Cabinet size: 20 x 7 x 5} inches. (01-A). Two controls. Volume control: rheostat. C- Cabinet size: x 10 x 12 inches. Price Consolette 22} $85. Price $40.50 including multivalve and 01-A tube. battery connections. Binding posts. Antenna: 75 feet. $145 including loud speaker. Prices: Model 27, $65; Model 271, $99.50; Model 272, NO. 452. ORIOLE 90 $125. NO. 440. FREED EISEMANN NR-8, NR 9, AND NR-66 Five tubes; 2 t.r.f., detector, 2 transformer audio. NO. 528. THE "CHIEF" All 01-A tubes. "Trinum" circuit. Two dials. Plate six 01-A tubes and one tube. Six tubes; 3 t.r.f. (01-A), detector (01-A). 2 trans- Seven tubes; power current: 18 mA. Volume control: rheostat on r. f. One control. Volume control: rheostat. con- former audio (01-A and 71). Neutrodyne. NR-8, two C-battery cable. C-battery connections. Antenna: 50 to dials; others one dial. Plate current: 30 mA. Volume Battery nection. Partial shielding. Binding posts. Antenna 100 feet. Cabinet size: 25} x 11} x 12} inches. Price outside. Cabinet size: 40 x 22 x 16 inches. Prices: control: rheostat on r.f. NR-8 and 9: chassis type $85. Another model has 8 tubes, one dial, and is with A without acces- shielding. NR-66, individual stage shielding. Battery Complete power supply, $250; shielded. Price $185. cable. C-battery connections. Antenna: 100 feet. sories, $150. Cabinet sizes: NR-8 and 9, 19 f x 10 x 10} inches; NR-66 x 12 NO. 453. PARAGON NO. 529. DIAMOND SPECIAL, SUPER SPECIAL, 20 x 10} inches. Prices: NR-8, $90; NR-9, $100; BABY CONSOLE NR-66, $125. Six tubes; 2 t.r.f. (01-A), detector (01-A), 3 double AND GRAND audio and dial. shield- NO. 501. KING "CHEVALIER" impedance (01-A 71). One Plate cur- Six tubes; allJOl-A type. One control. Partial rent: 40 mA. Volume control: resistance in r.f. plate. ing. C-battery connections. Volume control: rheostat. Six tubes. Same as No. 500. Coils completely shielded. Shielded. Battery cable. C-battery connections. Out- Binding posts. Antenna: outdoor. Prices: Diamond Panel size: 11 x 7 inches. Price, $210 including loud put device. Antenna: 100 feet. Console size: 20 x 46 Special, $75; Super Special, $65; Baby Grand Console, speaker. x 17 inches. Price not determined. $110. RADIO BROADCAST ADVERTISER 405

Universally Used byAmateur Builders

fe Adopted by JM .Leading Set M'fgrs.

, - - First Choice of Professional " Builders

Sold Everywhere Dealers Endorsed by by Leading Foremost Radio EnqineefS~ FIRST CHOICE of the Keenest Minds in Radio I

CHOICE because Durham was the first and orig- FIRSTinal "metallized filament" resistor because years of heavy production and the confidence ofleading radio manufacturers have given us time to produce a perfect product. Durham Resistors and Powerohms are the leaders in their

field because their uniform, unfailing accuracy and absolute reliability have been proved time and time again.

This is why they are the first choice of foremost engineers, leading manufacturers, professional set builders and informed radio fans who demand quality results. Like Durham Resistors and Powerohms, Durham Re- sistor Mountings are also the leaders in their field. The takes Durham standard resistors are made in ranges from 500 only upright mountings made; minimum space ohms to 10 megohms Durham Powerohms for "B" Eliminators and Amplifier circuits are made in 2.5 watt made of high resistance moulded insulation best quality and 5 watt sizes in ranges from 500 to 100,000 ohms. tension -spring bronze contacts. Single and double sizes. Adopted by Leading Radio Manufacturers Philco Fansteel Products Co. Kellogg-Switchboard Western Electric F. A. D. Andrea Sterling Mfg. Co. Kokomo Electric METALLIZED Garod Radio Corp. Browning-Drake Howard Radio A-C Dayton RESISTOR S POWEROHMS INTERNATIONAL RESISTANCE CO., Dept. D, 2% South 20th Street, Philadelphia, Pa. 406 RADIO BROADCAST ADVERTISER

