-" RADIO

VOLUME VII NOVEMBER, 1925 No. 11

'Radiotorial Comment

HE "hands off" policy of the government has been would prefer to go back to the old days of free-for-all compe- largely responsible for the rapid development of radio tition. Likewise it is to be hoped that all radio interests T in the United States. This is in marked contrast to will realize the compensating advantages of regulation. the restrictions imposed in other countries. Consequently History shows that whenever established law and order there are almost as many amateurs and radiocast stations in has not been strong enough to handle a bad situation, some the United States alone as in the rest of the world. sort of a vigilante committee has adopted drastic measures Results to date have more than justified Secretary to accomplish what it deems right. This always establishes Hoover's policy of a self-regulating industry. The annual a dangerous precedent and too often is subversive to the pub- advisory conferences of radio representatives have given his lic interest. Surely no one wants a vigilante committee department the benefit of the views of all branches of the in radio! industry. What adjustments as have been necessary to Consequently the outstanding discussions at the next radio settle disputes have been agreed upon in open meeting and conference will undoubtedly revolve around the question of have been accepted as the basis for the department's rulings. what kind of regulation will be most effective and practical. The chief point of discussion has been the allocation of Will it be sufficient, for instance, to rely upon a station's

wavelength bands for the various classes of service. During recognition . of the fact that its success is dependent upon a radio ser- t he past three years this has become increasingly difficult the maintenance of public good will? Should because of the expanding needs of radiocast stations. They vice commission be established? Or should greater regula- have already encroached upon the space previously assigned tory power be vested in the Department of Commerce? for ship and amateur purposes. But notwithstanding that In view of the evident and commendatory hesitancy of within four years their allocation has been increased from Secretary Hoover to ask for arbitrary power so as to handle a single 360 meter wavelength to the great band extending the situation, it may be well for the radio industry to fol- from 200 to 545 meters, there is not enough room to take low the lead of the baseball and movie man when they care of those who have been licensed, to say nothing of new feared the loss of public good will. Judge Landis and Will stations desiring space. Hayes have done much to inspire public confidence. Cer- Meanwhile the department has been functioning under tainly Secretary Hoover or Judge Davis could do likewise. N laws passed in 1912, long before radiocasting and other for radio, if either could be induced to relinquish his present modern inventions had been developed. The existing laws broader duties. do not provide for the suppression of man-made static nor Such men, with suitable assistants in various parts of the can motor -driven ships be compelled to carry radio equip- country, could determine whether a station is giving suffi- ment, simply because the law designates steamships. It has cient service to the public to justify the continued use of frequently been necessary to make rulings whose strict legal- the wavelength assigned to it. This implies the setting of ity may have been questioned. But be it to the credit of the standards as to power, location, broadness of wave, and par- radio industry that the justice, if not the legality, of the ticularly as to character of program, which might even limit decisions has always been recognized and conformed to. religious and other forms of publicity. It would involve a While it has been possible to thus "get by" with volun- censorship which is inconsistent with and abhorrent to gov- tary self -regulation during radio's infancy, it has now grown ernmental supervision, but which could be tolerated if the to be such a sturdy youth that some stronger method of con- standards were determined in accordance with a good sense trol seems necessary to protect the public interest. Since of the stations themselves. radio has reached the dignity of public service, the interest It is neither our intent nor our province to say which one of the public becomes paramount to the private interests of of these or other suggested methods is the best. Any one those engaged in the art. of them is better than the present functioning under obso- The private interests will naturally object to stricter regu- lete laws. But some means should be speedily adopted to lation, just as other public utilities originally objected to the protect the interests of the public and thereby increase pub- 4- establishment of public service commissions. But now there lic interest in radio. This is a real task for the radio is hardly a gas, electric power or railway company that conference.

RADIO FOR. NOVEMBER, 1925 9

www.americanradiohistory.com Fig. 4. Marconi Beam Station, PoWu, England. Marconi Radio Beams An Authoritative Description of This New Means Which May Revolutionize Transmitting Methods By H. de A. Donisthorpe

BEFORE describing the essential likely that these beams will cause the that beam. Compare for a features moment this of the Radio Beam it is existing high power long distance range new method of radio transmission with perhaps advisable to briefly re- stations to become obsolete within the that of the old, by referring to Fig. 1. view the more important factors govern- next ten years. The outstanding advantages of the ing the propagation of electrical waves The radio beam is nothing more than beam can be immediately appreciated ; as connected with the existing methods a concentration of electrical waves in for example, there is a minimum amount of radio telegraphic and telephonic trans- one direction, this being accomplished by of interference caused, together with an mission. These waves are radiated means of special reflectors. In this man- enormous saving in radiated energy, be- from an aerial so as to spread out sim- ner the whole energy from a transmit- cause with the beam there is .no waste ultaneously in every direction, their ting station can be directed into a beam due to waves being radiated out in direc- energy being dispersed more and more of not more than 15 degrees converg- tions other than that towards the intend- widely as they travel further from their ency and can be intercepted only by re- ed receiver. In the case of the existing source. Consequently only a very small ceiving stations lying within the arc of transmitting systems as has been pointed proportion of the energy transmitted from the antenna is intercepted by the intended radio receiving station. Going still further, it will easily be seen that the waves from such a trans- mitter can be picked up by any number of receiving stations for which they are c94-Are not intended, in fact by an unlimited T,pw,vsmvrre-, number of receiving stations providing they lie within the range of that trans- Be -AM /PECE/v,vG mitter. It follows naturally that a STA r/ON much greater amount of energy must be radiated from the transmitter than is really required in order to operate any O.PO/NARY one receiver. All the existing radio /PAo/o c.vs Tee ,vs Mi r rr,o telegraphic stations are rapidly produc- ing a congested ether and it is only a matter of time before a saturation point is reached when no further stations can be erected as the interference will be too ,Perewers 42,3 ori great to allow of useful working. not /n ósom and cormo/ '/."gr cep/ signo/s from Luckily the advent of radio beams Beam tronsm///er will go a long way towards eliminating unnecessary interference and a regular system has already been worked out whereby the outlying dominions of the British Empire will soon be linked up with the mother country by means of these beams. It therefore seems very Fig. 1. Selectivity Comparison of Ordinary and of Beam Transmitter.

10 RADIO FOR NOVEMBER, 1925.

www.americanradiohistory.com1 out before, the waves are thrown out in every direction like those surface waves produced by a stone striking the surface of a pond. The immediate result of this saving of i electrical energy is reflected in the initial outlay and maintenance costs of a trans- mitting station. Later on in this article, by reference to figures, it will be shown arithmetically how the beam station compares in efficiency with a station broadcasting its waves. It must not be thought that these beams are something quite new, as Mar- coni, in the very early days of his radio experiments, discovered that electro- Anfenna magnetic waves like those of light could be reflected. It will perhaps be of in- terest to study these early experiments, firstly, because of their historic interest and secondly, because they are closely ..3/ allied with the modern methods. The apparatus and circuits employed 4,. by Marconi in his original beam work are shown in Fig. 2. Here the waves The receiver consisted of the coherer were reflected by means of metal re- connected up with a battery and relay flectors of the shape shown, the waves across which was shunted an electric being produced by a spark coil through bell and it was shown that the bell the aid of the electrical oscillator, the would only ring when the aperture of the Fig. 3. Parabolic Reflector. spark gap of which was placed in the transmitter's reflector was directed to- line of the focus of the reflector. wards the receiver. By establishing a These experiments however, proved second reflector at the receiving end that only electro -magnetic waves of a with the coherer at the focus, it was very small wavelength could be used if possible to increase the range over which the reflectors were to be anything like a this arrangement would operate. practical size and in those early days of radio, short waves were very hard to produce owing to the type of appar- e atus then available. The advent of the thermionic tube and its use for the production of electromag- o netic waves solved this last named diffi- culty and consequently, during 1916 Marconi once again turned his thoughts toward his old experiments, having in /ldvc/io, mind an idea for using these beams for certain war purposes. The inventor was impressed with the possibilities such a system of radio telegraphy would af- TRA NSrr/ T TE -R ford in arresting the tapping of fa/ /Peflecfor messages by the enemy. This idea will become apparent by referring tò Fig. 1, once again, assuming that the enemy receiving stations lie on the left of the line XY. From that year until now, continual experimental work has been carried on, and not without avail, for some astounding results have been obtained. It is not the intention of the author to discuss the methods of producing elec- tric waves of short wavelengths as these follow those of ordinary radio transmit- ters and are doubtless known to all, so the remainder of this article will be de- voted to the description of the present day methods of reflecting electromag- netic waves, and to the results of their work. The first type of reflector used in re- cent work is shown in Fig. 3. It will be Co%erer seen that the. reflector in this instance Fig. 2. Marconi's Early Beam Apparatus. consists of a number of vertical wires

RADIO FOR NOVEMBER, 1925 11 www.americanradiohistory.com placed parallel to the antenna, and spaced in strength to those produced by the interest to dwell a moment on the around it on a parabolic curve of which waves re- emanating from an ordinary non - sults of the experiments carried out be- the antenna constitutes the focal line. directional 20 kw. transmitter. tween the Poldhu station and the Elec- The wires which comprise the re- These experiments were carried out tra. Throughout the cruise of flector are all tuned to the electrical the with a 97 meter undamped or continu- yacht wonderful signals were received wavelength of the wave which ous is to be wave. The actual transmitter util- during the night for long distances transmitted. size with The of the aperture ized eight transmitting tubes all connec- only 12 kw. of the reflector from the transmitter, al- is also an important fac- ted in parallel so as to dissipate some 12 though at times the receiving tor and to give the best was car- directional ef- kw. The antenna radiation from this ried out under adverse conditions. fects it has been found The that the distance arrangement was approximately 9 kw. signals during the day, between the however, were two ends of the reflectors If an ordinary station has been erected found to weaken A and B must and disappear at defin- be equal to 31/, wave- to give the same results at an equal dis- ites times according lengths of the wave transmitted. to the distance from With tance away from it, the transmitter the transmitter and depending regard to the first named condition would on the it is have had to be designed to ac- altitude of the sun at the site of trans- not necessary for the reflector wires to commodate 120 kw.; a startling differ- mission and reception. But it was found be tuned to the transmitted wave if ence in power but nevertheless true. that a reliable commercial radio -tele- their length is an undesirable or unprac- The receiving antenna on the yacht graphic service could be efficiently car- ticable one as a suitably proportioned throughout these experiments consisted ried out for a large portion of the twen- length will also produce good directional of a vertical wire 20 meters in length ty-four hours covering distances up to results. above sea level. This antenna was con- 2300 miles using only 1 kw. Fig. 4 shows picture nected of energy a of an actual to the usual type of inductively in the transmitting antenna. parabolic &am reflector as has been coupled receiver erec- with two stages of tuned Since this early form of reflector ted at Poldhu in Cornwall, radio frequency a England. and auto -heterodyning further type has been evolved This station has been detector which is used in all the re- tube circuit; an optional two undoubtedly more practical from cent experiments with radio stage amplifier a con- beams and was also included. structional point of view and worked in conjunction Before this is with Marconi's passing on to the very latest known as the flat type of reflector. yacht the S. Y. Electra, form This on which was of reflector it will perhaps be of new reflector, together with installed the receiver. the anten- With the results given by this re- flector B the great value of the beam be- .mew» V I... came apparent, as it was found by meas- urements ""'""''a `4 that the value of the energy re- rn..--. . /N _ - - ceived on the yacht was two hundred times greater than that which could be M -- received from that transmitted without ----.--- the aid of the parabolic reflector. Translating this fact into practical Iw/// figures shows that results can be ob- tained from a beam transmitter with a Fio. 5. Latest Form power of 0.1 kw. which will be equal of Antenna and Reflector.

na, is illustrated in Fig. 5. Here A represents the actual antenna whilst B. represents the reflector. The former consists of a series of vertical wires which may or may not be connected to- gether by horizontal wires and consti- tutes an antenna of most marked bi-di- rectional properties at right angles to its plane. This type of antenna approxi- mates as near as possible to a uniform current short circuit in which the cur- rent is everywhere maintained at the same relative value, by feeding it simul- taneously at a number of points by means of a special feeding ystem from the actual transmitter. The directional property of the energy radiated from such an antenna is a function of its di- mensions relative to the wavelength, which necessitates careful calculation in its design. By placing a similar arrapgement be- hind this antenna of wires the direction- al property of the same is made unidi- rectional and becomes the reflector. In order that this effect may become ap- parent it has been found essential for the distance between the antenna and the re- flector to be equal to one quarter of the wavelength transmitted. Fig. 6. Beam Station Masts Erected in Canada for a Flat Reflector. (Continued on Pye 61, le RA1)I0 www.americanradiohistory.comFOR NOVEMBER, 1925 Short Wave Reflectors Detailed Directions for Constructing a Parabolic Reflector for Increasing the Range of Amateur Transmission By Roy C. Hunter

the opening of the extremely X = Pef/eciov short ' wavelengths for amateur SINCEuse, directed waves, or beam trans- mission by the use of reflectors, has come into important notice. The fact that radio waves could be reflected has been known for a long time, but until Marconi performed his experiments with the use of parabolic reflectors noth- ing very definite was known. Due to the large size of reflectors de - j signed to be used on wavelengths over 10 meters it is not practical for the ama- teur to construct a revolving reflector for use with wavelengths greater than these. The 5 meter band makes it pos- sible to construct a moderate sized re- flector but it is still too large to be placed in the amateur's lab. The recent Fig. 1. Plan of Parabolic Reflector. opening of the / meter band makes it at least it is more handy and possible to construct a reflector that can in Fig. 1. It is formed by a number wavelength, economical. The closer the wires the be placed in the laboratory without tak- of vertical wires fixed in the shape of beam energy ing up much space.' a parabola. Each wire is supported at sharper the of transmitted, is be but at the same This band is practically unexplored. its ends by insulators. The length of which to desired, time allows part of the energy to escape It is a great deal harder to get a tube the wires may be 1, / or / the length back, called back leakage: to oscillate on this extremely low wave- of the wave to be transmitted. For out of the sides of parabola the length than it is on the higher wave- practical use the wires are made slightly The longer the the best reflector lengths. If the knowledge that has been shorter to compensate for the capacity sharper the beam. The a is one with moderate spacing of found on the 5 meter band and below effect between wires, which causes then the wires and with the sides extended. is applied it should be possible to get one higher wavelength. The aerial and practically no back or two five watt tubes to oscillate on counterpoise is one length of wire the This would give this wavelength. Two 199 tubes will same length as the reflector wires. A leakage and a very narrow beam. With for most oscillate on this wavelength without small loop is made in the center for coup- these instructions reflectors much trouble. With the use of a prop- ling to the transmitter. The aerial and any wavelength can be designed. is shown erly designed reflector for both trans- counterpoise are mounted vertically in How to lay out the parabola mitting and receiving the efficiency of the focus of the parabola. in Fig. 2. Say the parabola is to be as a reflector for wavelengths of these low powered short wavelengths Probably the best length for the ver- used English equivalent of e may be multiplied many times. The re- tical wires is slightly less than one-half / meters. The flector to be described here is designed 1 luViRi/iOGK v.. P saya .-r, to operate on / meter. However, in- structions are given whereby almost any ti sized reflector may be built. 0 The so-called / meter band extends kilocycles (equaling .7496 l''', from 400,000 meters) to 401,000 kilocycles (equaling .7477 meters). This band is large enough for one hundred radiocasting d stations to operate without interference and yet the difference between the wave- lengths of two adjacent stations would 4 k be only .00077 in. and the difference between the wavelengths of the highest x the lowest would be only .077 in. and C or less than 1/12 in. So you can get an idea of the difficulty of designing in- struments for use of these wavelengths. We have a great deal more to learn be- fore we will have the same efficiency on these wavelengths as we have on the W efik radiocast wavelengths. The reflector to be described is shown Fig. 2. Construction of Parabola.

RADIO FOR NOVEMBER 1925 13 www.americanradiohistory.com A Universal Radio Freq uenc y Amplifier Adapted for Use With Any Standard Receiver and Employing a New Method for Preventing Oscillations By A. .7. Haynes

THERE is always a demand for an This is not the only function, how- most sensitive adjustment easily constructed and efficient without al- ever, which the choke coil fulfills. The lowing it to go into oscillation. radio frequency amplifier unit circuit makes use of a principle which, This principle is applicable to two or which may be connected ahead of any as far as know, is I new in r. f. amplifi- three stages of tuned r. f. and in such standard receiving set. Many have at- cation. Without going into technical a case it is necessary that the values of tempted the construction of such unit, explanations it can be seen that the the but coupling circuits be carefully ad- few have succeeded due to careless- small r. f. choke through which the B justed. ness When only 'one stage is used in design and lack of attention to battery is fed to the plate of the radio ahead of details. a regenerative detector it is frequency tube is tuned to some natural not necessary to bother about Tuned r. f. amplification attaining at compara- resonant frequency, in this case approxi- this condition precisely, tively low wavelengths requires as the regenera- careful mately 550 meters. This choke is pur- tion in the detector tube acts work in assembly and selection as a com- of ap- posely designed to have a broad tuning pensating device. Due to the fact, paratus. Among the rules which must how- characteristic. ever, that the r. f. tube is working near necessarily be followed is to maintain a By properly proportioning the capac- its point of maximum efficiency over the high ratio of inductance to capacity, in ity of the coupling or blocking condenser entire wave band, even with no regener- the tuning controls, and to employ a low between the r. f. and detector tubes to- ation in the detector capacity tube, it is not neces- tuning condenser having a high gether with the inductive coupling be- sary to use the regenerative control minimum to maximum ex- capacity ratio. tween the primary and secondary of the cept on very weak or distant stations. The amplifier must have a method of r. f. transformer the following condi- The fact that both the r. f. and detec- coupling to the receiving set tuner where- tion can be attained : On the high wave- tor tubes can be worked at their highest by the amplifier is independent of the lengths, where the r. f. choke is effec- gain over the entire wavelength band type of circuit used in the receiver, and tive, practically all of the r. f. current accounts for the unusual sensitivity and can be used with any set. passes through the primary of the r. f. volume attained with this circuit. Such an amplifier is shown in the pic- transformer which results in a maximum In most receivers the ground end of tures, and the schematic diagram shown coupling between the two tubes. the primary or antenna circuit is con- in Fig. 1 will give the reader an idea As the received wavelength decreases, nected to either the plus or minus bat- of the arrangement of apparatus. In instead of this inter -tube coupling in- tery lines. If this is not the case, it the output of the r. f. tube circuit the creasing with the frequency, which is can be easily done by connecting the r. f. and d. c. currents are divided, the the case in the usual tuned r. f. circuits, ground post on the receiver to one of B battery being fed directly to the plate more and more of the r. f. energy is the battery lines. through a choke coil, while the r. f. com- shunted through the r. f choke which In Fig. 1, the r. f. unit is shown con- ponent in this circuit, being blocked by becomes less effective as the wavelength nected ahead of the three circuit DX the choke coil, passes through the .002 decreases. Thus an automatic safety tegenerative receiver, the general de- coupling condenser to the primary wind- valve is provided which when properly sign of which, since its appearance four ing of the detector circuit. set maintains the first r. f. tube in its years ago, has been followed more or U /PF I/N/T RECE/ /NG SET

.00025

i ,S r1 .00023

.007

Fig. 1. R. F. Unit Connected to Receivi',g Set.