NO. 530. KOLSTER, 7A AND 7B NO 433. ARBORPHONE NO. 494. SONORA E

Seven tubes; 4 t.r.f. (01-A), detector (01-A), 2 audio Five tubes; 2 t.r.f., detector, 2 transformer audio. Six tubes; 3 t.r.f. (01- A), detector fOO-A), 2 trans- (01-A and 12). One control. Volume control: rheostat All 01-A tubes. Two dials. Plate current: 16mA. Vol- former audio (01-A and 71). Special balanced t.r.f. on r.f. Shielded. Battery cable. C-battery connections. ume control: rheostat in r.f. and resistance in r.f. plate. Two dials. Plate current: 35 to 40 mA. Volume control: Antenna: 50 to 75 feet. Prices: Model 7A, $125; Model C-battery connections. Binding posts. Antenna: taps rheostat on r.f. Shielded. Battery cable. C-battery 7B, with built-in loud speaker, $140. for various lengths. Cabinet size: 24 x 9 x 10J inches. connections. Antenna: outside. Cabinet size: varies. Price: $65. Prices: table, $110; semi-console, $140; console, $240 NO. 531. KOLSTER, 8A, SB, AND 8C including loud speaker. NO. 431. AUDIOLA 6 Eight tubes; 4 t.r.f. (01-A), detector (01-A), 3 audio NO. 495. SONORA D (two 01-A and one 12). One control. Volume control: Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 trans- Same as No. 494 except arrangement of tubes; 2 rheostat on r.f. Shielded. Battery cable. C-battery con- former audio (01-A and 71). Drum control. Plate cur- t.r.f., 3 audio. Prices: standard nections. Model 8A uses 50 to 75 foot antenna; model detector, table, $125; rent: 20 mA. Volume control: resistance in r.f. plate. 8B contains device and uses antenna or detach- console, $185; "DeLuxe" console, $225. output Stage shielding. Battery cable. C-battery connection. able Model 8C contains device and uses loop; output Antenna: 50 to 100 feet. Cabinet size: 28-J x 11 x 145 NO. 482. STEWART-WARNER 705 AND 710 antenna or built-in loop. Prices: 8A, $185; 8B, $235; inches. Price not established. Six 3 2 transformer audio. 8C, $375. tubes; t.r.f., detector, All 01-A tubes. Balanced t.r.f. Two dials. Plate cur- NO. 432. AUDIOLA 8 rent: 10 to 25 mA. Volume control: resistance in r.f. NO. 532. KOLSTER, 6D, 6G, AND 6H Shielded. cable. connections. 4 1 trans- plate. Battery C-battery Six 3 t.r.f. detector 2 audio Eight tubes; t.r.f. (01-A), detector (00-A), tubes; (01-A), (01-A), Antenna: 80 feet. Cabinet sizes: No. 705 table, 26i control: rheostat former audio (01-A), push-pull audio (12 or 71). Bridge (01-A and 12). One control. Volume x x 13j inches; No. 710 console. x 42 x balanced t.r.f. Drum control. Volume control: resistance 11{ 29J 17J on r.f. connections. Battery cable. Antenna: inches. Tentative No. No. 710 C-battery in r.f. cable. prices: 705, $115; 50 to 75 feet. Model 6G contains output device and plate. Stage shielding. Battery C-battery loud connections. Antenna: 10 to 100 feet. Cabinet size: $265 including speaker. built-in loud speaker; Model 6H contains built-in B x 11 x 149 inches. Price not established. power unit and loud speaker. Prices: Model 6D, $80; 285 NO. 483. STEWART-WARNER 525 AND 520 Model 6G, $165; Model 6H, $265. NO. 542 RADIOLA 16 Same as No. 482 except no shielding. Cabinet sizes: No. 525 table. 19 J x 10 x 11} inches; No. 520 console, NO. 533. SR 9 AND SR 10 Five 3 t. r. f. detector 2 trans- SIMPLEX, tubes; (Ol-A), (Ol-A), 228 x 40 x 14 M inches. Tentative prices: No. 525, $75; former audio and One control. Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 audio (01-A 112). C-battery No. 520, $117.50 including loud speaker. connections. cable. Antenna: outside. Cabinet (01-A and 12). SR 9, three controls; SR 10, two con- Battery size: x x inches. Price: without ac- NO. 459. STROMBERG-CARLSON 501 AND 502 trols. Volume control: rheostat. C-battery connections. 16V2 &/, 7V2 $69.50 cessories. Battery cable. Headphone connection. Prices: SR 9, Five tubes; 2 t.r.f. (01-A), detector (00-A), 2 trans- table, $65; consolette, $95; console, $145. SR 10, table NO. 456. RADIOLA 20 former audio (01-A and 71). Neutrodyne. Two dials. Plate current: 25 to 35 mA. Volume control: rheostat $70; consolette, $95; console, $145. Five tubes: 2 t.r.f. (99), detector (99), 2 transformer on 1st r.f. Shielded. Battery cable. C-battery connec- audio (99 and 20) . Balanced t.r.f. and regenerative de- NO. 534. 11 tions. connections. device. Panel SIMPLEX, SR tector. Two dials. Volume control: regenerative. Headphone Output voltmeter. Antenna: 60 to 100 feet. Cabinet sizes: Six tubes; 3 t.r.f. (01-A), detector (00-A), 2 audio Shielded. C-battery connections. Headphone connec- No. 501, 25J x 13 x 14 inches; No. 502, 28 )?, x 50 (01-A and 12). One control. Volume control: rheostat. tions. Antenna: 75 to 150 feet. Cabinet size: 19$ x x inches. Prices: No. $180; No. $290. C-battery connections. Battery cable. Antenna: 100 11J x 16 inches. Price $115 including all tubes. ft 16J 501, 502, feet. Prices: table, $70; consolette, $95; console, $145. NO. 460. STROMBERG-CARLSON 601 AND 602 NO. 457 RADIOLA 25 NO. 535. MODEL S 27 Six tubes. Same as No. 549 except for extra t.r.f. STANDARDYNE, Six five 99 and one 20. Drum con- tubes; type type stage. Cabinet sizes: No. 601, 27i^ x 16-J x 14 fe inches; Six tubes; 2 t.r.f. (01-A), detector (01-A), 2 audio trol. Super-heterodyne circuit. C-battery connections. No. 602, 28f x 51J x 19| inches. Prices: No. 601, $225; One control. Volume control: rheostat (power tubes). Battery cable. Headphone connections. Antenna: loop. No. 602, $330. on r.f. C-battery connections. Binding posts. Antenna: Set may be operated from batteries or from power mains 75 feet. Cabinet size: 9 x 9 x 191 inches. Prices: S 27, when used with model 104 loud speaker. Price; $165 NO. 486. VALLEY 71 $49.50; S 950, console, with built-in loud speaker, with tubes, for battery operation. for opera- Apparatus Seven tubes; 4 t.r.f. (01-A), (01-A), 2 trans- $99.50; S 600, console with built-in loud speaker, tion of set from the mains can be detector power purchased former audio and One dial. Plate current: $104.50. (01-A 71). separately. 35 mA. Volume control: rheostat on r.f. Partially NO. 481. PFANSTIEHL 32 AND 322 NO. 493. SONORA F shielded. Battery cable. C-battery connections. Head- connection. Antenna: 50 to 100 feet. Seven tubes: 3 t.r.f. (01-A), detector (01-A), 3 audio Seven tubes; 4 t.r.f. (01-A), detector (00-A), 2 trans- phone Cabinet x 7 inches. Price (01-A and 71). One dial. Plate current: 23 to 32 mA. iormer audio (01-A and 71). Special balanced t.r.f. size: 27 x 6 $95. Volume control: resistance in r. f. Shielded Two dials. Plate current: 45 mA. Volume control: plate. NO. 472. VOLOTONE VIII Battery cable. C-battery connections. Output device. rheostat in r.f. Shielded. Battery cable. C-battery Antenna: outside. Panel: 17f x 85 inches. Prices: No. connections. Output device. Antenna: loop. Console Six tubes. Same as No. 471 with following excep- 32 cabinet, $145; No. 322 console, $245 including si/e: 32 x 45! x 17 inches. Prices range from $350 to tions; 2 t.r.f. stages. Three dials. Plate current: 20 loud speaker. $450 including loop and loud speaker. mA. Cabinet size: 265 x 8 x 12 inches. Price $140.

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listeners-in want crystal clear, undistorted tones more than distance. They seem to want to set their dials for a desired program and get it right to get it full, strong and free from the " annoyance of blurring and what might be termed "warped tones.

The one big thing that Carborundum Stabilizing Detector Unit does in any set is to improve the tone quality. Besides you will find that it increases the volume and gives you greater distance if you want it.

The .TULH1 ' Carborundum Beg.u.s.p.t.off. Company CLARIFIES RECEPTION '' Niagara Falls, N.Y. Do will Please send free v^apbonuuao.iLim Cjrria. JL/eats amo. Resistors Hook-Up Book D-2 Send for Hook-Up Book D-2 THE CARBORUNDUM COMPANY, NIAGARA FALLS, N. Y. street SALES OFFICES AND WAREHOUSES IN New York, Chicago, Boston, Philadelphia, Cleveland, Detroit, Cincinnati / Clry Pittsburgh, Milwaukee, Grand Rapids '/ The Carborundum Company, Ltd., Manchester, Eng. State Z1JIC RADIO BROADCAST ADVERTISER 407

Why all this stuff Jbr an aerial Sickles Coil Set No.lgAfor Roberts Circuit SICKLES Diamond - Weave Coils

new Sickles Shielded Tuned Radio THETransformer prevents both outside and local interference. It is remarkably compact, sharp tuning, sturdy. Sickles Diamond-weave coils have established an enviable reputation for low distributed capacity, low dielectric losses, and large range of frequency with small variable capacity. The ideal coil for the Naald Localized Control Tuning Unit and for the Tru- phonic Catacomb Assembly.

There are Sickles Diamond Weave Coils for all Leading Circuits, The F. W. Sickles Co. 132 Union Street SPRINGFIELD, MASS. when all COIL PRICES

No. 30 Shielded Transformer . $2.00 each No. 24 Browning-Drake 7.SO Set No. ISA Roberts Circuit " need 8.00 " No. 25 Aristocrat Circuit 8.00 yon " _ VsysS. _ , is this The trouble of BALDWINLOUD SPEAKERS and expense erecting an outdoor antenna are now absolutely unnecessary. The Dubilier Light Socket Aerial has taken the place Famous of loose wires, crazy poles, lightning arresters and all the other accessories of an old-fashioned antenna. Full volume is guaranteed. So is clarity and distance. You'll find, too that this remarkable device greatly reduces both static and interference. Convince yourself without risk all dealers sell the Dubilier Light Socket '"Benj. Franklin once said: Aerial on a basis. "My performance devotes itaelf 5-day money-back entirely to thy service and will serve thf-e faithfully and if it has the good fortune to please Price #1.50 its master, tig gratification" enough for the lator of Poor Richard BmW3J The Accurate is without comparison, due to the su- perfine quality of its unit. To-day, as Dubilier Metaleak 15 years ago, Baldwin performance is You'll like the still the standard by which others are Don't underestimate the impor- new judged, comparable to the sensitive tance of accurate and quiet tubular Dubilier Micadon mechanism of a fine watch. The New leaks in the performance of your Baldwin "99" can be used on any set. Dubilier receiver. Metaleak is smaller than Anewshape and moulded Bake- Ask your deafer to Approved Blocks most, but interchangeable on any hte case have made the "Stand- it. standard demonstrate for Power Units mounting. All resistances ard Fixed Condenser of Radio" 40c to 65c. At all a better and better -looking If you're building an Good Dealers Micadon. Fully protected from A-B-C eliminator, insist injury and outside Write For Booklets on the high factor of DUBILIER capacity. CONDENSER Terminals adapted to screwed safety found only in the -BALDWIN UNITS- or soldered connections. approved Duhilier con- CORPORATION Loudspeaker units. denser blocks. Phono adapters, and Raytheon 4377 Bronx Blvd. New York head sets are stand- and all standard circuits Prices 45c to #1.50 ard the world over. provided for.

J. W. & W. L. WOOLF Distributors and Exporters For NATHANIEL BALDWIN, Inc. 227-229 Fulton St. New York Condensers 408 RADIO BROADCAST ADVERTISER

More than IfiOO^OOO owners of General Electric Battery Chargers GETYBORS//2o,, - now havepepgy radio batteries always UICK

Don't wait! Send today for this wonderful book. See how 14,000 live radio dealers make bigger profits by buying from The Harry Alter Company, America's foremost wholesalers of receiving sets, kits, parts and accessories the largest stock of standard, nationally advertised radio goods carried anywhere. RADIO'S GREATEST CATALOG Compare its low prices with those of any other catalog. You will be amazed. Note: We sell only to radio retailers. Write for your copy NOW.

5-Ampere G-E Trickle Tungar Charger hel$arry Ulter Co 1754 Michigan Avenue CHICAGO

Keep your radio set ready at all times for all the good things that come over. NEW VITREOUS causes no radio Just turn on Tungar (the name ol the General Electric bat- Tungar Inter* ference. It cannot blow out ENAMEL RESISTORS at leave it as would the in the tery charger) night, you light tubes. hall .... in the morning your storage batteries are pepped An overnight charge costs a up and ready for active duty dime. More than 1,000,000 G-E Tungars are in use today. For the It is a G-E product developed in the Research Labora- established its for dependable, Tungar long ago reputation tories of General Electric. trouble-free, economical service. The 2- or S-ampere Tungars Your dealer can Ask him to show the charge 2-, 4-, and 6-volt"A" help you. you popular These Resistors are wire-wound and batteries, 24- to 96-volt "B" 2-ampere Tungar that gives both trickle and boost charging coated with a vitreous enamel winch batteries in series; and auto rates. It and "B" radio batteries and auto the wire from mechanical in- charges "A" batteries, too. No extra at- protects jury and oxidation. batteries, too. tachments needed. This hard, glassy enamel has the same rate of expansion as the porce- New Low Prices lain tube and the resistance wire (East of the Rockies) that is wound on it. Conse- quently the Resistor may b** op- 2-ampereTun par, now $ 14 erated at high temperatures without it. 5-ampereTungar, now $24 damaging G-E Trickle Charger, now These Resistors are guaranteed permanently $10 accurate within 5 per cent, of rated value.

! BATTERY ~CHARG ErT| Resistors from 750 to 20,000 ohms, two types Department 2 in. long, dissipating 20 watts; 4 in. long, 40 watts. General Electric Company dissipating Tungar a registered trademark is found only on the genuine. Look for it on the name plate. Bridgeport, Connecticut In Canada: Carter Radio Co., Ltd., Toronto Offices in principal cities of the world GENERAL arter Radio O MODERNIZE YOUR RADIO! UILD your own Battery-Less receiver with the ADVANCED 1928 MODEL SOVEREIGN A-C KIT. No more A Battery No A Batterv Eliminator No Hum No Michrophonic Disturbance JUST CLEAR CLEAN CUT TRUTHFUL REPRODUCTION powered from the never failing light socket by the mere snap of the switch. CONVERT YOUR PRESENT RECEIVER TO 1928 STANDARDS WITH THE ADVANCED 1928 MODEL SOVEREIGN A. C. KIT with but slight modifications, easily accomplished by following the detailed instructions supplied in each Sovereign A.C. Kit ANY CIRCUIT becomes light socket powered receiver. You need not be a Radio Engineer or master "radiotrician" to construct an A. C. Receiver or convert your present set. Just follow the very simple, definite, detailed instructions given FREE w!th Sovereign Equipment. That's all! When you purchase Sovereign Products you have the knowledge that nothing in the ratho industry today carries greater assurance of proper design construction satisfaction or guarantee. Sovereign A. C. Tubes acknowledged the "Crowning as they are non-michrophonic. Summing it all in a few Achievement" in the Radio Tube Field are unconditionally words. Sovereign Equipment means ECXJNOMY EF- guaranteed. They have more rugeed construction a FICIENCY MINIMUM SERVICING THE IDEAL longer life! Sovereign A-C Tubes improve tonal quality IN RADIO RECEPTION If your dealer cannot supply you, we will ship direct to you C.O.D. Sovereign A-C Kit can be furnished for use on no or 220 Volts 25 or 60 Cycles. SOVEREIGN A-C Kit no or 220 Volts 60 Cycles. Price $8.75 SOVEREIGN A-C Kit no or 220 Volts 25 Cycles. Price ^.7^ In ordering Kits specify Voltage of House Current No. of Cycles Type of Circuit No. of Tubes.

SOVEREIGN A-C TUBES Price Ji?.oo SOVEREIGN A-C POWER TUBES FOR LAST AIT.IO STAGE Price $6.00 We have prepared for you a comprehensive NON-TECHNICAL pamphlet on A-C Receivers and Tubes. Write for your copy today! SOVEREIGN ELECTRIC & MANUFACTURING CO. 12 No. Sangamon Street Chicago Illinois RADIO BROADCAST ADVERTISER 409

Adjustable "B" Voltages in any combination from to 180 also adjustable "C" Voltage from to 50 Type 445 Plate Supply Price $55 In Trouble ? ? UX-280 or CX-380 Has a moisture permeated bypass con- Rectifier Tube for denser ruined your receiver or amplifier ? A defective bypass condenser or coupling above, $5 condenser in a receiver or amplifier mars reception causes distortion. Type 445 Insure such troubles use the latest against Plate Supply AEROVOX development an AEROVOX bypass condenser sealed in a Bakelite case complete with non - wound to inductively impervious Tube, $60 moisture its electrical condition is as good after a year as the day it was installed. Made in all capacities up to 1 mfd and The rated at 200 volts D C working voltage. New

Bui'// 'Btlttr" 70 Washington St., Brooklyn, N. Y. GENERAL RADIO PLATE SUPPLY Embodying new and distinctive features in plate supply design

FROST- 1 . A djustable wire wound resistance -with sliding taps which control voltages so that any combination of voltages from o to 180 may be taken from the four positive "B" terminals. This method of voltage control is superior to the use of several resistances with exterior knob controls. It has the RADIO that once the advantage sliding taps are adjusted to the proper operating DE LUXE voltages of the tubes, they are tightened in place by thumb screws and voltages will remain constant, but are immediately available for readjust- APPARATUS ment whenever the unit is used with a different set. 2. Adjustable "C" voltage for tube now Is available at your favorite dealer's. These power new De Luxe items of Frost -Radio include Rhe- 3. High voltage test condensers in filter circuit ostats. Potentiometers and Variable High Resis- tance Units, with and without switch. Gem Rhe- 4. Uses UX-z8o or rectifier tube which has maximum of ostats and Fixed Resistances, all in a wide range of CX-jSo output resistance windings. You'll like them find them 100 milliamperes, thereby providing sufficient current for sets of the dependable, high in quality and fairly priced. multi-tube type.