14 RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com The condenser is placed directly across trol will have no effect on the r. f. tun- the antenna and ground binding posts ing, and it will be found that its adjust- of the single circuit tuner and a few ment, when the r. f. is added, is very turns of insulated wire are wound simple and not at all critical. around the filament end of the receiver's If the circuit should go into oscilla- tuning inductance. One end of this wire tion with a sharp thump when the re- is connected to the ground post on the generation is advanced too far, it means receiver, while the other end goes to the that a higher value of grid -leak should post marked P on the r. f. unit. Five be used, which applies to any regener- or six turns are usually sufficient. ative receiver whether used with the r. f. ~ In general, however, on all other unit or not. With the proper grid -leak types of receivers, binding post P on the circuit should slide smoothly into the r. f. unit is connected to the an- oscillation as the tickler is advanced. tenna post on the receiving set and the In using the r. f. ahead of the DX plus B post of the r. f. unit is connected receiver, the tickler coil or rotor should to the 45 volt tap of the B battery, be reduced to 10 turns, and the entire which is already being used on the re- 10 -turn primary of the coupler should ceiver. The minus and plus A posts of be used. The primary switch may be the r. f. unit connect to the A battery retarded if greater selectivity is desired on its respective terminals. The an- although this is seldom necessary. If ex- tenna and ground proper are no longer treme sharp tuning is desired, the pri- connected to ;he receiver itself, but to mary switch may be retarded fully, so the antenna and ground posts on the that only the one turn is included in the r. f. unit. primary winding, which will result in

Rear Panel Aiew of Amplifier. less closely by so many regenerative cir- cuit designers that it will serve as a good example for our purpose. The tuning inductance, or antenna coupler as it is commonly called, in this r. f. unit may be made in the form of a diamond weave spider web. It should have an inside diameter of 1Y2 in., the winding being made on 15 pins by the usual over two and under two method, 87 turns of No. 24 SCSS wire -being used, the exact number depending some- what on the condenser. The coil is tapped at the 15th turn from the inside for the ground connection, the inside of the coil being connected to the antenna binding post, while the outer end is con- nected to the grid of the r. f. tube and the stator plates of the tuning condenser. The choke coil may be wound on an ordinary small spool such as comes with Fig. 2. Pictorial Wiring Diagram of R. F. Unit. sewing silk. Its construction is not criti- cal, but should consist of approximately 400 turns of small insulated wire, any- The following procedure should be remarkable selectivity. Due to the fact thing from No. 30 to No. 40 being used in operation. The regenerative or that the tuning controls do not affect satisfactory. tickler adjustment on the receiver is each other, stations may be accurately Fig. 2 is a diagrammatic view of the turned to zero and the rheostats on both logged on the dials. back of panel, showing in detail the wir- the r. f. unit and the receiver are then ing for the r. f. unit, while those who adjusted to their proper points. The prefer to work from a schematic dia- tuning controls on the r. f. unit and When connecting a set up for the gram should use Fig. 1. The actual lay- receiver are then adjusted until some first time, it is best to connect the fila- out of the apparatus on this 7 x 4 x 3/16 station is received. The primary coup- ment battery, only, at the start, and see in. panel is indicated in the picture, the ling on the receiver should then be ad- that all the tubes light properly. Then view showing clearly the simplicity of justed either by means of its taps or by disconnect this battery entirely, and after the instrument, the condenser dial be- rotating it, as desired, until the set does removing the tubes, apply the plate sup- the only tuning control. ing not oscillate when tuned to a low wave ply, with a small 110 volt lamp (about station both tuning controls in res- The most valuable use for the r. f. with 15 watts) in series, and if it lights up, onance. When this adjustment is ob- unit is in connection with a standard re- or shows any glow at all, look for trou- generative receiver having an adjustable tained, the primary of the receiver may ble. If all is ok, then re -connect the or tapped primary. When the r. f. unit be left alone and the set operated exact- filament battery, and go ahead. This is used with single circuit receivers, the ly as it was before the r. f. was added, antenna and ground posts on the re- the only difference being that two con- small trick may seem unnecessary, but ceiver should be connected to a small densers must_ noww be tuned to the signal as it may save a tube, or even a set of fixed condenser of .00025 mfd. capacity. rather than one. The regenerative con - tubes, it will be well worth while.

RADIO FOR NOVEMBER, 1925 15 www.americanradiohistory.com An Ideal Audio Frequency Amplifier Directions for Making a Three Stage Impedance Coupled Amplifier of Unusual Quality, Adaptable to any Radio Set By Ernest ¡V. Pfaff

RECENT improvements in the sistance coupling but due to the kw source changes direction, all of the ar- quality of radiocast transmission ohmic resistance of the choke coils, prac- rows in the diagram will change like- and in loudspeakers have caused a tically the entire B battery potential is wise, including the lines representing demand for correspondingly high grade effective on the plate of the tube. No the magnetic flux. As these lines of audio frequency amplifiers, in order that greater amplification per stage, however, force collapse and build up again in the maximum enjoyment of music or speech is obtainable with the conventional type opposite direction, they cut across all may be attained. In the construction of of impedance coupling, than is possible the turns of wire in the coil g -e -f, in- such an amplifier, the key to high quality with resistance coupling, so that an ex- ducing a potential opposite in direction lies in the selection of inter -tube coupling planation of the theory of the auto - to the supply voltage. The induced vol- units which will pass all desired frequen- transformer will enable the reader to ob- tage in the winding e -f will serve to limit cies faithfully without introducing dis- tain a better understanding of why this the current in that coil to a very small tortion. type of amplifier is superior to others. amount, while the induced voltage in The three common methods of coup- Referring to Fig. 1, the current, which the coil g -e will act as an auxiliary vol- ling are by the use of transformers, re- is represented by the single headed ar- tage in series with the source. The to- sistances or impedances, transformer rows, flowing through the circuit a -f -e -b tal voltage will cause a current to flow coupling being the most popular because will set up lines of magnetic force, as through the circuit a -f -d-c -g -e -b, this of the high amplification possible per represented by the dotted lines. As the current being represented in the diagram stage, and the ease of assembly. A fair current from the alternating current by double headed arrows. Since the step - degree of tone quality has been realized g C with the use of well designed transfor- mers, and until the appearance of cone type loud speakers, transformer coup- ling was adequate for general use. Re- sistance coupling produces practically perfect reproduction over the entire musi- cal range, but has the fault of low ampli- fication per stage, and excessive B bat- tery consumption; due to energy loss in the plate resistances. It is evident that /S an ideal amplifier must incorporate the high amplification per stage and battery economy of the transformer with the practically perfect amplification char- acteristics of resistance coupling, and the amplifier herein described has these de- sirable qualities through the use of a modified form of impedance coupling with autotransformers. The impedance coupled amplifier op- /?afio / fo /5 erates upon principles very similar to re - Fig. 1. Current Relations in Auto -Transformer.

-A Fig. 2. Circuit Diagram of 3 -Stage Impedance Coupled Amplifier.

16 RADIO FOR NOVEMBER, 1925

www.americanradiohistory.com up ratio of input to output turns is 1 to in the diagram), which must be PARTS REQUIRED FOR 3 -STAGE high 1.5, it is obvious that the total output IMPEDANCE COUPLED enough so that it will not cause a loss in voltage will be greater than the supply AMPLIFIER voltage impressed on the grid of the tube. voltage and the resultant voltage avail- In the second stage, the grid leak is made able on Circuit the grid of the following vacu- Designation Description variable, so that an effective volume con- um tube to which the coil is connected trol is obtained. will be greater than if a single winding The vacuum tubes used in the first A-3 Thordarson choke coil were used. A -i, A-rz, Autoformers. two stages may be any of the A type It is not as difficult to design a good 3 C C-2 C-3 .5 mfd. fixed -v condensers. tubes, with amplification constant of 7 auto -transformer as it is to work out a 2 R-1, R-3 .5 megohm grid or more, but the tube in the last stage transformer of the conventional type, for leaks. 1 R -a 500,000 ohm vari- shoiñd be a power tube, such as the new the magnetic leakage is reduced and the able grid leak Centralab Modu- UX-CX-112 or the Western Electric coefficient of coupling increased to such lator. 216-A. The value of C battery given 1 Three contact a degree that with the use of a large J-1 jack. in the diagram is for the CX-112, but iron core of high grade, a winding of 1 J-2 Two contact jack. will serve equally 1 R-{ 6 ohm rheostat. well for the 216-A. very high inductance is obtained with Grid leak The C battery is very important in this low ohmic resistance. by mountings. Hence, wind- M Insulated top bind- circuit, each grid receiving its negative ing the coil in a manner such that the ing posts. potential 3 Cushioned vacuum with respect to the filament distributed capacity is low, we 'have a tube sockets. through the grid leak, and preventing 1 pair Shelf mounting practically ideal tube coupling device. brackets. the grid from becoming positive when a Fig. 2 shows the schematic circuit dia- 1 Panel, strong signal is 7 x10x3/16in. being received. gram of the amplifier which is shown in 1 Sub -panel, In 6x7x3/16in. building the amplifier, the accom- the pictures, the first two tubes acting as panying list of parts will aid in selecting voltage amplifiers, and the last tube as Miscellaneous screws, nuts, bus -bar appropriate apparatus. a power amplifier. wire and lugs. As explained in the The panel may be laid out in accord - theory of the autotransformer, voltage from the detector tube is applied to the primary winding of the coil, and the in- duced voltage in the combined primary and secondary windings is applied to the grid of the, first amplifier tube through the blocking condenser C1. Were it not for the step-up prop- erties of the autotransformer, the voltage applied to the grid of each am- plifier tube could not exceed the output voltage of the preceding tube, but in this case a voltage amplification is obtained in each coupling unit, with increased overall gain in the amplifier. The blocking condenser is used to pre- vent the B battery voltage from being impressed upon the grid of the following tube, the capacity being large in compari- son to the grid -filament capacity of the tube, and sufficient to pass the lowest frequencies of the musical scale. A value of .5 mfd. was selected as the prop- er size, a larger capacity requiring too long a period of time to be discharged, with consequent paralyzing of the tube grid. The discharging circuit of the Upper Side of Sub -Panel. condenser is the grid leak (R1, R0 or Rg

l t r¡-- -_

ALL MOLES le DRILL EXCEPT WMDRE NOTED. DOUBLE CIRCLED MOLE9 COUNTERSUNK

sore 10.L MOLlS tb DRR.L RXCEPr »MERE NOTBO

1 l' l' 1 *' l' lo' 9' Fig. 3. Front Panel Layout. Fig. 4. Sub -Panel Template.

RADIO FOR NOVEMBER, 1925 17 www.americanradiohistory.com ance with Fig. 3, and the driAing direc- The amplifier should be connected to STATIC tions for the subpanel MITIGATION are given in Fig. the detector of the receiving set, and for By HENRY W. HALL 4. If it is desired to use other appar- the sake of convenience, the wiring of While static can not yet be eliminated, atus than that listed, the mounting holes the detector tube is shown in Fig. 2 in the experimenter can greatly reduce the can be changed accordingly. It is good dotted lines, so that the same A and B severity of the intermittent or "click" practice to mount all the apparatus on batteries may be used to operate the re- variety by using two identical receivers the sub -panel first, and completely wire ceiver and the amplifier. No other audio and two antennas or loops. This is ac- it before attaching to the front panel. stages should be used, as three stages is complished by means of the bridge bal- Only a few parts are mounted on the ample for all requirements. In case the ancing principle illustrated in Fig. 1. front panel and these may be easily wired radio receiver is not equipped with a by- to the sub-panel apparatus after the pass condenser in the detector plate cir- brackets are installed. From the pic- cuit, it is advisable to connect a .002 tures, it can be seen that bus bar wire mfd. fixed condenser in the position was used for all wiring, each wire being shown with dotted lines. Otherwise, carefully bent, cut and fitted in position high frequency will get into the ampli- before attempting to solder it. The use fier circuit and may overload some of of flat soldering lugs will greatly facili- the tubes, resulting in distortion of the tate wiring, since they eliminate many audio frequencies being amplified. bends and result in neat appearing work. When testing the set, care should be Use rosin core solder in preference to taken to see that the springs of the jacks any other, and remove all excess solder are making good contact, and the tube

Fig. 1. Balancing Bridge Principle.

According to the familiar principles of the Wheatstone Bridge no current will flow through the loudspeaker LS if RI and R. are equal and if the potentials at V= and Va are the same. Let the two resistances be the plate resistances of the output tubes of the two receivers, and let the potentials be the voltages of the two B batteries. Then if we connect the outputs of the two receivers as shown in Fig. 2, we will have the same ar- rangement. If one receiver is arranged to receive only static while the other is receiving both signal and static, the static impulses coming at identical in- stants will not affect the loud speaker, if adjusted to equal intensity, while the signal coming in on only one receiver Lower Side of Sub -Panel. (and changing the resistanceof its out- put tube only) will unbalance the bridge from each joint so that there will be no socket springs should be polished with and cause current to flow through the danger of short circuits due to drops of fine sandpaper so that- a perfect contact loud speaker. solder in close proximity with each other. can be assured. The volume control This sounds quite logical and easy, When the amplifier is completed, a rheostat enables perfect control of the but the author wishes to warn those few simple tests will safeguard the tubes volume from zero to maximum, and for who try the circuit that considerable and batteries. Connect the A battery best quality, this should be set some- care in adjustment is necessary to ob- to the binding posts provided for it, where near the halfway mark, as the tain the desired result. The reason for insert the tubes in their sockets and turn first audio tube may become overloaded the use of identical receivers is in order on the filament rheostat. If the tubes with a very low volume setting. If that the wave shape of the static im- light and show proper control from the blocking occurs in spite of the adjust- pulses in the two output tubes will be rheostat, disconnect the positive A lead ment of the volume control, the grid the same. This would probably not be and connect it to the positive B binding leaks may be defective, and new ones the case if different receivers employ- post. If any of the tubes should should light, be substituted. (Continued on Page 90) there is a short circuit and it should be located before the B battery is connected. If no trouble is found, all the batteries may be connected and the amplifier is ready for operation. If UV -201-A or C -301-A tubes are used in the first two ca. stages, and a UX-CX-112 is used in the last stage, the B and C battery voltages given on the diagram are the proper ones to use. If other tubes are used, the C voltages specified by the tube manufac- ReceiLer 1irci /Fec©. ve turer should be employed. Fig. 2. Connections for Mitigating Static.

18 RADIO FOR NOVEMBER, 1925

www.americanradiohistory.com y

Marius Latour An Interesting Pen Picture of this French Inventor and of the Far-reaching Effect of His Patents By Walter Emmett THE backwash from the excitement miliar with the -fact that he had suc- frequency transformers, seas potentially, created by the visit of Dr. Marius cessfully employed iron in radio fre- at least-an infringer. C. A. Latour to the United States quency transformers, and had made and By his late entry into the field of basic in the spring of 1925 has died down stabilized reflex circuits, his later amaze- claims for patent control of the Ameri- sufficiently to allow a rational perspec- ment at the public demand for the cas- can industry, this brilliant inventor stood tive of his position in the radio situation cade and reflex amplifier embodying his ready to wield a financial wand com- to be obtained. His work in 1915 and ideas was genuine. pared to that in the hands of the victors later for the French War Radio Ser- When he came to us, various engi- in the regenerative or superheterodyne vice and the result of his researches. have neers denied the priority of his claims, system of receivers. commer- although in some cases they had devel- been extraordinarily effective No oné except Schloemilch and Von cially. oped their own ideas with the French Bronk, who antedate him for a single There was in 1916 no general appre- Army. Every American mánufacturer radio frequency ciation of the possible extension of the who used either radio or audio frequency tube reflex circuit and American use of radio reecivers in the coupling transformers, single B batteries, amplifiers, could apparently escape the future, and so, while Europe, and grounded filaments, or transformers, re - charge of infringement. Not even the France especially, were generally fa- flexed tubes in multi -stages, or iron radio "balanced" or "neutralized" systems of

RADIO FOR NOVEMBER, 1925 19

www.americanradiohistory.com avoiding oscillations in a reeciver were but now obscure products of the Middle immune. would, if rigidly enforced, have placed Ages. Real work often has been side- the American radio telegraphic «'ho, and what is this type of indus- inven- tracked in the minds of the public by try in a very dependent tor, who knows first what to invent position, but the and more superficial successes. field has now been second how to sit back until the develop- fortunately cleared For those who wish to know what his by mutually amicable settlements. ing radio art carries his work forward actual position in the modern world sig- Latour alternators are highly efficient, to commercial importance? nifies, it may be said that officially he and their only rival is the high power He is not fundamentally a radio engi- is a professor at the Ecole Superieure tube, such as those now being operated neer at all, paradoxical as this may seem. d'Electricité in Paris. He is a natural in Carnarvon, Wales, and in other Long before the radiocast era dawned, research engineer and has made this his places on competitive tests. The ad- Prof. Latour was a teacher and consult- hobby when he is not writing books on vantage ing electrical engineer of the tube is its great flexi- in France, with a poetry and philosophy. Hiram Maxim bility in very regard to range of adjustable firm position as a leader among the was a similarly endowed inventor and wavelengths. The designers of various types of alternating alternator, however, his work on the science of poetry will has the natural advantage of current motors. He developed a famous giving a repay comparison with that of Latour. purer wave than the tube, type of compensated repulsion motor unless special Latour is a linguist and his English means are taken in known by his name, where the latter to elimi- armature re- is just as perfect as that of Clemenceau, nate the families actions were balanced of upper frequencies out and very de- who was a school teacher in America or harmonics which sirable speed -torque characteristics are 'given off.. were for some time. Being a consultant and The scope of the obtained with the successful inventions made by use of a research engineer for the General Elec- Professor Latour covers commutator. A very instructive so many inven- and tric Company at Schenectady, N. Y., tions that, unlike the late Oliver brilliant controversy with an engineer in Heavi- from 1904 to 1911, a great many pat- side, he is already very comfortable, England on this subject followed and ents were fi- granted him along the lines nancially, from the proceeds of royalties. goes to show his many-sidedness. of X-ray tubes, high frequency oscillator His first electrical patent goes back He is a philosopher a to and student of circuits, high frequency alternators and 19 years ago, and strangely psychology, as well enough, is as a brilliant prac- repeater circuits. for a negative resistance tical technician. produced in a Like many brilliant It should not be forgotten that from mercury vapor tube. European engineers and mathematicians, The importance the date of the advent of the mercury of this device in certain applications Marius Latour is a of man of very broad arc and its use as a rectifier, which was voltage and current amplification, training in the "humanities." such His in- finally awarded to Peter Cooper Hewitt. as are illustrated in the "dynatron," terest in sociological questions and the will after a struggle with the General Elec- not be fully appreciated by the public general progress of mankind is much on tric Company, the ease of producing os- until their application in the radio art a par with that type of mind which has cillations from such a device was readily is further developed than it is today. made H. G. Wells a leader of thought seen by several inventors, among whom It is interesting to realize in England. Robert that the Thurston. probably was Vreeland. It did not require very necessity of distortionless amplification the greatest authority on the thermo- long consideration by a powerful mind in radio frequency transformers was dynamics of the steam-engine which to devise a negative resistance. Some of clearly forseen by Latour; as he distinct- America has yet produced, was of a these parents are the basis today of the ly specifies that radio frequency amplifi- similar type of : mind his interests licenses that have been granted to the cation, in order to be distortionless, ranged over the whole must field ut human Radio Corporation of America and oth- be "aperiodic." To secure this partic- activity and was by no means confined ers. The number of patents granted to ular result, he introduced resistances, to the exact sciences. "l'he practical suc- date is 14 and there are about 68 appli- and it is on these points that some work- cess of men of broad scientí`fìc training. cations pending. ers in the French Service from America whose interest in the general cultural Just before the War, Professor La- now dispute his priority, with what re- progress of the world does not prevent tour licensed a French company on a sults remains to be seen. intense application to technical prob- royalty basis to make and use his inven- Even in the question lems, is also shown in the heights reached tions, of "line -radio," and it was largely due to his ef- he has been able by men like Alexanderson and Stein- to dispose of patent forts as Chief of Staff of the Radio Re- rights to the Postal metz, who are illustrations ut the fact Telegraph Company. search Division of the French Army These will not interfere with that to understand any one science or that the the situa- reflex circuit was brought to tion as covered by the patents art thoroughly, a broad' foundation of G. O. of its state of efficiency during the War. Squier, which interrelations with allied patents are broadly indi- branches of American engineers who worked in cated cultural knowledge in the work of Hutin and Leblanc, must be kept up collaboration with this section of the all through life. Dr. John Stone and Professor Michael French Army seemed to have thought Pupin, dating back more than twenty Marius Latour is a typical inventor along the same lines, and some of them years and now lapsed. insofar as a problem when solved is to are challenging his priority in the mat- One of the first things that Latour him simply an. indication of a still more ter of coupled radio frequency trans- did was to use finely laminated iron core interesting field to be conquered. He formers so interrelated as to reduce the transformers to secure radio frequency has stated that his greatest hope for oscillations which usually produce howl- amplification. By using this type of fame rests nut on his technical work but ing and distortion in reception. It is transformer there was enough hysteresis on his highly original and significant not generally realized that Professor loss introduced to act as an book on "The Mathematics automatic of the Emo- Latour's patents on high frequency al- dampener of oscillations. Of course, tions" and is merely reflecting the real ternators have been developed by other the amplification voltage ratio was re- tendency of all inventors to whom the French engineers, such as Bouthillon, duced but the net performance was im- struggle is more interesting than the to a very high degree of refinement. In proved as regards freedom from oscil- result. fact, the alternators in the Eiffel Tower lations. He is nut of an over -sanguine tem- station are run with their rotors work- The question of the use of a common perament ; as his own opinion of his work ing in vacuo to reduce the power lost B battery for multi -stage sets is an in- shows that this book which he considers in windage. teresting one and is possibly capable of his masterpiece is not expected to bring Furthermore, his patents on the low being decided in favor of early Ameri- him true recognition for generations. antenna sectionalized cover the practice can inventors; as there is a great deal He does not fear that his favorite work of efficient long-range transmission. of early actual experimentation recorded will share the fate of some of the great These two patents, taken in. conjunction (Continued on Page 60)