5. Automatic cut-out switch breaks the no vclt A. C. circuit when cover is removed for adjusting voltages or connecting wires to taps, thereby making unit absolutely safe even in the hands of persons not familiar with electrical apparatus. 6. Designed to meet specifications adopted by the National Board of Fire Underwriters.

7. Absolutely guaranteed against mechanical and electrical defect upon leaving the General Radio factory. Cost, which has been a secondary consideration to over-all efficiency has been kept as low as peak performance and production economies permit. Price from your dealer, or direct from the factory if your dealer cainnil supply you Type 445 Plate Supply Unit $55.00 FROST-RADIO Type UX-280 or CX-380 Rectifier Tube for above $5.00 S-i8io De Luxe 10 ohm Bakclitc Cnmbi nation Licensed by the Radio Corporation of America only for Radio Amateur, Experimental Rheostat ami Battery Switch, $J.$5 and Broadcast Reception. HERBERT H. FROST,'- Under terms of R. C. A. license unit may only be sold with tube. Main Offices and Factory GENERAL RADIO COMPANY EL.KHART, IND. CAMBRIDGE, MASS. 410 RADIO BROADCAST ADVERTISER

Installations Safe

Safety Provisions Specified by the Board of Fire Underwriters in Making Antenna Installa- tions The Lightning Hazard Radio's Best Wire Danger From Power Lines "From The Ground Up" No chain is stronger than its weakest link. That's why the wire you use in your radio set or the wire that is By EDGAR H. FELIX used in the set you buy, is an important factor. Why take a chance, when for the same price and in many cases less, you can have the best by specifying "Corwico" ONCOMING bolt of never radio wires. Their superior merits and all-around effi- lightning ciency have been proven by amateurs, experts and radio stops to argue. It has only one thing in set manufacturers ANmind an incredible to reach receiving everywhere. hurry Mother Earth. Your little, puny pound of The next time you need wire for any radio purpose, ask antenna a few feet above your dealer for "Corwico." If he can't supply you, copper wire, strung up CORWICO "FLEXIBUS" write us direct. the surface of the earth, has no more influence in HOOK-UP WIRE attracting a bolt of lightning than a mosquito "Corwico" F 1 e x i b u s has to entice to a concert. If (Solid or Stranded) is "Corwico" Radio Wires you symphony a flexible insulated tin- Antenna Wire Hook-up Wire lightning ever strikes your antenna, it is merely ned copper hook-up (Solid, Stranded and braided) Lead-in Wire a coincidence. The or absence of an wire which makes a neat Complete Aerial Kits Annunciator Wire presence and efficient product for Magnet Wire Loop Aerial Wire antenna on a building has nothing to do with *' to and point point" Battery Cable Litz Wire either the attraction or of sub-panel wiring. It is Bus Bar Wire Flexible Wire repulsion lightning. covered with a varnish- There is in the atmosphere at all times, but ed cambric flame proof a insulation finished in more especially during the summer months, "Convico'* Radio Wires are sold by all leading dealers. red, green, yellow, Write for free booklet on radio wires and their uses. certain amount of static electricity present. brown or black. Any body of metal or wire tends to collect this CORNISH WIRE COMPANY atmospheric electricity if it is not connected to ground, and the electrical potentials built up 30 Church Street New York City may become of dangerous proportions. A lightning arrester provides an easy path to ground for these charges which tend to accumu- late on the antenna, but is so constructed that it does not afford a path to ground for the radio signals. When there is a thunder-shower in the " immediate vicinity, the potentials induced in the 'Superior to all others tested" antenna are greater than at other times, and almost continuous discharges take place through the arrester to ground. With a lightning arrester properly installed, there seems to be very little danger from this atmospheric electricity, or induced currents from near-by electrical disturbances. To support the contention, let us consider the evidence of experts. Victor H. Tousley, Chief of Electrical Inspectors in the Chicago District, reports that of the 34 cases where the Chicago Fire Depart- ment was called out in response to a fire caused by lightning, only 12 of the buildings had an- tennas; and, in only four of these was there any evidence that lightning had followed the antenna wire to the ground. William S. Boyd, an electrical engineer of Chicago, has, for some years, been compiling statistics regarding fires caused by lightning striking radio installations. His report lists only 15 damaged by lightning during the years 1922 to 1924 not a very formidable figure. Six of these accidental "hits" damaged only the antenna because the lightning arrester did its work effectively. In the entire district of Philadephia, there is a record of only one fire caused by lightning striking a radio antenna, according to an officer Recognized radio engineers have for a long time known of the Fire Underwriters' Association in that the excellence of Tobe Condensers. They have the city. The antenna and lightning arrester were quality of continuing to function perfectly over long destroyed, but no damage was done to the re- periods of time. Now the Tobe No. 662 high voltage set. B Block has been selected McMurdo ceiving exclusively by Another which on the Silver for use with the new Silver-Marshall UNIPAC hazard, depends purely matter of placement of the antenna and good and Mr. Silver has written us the above reproduced workmanship in putting it up, is the likelihood letter. Send for price list B-io. of the antenna coming into contact with electrical wires, either low tension or high tension. Tobe Deutschmann Co, The most important provisions, formulated by - S Cambridge - Mass. (Continued on page 412) RADIO BROADCAST ADVERTISER 411 New!

No More Socket Trouble

A socket's only job is to provide a perfect contact. The New Eby Socket has a 3 point wiping spring contact the full length of the prong, the most scientifically perfect type known. The prongs are completely enclosed TRADE MARK and fit snugly against the phenolic walls of the socket they can't spread. MAGNIFICENT TONE-SUPER SELECTIVE-POWERFUL DISTANCE GETTER \ With the New Eby Socket your socket troubles are gone. Easy to mount above or below Bakelite, Wood or Metal. L- or Set/ Specified in most of the leading popular Battery circuits. America's big, old, reliable Radio Corpo- ration* (8th successful year) guarantees its Deal Direct with Reliable Makers List Price 40c Big big, powerful, latest 6, 7 and 8 tube Miraco Your Miraco reaches you completely assembled, rigidly sets to most give "the finest, enjoyable per- tested, fully guaranteed. Easy to connect and operate. formance obtainable in high grade radios." 30 days free trial. 3 year guarantee if you buy. Choice THE H. H. EBY MFG. Co. of beautiful consoles latest built-in Unless 30 days' use in your home fully {with orthophonic INCORPORATED type speakers having 8 feet ot tone travel] and table it satisfies you and everybody who hears cabinets, also offered. You take no risk, you insure sat- 4710 Stenton Ave. that a Miraco is unbeatable at any price isfaction, you enjoy rock-bottom money-saving-prices by with one of radio's most successful for beautiful, clear cathedral tone, razor- dealing direct oldest, Phila., Pa. builders of fine sets. edge selectivity, powerful distance recep- Makers of Eby Binding Posts tion, easy operation, etc. don't buy it! Your verdict final absolutely no strings to this. Save or make lots of money on sets and equipment by writing for testi- tfsto mony of nearby users and Amazing Special Factory Offer. Run from "AC" Current or Batteries Miraco's work equally fine on electric house current or with batteries. Take your choice. Many thousands of Miraco users who bought after thorough comparisons tes- tify they enjoy programs Coast to Coast, Canada to Mexico, loud and clear with the magnificent cathedral tone quality of costliest sets. Don't comfuse Miraco's with radios. Miraco's MIRACO "Powerplus" DCM> , cheap, "squawky" have bothin8and7tubemodels one dial, finest latest parts, approved shielding, havemagnificently beautiful, I METAL SHIELDED/ clearcathedral tone Turn metal chassis, etc. as used in $200 sets. quality. one dial for stations everywhere. I .CHASSIS * MIDWEST RADIO CORP. Ultra -selective. Miraco multi- Btage distance amplification gives Cincinnati, Ohio ''power-plus' 'on far-orTstationa. Latest all-metal shielded chassis. [BEAUTIFULLY ILLUSTRATED Illuminated dial. 14975! Fully guaran- EARNS teed. Try one free for SO daysfi In His Choice of beautiful cabinets. RETAl L LIST] >ef $5OO. E lect rify Any Radio That's the record of Member Lyle Follick, Lansing Mich. Member Werner Eichler, MIDWEST NO-BATTERY Rochester, N. Y. writes, "I have made mil coupon over #50. a week in my spare time" With its proven money making plans, advice, co- Power Units operation in furnishing parts at wholesale and training, the Radio Association of America is helping its members start radio stores, secure better positions, M increase their salaries, earn $3. an hour upwards in A"."B"and"C* direct from spare time sets and as radio power, building serving light socket, with- "doctors." outbatteries! WriteforMidweetprices nd Unit* are the discount*. Midweat biffbat Join Association without delay, because we have tfrmd* Inntinsly dependable, quiet in up*r- a plan whereby yourmembership may not need not atioD, full ffuamiteed. cost you a cent. Only a limited number of these memberships are acceptable. Write before it's too late. 30 Dayi