RADIO FOR NOVEMBER, 1925

www.americanradiohistory.com 4- RADIO'S New Calibration Laboratory A Description of Its Equipment and a Statement of Its Purpose in Reader Service

PLEASURE is taken in announcing tube oscillator having a range from 50 up to 10,000,000 or more. They give a new service to readers of to 100,000 cycles, and having an output reasonably accurate calibration of any RADIO, in the form of a cali- free from harmonics and steady in value. vacuum tube or buzzer type wavemeters. bration laboratory, whose primary pur- Connected to the oscillator is a gain set, Besides the high frequency equipment, pose is to furnish a means by which which permits measurement of vacuum there are two capacity bridges, one for readers may have their apparatus, such tube amplification, frequency character- testing fixed condensers at audio fre- as fixed or variable condensers, induc- istic curves of audio or intermediate fre- quencies and the other for calibrating tance coils, wavemeters, etc., accurately quency transformers, resistance or im- variable condensers at radio frequencies. calibrated so that their equipment will pedance coupled amplifiers, in terms of An impedance bridge, which is at the contain no unknown quantities òr ap- either voltage amplification or in tele- right of the picture, enables measure- paratus of doubtful accuracy. phone transmission units. ment of the impedance of any inductance Heretofore radio publications have With the gain set it is possible to coil, audio or intermediate frequency generally confined the service of their measure the peak frequency of superhet- transformer or loud speaker, either with laboratory, where such existed, to test- erodyne transformers, and tune the the vacuum tube connected to the ap- ing new apparatus as it appeared on the filter transformer to match the inter- paratus, or without, as preferred. A market, and issuing certificates of excel- mediate frequency transformers. This laboratory standard high resistance volt- lence or other recommendation where will be particularly useful for those who meter and high voltage storage battery the apparatus was found to be of good have made their own transformers and is used to test the insulation of radio quality. Such certificates, when pub- desire to know at what frequency they apparatus and the resistance of grid leaks lished in the columns of the magazine, will operate best. or variable high resistances of any sort. are seldom of sufficient benefit to the Adjacent to the gain set are the crystal A Leeds & Northrup inductance bridge readers to warrant the space, and hence oscillator and its associated beating oscil- permits the measurement of inductance our laboratory service is confined to lator, as described by D. B. McGown coils, together with their low fre- such purposes as will give the most bene- in October RADIO. This oscillator quency resistance. fit to the experimenter, home set con- has crystals calibrated by the Bureau of In the lower picture is shown the structor, and the amateur. Standards, and will be used in checking General Radio Oscillograph, for analyz- The illustration shows a portion of the wavelength accuracy of Pacific Coast ing any frequency up to 5000 cycles. It the equipment. In the upper picture, radiocasting stations. The range of permits the measurement of noise in A along the back of the table, is a vacuum these oscillators is from 100,000 cycles (Continued on Page 64)

A Corner in RADIO's Calibration Laboratory

RADIO FOR NOVEMBER, 1925 21 www.americanradiohistory.com After the License--- What? Helpful Hints for the Aspirant to the Position of Commercial Operator on Ship or Shore By lamer W. Harte, WHE.

AVING decided that we are go- Arriving on board the operator will to be paid off, and ing to sea transportation must as a radio operator, in all probability find the door of the be furnished how them to the point of sign- do we go about getting a radio room locked. This is as it should ing on. job? We don't pick out a nice looking be. Inquiries will soon tell him who has These articles are signed before craft and decide that she suits a us and the key. It is usually left with the chief United States Shipping Commissioner, then approach the captain, or go the officer or the chief steward. Upon rounds go- who reads them aloud to the assembled of the various steamship offices. ing ashore in any port the operator crew. If we do we are doomed to disappoint- should leave the key with some respon- Vessels making short, regular coast- ment. sible authority, so that the government There wise voyages usually sign new articles are three large operating com- radio inspector or other proper officials every three panies which months, unless the whole per- render radio service to may inspect the apparatus. sonnel should change steamship companies. before that time. It is to one of After hanging our license in a con- On passenger these companies vessels sailing on sched- that the new operator spicuous place we should, whenever pos- uled time the rules should look for demand that the assignment. True, sible, check over everything with our radio men be on there are several board at least three steamship companies predecessor. After doing this we should hours before which have sailing. If the sailing time their own radio systems, but make out a requisition for the necessary of a vessel unless sorely pressed is uncertain it is advisable not for a man such com- supplies. Each operating company has to venture ashore before panies demand an experienced determining the operator. its own ruling on this, but all of them sailing hour from a responsible The man who has little officer of or no prac- hold the present operator responsible for the ship or the steamship company tical experience with radio on transmitters equipment and supplies. A junior oper- the dock. On vessels compelled will do better at the beginning to carry to seek ator will, of course, not be held respon- radio, since the ship is subject a berth as junior to a fine operator. However, sible except while he is on watch. if it sails without the hundreds of operators required, tyros have found themselves A very important thing to remember they make sure outside the breakwater that the radio men are with no one to is to be on hand when the ship's articles aboard. A cargo advise them. vessel, voluntarily are signed. These articles are an agree- equipped, may sneak- off without the In order to get any kind of a berth ment between the master and crew. operator. it is necessary to present ourselves at the They are usually drawn up for a definite On merchant vessels the radio local office of one of oper- the large operating period, six months or a year, new ators rank as junior companies, two officers. That is of which have their head- artitles being drawn up every voyage in they rank with the quarters on the Atlantic second officer, this Coast, the other the case of deep -water vessels. If the voy- despite the fact that many hardboiled on the Pacific Coast. We cannot expect age is completed before the stated time, mariners refuse to recognize to be placed immediately them as upon making the articles automatically expire. If the such. The great war did nothing to application. Nor can we expect always vessel is still away on a voyage, that is, change many of these opinions, for the to be notified to report far in advance of if she is not returning to a point men- radio operators during that hectic period sailing. If a ship is sailing sooner than tioned in the articles where the crew can were mostly enlisted men, while the expected, if an operator quits without be signed off, then the crew can demand (Continued on Page 66) notice, if for any reason an operator is required at short notice the man who is evE BEEN GETTING on the spot, or can be easily reached, has A LOTTA - HELLO 6E0.T - eve FOUNa the best RADIO TERMS ouTA 'RADIO - -ne TROUBLE -MY NEGATIvE ? chances for assignment. ILL SNOW GERTIE UNDER WITH PLATE WAS FULL OF'IONS'- ARID TECHNICAL DATA- I'LL fAKE I THE WAS SZDPPBI j Those steamship companies not main- D Mt-THINK eelTHE ./ uP -! taining their own radio departments have cecol+n nnacnHl!! yl `CA a service contract with one of the large dek operating companies whereby the latter Aoi4 maintains the apparatus, controls the ,,,,,, traffic and supplies the operators. How- ever, since I.!, the operators sign the ship's io articles, they are paid by the steamship company. This enables the operator to draw on his salary during the trip, a THE decided advantage over the old 140P-50CI¿ET ON THE WAS THE days XEDIAVATOR WAS o0T Z of OTHER FELLOW when the service company paid the oper- ALIGNMENT - THE ' BATTERY Q WAS CUT MucH ? ator, who, unless the recipient RAaIgwATNfiI Too MANY I Q of an in- OHMS 0 - THE RHEOSTAT o 1 I come, contracted many a debt if the trip HAD A SPIDER colt. was a long one. oN ITS RESIeTArKESTAII .. ;_ Having been selected to stand a watch n, in the radio shack of some vessel, the operator is given an assignment slip. This he presents either to the captain of the vessel or the marine superintendent olie. _ of the steamship company, whichever the case may be.

RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com The Beat Note By H. A. Highstone

ARD citizens every one, these men grouped about the council I I fire in the center of the rude illage, lithe, muscular men, beard- ed, and clothed in rough garments made of a coarse brownish cloth. Their im- plements of war and defense were for the moment laid aside, held by the women and children grouped outside the circle, spears, clubs, and bows made from the wood of the red yew tree. Every eye focused on the head man of the tribe, a tremendous bull of a fellow dressed in the skins of the mountain lion and topping head and shoulders above the wizened figure of the ancient í at his side. The chief had moved into the clear space by the fire and was speaking to the men of the council in a deep measured voice, turning from time to time to face every portion of the circle, that none might feel slighted. "There is a legend come down to us," he rumbled, "through four generations, of a time when this land of ours was not the place we know now. But a few of you are familiar with it, I know, for it is fast fading from the minds of all save the scribes. Exaggerations have, of course, crept into the substance of this story, for it is very old and it has been told and retold many many times, but even so, there is little doubt that at HE WAS old, very old, this ancient done for everything; smashed up the one time there were one hundred thou- man, and as he stood there in the whole works and left the country popu- living between the sea and sand people flickering light of the fire, blinking his lated with a bunch of damn cave men. rising to the the high range of mountains dim eyes and inhaling a last few puffs Radio! It made me and then it busted eastward of this valley." He paused for from a cigar of dried willow root, he me, like it did everything else. I was a moment as a little ripple of incredul- looked as though the sun and wind and running a gyp radio store up in a place ity passed over the crowd, and con- rain of a thousand years might well have called Oakland away up north of here, tinued. worked their will upon him. A tangled selling total -loss condensers and molded t "Aye, it sounds fantastic, but on a mass of white whiskers dropped almost mud sockets and bum bootleg tubes and. journey I and my father once made far to his waist from the bald dome of his the like and what with the `super -long- to the northward I viewed a great waste head. Deliberately he sucked at his distance' coils what I made for two bits cigar until the last permissible amount and sold to the suckers for eight dollars of ruins of an ancient city in which our of smoke had been drawn from it and I got along fine. I " Athos, chief might be lost a thousand times village then, after first warming his hands and of scribes, interrupted. (wer. But it is not now a time to argue then his back before the blaze, he began was this radio of which you and I see that many of you "What the matter speaking in a mumbling monotone, half speak ?" are curious to know from whence came the crowd and half to himself. to "Radio," answered the old man, "was this ancient man beside me, and for what "Lessee," he began hesitantly, cock- something that let you talk to people A sentry picked him up last ing one eye up at the moon and vigor- purpose. a hundred miles away, or ten thousand and brought him at ously scratching himself, "This here's night by the river miles away if you was a mind to with him for 2015 or maybe 2017; I've kinda lost once to me. I have talked with out.wirrs or anything else except some- track of things lately; anyway, this all many hours and he has told me many thing to send with and another jigger to happened about ninety years ago, a good a strange tale of the powerful people receive with. You put together what many years before any of you ginks were once the inhabitants of this they called a transmitting station who were born. and of the miracles which they man made land and "Things was different then; airplanes, when a a speech into it every- of one which at last de- wrought and railroad trains that whizzed you along body in the world could hear him if from stroyed them. We are come down sixty miles an hour, automobiles, big they had strong enough receivers. There this tribe and it is well that we should cities and millions of people living right were radiocast stations scattered all Qvei have the history of these mighty ances- here in this state, to say nothing of all the country and night times they sen tors of ours. One of them stands be- those who were still back in Kansas out music and speeches and songs an fore you. Speak, old man," he con- or Ioway. Heh! heh ! ; Great times- everybody as had a receiver could liste cluded and withdrew to his council seat. those days. But it was radio as how (Continued on Page 48)

RADIO FOR NOVEMBER, 1925 23 www.americanradiohistory.com Comparative Efficiencies of Coils A A Statement Based Upon Numerical Calculations of the Ratio of Inductance to Length By .7. E. Anderson TO determine the relative efficiencies the known value of the inductance; that three banked turns. of various coils which, from time is, This idealized 165,000 centimeters, and the known single layer solenoid to time, have been given the place shape ratio. was given the shape When this unknown had ratio which gives the highest of honor in radio store windows, the been determined inductance it was multiplied by the for a given length of wire. author has made a series of calculations constant and the numerical value of The value ,obtained for the ratio of their L/1 ratio, L being the inductance the L/1 ratio was obtained. L/l was 206.0, the required number of turns of the coil in centimeters 1 and the length As an illustration of how L/1 was was 55.8, and the radius , of the wire, also in centimeters. calculated, of the coil was In consider the single layer sole- 2.29 centimeters. The other words, the ratio is the number value obtained of noid. The formulas in the case are for the L/1 ratio centimeters of inductance per centime- (1) L=(27ra)2NnK for this coil is the (Nagaoka's for- highest of any of those considered. The ter length of wire. This is strictly a mula for inductance of solenoid). value is slightly high, however, measure of the efficiency of a coil at (2) 1=2nraN (Length due to of the wire). the fact that the turns in the actual low frequencies, but it may also be taken (3) 2an/N=2.46 (Condition for least coil are not placed quite so closely to- as a measure at high frequencies since resistance) . gether as they were assumed to be. But it may be assumed that the radio fre- in which is L the inductance of the coil the difference is small. quency resistance is proportional to the in centimeters, 1 the length of the wire The main advantages of this coil are length of the wire as well as the low in centimeters, a the radius of the coil that the inductance to resistance ratio frequency resistance. Assuming equal- in centimeters N the number of turns on is high and that a given inductance may ity, the constant of proportionality may the coil, n the number of turns per be put in a very small space. Where not be quite the same for all the differ- centimeter and K is the shape factor. compactness is the main consideration ent types of coils, but it will not be When condition (3) holds the shape this coil is most desirable. The main greatly different from the mean. factor is equal to .476, so this value may disadvantage of the coil is that it has For the sake of definiteness an in- be substituted in the formulas in place a high distributed capacity and hence ductance of 165,000 centimeters of was K. Also the size of wire assumed a high natural wavelength, which limits used as the basis of calculation for each makes the value -of n equal to 10. its tuning range with a given conden- coil. This is an average value of the Now if (1) is divided by (2) there ser. It is efficient provided it is not inductance in a radiocast receiver results in L/l=27rnKa=29.9a. The value operated near its natural wavelength. which a .0005 mfd. condenser is of used for a may be obtained by putting 165,000 The Two -Banked Wound Coil tuning. Also the same size of wire was for L in formula (1) and by eliminating The two -banked wound coil is simi- used in every instance, the hypothetical between N this changed (1) and form- lar to the previous coil in the method of size which winds exactly 10 turns per ula (3) . This gives a=4.77, and this winding except that only two turns are centimeter, i. e. 25.4 turns per in., which multiplied by 29.9 gives L/1=142.5, the banked instead of three. That is, two is an average size of wire as used for ratio sought. The ratios for the other turns occupy the same space tuning coils. The shape along the of a given coil forms of coil were obtained in a similar axial length as one was made such, turn of the same size wherever it was pos- manner. wire would in sible, that the inductance the single layer sole- for a given The value of the L/1 ratio is not a noid. Hence for the purpose length of wire was maximum. of calcu- It was constant for all values of inductance, lating the inductance it may be assumed assumed that the diameter or other wind- and for that reason the same inductance that the wire is such that it winds 20 ing form was made to fit these conditions has been used in each case, the ratio turns per centimeter instead of exactly, and also that 10 with- the number of being greater, the greater the inductance. out any change in the turns, to a conductivity of fraction of a turn, was put If a wire size other than that assumed each on the form. turn. The diameter used in the Only the form was as- be used, the ratio may be different; but calculation is sumed, and not the mean between the any solid matter in the for a given number of turns, the diameters form to support L/l of the inside and outside the wire. In other ratio will be the same for all sizes of turns. words, each coil is strictly an air wire as long as the product of n and core inductance. a The value obtained on these assump- remains constant. That is, the diameter tions for the L/1 ratio The method of calculating was 178.0. The the L/1 of the wire must be proportional to the calculated radius was ratio was as follows. First 2.97 cm. and the an expres- diameter of the coil. number of turns was 48.3. account sion was obtained for the inductance On in The various coils investigated will of the fact that the turns are separated terms of the dimensions. The best now be taken up in detail, and some of by finite distances the L/1 ratio ob- formula available for the inductance the of advantages and disadvantages of the tained is slightly too large, but it does a coil of given form was used coils for this will be pointed oùt. not deviate as much from purpose. Then an expression the true value was ob- The Three -Banked Wound Coil as did the three -banked coil. tained for the length of the wire, and The inductance of this coil was ob- The advantages of this coil are the one was divided by the other. The re- tained on the assumption that three same as those of the three -banked coil, sult gave the L/1 ratio in terms of a turns occupied the space of one of the namely, a high constant and the radius inductance to resistance of the coil or wire used, or that the number of turns ratio and compactness other dimension, or in for a given in- terms of some per centimeter was 30 instead of 10, ductance. constant and the number Neither is as great, however, of turns on the but that each turn of this wire had the as the corresponding coil. The unknown quantity, advantages of the whether same conductivity as the heavier wire. three -banked coil. The disadvantages it be a dimension or the number of turns, was It also assumed that the diameter are also the same in quality but not in was then determined by making use of of the coil was that of the mean of the (Continued on Page 76)

24 RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com An Improved LoopReceiver By R. Lewis Rockett

of 8 RECEIVING sets employing radio LIST OF PARTS the remainder the primary with frequency amplification have 1 1st stage r. f. transformer. turns in the opposite direction on a piece , 1 2nd stage r. f. transformer. of paper tubing which will just fit in- proved very effective in long dis- 2 Audio transformers. tance reception. Used with a loop an- 1 200 ohm potentiometer. side the 3 in. tubing. Place the 8 turn 2 .0003 grounded rotor condensers. tenna added selectivity is obtainable and 1 Vernier condenser. part of the primary directly underneath can easily be moved from place 2 0 ohm rheostats. the 20 turn section, which is wound at the set 5 Sockets. to place. 3 .00025 mica fixed condensers. one end of the tubing. The secondary 1 .005 mica fixed condenser. is a A workable combination involving 1 .001 mica fixed condenser. tuned with 13 plate condenser hav- stages of radio frequency amplifi- 1 41/ V. C battery. ing a capacity of .0003 mfd. three 1 Single circuit jack. cation, detector and two stages of audio 1 Double circuit jack. In series with the B battery is placed 1 Filament switch. amplification is shown in the illustra- 1 Panel, 7x24x3/16 in. a 1Y2 volt flashlight bulb, which will 1 3 in. length 3 in. composition tions, there being only five tubes used. tubing. blow out in case a short circuit develops A study of the circuit diagram, which 1 Shield 21/x21/2 in. in the set, in the B battery leads. One 1 Baseboard 91/2x24x1/2 in. is shown in Fig. 1, indicates the sim- Binding posts, wire and spaghetti. of the new G. E. protective tubes will plicity of the wiring, and the manner also serve the same purpose. If more in which the third radio frequency serves connected to the ground binding post. volume is desired in the last audio stage, also as the first audio amplifier, by the In wiring the set, avoid parallel leads than is possible with A tubes, one of the 411. use of the reflex principle. Two stages as much as possible, particularly in the new UX-CX-112 tubes will be the best of untuned r. f. amplification, with a grid and plate wires of the r. f. stages. to use, with the additional B and C bat- third stage of tuned r. f. provide the This makes the, set somewhat irregular tery voltages specified by the manufac- set with sufficient sensitivity for opera- as regards wiring, but is the best method turer. For 135 volts plate, the C bat- tion with the loop antenna, the two tun- in the long run. The construction of the tery should be 9 volts. ing controls being the loop condenser tuned transformer is as follows: The loop antenna, which is shown in and the variable capacity across the sec- On a 3 in. bakelite or fiber tube 3 in. the picture, has an untuned primary. Fig. ondary of the tuned r. f. transformer. long wind 64 turns of No. 24 D. S. C. 1 indicates the manner in which the loop The panel layout is shown in Fig. 2, wire for the secondary, and over this windings are connected. The loop may the center holes of each piece of appar- winding place 20 turns of the same size be constructed from two pieces of 1 x 1 atus being shown, as equipment differ- wire for part of the primary and wind in. wood 29 in. long fastened together ent in dimensions from that used in the experimental model may be used, and the holes for the mounting screws would not always be the same. The layout of ap- paratus on the baseboard is shown in Fig. 3, the most essential dimensions be- ing shown for convenience in mounting the various parts. The list of parts shows the amount of material required, the tuned r. f. transformer being home- made. A shield should be placed between the untuned transformers, the shield being fir13"2" View of Completed Set.