Tr'al MIDWEST RADIO CORPORATION COUPON RADIO ASSOCIATION OF AMERICA Pioneer Builders of Sets NOT 406-C Miraco Ohio. Dept. RB-10 4513 Ravenswood Ave., Chicago 6 tube Building, Cincinnati, ORDER Send me your book and details of your Special Without Membership Plan. ft obligation, s,-iid free catalog, AMAZING SPECIAL WHOLESALE i Super PRICE OFFER, testimony of nearby Miraco users.

Name . . . I NAME dddrtss .

.... . City State ADDRESS 412 RADIO BROADCAST ADVERTISER

Safe Radio

the Board of Underwriters, are abstracted as A "Million-Dollar" Front follows: PERTAINING TO THE LIGHTNING HAZARD

1. LIGHTNING ARRESTER. Each lead-in For Your Receiver wire shall be equipped with an approved lightning arrester, operative when 500 volts or more are impressed on it, and connected to a ground either inside or outside the building, as near to The New the arrester as possible. The arrester should not be installed near any inflammable material. If a grounding switch is used, it should shunt the HAMMARLUND arrester, and should have a capacity of 30 amperes at 250 volts. Illuminated 2. APPROVED GROUNDS. The ground used is preferably made to a cold-water pipe, where such a pipe is available and is in service and connected to the street mains. Other permis- Drum Dial sible grounds are: the grounded steel frames of buildings, the grounded metal work in the build- artificial such as driven An up-to-the-minute tuning ing, and grounds pipes, etc. Gas shall not be set- rods, plates, cones, pipe improvement every used for a ground. The ground should be in- builder will want to install. stalled so as to be safe from mechanical injury. An approved ground clamp should be used for connecting the wires, and the pipe should be thoroughly cleaned.

3. GROUND WIRE. The protective grounding conductor may be of bare or insulated wire made of copper, bronze, or approved copper-clad steel. The ground wire shall in no case be less FRONT VIEW in current-carrying capacity than the lead-in wire, and in no case shall it be smaller than No. waited to produce 14 if copper, nor smaller than No. 17 if of bronze or steel. The wire should HAMMARLUNDa drum dial that would make the copper-clad ground be run in as straight a line as possible from the of condensers really single-control tuning protective device to the ground connection. In- practicable. side wiring should be fastened in a workmanlike BACK VIEW manner and should not come closer than two Local stations can now be tuned in over the inches to electric conductors, unless movement Mechanical Features porcelain entire wave band by the simple tubing forms a permanent separation from Over-size die-cast frame of two fingers. Distant stations, requiring ; such conductors. This last applies to all inside Bakelite drums, with wires. a finer adjustment, are brought in by a knurled translu- fuses shall halves edges ; 7. FUSES IN GROUND LEADS. No slight realignment of the individual cent celluloid wavelength be used in any lead-in conductors or in the ground of the dial. scales, illuminated by a the the new Hammar- small with Viewed from front, electric light, REQUIREMENTS FOR PROTECTION FROM HIGH lund Drum Dial gives to any receiver a handy switch, connecting VOLTAGE finish. The bronze with the "A" Battery cir- delightful, professional 8. INSTALLATION NEAR HIGH VOLTAGE and oxi- cuit. Adaptable to all escutcheon plate, richly embossed MAINS. The antenna and counterpoise, out- standard panel propor- endows the with a classic side the building, shall be kept well away from dized, panel tions. wires carrying a potential of 600 volts or beauty. any more, including railway, trolley, or feeder wires, MANUFACTURING COMPANY in order to avoid accidental contact. These HAMMARLUND voltages are sufficient to cause shock dangerous fires. Antenna installations York to life and to cause 424-438 W. 33rd Street, New near electrical wires of less than 600 volts potential must be installed in a durable manner SfiitoK. T^jctdLu-V and shall be provided with suitable clearances 3o*o Dealer Already many leading ra- inquiries invited so that there is no possible chance of accidental dio designers have offi- concerning several other contact, due to sagging or swinging. cially specified Hammar- new and appealing Ham- Precision Products marlund lund ItammarlundF> TC IS ION developments t SPLICES IN ANTENNA WIRE. Splicing 9. for their latest circuits. ^| having a wide sales apfeal. B -HI f~ . .. ^~^v 1 v I I X^- T~ ^^ in antenna or lead-in wires should be soldered PRODUCTS unless made with an approved splicing device. 10. LEAD-IN CONDUCTORS. Lead-in conductors shall be of approved copper-clad steel or metal which does not corrode other excessively, ; of no smaller gauge than No 14, unless approved be RADIO PANELS copper-clad steel is used when the gauge may BAKELITE HARD RUBBER No. 17. Cut, drilled and engraved to order. Send rough sketch 11. LEAD-IN CONDUCTORS OUTSIDE THE Tubes and for estimate. Our complete Cataloe on Panels, BUILDING. The lead-in conductor shall not ( Rods :ill of genuine l..,keiitc or Hard Rubber mailed come closer than four inches to any electric BIGRAOIO CATALOG on request. therefrom From the "Big, Friendly STARRETT MFG. CO. light or power wires unless separated 111. fixed non- Radio House" 521 S. Green Street Chicago, by a porcelain tube or other firmly 1928 Book offers finest, conductor. parts, NEWnewest well-known sets; 12. LEAD-IN INSULATOR. An approved eliminators, accessories at lowest lead-in insulator should be used. prices. Set-builiiers.dealers,aRent8 for this CATALOG ! An im- WRITE 13. STORAGE BATTERY CIRCUIT. is thel portant and new provision rarely obeyed requirement that fuses of not less than 15- shall be installed and located Late8t amperes capacity advanced circuit. AH preferably at or near to the battery. An ap- eteel chassis totally shielded. circuit breaker of the same minimum Balanced parts of best quality. proved Marvelous power and selectivity. Geta be used. The leads from the bat- tbe long ranee stations as clear as a bell. capacity may | One dial single control. An unsurpassed valu to the receiver shall consist of conductors ifestemBadioMfgCo. just inic t>f uur many mighty bargains. tery FREE Log ana Call Book having approved rubber insulation. 134 West Lake St. Dept. 47 andBlgNwCtloB-justoffthepresa. Pull of nuwl Ratliu Bantains. Send for your free copy these rules are and com- ILL. American Auto & Radio Mfg. Co. Clearly, simple easily CHICAGO, HRY ScWART7,BKKG, Prea. on Dept. 122 American Radio Bldn.. Kansas City. Ma (Continued page .// /) RADIO BROADCAST ADVERTISER 413

All-Metal Cabinet For 1927-28 Hook-Ups!