.0003

20o c.+ .003

- 90 e

Fig. 1. Schematic Wiring Diagram.

RADIO FOR NOVEMBER, 1925 25 www.americanradiohistory.com zt- T 4-1

El)

I I

1 -

k I Ì 3z 3z - 31' I I Fig. 2. Panel Layout.

in the form of a cross as shown in the tom to support 20 turns of wire spaced and placing the tubes. The best plan illustration. To each end of the cross in. apart. A swivel base of conven- is to connect the A battery and light tional design enables swinging the loop the filaments of the tubes, after which to the desired angle, and the terminals the positive A connection should be suc- are mounted on the base, with pigtail cessively made to the 45 and 90 volt leads to the loop. The untuned primary positive B terminals. If the filaments consists of 4 turns of No. 18 d. c. c. light, or a spark is seen when the con- wire wound in the opposite direction to nection is made, there is a short which the secondary, which consists of 16 turns should be located before the B battery is of No. 18 wire, tapped at the second. connected. These tests should be made turn. The tap is at the end of the sec- with the suggested fuse out of the cir- ondary nearest the primary winding, and cuit. The volume control is obtained by is brought out to a small two point means of the 200 ohm potentiometer, switch which is mounted on the side of the slider of which is connected to the the loop. With the untuned primary, grids of the first two r. f. tubes. The the antenna may be connected if extreme potentiometer may work satisfactorily distance is desired, and if the loop with- with only the grid of the first r. f. tube out the antenna is satisfactory, the pri- connected, in which case the second r. f. mary winding may be disregarded. tube grid may be connected to the nega- When using both the antenna and tive 4/ volt C battery terminal. For ground, the dotted lines 1 in Fig. show convenience in tuning, a vernier conden- the proper connections. The grid return ser of .00005 mfd. capacity may lead should go to the end of the loop be shunted across opposite to the antenna connection, al- the first tuning conden- ser, though this is not necessary if a small although a vernier dial for this con- indoor antenna should be used. denser will obviate the necessity of the Appearance of Two Winding Loop. In operating the set, the usual pre- extra control. In the experimental set, cautions and tests should be made to lo- two C batteries are shown, but one bat- glue a piece of bakelite 5/ in. long cate any possible short circuits in the tery can be made to do the work of two, and 1 / in, wide, grooved at top and bot - wiring, before connecting the batteries as is shown in the wiring diagram. 2'

Fig. 3. Arrangement of Baseboard Apparatus.

26 RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com Building for the Future Complete Directions for Building a Simple Radiocast Receiver for Hearing the Very Short Wavelength Transmissions By Harry A. Nickerson

THE AMATEUR, who is pri- ing one stage of audio. Of course a times experienced in "getting the set to marily interested in telegraphy great deal depends on location of the work" is not likely to be experienced. knows a great deal about the very receiving set and unless one heard WGY A pasteboard tube dipped in boiling short waves, having tried the various or KDKA well on the normal broadcast paraffin is used for the stator ; a paraf- single and double circuits with a few' wavelength, it should not be expected fined wooden rotor is mounted on a improvements of his own. It is unnec- that WGY and KDKA would come in hollow brass shaft, which turns in bush- essary to tell him what he should be well on their special experimental low ings set into the walls of the stator. able to hear below 100 meters, but the waves. Double cotton covered No. 16 or No. radiocast listener has much to learn A high ratio audio transformer theo- 18 magnet wire is used for the winding, about that wave band. retically should give greater amplifica- principally because it is cheaper and First, what can one hear on a low - tion than the lower ratios and for one easier to procure than silk covered. The wave set? The amateur would say stage of audio, distortion should not be stator may be 3 to 4 in. outside diam- "Code, and lots of it," which is true. noticeable. The writer uses one of the eter, with the equivalent of about 12 "Ah," says Mr.- B. C. L. "Not for General Radio 5.95 to 1 ratios, not be- turns on a 372 in. tube as the secondary me. I hear more commercial code than cause of the high ratio, but because in and 5 turns on the same tube as the I want on my 200 to 550 meter play- practice it seems to give high and equal "untuned primary." The rotor or ground, so why bother with code below amplification. A second stage of audio "tickler" should have the equivalent of it?" As a matter of fact, on these low may be added to the "hook-up" shown about 14 turns on a 272 in. ball rotor. waves, there are stations radiocasting in Fig. 1 in the usual manner. At least The shaft bushings are placed at the the same programs that are heard on middle of the secondary winding. Fig. the 200-550 band of waves, although the 2 gives further details. listener -in on short waves is quite likely All windings are in the same direc- at times to feel that he is entering into tion, including the rotor. The use of a great field of silence out of which No. 26 or slightly smaller double cov- comes pure music, unmarred by the ered magnet wire is advised for the ro - squeals of regenerative receivers, the heterodyning whistle of overlapping AFT radiocast transmissions, and the subdued background accompaniment of the per- sistent local radiocaster, who will never quite "tune out." What stations are using the low wave- lengths? In the eastern part of the n.f country, KDKA operates between 60 +22v gm+ 90v and 70 meters and WGY usually at 100 meters, along with a host of other stations. To be sure, the "host of others" is not listed in the call books Fig. 1. Circuit Diagram for Short Wave Radiocast Receiver. and many of them would much rather they were not heard on low waves at all. 67 volts should be used on the plates of tor,-the idea being to give a large in- The explanation is that many of the sta- the audio stages in order to get good ductance in the rotor with only a small tions have audible so-called "harmonics" volume. The detector tube alone does amount of metal in the wire to act as on, say one-half of their normal or fun- not give satisfactory volume even for one plate of a condenser with the stator damental wavelength. Some stations headphones, except possibly for nearby winding as the other. The added re- have louder harmonics than others andr stations. sistance of the smaller wire in this par- many stations which have harmonics The easiest way to "make" a 100 meter ticular part of the circuit is of trifling audible locally would not send out these set is to buy one of the manufactured importance. harmonics with sufficient volume to be tuners specially designed for the pur- By cutting an opening in the hollow audible at a distance. pose and assemble it in a set. An ordi- shaft of the rotor, inside the wooden It often takes considerable skill to nary coupler, preferably of the 180 de- ball, pigtail connections may be brought tune in these harmonics, because they gree type may be rewound with the out to- the rear. By running these pig- are so weak in volume, and the "space" proper wire and number of turns, for tails direct to the binding post "P" on occupied on the tuning dial is but a small low wave work. tube socket and B Plus on audio trans- fraction of a degree. It seems like going back into the former, losses incident to most commer- In order to get comfortably loud sig- "dark ages" to describe the making of cial couplers may be saved. nals on distant stations it is suggested an ordinary variocoupler, when this has The rotor may be kept properly cen- that one stage of audio amplification be been so long a time used in radio, but tered between the bushings by using a used with any short wave set. The since the one to be described is simple piece of metal tubing slipped over the writer has heard WGY and KDKA and of rather low "losses," the descrip- rotor shaft between the rotor and wall down stairs on a speaker, with short tion is given. If a coupler is made ac- of stator at the front, while at the other wave set located in Boston, Mass., us- cording to directions, the difficulty some- end of the shaft, a coil spring, with

RADIO FOR NOVEMBER, 1925 27 www.americanradiohistory.com probably cause a strong local station, 4 operating on a fairly low wavelength, A:',, ^1 o-Movniiny .Sc,-.., to "come in all over Stort Ni the set," although the set may pick up low End .....;--., N , S turns vnsoac-ed wave stations rather well, even with a long antenna. SfartSec \hQ With all respect to the more conven- .f tional method of "lining up" detector hI ^ and amplifier tubes, whereby the detec- tor tube -0`/67 .D CC is placed at the right hand side . e hN Shaf/ 105 over /vr71S of both coupler and tuning condenser, Hiira \ I l'''Ogri..rhirlq /2 S/oqCed _ wi f/1 Arme it is demonstrable that shorter, more di- rect leads may be had by placing the de- tector tube Eisd Sa r I socket between coupler and condenser, preferably with the coupler Movni.nq Sc re. be, VI at the right hand side. This not only \InZ O,' j1. Fig. 2. Stator of Short Nave Co: pier. .000/ of /ass washers to protect the wall of the stator with the antenna lead,-a value even and rotor, may he slipped over the shaft smaller than .0001 mfd. may be neces- to keep it from turning too freely. A sary. This smaller value of fixed con- piece of busbar swaged into an opening denser may be obtained by connecting in the shaft wall so that rotation of the two or more .0001 mfd. in series. 3 7 Tax; shaft will cause the busbar to strike a Fig. 3 shows a method of connection small machine screw in the panel is a whereby with switch arm and switch simple form of stop. Sometimes the points, either the full 5 turn untuned ridge inside a dial may be used as a primary, a tapped (3 turn) untuned stop, striking against the projecting head primary, or the 5 turns in series with a of a machine screw driven into the panel fixed .0001 mfd. condenser, may be front. used. The aerial should not be longer The coupler may be mounted on the than 50 ft. The insertion of the small panel of the set with a machine screw fixed condenser, however, will permit inserted near top and bottom of the the use of a somewhat longer antenna stator tube, keeping the coupler well with good results. It is suggested that away from the panel by use of spacers trial be made with and without the Fig. 3. Method of Connecting Coupler. cut from a piece of hollow brass tubing. fixed condenser in series, and that the Builders of "untuned primary" sets of switch arm and points be not incorpor- keeps the grid leads short but permits the double circuit type 1 shown in Fig. ated permanently into the set unless the plate lead from the rotor to be kept often are troubled with a "dead spot" at necessary. The addition of such points short. some low wavelength setting of the tun- and the switch lever, with extra wiring, At least a 7 x 12 in. panel should be ing dial. If such a spot appears, one means so much more in the way of used to mount detector and one stage method of eliminating it is to insert a "losses." of audiw. The coupler and variable con - small value of fixed condenser in series A long antenna of say 125 ft. will 1 Continued on Page 82)

Yw.-C...ti.ri,..-../ e

3J 4 -. 3j

12 - Fig. 4. Panel Layout for Detector and One Stage of .4udio.

28 RADIO FOR NOVEMBER, 1925

www.americanradiohistory.com The Vacuum Tube as a Generator The Simple Theoretical Basis for an Understanding of the Design, Construction and Operation of Amateur Transmitters By Lieut. Jennings B. Dow, U. S. N.

BY C O N FINI N G attention to quently the strength of the current, will new condition of stability ensues where- those properties and -characteris- be dependent upon the plate potential. in no increase in plate current will re- tics of a vacuum tube which en- As shown by Al of Fig. 2, the plate cur- sult with increasing filament tempera- able it to function as a generator of elec- rent increases from zero with zero plate ture. At this. point, the quantity of elec- trical oscillations it is possible to get a potential to a certain limiting value. trons, or the negative space charge, is better understanding of the action of When all of the electrons emitted by in excess of the amount which the plate, a radio transmitter than may be ob- the filament are attracted to the plate, at the given potential, is able to attract. tained when the text is confused by a no further increase in plate potential will When this condition is reached, it is nec- discussion of its action as a detector or essary to increase the plate potential to amplifier. Fig. 1 shows the plate and obtain an increase in plate current. The filament portions of a vacuum tube cir- family of curves shown in Fig. 3 is typi- 4 cuit, without present consideration of cal of this condition. the grid circuit. It includes an A bat- Effect of Gas in Tube. What has tery for heating the filament and a B already been stated applies only in the battery for maintaining the plate at a case of a perfectly evacuated tube. As positive potential.

Fig. 2. Relation of Plate Current to Plate Potential at Different Filament Fig. 1. Plate and Filament Portion of Vac- Temperatures. uum Tube Circuit. cause an increase of plate current. This If the filament is heated by the bat- is indicated by the curve Tl of Fig. 2. tery A, it will emit electrons into the At this point the tube is said to have Fig. 3. Relation of Plate Current to Fila- evacuated space it, num- ment Temperature 'at Different surrounding the reached the saturation point for a given Plate Potentials. ber depending upon the temperature of filament temperature. If the filament its composition, the filament, diameter, temperature is increased to a value of this is only approximated in practice, it and length. For a given filament, the T2, the plate current can rise until a will be well to consider the effects of number of electrons emitted per unit new saturation point is established as in- gas within the tube. Since the velocity time will be constant if the filament tem- dicated by the flat portion of this curve. of the electrons attracted by the plate perature is constant. The plate current may therefore be in- is dependent upon the plate potential, If the plate is made positive with re- creased by increasing the filament tem- and since this velocity often reaches : a spect to the filament by connecting a B perature until the condition of equilib- value of many miles per second, their battery into the circuit, a flow of elec- rium is reached wherein all of the elec- kinetic energy is sufficient to break down trons will be established between the trons emitted by the filament are at- the gas into free electrons and ions. filament and plate, tke negative elec- tracted to the plate at the same rate as The ions move to the filament, and the trons being attracted by the positive they are emitted. electrons to the plate, resulting in an plate. This movement of electrons con- Next, consider that a fixed positive increase of plate current just as though stitutes an electric current flowing in potential is applied to the plate as the more electron emission took place as a the plate circuit. Because of the con- filament is gradually heated. Before result of increasing the filament tem- the vention adopted before electron the filament reaches a temperature where perature. The well known blue glow is theory was understood, an electric cur- electron emission begins, no plate cur- indicative of the presence of gas within rent being assumed to flow from the posi- rent will flow. As the filament is the tube, and it will be observed that tive to the negative terminal whereas heated, more and more emission occurs. this blue glow usually begins around the the electrons actually move from the Due' to this fact and to the fact that plate where the electrons have reached negative to the positive, this current is the electrons move with a finite velocity, the maximum velocity. conventionally indicated as flowing from there is always present in the space be- The Grid. Let us now consider the the plate to the filament inside of the tween plate and filament a cloud of elec- effect of the grid or control element be- filament plate in tube and from to the trons which has been designated, by com- tween the filament and plate as shown in external circuit. The number of elec- mon usage, a space charge. Fig. 4(a) where the B battery poten- trohs attracted to the plate, and conse- As the filament is further heated a tial E causes an electric field between

RADIO FOR NOVEMBER, 1925 29 www.americanradiohistory.com tween grid and plate. This factor is tity we are generally interested in when called the amplification factor of the studying tube behavior. tube and is conventionally represented Because the slope of the solid curve by µ. is not constant, the internal a. c. resist- The grid may therefore be considered ance is not constant. At some point C, as a valve, which, by its potential, regu- where the slope of the curve is a maxi- lates the flow of current in the plate mum, the internal resistance is a mini- circuit. The greater the amplification mum. At any other point it is greater, factor of the tube, the less will be the becoming almost infinite for zero plate change in grid potential required to pro- current. Between two points such as E duce a given percentage change in the and C of Fig. 5, it can be shown mathe- plate current. matically that the a. c. internal plate The internal plate resistance is resistance is one-half of the d. c. value, so-called because, like the energy loss as is also evident by inspection of the due to the ohmic resistance of a conduc- dotted and solid lines. tor, an energy loss as heat is caused by Internal Plate Impedance. When the impingement of the electrons on the a tube is used as an oscillator, the plate plate. plate As the potential is in- current, instead of being steady, is pul- creased sufficiently the resulting in- EP I + sating, behaving very much as would creased velocity of the electrons develops I I_ an alternating current with respect to enough energy kinetic to make the plate capacities and inductances. So at (a) white very hut. high frequencies, the capacity of Fry. 4(a). Unbiared Grid. the lf, with constant grid voltage, the plate with respect to the other elements plate current is plotted against plate po- of the tube becomes an important fac- the plate and the filament. Thr grid is tential for present types of low power tor in its behavior. When consideration at the same potential as the filament be- transmitting tubes, a curve will be ob- is given to the effect of this plate capac- cause of the connection tained indicated. The resembling the solid line in Fig. ity, the term "internal plate impedance" effect of the plate is 5. to attract the ele- assuming that the resistance of the is often used in contrast with the trons through the openings in- in the grid. ternal a. c. plate resistance. For prac- If the grid is nearer to the filament than tical purposes at ordinary frequencies no is the plate it is obvious that we :an harm results from using the terms in- nullify the effect of the plate by putting terchangeably. a negative potential, as in Fig. 4(b). un the grid, this bring less than the plate The amplification factor of a tube is dependent upon potential. But if the grid were vert the size of the grid wires, the distance between close to the plate. .ts compared to its the wires and the distance between grid and plate. It may be computed approximately from these constants or may be experimentally determined, as can likewise the internal plate resistance or impedance. By defi- nition, the amplification factor of a tube is the ratio of plate and grid potential variations which will produce identical plate current variations. Dynamic Characteristics. The static characteristics of any tube are those resulting from a study of the tube in its cycle of operation with various constant plate potentials and variable grid potentials. In order to understand the phenomena attending the operation of the tube in a circuit wherein the con- a 111. stants of the plate circuit influences its rio. 5. Carver .l lurrsa/ Platt Rerittaate. behavior, recourse must be made to the IIII_ EP _III+ dynamic characteristics. external plate circuit, including the B (The author here makes a quantita- battery, is negligible, the internal direct the analysis of the static and dynamic (AN current resistance of the tube at any characteristics of a typical oscillating itbl. /tiered Grid point .1, when the plate potential is circuit. This is omitted because it is 350 volts and the plate current 50 milli- of little interest to most readers who proximity to the filament, this negati'. e amperes (.05 ampere) is equal to are concerned with the qualitative de- potential would have to be almost equal 350, .05 or 7000 ohms. (Ohm's Law). ductions. In general, it is shown that to the plate potential in order to nullity If the slope of the dotted line 0.1 the impedance of the external plate cir- it. represents the ratio of plate current tu cuit, which may be very great and is in Consequently, it is evident that the plate potential, the inverse slope is the the nature of a resistance, greatly re negative potential required un the grid ratio of plate potential to plate current, duces the plate current, whereas, with an to nullify the effect of the plate in at- which has just been shown to be equal oscillating current in the grid, the plate tracting electrons, and thereby establish to the internal direct current resistance potential may be much greater than the a plate current, varies directly as the of the tube. Likewise, the inverse slope constant potential source.-Editor.) positive plate potential, and inversely as of the solid line at any point 4 is de- Mutual Conductance. This im- a factor depending upon the construc- fined as the internal a. c. plate resist- portant quantity is a measure ut the tion of the grid and the distance he- ance at that point, this bring the quan- effect of grid potential upon the plate

3. RADIO FOR NOVEMBER. 1925

www.americanradiohistory.com current. It is numerically equal to the The oscillating circuit of a simple this current will vary with the voltage quotient of the amplification factor and tube transmitter may be thought of as of the grid ; it can become zero when the the internal plate resistance measured a capacity C in the form of an antenna grid is highly negative but can not re- under dynamic conditions. Its value is and the inductance L, which includes verse in direction. Also there can be a a direct measure of the value of a power the coil in the antenna circuit as well flow from grid to filament inside the tube. as the inductance of the antenna and tube, the current returning from fila- Since the internal plate resistance is ground leads. The resistance R depends ment to grid through the coil Lg, in the not constant, so the mutual conductance upon a number of things, the more im- external circuit. This latter current is is not constant. Consequently, its aver- portant of which are: appreciable only when the grid is posi- age value must be used. It is decreased 1. The radiation resistance and other tive with respect to the filament. Ex- by the resistance in the external plate cir- constituents of antenna resistance. cept for effects which are extraneous to cuit. 2. The plate -filament resistance of the this treatment, this current is also uni- Oscillation Generator. Now that tube. directional. consideration has been given to all the 3. The grid -filament resistance of the When the tube is in the oscillating factors which affect the behavior of an tube. This is of negligible moment condition, these currents will not be oscillating tube and the action of the grid when the grid is negative. steady, but will become pulsating. The in controlling the current in the plate The current which flows in the oscil- pulsating currents generated by the tube circuit, let us connect a tube as a gener- lating circuit of a tube transmitter is enter the circuit from the filament and ator E in a simple circuit consisting of therefore governed by a number of re- leave it through the plate and grid con- inductance, capacity and resistance in sistances. Notwithstanding this fact, nections; they are pulsating, and not al- series, as shown in Fig. 6. the effect of such resistances may be ternating, on account of the unidirec- made small enough to make the oscillat- tional conductivity between filament and ing current in the output circuit of Fig. plate and filament and grid. The cir- 7 very great for the value of plate po- cuit LgLpC is resonant to the funda- tential impressed across L. mental constituents of these pulsating Fig. 7 represents the so-called Hart- currents, and an oscillatory current is ley circuit, which is typical of the cir- generated so as to circulate around this cuits used for generating oscillations. branched circuit, flowing in series The grid and filament of the tube are through the condenser C and the coils connected to the branched circuit con- Lp and Lg. This current, which will taining inductance and capacity, consti- be called the output current, can be tuting the oscillatory ,circuit, in such a many times greater in amplitude than manner as to include a portion of the either of the pulsating currents. inductance of that circuit, that is the The pulsations in the steady current, coil Lg. Likewise between the plate and which flows during the static condition filament of the tube is included the coil from the filament to the plate, are Lp. In this particular circuit no mutual caused by periodic variations in the po- Fig. 6. Simple Oscillating Circuit. inductance exists between Lp and Lg. tential of the grid with respect to the Suppose, first, that the tube is not filament; these variations in grid poten- If this circuit is put in resonance, generating oscillations. Under the ac- tial are induced in the grid coil Lg by either, by changing the frequency or by tion of the plate battery a steady cur- the output current. There is a similar changing the value of L and C, the ef- rent will flow from the plate to the fila- voltage induced by the output current fective current I is equal to E/R. In ment inside of the tube and from fila- across the plate coil L. the construction of an oscillating circuit, ment to plate through the coil Lp in It is true of this circuit, and typical R is made as small as possible by the use the external circuit. The magnitude of (Continued on Page 84) of large wire or tubing in L and by us- ing a condenser C with low internal losses. Thus the current, at resonance, may rise to a high value.