Model 250 For A. C. or Battery Sets Using 7x18 7x21 8x18 8x21 Panels

Pric. $1.75

Inside dimensions 25"xl4%"x9Vg". Hinged top with stay joint. Rigidly formed for strength and appearance. Felt foot rest rubber lid stops. A welded job doing away with troubles of swelling, shrinking, cracl::ng, splitting and uncertain fit.

The original beauty of natural wood grains Spacious interior dimensions are demanded combined with the efficiency of all metal for housing all the latest hook-ups! Vee Dee construction ! By our photo litho process, we metal cabinets are designed for that purpose. reproduce mahogany and walnut hardwood, 909oofall the 1927-1928 hook-ups are cov- and novelty finishes, so gorgeous in their con- ered by the dimensions of Vee Dee No. 250 Best tubes- seption that they excite the admiration of all cabinet illustrated above. Beautiful prac- who see it. tical! Low price! Best reception New broadcast developments make it necessary to have the latest types of tubes for fullest enjoyment of your set. receiving Metal Panel for Citizens Super Eight Bring it up to date with a Constructed in accordance with McMurdo Silver, Rernler, Cock-* complete installation of the Citizens Radio Call Book and aday co-ordinated designing new Gold Seal radio tubes specially developed for mod- Metal Panel and Chassis for Sil- ern reception. You will be ver-Marshall 1927 Model delighted with the improve- "^ Super-Heterodyne ment. Complete assembly consisting of panel and chassis, You can make the changes fully drilled, beautiful wood finish with special two- color all fibre and washers in- no trouble. decoration, bushings yourself Our time*.* cluded, also screws, bolts and hardware accessories. new booklet'tells you all about it. Send today for your S. C. 2 Assembly Unit copy it is free. Use coupon Complete Panel, Chassis, 7x18, fully drilled. Beautiful below. wood grain finish, handsomely decorated. Kit includes all necessary bushings, washers and hardware accessories. All Standard Types

Gold Seal Electrical Co.

I 250 Park Ave., New York Unipac Housing I I Send me copy of the new booklet. Especially designed and provided for Silver-Marshall I Power Hook-ups including cabinet and chassis, drilled Name and with all small hardware. I

Address I Metal Panels and Chassis in All Standard Sizes

I !i^ JOBBERS, DEALERSWRITE FOR PRICES Set Builders if your dealer cannot supply you, write direct Gold Seal Radio Tubes t The Van Doom Company 160 North La Salle Street Chicago, Illinois Factory. Qttincy, Illinois 414 RADIO BROADCAST ADVERTISER Voice afe Radio tf a Kind with. Compliance with them gives you What plied safe installation. Failure to follow them invites unnecessary and totally avoidable risk. Fur- ^wLoud Speaker? thermore, failure to comply invalidates your fire insurance policies automatically. Does It BOOK REVIEW

A Home-Constructor's Handbook

PRACTICAL RADIO CONSTRUCTION AND REPAIR. By James A. Moyer and John F. Wostrel. Published by the McGraw-Hill Book Com- pany, Incorporated, New York. 319 Pages and 157 Illustrations. Price $2.00.

IRACTICAL Radio Construction and Re- useful and pair" contains a potpourri of Its authors have practical information. compiled their pages out of a large practical knowledge and experience in set building. The radio construction title implies a handbook of volume for the DoesItWKirve? and repairing a reference dealer's service man. It does not fail in that as it does orUo respect so much from incompleteness to com- from poor arrangement. But it has much mend it. Register with what The first part of the book deals Cleai: Natural Jfuman Tones ? may be termed the accessories of the radio receiver the antenna, the vacuum tube and its with these sub- power supply, and, tucked away on the tool needed for Muter jects, a chapter equipment radio construction. Then follows a series of describ- chapters on radio-frequency amplifiers, almost unbelievable improvement in miate. unit of istorted voice issuing from the speaker ing several methods controlling regeneration few words about and including a super-hetero- a brief dyne amplification. Next follows description of systems of audio-frequency amplification. few deal with con- -. The subsequent chapters liberal guarantee you won't recognize you. DEALER or SEND DIRECT structional details. The first set to be described SEE YOUR in detail is the Browning-Drake receiver. The for from leading can easily secure Muter Product* you Jobbers.^_however,,ymj Dealers writers then again return to audio-frequency have any difficulty in oh - ,..- a case for a will be made upon receu*.. amplifiers, presenting strong popular Mail today. duce its utmost. coupon kit. The superiority LESLIE F. MUTER CO. resistance-coupled amplifier of resistance coupling over transformer coupling 822-N, CHICAGO. ILL. 76th O Greenwood AT... Dept. of a set of curves. is emphasized by means Ap- transformer and a parently, an inferior superior used as the basis of the F. MUTER CO. resistance amplifier were on 76th & Greenwood Ave., Dept. 822-N test. A chapter impedance amplification, Chicago, III. devoted to a description of the Thordarson pre- D Send Muter Clarifier at once, postage follows that comparing resistance and C. O. D. amplifier, is enclosed. U Send DEPENDABLE PRODUCTS paid. $6.00 transformer coupling. Muter Catalog. Line Send ccaiplete to sets, the authors The complete Quality Popular Priced D Returning again receiving catalog the "Universal," the Acme reflex, Send for comprehentioe Name next describe the Cotton super-heterodyne, and a short-wave ' follow AJJreu receiver. In general, these descriptions style of ex- 5tate closely the conventional magazine Ctlu of and details for as- position, with lists parts, receivers sembly and operation. No commercial or even considered. Independent Radio Corporation are described Set Builders! The appeal of this book is confined generally Manufacturers of his and Be first to build the new to the home constructor and problems 8-8 Circuit Maenaformer dealer service man; an out- Commander-in-Chief ol not to those of the Ra- Precision Radio the the Air featured by Apparatus is the last chapter, where dio Authority G. M. Beat standing exception and Oct. Radio. remembered. This last in Sept. 1516 Summer Street Philadelphia service man is suddenly Read his articles. See also as makes interesting reading, containing, Sent,- and Oct. Popular chapter 10 and C. R. Call Book. and set of it does, a fairly complete practical in a radio re- troubles likely to be encountered I few biief ceiver under various conditions. A WHOLESALE are to show the type of informa- 'Jl samples quoted r 1928 Radio Catalog rite for my Big tion in this section: off the press. Thousands just" marvelous bargains in nation- It's a ally advertised goods. All the SET GIVES SQUEALING SOUND CONSTANTLY.- regular , ,ATEST IN RADIOS and sound in a receiving set is . constant encyclope- luipment. Loweatwhole- A squealing Radio. defective vacuum tube whu diaon sale prices. generally due to a All abou I Irouble llnd Agents of time has become soft or gassy. FREE Log n.. > in the course MAIL COUPON NOW Wanted. be due to a very l it. L "<> ChleaRo. . also Radlart Lab. Co.. Otei. 57. ', Call Book and Cat- NfiF Continuous squealing may Flense send me tree dencrlptive literature regarding Magna- Get copy to- to a less to slog. your -28 badly run-down B battery or, degree, former performance. day. Send postcard no... burned-out American Auto a Radio Mfg. Co. a worn-out C battery. A primary Name HARRY SCHWARTZBBRO, PRKS. Ml on page 416} Depl. 123 Amencin Hidin Bldg.. Kllls Cily. (Continued Address. . RADIO BROADCAST ADVERTISER 415

Radio Is BETTER With Dry Battery Power Transformers

Two additions to last year's Radio Sensation The Amazing Achievement in Audio Amplification

Designed to fulfill the exacting requirements of set builders who demand

f EFFICIENCY ~[ SENSITIVITY 3 made to run PRECISION AND HIGH QUALITY J the/w// race / 1 The new C-16 and C-25 Trans- formers will work in any circuit Y horse can make a and will improve any Radio Set. good start But it takes real stamina to finish!