J

/9

Fig. 7. Di ect Coupled Generating Circuit. Fig. 8. Output Circuit of Fig. 7.

RADIO FOR NOVEMBER, 1925 31

www.americanradiohistory.com The Life of a "B" Battery An Analysis of the Factors Whereby it May Be Lengthened By Arthur Hobart

THE probable life of a B battery of a battery is the manner of its use. of current drain on 1, 2 and 5 lb. bat- of the dry cell type can be predicted If a 22/ volt battery is used two teries. It shows, for instance, that 10 from the conditions under which it hours a day until it finally drops to 17 milliamperes will not be supplied by a is to be used in a radio receiving set. Sev- volts it give will nearly twice the num- 1 lb. battery, that a 2 ib. battery will eral of the manufacturers have conducted ber of hours of service as if it were used have a life of only 100 hours in such tests, published from the reports of continuously. Practical tests are based service while a 5 lb. battery is good for which it is possible to determine when on intermittent use. 400 hours, or say six months under such the battery will reach the end of its The final general factor is the age of conditions. useful life. the battery when put into service. A bat- Fig. 2 shows the average B battery The first factor in such a determina- tery deteriorates somewhat when stand- current drain for an A type 5 volt tube tion is the personal judgment of the user ing idle. The small batteries have an at various plate voltages and with as to when a battery is dead. The sound idle life of about one year. The large various grid bias or C battery voltages. intensity from a loud speaker decreases batteries are usually good for 18 months. Similar information for a small 3 volt as the battery gets older. So the smaller Therefore it is evident that the small tube is shown in Fig. 3. By the use of the volume that satisfies the user the batteries should be used only when the these curves it is possible to determine longer the battery is alive. One widely available space or the desirable weight how much current is drawn by a tube accepted standard sets the "cut off" volt- is limited. The greatest life and con- and from this to determine the required age of a 22/ volt battery at 17 volts. sequently the greatest economy is se- B battery capacity as shown in Fig. 1. This will be adopted as our basis of com- cured by using the large sizes. For Consider, as an example, a five tube parison. multi -tube sets having a heavy current neutrodyne with two stages of radio The larger batteries, being made up drain the extra large size should be used. frequency, detector, and two stages of of large cells, live proportionately very And always should it be remembered audio, using "A" tubes. Comparatively much longer than the small batteries. that the highest efficiency in the use of few of these sets have a C battery when The products of different manufactur- batteries for amplifiers is secured only by sold, as only one neutrodyne manufac- ers vary somewhat in weight but the adding a C battery. turer has secured a license for its use. average small 22/ volt battery weighs These general facts are specifically il- It is common practice to employ four about one pound, the medium size about lustrated in the accompanying curves 22/ volt B batteries to supply 90 volts two pounds, and the large size about five taken from the report of one manufac- to the amplifier tubes, two of them also pounds. The corresponding sizes of 45 turer. These curves are plotted from being used to supply 45 volts to the de- volt batteries are almost twice as heavy, the results of many tests and represent tector. the extra large 45 volt type weighing an average that may be used as a basis It will be noted from Fig. 2 that for about fourteen pounds. for calculation. 90 volts B battery and zero grid poten- Tests show that 5 milliamperes will Fig. 1 graphically illustrates the de- tial (no C battery) each amplifier will be delivered for 100 hours by a small crease of the service hours with increase draw down 53 milamps, or 23 milamps battery, for 300 hours by a medium one, and for 1000 hours by a large one of /000 1I the 22/ volt type. Thus an increase 500 of 5 times in weight gives 10 times the -/ number of hours of service for the same 600 rate of current supply. The greatest single factor in reducing -¢-00 the current drain on a B battery and 300 therefore in prolonging its life, is the use of a C battery in all amplifier cir- 200 cuits. When properly installed, this also improves the quality of sound delivered /50 by a loud speaker. The C battery sup- plies a negative voltage to the grid of the /00 vacuum tube. The greater the negative 80 voltage, within reasonable limits, the less the B battery consumption. A 4/ volt 60 C battery will give three times the life to a 90 volt B battery supplying 201-A Approved or 301-A tubes. practice calls 30 for the use of 1Y2 volts C battery with 45 volts B, 472 C with 90 B, and 9 volts 20 C with 112/ to 135 volts B battery. Then again, the greater the current /s drain (the more tubes used), the short- er the life. Thus a large battery may o give 5 milliamperes for 1000 hours and /0 20 30 40 25 milliamperes for only 100 hours. Ail/Man./per-es. Cvrren/ Another important factor in the life Fiy. 1. Relation of Service -Hours to Current Drain.

32 RADIO FOR NOVEMBER, 1925

www.americanradiohistory.com for the four, and that the detector will 6 draw down 1% milamps, a total of 24% 4 milamps. From Fig. 1 it will be noted that a 5 lb. battery will give 25 milamps for 100 hours, which places a probable battery life of less than one month for S average use. On the other hand, the addition of a 472 volt C battery, as may be noted in Fig. 2, will reduce the current drain to 2/ milamps for each amplifier, or 10 4 milamps for the four. By reference to Fig. 1 it may be seen that this drain should giv a B battery life of over 300 hours.' Thus one C battery costing 60 cents will more than treble the life of 3 four B batteries costing $8.00. Ob- viously the pair of batteries supplying only the amplifiers will have a slightly longer life than the two supplying both the detector and the amplifier. 2 3/ás In the same way it is easy to calculate o the advantage of using a large battery, o 1 particularly in multi -tube sets. Consid- er, for instance, an 8 tube superhetero- dyne using dry cell tubes with 45 volts on all but the two audio tubes, which have 90 volts. Good design in such a super calls for 1 / volts C battery on the oscillator and the three intermediate frequency amplifier tubes, and 4/ volts o on the first detector and two audio tubes, D 20 10 60 80 /00 there being no grid bias on the second detector. . >a/B I/o//cr9e Consequently the B battery consump- Fig. 2. "B" Battery Drain Caused by "A" Tubes. tion may be estimated from Fig. 3. The second detector requires 1.3 milamps; 6 the oscillator and three intermediate fre- quency amplifiers 0.75 milamps each, or 3 milamps for the four; the first detector needs 0.6 milamps; and each audio 2.4 milamps; a total of 9.7 milamps. Thus less B battery is required for this 8 tube super than for the 5 tube neutrodyne with C battery, due largely to the use of the smaller tubes. While on the subject of dry cell bat- teries, it is of interest to consider them as a source of filament supply. A single dry cell, whatever its size, supplies 1Y2 volts. Thus the 22/ volt B battery is made up of 15 cells connected in series. Two in series gives 3 volts, the requirements for the filament supply of a "99" type tube. But as the voltage drops with use it is customary to con- nect three in series and cut down the Gr -y excess voltage with a rheostat. The standard A battery cell is 6 in. in height and 2/ in. in diameter, weighing about 2 lbs. Its normal and most ef- ficient rate of discharge is from / to ampere to an end voltage of 1 volt. The average ampere hour capacity is about 25, giving a theoretical life of 100 hours for a / ampere rate and 200 hours for a / ampere rate of dis- o charge. 0 20 'fO 60 8o /00 The UV -199 or C-299 tube requires .06 ampere filament supply. Four of di A'/A/e voi/e7ge these tubes draw down about / ampere. Fig. 3. "B" Battery Drain Caused by "99" Tubes. (Continued on Page 74)

RADIO FOR NOVEMBER, 1925 33 www.americanradiohistory.com The Neon Tube as a Rectifier By JPilliam H. Fortington, English 6í1G.

OF THE three general methods circuit may be composed of 15,000 turns battery chargers. This is the hot of rectifying an alternating cur- of No. cathode 33 double silk wire, scramble or filament type rectifier employing rent for use in an A or B bat- wound ar- on a suitable former. The lam- gon gas as a conducting medium tery eliminator-the hot cathode or elec- ination in the for the iron core should be L tube. It has of course the disadvantages tronic emitter, the chemical or electro- shaped, not staggered but having an air of having a filament to burn out, lytic, and the gaseous conduction tube- space at their al- point of contact. This though its life is perhaps more pro- the last seems to offer the greatest pos- tends to keep the saturation point of the nounced than other types of rectifier sibilities. This is especially so in the core down. Only good condensers tubes. It is capable of passing severe case of the neon tube, which the writer should be used, as the writer has ex- currents. finds will pass a heavy current and has perienced considerable trouble due to While on the subject long life when used in the B battery of filamentless gaseous tubes, it might be eliminator to be described. mentioned that the writer has at present a tube The rectifying action of this tube, P.T/nw.rr capable //00 of passing of an ampere, and like of id/qJ 92 / that any other gaseous conductor, simultaneously rectifying both sides of depends upon a great difference in size the wave. By employing one tube to between the electrodes. The polarity of accomplish full wave rectification the the electrodes changes with each half differences in the characteristics of two cycle, so that if one has a much greater separate tubes is overcome. At present area than the other, the larger will this tube is in an experimental stage, and throw off many more electrons and estab- . it is hoped SCCONO.IRr) that details will be available lish a uni -directional current by ionizing Iscn hew '32 later. the gas in the tube. Other determin- L ants are the pressure and purity of the KINK FOR MOUNTING cors ,¡ose rues A gas; the quality of the material of which VARIABLE the electrodes are made, the frequency Fig. 2. Transformer Cross Section. CONDENSER of the current, and the voltage with ref- By CHARLES F. FELSTEAD, 6CU erence to the distance between the elec- breakdown. Some To make a neat job of mounting trodes. means of varying the a detector circuit output is desirable, and variable condenser without the aid of The essential parts for a B battery a variable resistance capable of carrying a template is a very difficult feat unless eliminator using a neon gas tube are the at least 10 milliamperes should be used. some stunt is employed to locate properly tube, a 110-240 volt transformer, a the holes for the shaft and mounting choke coil, two condensers that will screws of the condenser. When a dial withstand 500 volts ; one 6 mfd., the is to be used on the condenser, such ex- other 4 mfd. and a fixed or variable re- treme care in locating the holes for the sistance of sufficient ohmage to supply mounting screws is not so necessary be- the required voltages. cause the holes are hidden; but when a A neon tube may now be bought from knob and pointer are used, neatness is most radio or automobile supply dealers. necessary for the sake of appearance. The general arrangement of the parts is A simple way to do this is fist to find shown in the circuit diagram of Fig. 1. the exact place where the condenser is The transformer may be bought or to be mounted on the panel, and then may be made up by the experimenter. to drill a hole there that will fit the The core is built up of laminated strips condenser shaft snugly. The screws are 4e!/A44 recess of silicon steel / in. thick, having over- NOT Srw taken out of the mounting pillars on Fig. 3. Choke all dimensions of 23/4 x 3 in., the lamina- Coil Cross Section. the condenser, and the pillars smeared tions being staggered or overlapping. on the ends with red lead or paint. The shaft is then The primary winding consists of 1100 The carbon compression type put through the hole in of resist- the panel from turns of No. 27 enamel on double silk ance is suitable for this purpose. the back, and, taking care that it is held level, covered wire. The secondary has 2400 There is infinite scope for experiment the condenser is of No. pressed firmly against turns 32 or 33 wire. Where along these lines, utilizing gaseous con- the panel. The exact center of the enamel wire is used the winding must be duction tubes as rectifiers. Perhaps the rings of red lead or paint left on the layer wound. most successful gaseous tube on panel by the mounting the mar- pillars can A suitable choke for use in the filter ket is the commercial then be center -punched and tungar, as used in drilled. Anode Choke When mounted, the condenser should be found to fit perfectly if care has been taken in the drilling. The hole for the Caf/,ode condenser shaft can now be enlarged to or / in.; so there will be no chance of the condenser shaft binding, and so the dial or pointer and knob can run perfectly true without hindrance. This enlarged hole also helps to better insu- -B late the condenser, for air is a superior Fig. 1. Circuit Diagram for Neon Tube "B" Eliminator. insulator to bakelite or hard rubber.

34 RADIO FOR NOVEMBER, 1925

www.americanradiohistory.com The Helium Tube Rectifier An Account of the Theory and Practical Construction of A New "B" Battery Eliminator By Edwin E. Turner

ARECTIFIER for use in B bat- trode the smaller is the back current tery eliminators should possess PARTS REQUIRED and hence the more complete is the rec- 1 Raytheon Type B rectifier tube. certain qualifications, in order 1 Power transformer, General Radio tification. prove Type 365, Dongan Type 509. Heretofore the difficulty of insulating that the device as a whole will 2 Choke coils, Dongan Type 514, equal to the exacting task which it is General Radio Type 360 (1 re- the positive electrode in the presence of quired). a gaseous discharge gave a practical limi- called upon to perform. These are: 5 2 odd. Tobe Deutschmann, Bubi- complete rectification, long life, good 11er-Filter. tation to the reduction of its size. But 1 1 mid. 'l'obe Deutschmann, Bubi- regulation, high voltage output, high lier -Filter. 1 .5 mid. 'l'ube Deutschmann, Dubi- current output and stable characteristics, lier-Filter. tube, which closely ap- 2 .1 mid. 'i.'be Deutschmann, Bubi - A new helium Her -By -Pass. proximates the ideal, has been placed 1 Variable resistance, 10.000 to 100,- 000 liradleyohm, Centralab Po- tentiometer. 1 Fixed resistance, 10,000 ohms, Daven.

served phenomenon that the smaller the distance between two points the more readily a spark will jump between them due to the ionization of the gas. But if the distance is small enough and a suitable gas is used at sufficiently low pressure an electron may encounter no gas molecules in its path between the points and there will be no ionization by collision. Consequently the inert gas helium may be made to act as a perfect insulator at low pressures. Furthermore it has been found that when the larger electrode of a gas con- duction tube is negative there is a greater /Yeyebea current flow than when the smaller elec- Posifive E/ec/iodes E/ecfmde trode is negative and that the smaller Fig. 2. Constructional Details of Helium the positive relation to the negative elec- Tube.

ieo

/ao Fig. 1. General Appearance of Helium Tube, on the market under the trade name of "Raytheon." The tube is an out- growth of the same fundamental elec- trical laws which gave rise to the "S" tube, but it is a new development in it- /30 self. Full wave rectification is per- formed in the single tube, rectification is unusually complete, the regulation is good and the life of the tube, when sub- jected to the conditions of ordinary re- /20 ception, is unusually long. This gaseous rectifier operates upon "the short path principle," whereby a rarified gas acts as an insulator between 20 25 .90 3,3" points which are in close proximity. This /N M/LL/qMPERES is an apparent contradiction of the ob- Fig. 3. Regulation Secured in "B" Battery Eliminator.

RADIO FOR NOVEMBER, 1925 35

www.americanradiohistory.com in the tube the "short path principle" eliminates the difficulty. Fig. 1 indicates the appearance of the tube and Fig. 2 shows its construction. The two small positive electrodes AA are carried through two small glass tubes imbedded in a lava insulating block L so as to project very slightly into a rela- tively large cup C whose walls consti- tute She negative electrode, being con- nected to the negative terminal through the base. The diameters of the small wires and the diameters and position of the holes whereby they enter the cup are so proportioned as to give the necessary short path to the negative electrode. Thecup C contains helium gas at such Fig. 4. "B" Battery Eliminator low pressure as to prevent gaseous con- Using Helium Tube. duction. vice is lowered by means of This gives an insulation of great re- the voltage plify the construction and wiring, the divider R1, 122, so that a suitable liability and long life. It makes pos- low experimental model was mounted on a value may be obtained sible extremely small anode surfaces for the detector. brass plate secured to a wooden base- Condenser Co is used in which reduce the back current to a negli- shunt to the board, the apparatus being grounded di- fixed carbon resistance gible quantity. necessity R., to prevent car- rectly to the plate. In this way a major The urgent bon noises. for the reduction of back current in a part of the connections are made through rectifier to be used in battery eliminators For those who want to construct their the plate, and with this method of con- is not generally recognized. Beside own power transformer, the following struction the wiring is a simple matter. The rectifier shortening the life of the insulation as data will be useful: Core is 4 in. tube is designed to fit the above described, back current increases square and is built in the form of a standard 201-A socket. The two anodes, the load on the filter circuit, making the square window having inside dimensions marked FF in Fig. 5 correspond to the elimination of the hum almost impos- of 44 in. on each side. The primary filament terminals of the socket and the sible. It lowers the current and volt- is wound with 1220 turns of No. 28 cathode P to the plate terminal of the age output of the device and makes for enameled wire, over which is wound socket. The grid terminal is not used poor regulation. The regulation of the the secondary, which consists of 544-0 and may be left without connection. The model model built by the author is shown by turns of No. 33 enameled wire, with a shown in the photograph uses a second the curve of Fig. 3. This regulation is tap at the center turn. A layer of thin variable resistance . of 10,000 to partly a function of the filter circuit paper should be placed between each 100,000 ohms set at minimum in place used. layer of wire, and a piece of empire of the fixed resistance of 10,000 ohms A B battery eliminator, using the new cloth should be used between the pri- called for, since a fixed resistance (if this value rectifier is shown in Fig. 4. The sche- mary and secondary windings. was not available at the time. The fixed matic diagram of the eliminator is given The choke coil may be made by wind- resistance may be used here more economically. in Fig. 5, the constants being shown for ing 6000 turns of No. 31 enameled wire all apparatus. on a core having a square window 2 in. In connecting the choke coils, if both windings The input voltage of 110 volts 60 on a side, and having a cross section are on a single core, care should be cycles is passed through a transformer, x ri in. A 0.003 in. air gap should taken to have the polarity cor- rect in order shown at the right of Fig. 4, which de- be provided at one joint of the core that the inductances are series aiding. livers a secondary voltage of 250 on each pieces. Particular care should be taken in the selection of condensers side of the center tap. The rectifier, In constructing the eliminator it for this device. It is important that the operating during both halves of the cycle should be noted that the cases of the condensers have high internal resistance, delivers a pulsating direct current to the transformer, the chokes and the con- high dielectric strength and that they filter system L1i L C3, Co and Co in densers, together with one side of each agree within 10 per cent of their rated Fig. 5 which smooths out the variations, condenser, the center tap of the trans- capacity. The choke coils may be had delivering a pure direct current to the former and one side of the fixed resist- from a number of manufacturers who resistances R1, R: and to the external ance R2 are connected together and to have built them to very rigid specifica- load. The terminal voltage of the de - the B minus terminal. In order sim- to tions. The filter circuit in this elimi- nator was designed by Prof. F. S. Del- 3 f lenbaugh of the Massachusetts Institute L cj of Technology, one of the foremost 10.Ve.w9K1 70.vew,ro Be //O V 419612 authorities on filter design. The per- 60/1" j formance on this particular type of plate /qcroo supply is extremely gratifying, /45 Aog000w for it acts AR/ as theory dictates it should. On a ten tube superheterodyne receiver, using A cotre Oe! tubes with a total current consumption of 37 milliamperes the hum was entirely - negligible with the loudspeaker in oper- ./ N/ _/'F ¢M. rI J yF /0,000LY ation. The quality was equal to that by c, delivered a storage B battery supply, which was alternated with the elimi- P nator. On sets using less tubes the per- formance was slightly better, the hum Bwss Bose le ',JAI' being indistinguishable with the receiver Fig. 5. Sr/,ematic Diagram of "B" Battery Eliminator. unmodulated.

3u RADIO FOR NOVEMBER, 1925 ' www.americanradiohistory.com Questions submitted for answer in this department should be typewritten or in Ink, written on one side of the paper. All answers of general interest will be published. Readers are invited to me this service with- out charge, except that 25e per question should be forwarded when personal answer by mail la wanted.

Have a 5 -tube Fada Neutrodyne and would like to know if it would be of any advantage for me to buy a Western Elec- tric 25-A amplifier and cone type speaker. Will the speaker function properly with my set if I do not buy the amplifier, and 4 if I use the amplifier, will it interfere in any way with the use of a Valley B bat- tery eliminator?-H. A. C., San Francisco, Calif. If your neutrodyne has an audio fre- quency amplifier equipped with C batteries, you can employ one of the new UX or CX-112 tubes in the last audio stage and operate the Western Electric speáker satis- factorily. Otherwise, you will require the 25-A amplifier in order to obtain real volume from the cone speaker. The use of the amplifier will not interfere in any way with the B battery eliminator. Please show me how to add a stage of Fig. 2. Modifications of the "DX Bringer -In" untuned radio frequency amplification to my Harkness two -tube reflex receiver. circuit, as it has no appreciable external length will be considerably lower than at Will this extra stage complicate tuning? field, and coupling from other parts of the present, and you should be able to tune to -J. H. L., Cicero, Ill. circuit, to this coil, would be at a minimum. 550 meters, if you have 53 turns on a 4 in. In Fig. 1 is shown the circuit rearrange- Have built the "DX Bringer -In" set de- tube, as specified in the article. Fig. 2 ment, with an untuned radio frequency scribed in September 1923 RADIO and shows how to add the audio frequency transformer for coupling between the 1st and have had fine results with it. Wish to stage, and shows improvements to the cir- 2nd r. f. tubes. If you are careful with add another tube, and would also like to cuit as suggested. your wiring and arrange the coils so that be able to tune in stations around 200 I would like to know the input to my coupling is at a minimum, you may not need meters, which I cannot do at present.- transmitting set, which uses a standard a potentiometer in the grid circuit, but if J. C. H., St. Joseph, Mo. C-302 tube. The plate voltage is un- oscillation troubles -result, the grid of the A single stage of audio frequency ampli- known, the plate current is 18 milli- 1st r. f. tube should be connected to the fication, using a high quality transformer, amperes, and the filament voltage 7%2.- slider of a 200 ohm potentiometer which is will increase your range somewhat, and A. W. K., San Francisco, Calif. bridged across the A battery, instead of to will not necessitate great changes in the set. If the plate voltage is not known, it is the C battery as is shown in the diagram. If you will use a condenser having a ca- difficult to even hazard an estimate for the One of the new balloon type inductances pacity of .0005 mfd. instead of the .001 mfd. plate input. Assuming that the curves fur-

would . be very satisfactory in the antenna condenser now used, your minimum wave- nished by the E. T. Cunningham Co., in

Oovce,vNVT UNTf/NEO TI/NEO !! o.o CO/L R F. TRANs TRANs T/r.9NJ Se -0« I I .0005 o 405 f

C

- - 4 + .B ,I11+ 90e 11iliF-IIe- Fig. 1. Harkness Reflex With Radio Stage Added.

RADIO FOR NOVEMBER, 1925 37 www.americanradiohistory.com their tube data book, are correct for your Please publish a circuit for a good 5 - and 45 volts to the tubes in the radio particular tube, your plate voltage is watt fre- 350, transmitter, using rectified a. c. for quency end of the circuit, the ratio of and in that case, your power input into the the plate supply, to operate the on 40 meters. 120 volt line to the 45 volt supply is 2.7 to 1. plate circuit is 6.3 watts. -J. F., Porterville, Calif. Probably the wiring from The the power mains Please tell me how the minimum re- circuit shown in Fig. 3 is for a 5 -watt to the house is not large enough to properly transmitter, using ceiving range of the 300 to 30,000 meter a reversed feedback cir- carry the load of the range as well as the receiver described in February RADIO can be reduced to 30 meters. Would the addition of 2 stages of radio frequency amplification help, together with the use of straight line frequency condensers?- W. J. B., San Francisco, Calif. -innlò P/ CNo+'es The simplest method would be to con- struct special plug-in coils to fit the honey- fltliI T T comb coil mountings, for it would not be advisable to take taps from the coils pro- 00003, 00003> vided for the 300 to 700 meter range. For II a range from 30 to 100 meters, the primary should be 8 turns, the secondary 12 turns and the tickler 10 turns, all on 3 in. tubing. For 100 to 300 meters, the primary should be 20 turns, the secondary 25 and the tickler 20 turns. Radio frequency amplification with this type of receiver is out of the ques- tion, especially at the waves below 100 la? meters. Straight line frequency condensers will separate the stations at the lower end of the wavelength range better than the condensers shown in the article, but will not Fig. 3. Circuit lower the range of the set. for 5 -Watt 40 -Meter Transmitter. Have built the Best Superheterodyne cuit. See the described in January, 1925 RADIO, and article on tfiis type of trans- house lights and a considerable drop mitter, on Page 39 of want to know if there would be any ad- September RADIO. in voltage results. This will affect the The circuit is almost identical vantage in rebuilding this set according with that battery eliminator in proportion, and for a used on the Yacht Eloise, to the directions in the September issue? and a description drop of 15 volts in the line, the 45 volt sup- of the transmitter was given I wish to use all UV -199 tubes.-J. on Page 11 of ply will be reduced to 38 volts, thus S. the same issue. reduc- Riley, Kansas. The key may be placed in ing the overall amplification in the super- the negative high voltage lead between the 1f you de not wish to receive heterodyne receiver noticeably. It is then on the very filter and the rectifier, or at any other con- short waves, or at wavelengths above necessary to cut out some of the resistance the ventional position that will produce no key in the present radiocast band, there is no partic- eliminator, in order to bring the volt- click interference. age back to normal. only ular ad vantage in rebuilding the set, espe- In the The remedy pos- article by William Hawk on the sible will be the replacement of the existing cially since you want to use all dry cell construction of a cone type loud speaker, tubes. which conductors from the pole terminal to the appeared in August RADIO, no di- meter with wires of larger Could a neutrodyne rections were size, which coil be used in given as to the best method should be done by the power company. place of the coupler shown for use in the of mounting the loud speaker element to antenna tuner, in the Superheterodyne the bracket. How can this be done7- described in August RADIO? Could one C. L. P., Redding, Pa. The hinges on a radio cabinet can of- stage of radio frequency amplification be The receiver element should be fastened to ten be used to bring the leads from added ahead a of the frequency changer7- a strip of wood which is placed across the loop to the inside of the set. This al- J. T. M., Wapato, Wash. bracket shown in Fig. 3e, in the article, so lows the loop to be mounted in the You can use the neutrodyne antenna that the element is in the exact center of coil the circle. If no convenient holes lid, and a suitable socket placed there- if you wish, but the selectivity will be very are pro- poor compared with vided in the receiver element, the heavy in, without the usual trouble of either the circuit recommend- magnet ed. 1f you are at some distance from on the base of the receiver can be a socket inside the set, or binding posts a drilled and tapped for 6-32 high power radiocasting station, you will not a machine screw, and a hole drilled through on the front. need super -selectivity, and the untuned an- the wooden strip to pass the screw, so that the tenna primary circuit can be adopted. A receiver is radio frequency stage can be added, firmly fastened in place. BOOK REVIEWS but The B this results in complications and is not rec- eliminator which was described "Vision by Radio. Radio Photographs" by ommended unless special in June 1924 RADIO does not seem to directions for wind- give the C. Francis Jenkins, 140 pp. 6x9. Published ing the coils are available. Read the article proper voltage to the detector by Jenkins Laboratory, Inc., Washing- by A. J. Ilaynes in July tube in my 7 -tube superheterodyne re- C. RADIO, and you ceiver. What value ton, D. will see how the radio stage can be added. of resistances should In its suggestions of future possibilities Mr. Ilaynes gives directions which be used, and what changes in the set and in its record of past accomplishments can be should be made applied to the Best superheterodynes with- to overcome the squeal- this book demonstrates that the eye as well ing I out difficulty. which get when using the elimi- as the ear is soon to be served by radio. nator.-R. M. B., Syracuse, N. Y. In building the Haynes De Luxe Super- Each of the various systems now employed heterodyne A Bradleyohm, or other variable high re- are briefly and clearly described, especial described in February and sistance should July issues of RADIO, be used to control the volt- emphasis being placed upon that developed what ratio audio age of the detector tube, and a 2 mfd. con- transformer may be used? Can a panel by the author. Many pictures of the equip- type battery denser should be connected between the re- ment used and of the results attained are switch be used instead of ceiving set side of the resistance, and the the knife switch? Will Baldwin Pacific, shown. The book should interest every negative B connection, to prevent oscillation radio experimenter. Remler or Branston intermediate trans- due to coupling through the resistance. "Radio in the Philippines" by Fred J. Ei- formers work in this circuit? I cannot Without the condenser, the set will oscillate sen, 140 pp. 5x8. Published by the author locate any No. 24 S. C. S. S. wire recom- continuously. mended for the radio frequency trans- at Manila, P. I. former. What may be I have a "B" battery eliminator, using The title of this interesting volume is a used in its place? UV -201-A H. P., Brooklyn, N. Y. tubes as rectifiers, for supplying misnomer as it is really an elementary plate voltage to an 8 tube superhetero- treatise on the principles of radio commu- A transformer having a ratio not over dyne. When the electric range in the nication. It is written primarily to interest 3:1 is recommended. It is better to use the kitchen is turned on, the signals from the neophyte BCL and amateur resident in knife switch, as the panel switch has too distant stations fade away, and it is nec- the islands. Its chapters are concerned with much capacity between the blades and will essary to adjust the battery eliminator radio reception, principles of radio propaga- act as a small fixed condenser in a very before the station again becomes audible tion, antenna construction, simple transmit- undesirable place. Any of the intermediate What is the cause of this fading and how ters, the radio telephone, formulas and regu- transformers mentioned will work in the cir- can it be eliminated?-E. E., Berkeley, lations. The treatment indicates that the cuit. No. 24 double cotton covered wire Calif. author is thoroughly familiar with his sub- can be substituted for the single cotton Assuming that your B eliminator is fur- ject and has the ability to impart his knowl- single silk wire. nishing 90 volts to the audio frequency tubes, edge to others.

38 RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com With the Amateur Operators

AN UP-TO-DATE TRANSMIT- TING ANTENNA MAST By A. BINNEWEG, JR., 6BX When working on short waves below 80 meters it is possible to use a vertical an- tenna without the usual expense of erect- ing a very high mast. The antenna system described herein has proved so successful as regards efficiency and weather resisting properties that a short description of its con- struction will interest transmitting amateurs. The pole which is shown in the picture, consists of three sections securely bolted to- gether and well guyed. The lower section is a piece of 4 x 4, 24 ft. long, either sunk into the earth or bolted to the side of the shack. The next section consists of two 2 x 4's spaced 4 in. at the bottom and 2j/2 in. at the top, the space between them be- ing bridged with short lengths of 2 x 4 spaced 2 ft. apart at the bottom and 21/2 ft. at the top. This section fits over the 4 x 4, overlapping it 4 ft. and is bolted to it with three 9 in. bolts. The last section fits into the second for 5 ft. It may be either a 21/2 x 21/2 in., 26 ft. long, or, if one can be secured, a straight pole 3 to 31/2 in. at the butt and 21/2 to 3 in. at the tip. This is bolted into the preceding section, a clear view of the construction being shown in Fig. 1. The material for a 65 ft. pole is as fol- lows: 1 pc. 4 x 4 in. x 24 ft. 2 pcs. 2 x 4 in. x 24 ft. 1 pc. 21/2 x 21/2 in. x 26 ft. or 1 straight pole as described. 3 in. bolts (for bolting to shack). 3 h x 9 in. bolts. 3 / x 5 in. bolts. 1 x 30 in. galv. iron rod. 25 lbs. galv. No. 12 guy wire. 20 No. 0 screw eyes. 20 porcelain strain insulators. 140 ft. of rope. 1 galv. iron pulley. Paint as desired. All wood should be free from knots and if the pole cannot be placed against a build- View of Completed Antenna System. ing, sink it 4 to 5 ft. in the earth and guy the first section securely with several heavy ing the building when a high wind comes ft., and then every 21/2 ft., spacing the last guys just below the first joint. Otherwise it along. Next drill three holes evenly spaced few feet so as to come out even. Now drill will be exactly the same. along the building and bolt through. the three / in. holes so as to exactly cor- It will be well to give the lumb a co_t For the second section lay the two 2 x 4's respond with those drilled in the preceding not of paint only for preservation but for side by side with 2 in. edges up and select section and drill 3 holes at the top, measur- appearances also, light lead being prefer- the strongest end of the poles to serve as the ing them out and drilling from both sides. able. When dry, drill three holes in the bottom. Lay off 4 ft. 1 in. from the bottom Be very accurate with these holes, as they 4 x 4, as shown in Fig. 2 and set it against and put in a 4 in. piece of 2 x 4, securely are extremely important. If a pole has been the shack in the desired position. -If the nailing from both sides of the poles. Now secured for the last section, it must be cut shack is of the usual home brew variety, it 5 ft. from the other end put in a similar down slightly to fit the preceding piece. be to may well sink the pole a few feet in piece 21/2 in. long and starting at the bot- About 5 ft. from the butt place a saw cut on the earth so as to prevent it from over-turn- tom, nail in a piece every 2 ft. for about 8 opposite sides deep enough so the remaining 6-1----36=

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F 26 H Fig. 1. Dimensions of Three -Section Mast.

RADIOwww.americanradiohistory.com FOR NOVEMBER, 1925 39 wood is 2/ in. through, chisel back the end to the bottom of the last pole. Pass this wood tion could still be heard in England, and to make two parallel plane surfaces, up through the crotch at the top and place most of the message plane them smooth so that the text read correctly. thickness at a clamp around the two. The clamp may Station Z4AG is another New Zealander the butt is also in. Bore two % in. be 2/ made from two 1 x 7 in. pieces of 1% in. with a fine set of distance records, holes in. apart and in. from one end having / / strap iron, bolted together with % x 5 in. established daylight communication of the in. iron rod, which is to support the bolts. With assistants with 3 at all guys, hoist into English station 20D with an input of 150 antenna. Determine which way the rod must position, and while it is held in place, pass watts at each station. be set into the pole so that the The picture shows antenna will the bolts through, tightening up and securely the transmitter used at Z4AG, the be vertical and then drill a 5/16 in. hole fastening four coil the last guys. Meissner circuit being used, as is shown 2 ft. from the top of the pole, driving the Having now completed the mast, the screw in the circuit diagram. rod in until its end is The tube obtains flush with the side. eye which you used for the block and tackle power from the city mains, through Through one of the holes in the rod pass may be an elec- used to pass the antenna guy rope trolytic rectifier, and is coupled to the an- a piece of guy wire and securely fasten at through, thus keeping it free from the an- tenna through the top. Through the the set of coils shown in the other hole fasten the tenna. The lead-in insulators for the an- picture. The gril coil galvanized pulley by means consists of 16 turns of of a piece of tenna system shown in the picture were No. 14 wire wound low -loss fashion wire, and drill three holes in the butt of bowls, to a pyrex with holes drilled in the center 2% in. diameter. This coil is loosely the pole to correspond with the holes at the of each bowl so as to pass a No. 10 wire. coupled to the lower top of the last section. aerial coil by being The strain insulator at the top was made suspended from an ebonite rod resting across from a piece of thick walled / in. glass the supports of the coil. Across this coil, tubing, looped at each end to receive the for 80 meters only, is a .00025 mfd. variable antenna wire or guy rope. condenser. The plate coil is similar to the grid coil and is coupled to the upper aerial SHORT WAVE RECORDS OF coil. Using a single wire inverted L an- NEW ZEALAND AMATEURS tenna, 90 ft. long, and 50 ft. average height, the radiation During the past few months. amateurs is 1.3 amperes on 20.5 meters, in New Zealand and England using the third harmonic of the antenna, have been which has accomplishing wonderful work in low -pow- a fundamental of 60 meters. The receiver used at Z4AG is a single tube ered communication, especially the perform- Reinartz, ance of Z3AL in working no audio stages being used for English station any of the distance 2LZ with a power of 21/2 watts. By pre- records attained. arranged agreement, these two stations es- tablished communication 6ZD, Pacific Coast A. R. R. L. director, with their usual has received power, the New Zealand station being a letter of thanks from the Secretary of the Navy for his equipped with one 5 -watt American made work in ex- tube, and the pediting the transmission of the news of the English amateur having one finding 250 -watt British tube. After of the PN9-1 to the Pacific Fleet at Fig. 2. Two Methods of Securing Mast. exchanging Tahiti. This he test messages on full power, the power of did by communicating on 40 meters with Schnell, NRRL, on the New Zealand station was gradually de - the Determine the direction of the prevailing Seattle. His performance is an excellent winds and run one of the guy wires from indication of what can be done through each section in this direction. At least two static with a 100 -watt short wave transmit- guys should be run to compensate for the ter, -4000 miles. strain due to the antenna rope pulling down- ward, and the remaining guys should be 6BAA, Amos Kanaga, 4228 26th St., San spaced at equal intervals. Having deter- Francisco, Calif., has put in a 50 -wafter mined the approximate positions for the guy and will appreciate reports of his experi- wires, set in the scret, eyes which are to mental work on 40 meters. be used for securing the guys to the pole. In determining the length of the guys be- 2 AHU, Benjamin L. Berger, 166 Mont- fore cutting the wire, obtain the square root gomery Avenue, Irvington, N. Y., has 5 watts of the distance in feet from the bottom of on 40 meters. the pole to the guy junction plus the dis- A. Kalachnikoff of Tomsk, Siberia, Rus- tance from the center of the pole to the guy sia, Krasnoarmeiskaja St. 66 is a Russian anchor you amateur wishing to correspond with and will have the proper size. Arrangement of transmitter at Amer- Run the guys out in Z4AG icans who enclose a 30 to 60 -cent Interna- the yard and insulate Dunedin, N. Z. them about every 15 ft., having one of the tional Reply Coupon with their letters. insulators about 5 ft. from the end. Select creased until finally only 160 volts was ap- the proper anchoring points, which should be plied to the tube, with a plate current of The QRA of 6ALR is Harry Billings, capable of withstanding a pull of 50 lbs., 16 milliamperes, making a total of 2.5 - North Avenue, Fresno, Calif., operating 5 and drive in one of the large screw eyes into watts input into the tube. With this ex- watts c.w. and phone. All Q.S.L.'s answered. each. tremely low power, the New Zealand sta - 5AUQ at 712 East Mississippi Avenue, In raising the completed sections, prepare Ruston, La., is on the air with 20 watts a pole 30 or 40 ft. long of old lumber, and phone and c.w.; 150-200 meters; operated determine which is the easiest side to raise by Gaston Johnson. Q.S.L.'s answered. from, placing the section so as to raise from that side. Nail a small piece on the oppo- site side of the first section to prevent this one from falling though and place the bot- tom hole in the second section over the cor- responding one in the first and bolt though. Do not screw down the nut too tightly or you will have difficulty in raising. Secure the prepared pole to the top by means of a nail, and secure the assistance of two helpers to 000.24- sunnort the job while you a.- raising it. Two temporary screw eyes should be con- veniently placed and assistants instructed .30o whether to haul in or pay out at a given '11`òl ilòl o signal. Raise the section clear and hoist up Y while they pay out on the gt."s, keeping the 001 pole straight. When it is vertical, have one 30 , of them hold it while you run in the bolts, diutun 'ó13'ìòóá31--o securely fasten all guys and take up the slack with turnbuckles. If well tightened, this section may be climbed with impunity. To raise the last section secure a block IP_ and tackle with a mechanical advantage of at least two. Fasten a screw eye about 3 So,v 230 v ft. from the top and put one end of the rag") tackle through the eye, attaching the other Circuit used by Z4AC.