So it is with batteries. Stay- ing power is the quality to look for unfailing power over a long period of serv- H. F. L. C-16 Audio ice. Millions prefer Burgess Transformers and C-25 Neu; Chrome Batteries for just this output Transformer a reason. They hold up companions of Qreat Unit, ivill work in any circuit last. They and improve any radio set. Next time, buy black and white Chrome striped Burgess H. F. L. Units Give Wonderful Batteries. You are certain to Clear get longer and better service Reception H. F. L. Facts acclaim H. F. L. C-16 for your money. Engineers a marvellously efficient Audio Transformer. It carries H. F. L. Units have been signals at c ^e reserv * n e ' e" d)TOtTl6 P g used, approved and moat highest volume and lowest amplitude without ment used in leather, highly endorsed by Radio News. Citizens Call blasting or harmonics. with metals, paints and other materials Book. developing Operates Radio Review, Radio Age. to is also used in all tubes as well as standard tubes. subject wear, Radio Engineering. Radio power Burgess Batteries. It gives them un- Mechanics, Chicago Eoening H. F. L. C-25 Output Transformer handles the the News and usual staying power. Burgess Chrome Post, Daily others. Thousands of voltage of at the Batteries are engi- output power amplifying tubes, patented. neers and fans, who have same time matches the of the turned to H. F. L. Units for impedance average cAik Radio Any Engineer better reception, hail them speaker to the tubes. Protects loud speaker unit as the finest transformers BURGESS BATTERY COMPANY known to Radio unex- without reducing plate voltage. Central Salts Office: CHICAGO celled for Power. Selectivity Mechanical features of these two transformers are: Canadian Factories and and Purity of Tone. Officts: coil Niagara Falls and Winnipeg A designed and treated to exclude moisture Perfe, matched, skill- ctly and withstand electrical fully designed. carefully heavy surges without made, rigidly tested in a breaking down to word, H. F. L. transform- complete magnetic shielding ers are technically correct avoid interstage coupling terminals brought out to the minutest detail. so as to insure short leads.

All H. F. L.. transformers Endorsed by America's the are for baseboard Leading Engineers Guaranteed by designed Manufacturers mounting or invisible sub- pane! wiring each unit is enclosed and sealed in a PRICES genuine bakelite moulding. No. H-210 Transformer $8.00 No. H-215 Transformer g.OO H. F. L. Units are easily No. C-16 Transformer 8.OO connected into the assem- No. L-25 R. F. Choke 5.50 bly, simplify set construc- No. U41O R. F. Transformer 5.5O tion, and make a beauti- No. C-25 Output Transformer 8.OO ful finished job. Set Builders Dealers URGESS If your jobber cannot supply you with H. F. L. Transformers, write FLASHLIGHT & RADIO us for name of nearest jobber. HIGH FREQUENCY LABORATORIES BATTERIES 131-M NORTH WELLS STREET, CHICAGO, ILL. 416 RADIO BROADCAST ADVERTISER

Book Review

winding of one of the transformers or a poor connection in the jack connecting the loud speaker and closing the battery circuits will also cause this same effect. SET OPERATES WHEN PLUG OF TELEPHONE RECEIVER Is PUT IN JACK OF DETECTOR CIR- CUIT, BUT DOES NOT OPERATE IN STAGES OF AMPLIFICATION. This difficulty may be due to Pattern reversed connections of the A battery, or the primary winding of the audio-frequency trans- No. 135 former in the detector circuit may be burned out. Radio No serious attempt is made to correlate the Voltmeter practical information in this last section in a manner lending itself to easy reference. A The set constructor will find much of interest

in the book because it is, on the whole, reliable Qu ality and accurate. We might pick out statements Instrument here and there to quibble over, such as that in the chapter on audio-frequency amplifiers. Speaking of audio-frequency transformers, the authors say: "Some manufacturers claim that they can make transformers which amplify Your Radio Will Be over a wide of consistently range wavelengths," a correct, though rather unconventional way of referring to audio-frequencies. Another case of " a different kind: If the sound volume from the Better loud-speaker is weak, tap the vacuum tubes with a finger nail to determine whether or not the audio amplifiers are operating satisfactorily: if Voltmeter control of filament will make radio voltage any they are not, the tapping by the finger nail will receiving set better. It enables you to retain that nicety of balance cause a ringing sound in the loud speaker." To in filament emission, which brings in reception clear and exact with include, in a final summary of testing instructions, so broad a generality, having so many maximum volume. It will prevent premature burnout of the radio conceivable exceptions, is, to say the least, tubes due to excessive filament with a voltmeter voltage, for, somewhat careless. to the will mounted on the panel and connected filaments, you know A general criticism which may be made of at all times just what voltage is being applied to the filaments. many radio books is the superficial knowledge of their authors. Moyer and Wostrel are certainly The Jewell Pattern No. 135 voltmeter is good looking and exempt from any such accusation because they have the outstanding virtue of knowing what rigidly constructed and is the ideal instrument for filament control. they are talking about. But they have not met The black enamelled case is two inches in diameter and contains a the needs of service men working for the radio D'Arsonval coil move- miniature, but very high grade, moving type dealer; the authors' viewpoint is that of the ment, which is equipped with a zero adjuster. Movement parts are amateur set builder. The circuits for all silvered and the scale is silver etched with black characters. preferred home construction are well selected and described; there are plenty of diagrams to browse among and, to one who The addition of this meter to your set will improve its appear- reads the book from cover to cover, many new ance besides a to better and economical being great help reception facts are likely to be discovered. Cut, if one wants to find out in a hurry such a practical constructional as whether the; should be so Write for descriptive circular No. Jj6 and ask for a copy of our point jack wired that the sleeve or the tip of the plug goes radio instrument catalog No. to the B-plus lead, or the quickest way of finding safely which tube is burned out with a set in Jewell Electrical Instrument Co. which the filaments are wired in series, there is no telling if, how, and where the desired information will be found. 1650 Walnut Street, Chicago EDGAR H. FELIX. ''27 Years Making Good Instruments'*

Builders! Set -fc *n-^ij_L ' My big 1928 Radio Cat- * All socket devices must power ,^_J alojj, Call Book and Trou- USE THIS COUPON FOR COMPLETE SETS depend upon Condensers for ble Finder. 132 pages about Hi- successful operation. Fast w Radio. Chock full of newest cir- RADIO BROADCAST SERVICE DEPARTMENT Condensers have extra f Teat cuits kits, transmitter parts, short RADIO BROADCAST. Garden City, New York. and are built to with- capacity wave outfits, eliminators and speakers. Please send me information about the following manu- stand every requirement Mill- Thousands of bargains at lowest wholesale prices. ions now in use and since 1919, A regular Radio Encyclopedia Frae. Write today. factured receivers indicat:d by number: one of the oldest established American Auto & Radio Mfg. Co. and reliable manufacturers, HARRY SCHWAKTZBRKG, PRES. Pep*. American Illustration shows condenser pack used in Q. R. S. or Ray- 1Z5 Radio Bldg., Kansas City, Mo. theon A-B-C unit. For perfect operation, build your A. B.C. picks with Fast condensers, whether specified, or not. They lit all units. Features of Fast HI -Test Condensers Condenser life depends upon its dielectric strength. Fast condensers have extraordinarily hitrh insulation resistance. condensers are all of the affording R U ONE? By-pass short-path type, zero resistance to radio frequency curve. Absolutely non- Co-operative member- inductive. ship in E I A RADIO is An rxrlusivp feature by-pasa condensers enclosed In one- establishing an honest, piece dies-press steel housing, makes them positively im- | Name pervious to all climatic conditions or abuse. Before being industrious man in each encased condensers receive special laboratory treatment locality in a successful Address whereby moisture content is effectually removed and once radio industry of his 1 removed, they stay that way, for the housing seals them own. Young married (Number) (Street) permanently thereafter. That's why Fast Hi-Test conden- men sers give such excellent, dependable service. preferred. Apply Free condenser booklet brings the facts. Dealers and job- by letter, giving the (City) (State) bers, lend for pi ice list. name of your county, to ONLY JOHN E. FAST 8 CO. 3982 Barry Ave., Dept. D, Chicago. U. S. A. EQUITABLE INDUSTRIES ASS'N, RADIO DIV. ORDER BY NUMBER 350-B Broadway, New York This coupon must accompany each order. RB 1027 SingleControl 7-Tube