40 RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com By 6CLZ-6COW, 1288 Peralta Avenue, NAVY BROADCAST TO Berkeley, California AMATEURS laao, lac', laep, lahg, fahl, lana, lang, CALJLJs lapc, lare, larf, laxa, lbqt, leak, lccx, On October 27th various stations of the lckp, lcmx, ika, lkp, imp, 1pm, its, lxg, S. Navy will transmit a message of vital lxu, iza, lzw, 2aes, 2afn, 2agb, 2aim, 2bqa, U. 2bum, 2bur, 2byw, (2cgj), 2cth, 2cty, interest to all amateurs, who are invited to JdFA2D 2cvj, 2cxw, 2cyu 2bw, gds, 2ha, 21u, 2mu, tune in to any one of the stations operating 2nf, 2wc, ilxaf, 2xí, Say, 3bva 8ckg, 3hg, under the following schedule: 81w, 311, Sot, 8vx, 3wo, 4bf, 4cu, 4er, 4f1, 4fu, 4gy, 4hh, 4ív, 4js, 4rm, 4s1, 4tv, kdka, 7:15 and 9:15 p. m. NPG at San Fran- kel, kfkx, kfuh, kfvm, kwh, naj, nee, cisco on 43 and 45 meters. nedj, nisv, nkf, npg, nrt1, numm, nve, 7:30 and 9:30 p. m. U. S. S. California at wap, wgy, wir, wiz, wql wqn, wwdo, on 120 wyh, cxl. Alaska: 7ahb, (7de).Australia: Bremerton Navy Yard, Washington, 2bb, 2bc, 2cm, 2cs, 2ds, 21j, 2tm, 2yí, 3bd, meters. 3bq, Set, 3ju, 3yx. Canada: 3aa 4aa, 4aj, 7:45 and 9:45 p. m. U. S. S. West Virginia 4bf, 4bv, 4gt, (fiba), 6bf, 6bm, act, (5ef), Calif., on 40 meters. fifk, ego, 6gt, bhp, ((Mt), vdm, Ceylon: at San Pedro, By F. L. Ulrich, aboard U. S. S. Langley, dcb. Chile: 9tc. Great Britain: 2nm. 8:00 and 10:00 p. m. U. S. S. Litchfield at Enroute to Hawaii. Guam: npn. Hawaii: 6aff, Sbuo, 6tq, fxl, San Diego, Calif., on 40 meters. April 2st, 1020 miles SW of San Francisco. npm. Mexico: laa, laf, lb, 1k, lx, 9a, laa, iwl, :labt, 1-awx, laja, ipa ficke, 2ae, 2xa, laf, lga, 2ud, 2rk, 2bgm, 2fz, 2adìc, 3zo, xda. New Zealand: lax, lac, 4ku, 4aa, 4ag, 4ak, 49.1, 4ar, 4as. Philippines: STANDARD RADIO 3bcm, 3ot, Said, 411, 4gw, 4eq, 4xx, npo. Samoa: 6zac, npu, gra7, f8z, grll, bajj, 5za, 5oí, 6aiu, 5uk, 5ov, Said, 5alh, gladly answered. FREQUENCY TRANSMISSION, 5mg, 6qh, 6bf; 6's and 7's too numerous; 6clz, 6cow? All cards 8aai, 8xg, Balg, 8ba, 8cpi, 8gt, 8cdf, 8bu, NOVEMBER TO JANUARY Sana, 8bcp, 8bde, 8ob, 8doo, 8abs, 8chy, 8ro, By 6ALV, Alameda, Calif. 8b1, 8ccq, 8xb, 8dgv, 8jz, 9cjt, 9auy, 9zt, lbql, 2ahm, 3bta, 4j1?, Osa, 5wí, 6cst, The Bureau of Standards transmits, twice 9mm, 9mw, 9ada, 9ehy, 9cfo, gala, 9it, (7ay), 8zf, (9bmx). Foreign: c3aa, (c9ck), a month, radio signals of definitely an- 9cpm. At Honolulu, April 29: lawx, laja, c4b1, miaa, m9a, a3zm, (a3 x), (a3bd), nounced frequencies. for use by the public 1pa, lbdt, ficke, 2rb, 2aey, 2bgm, 2kf, 2rk, (a2y1), (P.I. 1hr), jiaa, (nrrl), nirr, nirx, 2ud, 2wb, 3zo, 31y, Sape, 3bco, 3cmf, 3oq, npm, npn, npo, nisv, f8z, (nedj), numm, in standardizing frequency meters (wave - Sot, 3wb, 411, 4gw, 41o, 4io, 4ke, 4eq, 4xe, nwud, wap. meters) and transmitting and receiving ap- 4xx, 5za, Sau , 4aiu, 5cn, 5vo, 5sd, 51h, bvo, signals are transmitted from 5hn, 5se, 5uk, 6abh, 6ask, óagk, 6bm, 6css, í0y NUMM, U. S. S. Litchfield (338), care paratus. The 6chx, 6chr, 6chr, 6chz, 6zh, 6cdn, the Bureau station WWV, Washington, 6cgc, Postmaster, San Francisco, Calif. 6bas, 6bur, 6cto, 6egw, 6xad, Beb, 6ew, ,.Stations heard at Christchurch and Wel- D. C., and from station 6XBM, Stanford 6awt, 6cmu, 6pl, 7uk, 7sg, zum, 7uk, 7hs, lington, New Zealand, August 11 to 23, California. 7h1, 7df, 7pz, 7us, 7ku, 7gj, 7kw, 7ao, 7uq, Spl, University, 7sb, 7dd, 7dm, 7ob, 8aai, 8abn, 8gs, 8xb, inclusive: lbaj, lcap, lebg, lcmk, lkt, The transmissions are by unmodulated 8aad, 8gz, 8ccq, 8bem, Scko, 9ada, 9cmp, iva, lzs, 2aiv, 2bee, 2ebg, 2cgw, 2cvj, 2gy, A com- 2ae, 21u, 2mu, 3bct, 3btq, 3chg, 31p, 4ael, 4am, continuous -wave radio telegraphy. 9coc, 9ehy, 9bdt, 9vc. New Zealand: 4jr, 4sa, 4r1, 5acl, Sagn, 6adz, 6ew, 6hp, transmission includes a 4aa. Canadian: 3ap, 3x1, 9bm, 5go. Porto plete frequency Rico: 4sa. Mexican: lx, bx. 5kc, 6oq, fox, 5uk, 3xc bzai, 6z1, 6add, "general call," a "standard frequency sig- 6aij, 6akz, Gaol, fiapq, 6awt, 6bgo, 6bgv, "announcements." The "general 6bhz, 6bil, 6bjj, 6bjx, 6bmw, Sbtm, 6bup, nal," and At 6cpg-óbhr, Earl Wiseman, 6bvy, 6cah, 6cai, 6cfe, 6egw, 6chl, 6chs, call" is given at the beginning of the 8 -min- 1604 Spaulding Avenue 6cmq, 6ct, 6ctm, 6dah, tidal, 6dcf, 6fa, ute period and continues for about 2 min- Hollywood, Calif. 61h, (6jp), 6km, 611, 6rw, 6sb, ókí, 6vc, 6vr, includes a statement of the fre- 1pl, fite, lyb, laao, labt, 6zac, 6zbn, Bzd, 6zh, 7ay 8ay, 8axn, utes. This low, lxu, lxz, 9aed, 9akf, 9bht, 9ctu, 9ded, quency. The "standard frequency signal" is lami, lare, lemx, 2bw, 2cv, 2gk, 2kr, 2qh, 8bgn, 8p1, 8sf, 2aey, 2agw, 2cee, icyx, 2hg, 3ym, 4rm, 4rt, 9dkv, 9dpx, 9eht, 9ek, 9ff, 9hp, 9uq, 9xn. a series of very long dashes with the call 6bf, fite, Sew, 5hi, 5ío, 6nj, 5nw, 5ov, Box, Hawaii: Gaff. English: 2ec, 2kf, (21z), (2od), (2nm), 51f, 6rra, 6tm. French: letters (WWV or 6XBM) intervening. This 5ph, buk, 5vf, 5v1, 6wi, 5zm, Baal, 5aav, (2xy), Brazil: for about 4 minutes. The fad, 5aec, bahr, 5aij, 5aks, 6amw, 6asv, 8bf, 8bp, 8fq, (8tok), 8uiv, Swag. signal continues 5asr, 5ath, 5atv, 7ay, 7cw, 7dc, 7ec, 7en, (lab). Argentina: a8, bal. Canada: 4gt. "announcements" are on the same frequency 7fr, 7gb, 7gj, 7gy, 7iy, 7ku, 71q, 71s, 7mf, Mexican: laf, lb, 1x. Italy: (1rt). Chile: frequency signal" just leg, 9tc. Philippines: ihr. Holland: osv. as the "standard 7nh, 7nt, 7nx, 7ny, 7pz, 7r1. 7ws, 7wu, 7ya, 2bb, 2cm, and contain a statement of the 7zz, 7adm, 7aek, 7aij, 7akk, 8er, 8gz, 8jj, Switzerland: 9ad. Aust.: 2bg, transmitted 8nx, 8ry, 8to, 8abm, Sajn, 8apw, 8avl, 8ayy, 2nj, 2tm, (2y1), (3bd), 3bm, 3bq, (3ef), frequency. An announcement of the next 8brc, Sbsv, 8chk, 8dme, 9ee, 9e1, 9oo, 9rz, 3ju, 3ot, 3tm, (3yx), (4an), 5bg. Naval: frequency to be transmitted is then given. 9sr, 9sv, 9wo, 9x1, 9zw, 9aac, 9adg, 9aey, naj, nas, nirx, nkf, npg, npm, npn, npo, There is then a 4 -minute interval while the 9afe, 9aio, 9aot, 9ayg, 9ayp, 9baa, 9bdu, npu, nrrl, nve. Commercial: (kfuh), vis, 9bdw, 9bfp, 9bjp, 9bmx, 9bnf, 9brf, 9brk, wap, wiz. Miscellaneous: fxl, ab (qra?). transmitting set is adjusted for the next fre- 9brx, 9bvo, 9caa, 9ccs, 9c1d, 9cul, 9cxw, PSE QSL IF U HR NUMM. Ops: J. R. quency. 9cxx, 9dat, 9dbz, 9ded, 9dex, 9dfh, 9k1, Mohler, R. B. Brightman, D. W. Imel. be heard and utilized by 9dum, 9dun, 9eck, 9ejy, 9elb. Naval: nkf, The signals can nrrl. Canada: 3qs, 6gf, 5ba. Mexico: lb, By E. Stine, 122 Kingman Ave., stations equipped for continuous -wave re- lk, 2t. Porto Rico: 4sa. Hawaii: 6buc, Battle Creek, Mich. ception at distances within about 500 to 1000 6cst, npm. Japan: Iaa. Australia: 2bk, óagk, 6ae, 6aff, 6afg, 6afz, 6ahq, Gail, mile's from the transmitting stations. Inform- 2cm, 2ds, 2yi. New Zealand: lao, 2ae, 6ajm, Bapk, 6aop, 6arw, baum, 6bbv, 6bgv, 2xa, 4aa. 6bgb, 6bil, 6bjd, 6bjv, 6bvy, 6bwa, 6bww, ation on how to receive and utilize the 6chx, 6chs, Let- 6cbj, 6cej, 6cfi, 6egw, 6cgc, signals is given in Bureau of, Standards At Sbrb, Apollo, Pennsylvania 6cix, 6cmx, 6cpf, Gorr, 6csw, 6ct, 6cto, ter Circular No. 171, which may be obtained lafn, lajg, lare, larh, 6das, 6dat, Gdck, 6ew, 6hw 61h, Bjc, 6jp, on application from the Bureau of Stand- lasa, laum, lawv, 6js, 611, fitz, 6vr, 6zh, 7aek, flay, 71t. Can.: laxa, lblp, lbs, lbvl, lckp, low, iql, lqm, Shp, 5gt. Mexican: lb, 9a. Chilean:l 21d. ards, Washington, D. C. Even though only lut, lvd, 4bs, 4cu, 4cv, 4du, 4kb, 4pu, 4sc, Argentine: cb8, bai. New Zealand: 2ac, ob- 4tm, 5adh, 5agz, 5aih, 5ail, fais, 5ajh, 2bb, a few points are received, persons can 5amw, 5asv, Baty, fco, 2ae, 2xa, 21j, 4ak, 4ä1, 4ag. Australia: as a wavemeter calibration 5gm, Spy, 5uk, 6aad, 2cm, 2y1, 3bd, 3bq. Miscellaneous: nrrl, tain complete óagk, 6awt, 6bfn, 6bgz, 6bhz, 6bnip, nedj, kfuh. All cards QSL'd. as desired by the. method of generator har- 6bni, 6cc, 6c1p, 6clr, 6cpf, 6cse, 6crp, 6cto, npg, nerkl, monics, information on which is given in 6dgz, 6fm, him, 6jp, 6km, End, 6ts, but, 6vc, 40 S. Beaver St., York, Pa. 6vw, 6xap (6zb or 6zde), 7abf, 7ay, 7gb, 3BVA, the Letter Circular. 7gj, 7mf, 7nt, 7nx, 7r1, 7ya, 7zu, 9xi, 9xn, (5aaq), (5ac), (fadz), (5afd), (6aj), The schedule of standard frequency sig- 9zt, nrrl. Canada: tes, 4tk. Mexico: lk. (5asd), (5atp), (5atv), (fax), (5ce), (5ed), France: 8ss. B. Sad. A. loj. (5ew), (5hi), 6jd, 6jf, 5kc, (51n), 5ms, nals from both the Bureau of Standards and (6nj), (6nq), (5oq), (Box), (5ph) 5rg, 5uk, Stanford University is as follows: (5va), (6v1), Bzai, 6aak, óagk, 6akz, 6ajm, WAVELENGTH OF ARGENTINE (6a1u), 6acip, 6avj, 6awt, 6ban, Ebel, 6bil, SCHEDULE OF FREQUENCIES IN KILOCYCLES AMATEUR STATIONS 6bjv, (6bkx), 6bq, 6bur, (6cai), (6cah), (Approximate wavelengths in meters in parentheses) (6ccv), 6cev, (6egw), 6cgc, (6chs), liche, Mr. Federico Nosiglia, of Buenos Aires, 6cix, fient, 6css, (6csw, (6cto), (6dab), ! Time Nov. S Nov. 20 Dec. 5 Dec. 19 Jan. 5 Jan. 20 Argentina, informs us that he is operating (6dah), 6dao, 6dar, Gdh, 6fh, Bfa, (611), '^:00 to 3000 125 300 550 1500 3000 station AH -2 on a wavelength of 30 6pb, 6nx, 6sk, bur, (eve), (6xad), 6xg, 10:08 p.m. (100) (2400) (1000) (545) (200) (100) meters, and together with several other 7aek, 7df, (71j), (71t), (7nx), (7uz), 9bm, Argentine amateurs, has a calling sched- 9caa, (9efy), 9dfh. Special: naj, nas, 10:12 to 3300 133 315 630 1650 3300 ule from 9:30 to 12:00 o'clock midnight, nerkl, nkf, nkf-1, nisr, npg, npu, nrrl, (91) (2254) (952) (476) (182) (91) E. K., in an effort to reach American ama- 10:20 p.m. These numm, (nve), kfuh cgrr, sge, wap, (wnp). 10:24 to 3600 143 345 730 1800 3600 teur stations. amateurs are great- Porto Rico: (4kt), (4o1), (4rí). (4sa). ly interested in intensifying inter -Ameri- ldd, 4cr, 10:32 p.m. (83) (2097) (869) (411) (167) (83) can radio relations, and will greatly Canada: (lac), laa, (lam), lar, from 4gt, Sef. Bermuda: (Ber). Chile: leg. 10:36 to 4000 155 375 850 2000 4000 appreciate reports those hearing Hawaii: 6bue, 6zac, 1x-1. Brazil: (lab), their stations. Eng- 10:44 p.m. (75) (1934) (800) (353) (150) - (75) laf Argentine: fl,'(2 land: s2cc, (2kf), 2kza (2lz)? (2nm), 2od, 10 :48 to 4400 166.5 425 980 2200 4400 Ed Craven, 4JJ, 498 2w-j, . 2sz, 6dh, (51f), brin, fqv, (61j), 6tm. 10:56 p.m. (68) (1800) (705) (306) (136) (68) By Edith Place, France: 8bf, 8bv, (8ct), 8eu, 8fq, 8gn, 8qq, Memphis, Tenn 8rdi, (8yor), swag, (8uini). Italy: (ter), 11:00 to 4900 205 500 1130 2450 4900 6fg, Guo, 6aji, 6bgj, 6bhm, 6bjv, 6bni, (lmt), lrg. Switzerland: (9ad). Holland: 11:08 p.m. (61) (1463) (600) (265) (122) (61) 6bsc, 6btu, 6egw, 6cmq, 6cgc, Bonk, 6dah, (2pz), pccm, (o-sv). Belgium: 4yz. Aus- 11:12 to 5400 260 600 1300 2700 5400 6zbn, 7ec, 71t, 7uz, 7aek. Canadian: 3aa, tralia: 2ay, 2bc, (2bb), 2bk, tom, (2ds), (500) (231) (55) lar. Cuba: 2mk. Mexico: lb, (1k), lx, 2ij, 21o, 2me, 2yg, (2y1), gym, 3bd, 3bq, 11:20 p.m. (55) (1153) (111) laf; 9a. Argentine: cb8. British: 21z, (3ef), 3ju, (5bg)., New Zealand: lao, 11:24 to 6000 315 666 1500 3000 6000 2nm. Australia: Zit, 2tm, 2y1, 3bd, 3bm (2ac), 2ae, 2ap. (2xa), 4aa, 4ag, (4ak), 11:32 p.m. (50) (952) (450) (200) (100) (50) 3bq, 3ef. New Zealand: 2ac, 2xa, 4ag. 4a1, 4ar, 4as. Mexico: (laa, laf, lax (1b), Miscellaneous: (nerk 1), (br7), xda, wap, (1k), lg, 1n, lx, 2eí, (9a). Denmark: nrrl, (nve), npg. Unknown: 2re (qra?). 7ec. Sweden: smyy, smzs. Cuba: 2by. *Eastern standard time for WWV, Washington, D. C. Will qsl to any of above on request. 5 Pacific standard time for 6XBM, California. watts here. (Continued on Page 44)

RADIO FOR NOVEMBER, 1925 41 www.americanradiohistory.com FROM TH E MD,IC M UFAC TURE RS - ,r,- ciNul- :: ,::...... ,iilU i7 . 'î. jd .,.- á. .

The Elkay super -selector is a five -tube The Hemco tube vitalizer is a compact receiver consisting of one stage of The Pacent Universal base is a new tuned device for giving a brief over -voltage to form r.f. detector, one transformer audio and the of tube socket made of Isolantite. two resistance filament of a vacuum tube so as to It permits interchangeability, coupled audio. It uses bring a fresh supply of lowers the thorium from total capacity of a circuit, and gives the inside of the filament to the surface. bet- Here it becomes active as the source of electrons necessary for the operation

ter contact with the tube prongs, which are given a firm side grip by concealed contacts. It is especially adapted to radio frequency circuits. any style of tube and is claimed to have The sfi; unusually good tone quality, selectivity Comparaphon is an instrument for making a comparative and sensitivity. The operator has test of loud- full speakers in a dealer's stores control of selectivity and oscillation in by means of a patented clarifier adjustment. a phonograph when radio music is not of the tube. The results from any tho- The Lombardi straight line condenser riated filament Is made in two tube can be greatly im- types, one giving straight proved by an occasional treatment line wavelength tuning, the other straight this in line frequency, device. It operates from either an thus enabling separation a.c. or d.c. 110 volt circuit. of short wave stations. It is designed for minimum loss or variation rated from capacities of .00025, .00035 or .0005 The Clarostat is a new rheostat giv- tug a remarkably gradual change in re- sistance as the knob is changed. The de-

available. It gives the prospective pur- chaser the privilege of judging tone qual- ity without the need for a home demon- stration.

The Thompson "Minuet" is a com- plete dry battery tube receiver built into a cylindrical cabinet 18% in. wide, 21% in. high and 10% in. deep. The mfd. It is made up as a single, double front part contains a cone type speaker or triple unit, the last being illustrated herewith. Its geared vernier shaft runs through the rotor shaft so that one panel hole suffices for both. The Zinke dual charger is a new device for charging A and B batteries of all makes. It uses two Tungar 2% ampere vice is built like a watch so as to insure uniformity in movement. It is designed to accurately control filament current.