RETAIL PRICE Completely Assembled

BIGGEST DISCOUNTS to AGENTS and DEALERS either full or part time and WORKmake big money. Tremendomadver- tising campaign helps you sell. Regard- seven-tube radio at factory price. Test it with- less of whether -POWERFUL1- you have ever sold before, out spending a cent. We claim the Randolph Seven will be sure to get our proposition. The Ran- out-perform any radio and we want you to satisfy yourself dolph sells on first demonstration. Men and that it will. To do this, we will send you this powerful radio to try for 3D women both can make money this days. Test it for distance, clearness, ease of operation, tone and every easy way. Get your demonstration set for other way you can. Unless it more than satisfies you, return it to us. Every thirty days FREE TRIAL. Randolph set must make good before it is sold. Battery or ELECTRIC OPERATION The Randolph Seven Is sold for use -with batteries or connected for operation direct to electric light socket absolutely batteryless no chargers or batteries just plug in socket and tune in. 100% efficient either way. Its construction and performance have been tested and approved by leading radio engineers and authorities and leading radio and scientific publications. Single Control Illuminated Drum One drum dial operated by one simple vernier control tunes in all stations with easy selectivity to tremendous volume. No overlapping of stations. Illuminated drum permits operation in the dark. Volume control for finer volume modulation. This is a 7-tube tuned radio frequency receiver with power transformers and power amplification. Space wound solenoid coils Full and completely shielded. A real receiver of the highest quality. Tremendous distance, wonderful tone quality, simple to operate. The Randolph cabinets are in themselves beautiful pieces of furniture made of carefully 7he selected solid burl walnut. Bas-relief bronze es- 6-Tube Pandoltth cutcheon plates are mounted on the dial panel. In design and appearance it is a cabinet worthy of the Now yon can have a new, modem, single- control, six-tube radio. Do not it beauti- con.pare high-quality radio contains. Solid walnut this set with old style 2-dial 6-tube seta s,-ll- fully shaped surrounds the soft verdi-green panel. HIK for about the same price. The Randolph lltL'.s Sfru..r Six has also been tested and ap- Nothing has beenspared to make the RandolphSeven proved by the leading: radio engineers. the radio receiver. We are so sure that it will Cornea in a beautiful solid walnut cabinet leading oJ hand -rubbed finish. Single control. surpass even your b^st hopes that we know how safe Illuminated Drum with apace for logging. we are in making the 3O free trial offer. Absolutely dependable and very selective. day Sent for 3O Days Free Trial. You test It before you buy. Read What Owners Say Mail Coupon Now I 50 to 55 The Randolph Radio Corporation are pioneers have logged more than stations from coast Retail Price in the manufacture of radios. All of its vast coast. Lloyd Davenport, Littlefield, Texas. und unlimited resources have been UBed in I have logged 52 stations from Cuba to Seattle the making and perfecting of the Randolph Re- ceivers. Because of our and successful set is a beater. J. Mich. SINGLE long world Tampkinson, Detroit, experience in the radio business, we are per- Your set is a revelation has all others tied to the fectly confident in Bending out a Randolph CONTROL . Radio on trial. We know what it will do. post for distance and selectivity. Waldo Powers, Mail us the coupon now for the greatest Vergennes, Vermont. radio offer ever made. its On strength of performance sold two more | Bets this week. T. Scanlow, Orlando, Florida. Beautiful Ampliphonic USE THIS COUPON TODAY! Console Set Randolph Radio Corporation. 711 West Lake Street, Dept. 121 Made of the finest carefully selected solid walnut. Chicago, Illinois. Two-tone shaded finish. Has built-in cone loudspeaker that compares wi th any on the market and Send me full particulars about the RANDOLPH Six and and low notes. Send for Seven -Tube Table and Console Sets with details of your accurately reproduces high Trial the folder today that shows this beautiful console in 30 Day FREE Offer. full colors and gives complete details. Compares with most table sets in price. For battery Name- or all-electric operation ready to plug in and tune in. Write for complete descriptions. Address Randolph Radio Corporation City State. W. Lake St. 111. 711 Dept. 121, Chicago, Mark here ( ) if interested in Agent's proposition. Plug In- and Tune la

* A Real Electric )Set 30 Three Year Guarantee Shipped direct from our factory at rock bottom prices cost less than most battery sets No Batteries, Chargers or Eliminators No Acids; No Liquids Plug In Press But ton "Tone In*

AGENTS! DEALERS!) BIG PROFITS! Make big money taking orders for I dynes. AH or part time. Metrodyne _ Electric are in a class themH fitrod Radios by selves* Unequalled for quality, performanc and price. Demonstrate at home and tak ALL ELECTRIC RADIO orders. Lowest wholesale prices. Yo demonstrating set on 30 days' free \ Mail coupon below for details. 7 Tuhes Single Dial Set Electric Radio BEAUTY EFFICIENCY 100% DEPENDABILITY At last I The radio you've dreamed The Metrodyne All Electric Radio is about ! If you have electricity in your home a 7 tube, dial set. Only the highest you can now really enjoy coast to coast single quality low loss parts are used throughout. radio reception without the care, bother and Solid walnut cabinet, beautiful two-tone ef- muss of batteries, chargers, eliminators, etc. fect, with handsome gilt metal trimmings. The Metrodyne All Electric is a real, gen- Size of cabinet, 28 inches long, 13 inches uine radio set. insert the batteryless Simply deep, 10 inches high. Has electrically lighted plug in the socket, press the switch button dial so that you can log stations in the dark. and "tune in." You could not possibly buy a Only one dial to tune in all stations. Excel better radio set than the Metrodyne All lent tone qualities wonderful volume Electric, no matter what price you paid. very selective. CostsLess Than MostBattery Sets Do not confuse the Metrodyne electric radio with ordinary light socket sets, because the Metrodyne is truly an all electric radio consumes less than 2c worth of power a day. Comes to you direct from the factory. Its low cost brings it down to the price of an ordinary battery set. We are so confident that you will be delighted with this wonderful, easy-to-operate batteryless radio that we offer to ship it to your home for thirty days* Gorgeous Console free trial you to be the judge. Electric Radio Here is the Mctrodyne All Electric Console Radio a gorgeous, genuine walnut cabinet, in a beautiful two-tone finish. Has a built-in Mail This Coupon genuine Metro-Cone large size speaker. Brings We are one of the pioneers of radio. The *%&l&!j*C in programs with great volume, reproducing the success of Metrodyne sets is due to our lib- entire range from the lowest to the highest notes eral 30 days' free trial offer, which gives 'l^' with remarkable clearness and distinction. All you the opportunity of trying before buy- metal parts are finished in old gold. Wonderful ing. Thousands of Metrodynes have been electric radio, in a cabinet that will beautify bought on our liberal free trial basis the of home. WRITE TODAY! METROappearance any ELECTRIC COMPANY 2165 N. California Ave. Dept.6O7, Chicago, Illinois

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