The Thorola Islo-dyne is s five-tube tuned radio frequency receiver employ- ing doughnut coupling coils and radio frequency transformers with straight line frequency condensers. It is designed to

around the periphery of which a tuning tubes wired in handle may be moved to a desired scale parallel so that should give equal amplification on all one burn out the other may be used for lengths wave- setting. Two small compensation knobs charging and to be extremely selective. are used for fine adjustment in tuning. at the 2% ampere rate instead It has three dials, which may be logged, of 5, as when both are used. and Of the five tubes, two are r. f. ampli- a separate volume control. fiers, one detector and two audio. 42 RADIO FOR NOVEMBER, 1925 www.americanradiohistory.com OU made this radio receiver. To answer a tremendous I demand for simplicity without sacrificing efficiency, Mu -Rad Engineers developed this New One Dial Receiver for you. This innovation in radio reception marks the most distinctive advance since the conception of radio. In addition to the one dial control, Mu-Rad Receivers embody every prin- ciple necessary to good radio reception. Just a slight turn of the one dial brings in any local or distant station. A station once logged always comes in at the same dial setting. It is so simple a child can operate it.

MODEL B-$125 Sockets Fit All New Type Tubes

General Sales Offices: 972 Broad Street, Newark, N. J.

you saw it in RADIO Tellwww.americanradiohistory.com them that CALLS HEARD (Continued from Page 41) EX 7NQ Now 7TK, 612 4th St., Hoqufaas, Washington laf, led,led ltr, 2by, 2gz, 2kj, 3bau, 3ccy, 3gq, 3oe, 4dy, 4hh, 411, 4ss, 4tj, 6afb, salz, (5amh), 5apq, (5asd), 6bz, (6cg), Sfr. cATO1// (6q1), Erg, (6abg), Saoz, (Satn), baum, 6bcn, (6bgb), Sbec, 6bis, 6bnh, 6btn, 6bsf, 6bsj, 6bnm, (6cah), (6eck), 6ccv, ócku, (6chx), 6cel, 6cmi, hero, 6crz, 6cux, (6cvk), forTun&RadioFreauençy. (6dbc), (6fg), 6fm, Sie, (6jj), (6m1), ósí, (6sz?), (6tj), 6uci, (6uo), 6wd, nnumeronus, Sxg, 6zbt, 8g), bm, 8cye, (8jq), 8xas, 9ce, 9act, (9adr), 9az, 9baz, 9caa, 9ca, (9ckh), 9cko, 9coo, 9cuo, 9cuo, 9cv, 9cvn, 9cuo, 9dbg, 9ded, 9dgo, (9d1a), (9dmj), 9drz, (9dv1), 9eji, 9ek, 9eky, 9fp, 9q1, 9qs, 9x1. Canadian: 3xí, 4dy, (4fv), (410), (5af), (5as), Sbf, Sbh, 6co, (5cu), 6dd, (gds), (5fk), (bhk), (bhp), 6hs. COILS! By 1ALP, Frank L. Baker. Jr 30 Minot Gwrio Street, Neponset, Mass. The only Tuned Radio Frequency 4aae, 4ask, 4au, 4er, 4js, 4kw, 4me, 4mf, 95% 4mg, 4m1, 4nj, 4oa, 4oy, 4p1, Kit comprising 3 units 4rz, 4sa, 4sb, Air Dielectric whose sec- 4tv, 4xe, 5amh, 6kc, box, Erg, 5sy, 6uk, 5va, ondaries are identically matched. 6bhz, 9adk, 9aeg, 9aot, 9ape, 9bdw, 9bht, Dopeless 9bmx, 9cap, 9dcq, 9dpx, Seco. (9es), 9ff, AIr-Spaced (9og), 9an, c -lac, (c-2be), c-3vh. Will con- Windings firm any of these reports by asking. All UseAERO COILS on 40 meters for the month of August. fly 7MF, Harold De Voe, 1310 West Main In Any Circuit Street, Medford, only Air Dielectric Oregon Having Variable Primaries lang, ika, Spi, 2fb, 2mu, 2xaf, 3ab, 3ckg, In Antennae Circuits 411, 4oa, 4si, 6aj, 6arn, 6kc, Szai, ócod, (Hawaii), 8ayy, 8bpl, 8chk, 8cnl,' 8eq, 8jq, 3 Circuit Tuner Rks. 8qf, 8xk. Rzv, 9adr, 9akf, 9aod, 9amm, 9apn, 9anp, 9bek, 9bht, 9bpb, 9brs, 9bvh, 9bwx, 9bxq, 9cdf, 9cdv, 9cxx, 9dex, 9dfq, 9dlt, 9efy, 9egn, 9ek, 9eq, 9je, 91t, 9oq, 9pz, 9qr, 9uq, 9xn. Australia: (2bc), (2y1). Canada: c4aa, 4gt, 9ck. Chile: leg. Eng- land: 2yt. Mexican: laa, lax, lb, lx. New Zealand: 2ac, 2xa. Naval: naj, nie, nkf, npg, npu, nqg, nrrl, nve. Miscellan- eous: gbe, kfuh, wap, wbz, wir, wiz. Carda NOW you can build a set and have all three tuning will be sent to any of the above on re- dials tune exactly the same -or, you can build a quest. All QSL's appreciated and ans- wered. 60 watt cw. on 40 meters one control set using a gang condenser and know that Another adaptation of the pat. pro- ent. at pres- it's going to work right. AERO Coils are matched! tected Aero Coil construction;á8.O0 By 6AE, Geo. W. Carter, 4409 So. Harvard But-the matched feature of Aero Coils is not their Radio Frequency Blvd., Los Angeles, Calif. only exclusive feature. Regenerative Kit U. S: 2acf, lbqt, 2bur, 21u, 3bq?, 3ckg, 3ot, 4do, 4f1, 4oa, 4rm, 4si, Said, 5amd, Aero Coils are, by electrical measurement and by use 5ako, 6akz, (5a1j), 6arn, 5asv, 6aty, (6agw), tests, the most powerful, most selective and most sen- (Sagn), 5ew, She, 6kc, 5nj, (Sse), btg, sitive inductances ever designed. They will enable your 5uk, 5qs, (7ay), 7dc, 7dt, lit, 71j, 71y, 7112. set to sharply powerful locals and will (8ac), 8aly, 8bsc, 8byn, 8er, (8g1), 8drs, cut through bring (8jq), 8p1, 9aey, 9bht, 9bng, 9bst, 9cdv, in, with tremendous loud speaker volume, signals you (9cdo), 9czz, 9cia, 9dfh, have always had to listen to on head phones. 9dvr, Sdfj, (9ek),9efy, 9ó1o, 9wo,( (9úq), Makes the most powerful, most se- 9xa, 9xn. Hawaiian: gaff, 6asr. Canada: Build with Aero Coils. You are sure of their superiority lective 4 -tube, non -radiating set pos- 4go, Set Sgf, 9ck. Mexico: 1aa, 1k, lx. because that which makes them so is patent -protected. sible to build, Matched - - 311.0o 9a. Porto Rico: 4r1. Australia: 2y1. The Tuned Radio Frequency Kit is $12.00 complete Naval: (nve), npg, nkf, flay, npm. All Wave Trap Unit reports appreciated and promptly QSLed with circuit diagrams and instructions. At your dealers Also for Crystal Sets at this station. -or direct, if your dealer hasn't them. Makes an exceptional- ly efficient wave trap By 7MF, Harold De Voe, Medford, Oregon. Free booklet giving valuable information on for crystal set $4.00 frequency U. S.-laao, lahg, lang, lbvl, lbyx, 1pl, radio amplification sent on re- 2ds, 2nf, 3ab, 3aha, 3bta, 3ckg, 4fg, 411, quest. Write now for the "Aero Booklet". Oscillator 4oa, 4a1, 4tv, 5ado, 5adz, bakn, 6aty, Sew. bko, 5zai, baff (Hawaii), ócod (Hawaii), ózac (Samoa), ózbe, 8avl, 8ayy, 8bf, 8bgn, .HERO PRODUCTS, Inc. 8bpl, Sbrc, 8chk, 8cyi, 8deb, 8dke, 8eq, 8jq, 8ks, 8p1, 8qf, 8ry, 8xk, 9ado, 9adr, 9aey, 1772 Wilson Ave., Chicago 9agl, 9ald, 9aod, 9ape, 9apn, 9atq, 9bbh, 9bek, 9bfg, 9bht, 9bmx, 9bpb, 9bny, 9brs, 9bvh, 9bwx, 9caa, 9cdf, 9cdo, 9cdv, 9cjw, 9clo, 9cxx, 9ded, 9dex, 9dkv, 9dpr, 9dpx, C 9dvl, 9ecc, 9efs. 9efy, 9egn, 9ek, 9ff, 9je, o 9oo, 9pz, 9se, 9wo, 9xn. Australia: 2bb, Tremendously increasestheefficïen- 2bc, 2cm, 2y1, 3bq. Canadian: 4aa, 4a1, #WRDAll Aero Coils embrace l11444 cy of the oscillator circuit in any 4cr, 9ck. Chile: leg. Mexican: laa, lax, a patent -protected method of construction Super Heterodyne receiver $5.50 lb, lx. N. Z. 2ac, 2xa, 4ak. Naval: naj, which makes possible a far more efficient induc- nkf, npc, npg, npm, nqg, npu, nrrl, nve. tion performance than is possible with any other typeof coil. Misc.: kfuh, kie, wap, wbz, wir, wiz. 7MF is on 40 meters with a fifty watter. All reports appreciated and crds all ans- ARE YOU A SUBSCRIBER? wered. WIll QSL to any of the above at SEND FOR TRIAL SUBSCRIPTION request. CATALOG FREE $1.00 FOR SIX MONTHS 0 Albert E. Scarlett, Jr., 23 Cooley Place, Mount Vernon, N. Y. FAMOUS 'COAST TO COAST' 40 meters. U. S. A.-6ahq, 6alf, 6aqp, MIRACO GUARANTEED Sbbv, 6bll, 6cfe, 6cgw, 6cix, 6csw, 6dai, 6fa, RADIOS-S FACTOR'tAVET0PRICES oEst 6js, 6xad. Greenland: wap, wnp. Ber- DISCOUNIÌ muda: ber. Chile: leg, 21d. Germany: (Jeer. everywhere report Mireco Radios get aga, pof. Holland: pcuu. programs coast to coast on loud speaker; of Denmark: 7ec. outperform seta times au Brazil: lab, 2sp. Belgium: ke, w7. Cuba: :LTbear foreignfore gn countries. Radio s 2mk. England: 2cc, 2cs, 2dx, mat aka values in fac- "RADIO DEALERS 2kf, 2nm, fen-built. Victory .teeter long 2sz, 5bv, Sdh, 61f, 5sí, 61j, firm, 6tm. France: gate -let testimony of ,sera convince you. A lifetime opportunity is open for you as a radio 8cb, 8gm, 8tk, ftj. Porto Rico: 4ja, 4jv, Powerful New Multi. dealer. Radio promises its biggest record- tube Miraco gets b.eaking season. 4o1, 4r1, 4sa. Samoa: ózac. Fanning WRAC() long distance on Make the moat of It by getting Island: kfuh. New Zealand: 2ac, 2xa, 4ag, speaker.. Set, p our new big catalog before you buy. Huge RADIO ONLY stocks of standard radio parts, seta, kits ready 4ak, 4a1, nedj. Australia: 2cm, 2ds, 2ij. re for quick shipment lowest rock -bottom 2tm, 2y1, FREE'! teturen on latent at 3do, 3bq, Set $ju, nrrl. Indo GETS'EM mproved Ito 6 tube mod- wholesale críe n. Wonderful opeoial often. on finest outs, em, new low price. testimony o tubes. butt .rues. Write for loco sot, NOW. China: hvd. Off Panama: nve. Atlantic COAST ib twee. and Specu Ovyga. Write.LERSAóftirCS Ocean: ln. Unknown: age. All hrd dur- COAST MIDWEST RADIO CORP'N W ing August on 1 audio aad 80 ft. indoor Ho,uer Builder. of Seta W. C. BRAUN COMPANY 3-2.!-,»%,..z Ä antenna. 414 -C E. Sth St., Cincinnati. Ohio (Continued on Page 92)

44 Tell them that you saw it in RADIO www.americanradiohistory.com ?heXew WAVE MASTER -a Radio Set Worthy to Bear the KELLOGG Name

i The Wave Master Console Model A handsome genuine maho- gany design with battery compartments and inbuilt horn. Price, $275.00 Without battery table, price - - $225.00 Also made In the beautiful Con. solette model, genuine maho- gany, price, $235.00

,<.,. "I never dreamed it was such fun" "I used to be content to enjoy radio merely as a listener, never realizing how much greater pleasure I was mis- sing. I had no idea of the fascinations of radio tuning -the fun of going after any station and getting it." WHEN you make a telephone call, the operator con- A Year Ahead! The WAVE MASTER, 5 -Tube Standard Model nects you first with the "exchange" and then with Cabinet of solid, Genuine Mahogany, beautifully finished, the desired number of that group or division. 28 inches long. ll inches high. Price To "connect" the WAVE MASTER instantly with any de- $125.00 sired broadcasting station, you first set the pointer for the "Exchange" or wave zone group to which the station be- longs and then merely turn the Station Selector dial. "Ex- pert" tuning becomes child's play. To separate stations very close together in their wavelengths, is astonishingly easy. When buying any radio set, protect yourself by learning something about the firm that produced it- their reliability and experience. For 28 years Kellogg has produced the finest of telephone apparatus. Since radio begin Kellogg has built the highest quality parts. If you do not know where you can see, try and hear the WAVE MASTER in your neighborhood, write us. We'll give you the name of your nearest dealer, and, if you wish it, a full technical explanation of the Wave Master Circuit. Ask for Folder No. 2e. Radio Dealers and Jobbers Kellogg The WAVE MASTER franchise backed by Kellogg resources Symphony and our powerful advertising campaign, is most valuable. Reproducer Open territories are being rapidly taken up. If interested, A Separate Circuit for Each $25.00 wire or call on us promptly for our money-making proposition. 40 Meter Wavelength Band `One -Dial Control, Yet Greater Selectivity. Kellogg Switchboard & Supply Company 1066 West Adams Street, Chicago, Illinois KELLOGG

SWITCHBOARD & SUPPLY CO. E ,:. Tall them that you saw It in RADIO 45 www.americanradiohistory.com III 1111111 I 111111111 l l 1111/11111111 Ill11IIII 111 11111 1111111111111 Ill ILII11111111 1111111111111 11111111 111111111111111 II 1111111111 111 111 11111111111111111111111

'==_'i1IIIIIIIIIIIII111111111iI11111111U'''-=

1111111111111 11111111111111111111111111111111111111

-1111111. 11 ALL-ArttcAN Beauty and Permanence Radio Built for the Years to Come

Model R Receiver Complete without tubes $9 0 The radio receiver here pictured is offered to the public by the ALL-AMERICAN RADIO CORPORATION, a pioneer in the man- ufacture of reliable radio apparatus, as an ideal example of the solid value which a thoroughly equipped and experienced organ- ization can build into a product. Forget for a moment the entire question of price. Think of any radio set you have ever admired or wished to own. Compare, first, its construction, with this brief outline (on opposite page) of the value which is built into the ALL-AMERICAN Model R. Then, apply the final test-compare the performance with that of your former ideal of a radio receiver. After that-and not until then-remember the price at which it is offered, and simply ask yourself-"What can I get by paying more?"

IIIIIIIIII 111111111111111111111111111111 1 111111111111111111111 111111 11111111111111 II IIII II IIIIIIIIII IIIIIIIIII IIII VIII 111111 1111111111111 111111111111 II 111111 II 1 II 111 11 1111111111111111111111111111111111111

46 Tell them that you saw it in RADIO

www.americanradiohistory.com 1 1111111110 11111111011 I 1 101111111111111111111111

rAIIIIIIIIIIIIIIIIIIIIfVIIIIl11I

ill!1!1!111111111111111111111111111111111 !III ti Built and wired complete in the new ALL-AMERICAN factory, the Model R embodies many notable improvements developed in the ALL-AMERICAN Laboratories. It is offered at a moderate price, but with the emphasis upon its superlative quality, deliberately inviting your frank investigation of this question- What Can You Get by Paying More?

ALL - AMERICAN challenges comparison on the basis of the Six Vital Principles of Solid Value in Radio Receivers

1. Quality of tone In the belief that tonal perfection is all-important, the ALL-AMERICAN Model R is equipped complete at the factory with Rauland -Lyric tone amplification. These laboratory -grade transformers, designed especially for lovers of artistic music, are recognized by highest authorities as the very finest on the American market. 2. Ease in Tuning Two dials (360° type) control the ALL-AMERICAN Straight -Line -Frequency TUNING, reaching easily all wave channels, new and old, and eliminating all crowding of the low -wave stations. Touching the fingers to the dials does not affect the tuning. 3. Quietness Practically all the various noises picked up directly from the air by ordinary coils have been eliminated in the ALL-AMERICAN Toroids. The unequaled quality of the Rauland -Lyric tone amplifier results in a remarkable quietness. 4. Selectivity A test of the ALL-AMERICAN Model R will be a revelation to the experienced listener, in the sharpness of tuning which has been achieved solely through im- proved condenser and inductance design, without impairing tone quality in the slightest degree.

5. Sensitiveness to The ALL - AMERICAN Tuned -Radio -Frequency system embodies the most ad- vanced refinements of the present year. The result is a sensitiveness which chal- distant signals lenges comparison with any other set made, irrespective of the number of tubes employed. 6. Appearance and The ALL-AMERICAN Model R comes in a beautiful two-tone mahogany cabinet, with inlaid designs, which accords with the decorative scheme of the most fastid- serviceability ious home. Ample space is provided within it for all batteries, or for a "B" socket -power if preferred. The ALL-AMERICAN "steel chassis" construction rounds out a set that will be a source of uninterrupted enjoyment for years to come.

Have your dealer demonstrate the Model R for you The leading wholesaler of radio apparatus in your community has probably been, for years, an ALL - AMERICAN Authorized Distributor. ALL - AMERICAN Guar- anteed Radio Products are sold everywhere by responsible and reliable dealers.

ALL-AMERICAN RADIO CORPORATION, 4209 Belmont Avenue, Chicago, Illinois E. N. Rauland, President

R .M A OWNING AND OPERATING STATION WEN R-266 METERS

Pioneers AMEIUCANin the Radio Industry

Tell them that you saw It in RADIO 47 www.americanradiohistory.com THE BEAT NOTE (Continued from Page 23) to them; that is, until along about 1927, MEETING POPULAR DEMAND or somewheres around there." "Applesauce !" growled Athos, reLh- ing for another piece of parchment. "It was in 1925 that the trouble really started. Up until then anyone who had a receiver anyways selective could pick and choose pretty near any sta- tion in the United States except maybe in the middle of summer, when you had to be satisfied with locals unless you had an extry good location. Even up in Oakland with two or three locals going every night we managed to get DX pretty good until everyone began to get this `super -power' idea in their heads. It was a station called IFFY down in Los Angeles that started it when they got leave from the government to in- crease their power to 5,000 watts so that they could reach out farther and The new five ampere brag a lot more about themselves. A Tungar-at the bunch of windbags same price as the for fair,. them; I - old-means a quick mind how they used to sign off `KFY, charge of all kinds of storage batteries. Los Angeles-First in Everything- -It is more silent than ever. Where April showers come in March.' "Well, now up in Oakland there was -It cannot burn out Radiotrons. another station-KDO, operated by the -It cannot create radio interference. Majcr-General Electric Company and is ideal for auto batteries-and no sooner had KFY started in with -It their 5,000 watts than they had 2 to get charges to 6 volt radio "A" bat- a license for the same amount of power, teries, or 24 to 96 volt "B" batteries, although they had been running on in series - all without attachments. pretty near ten kilowatts before that anyway, and just about paralyzing everything for The Tungar is a G -E more'n half a mile product developed inithe around. They raised their power, great Research Labora- so torieeof GeneralElectric. they claimed, so that they could bat through Two ampere Tung a r the summer static, but the main (East of the Rockies). idea they had in mind was the same as $18.00 that of the KFY outfit-they wanted to Five ampere Tungar be the biggest toad in the puddle. (East of the Rockies). T UNG AR-a registered tradem ark-ie found only "This super -power stuff made busi- $28.00 on the genuine. Look for it on the name plate. ness pretty good, seeing as how lots of 60 cycles -110 volta Merchandise Division people had to junk their sets and get General Electric Company, Bridgeport, Conn. new ones which would let them listen to something else besides KDO when they took a notion to. Of course the superhets and the neutrodynes and some GJENERAL ELECTRIC of the tuned radio frequency sets weren't bothered much but the rest of them had mighty hard sledding, wave -traps or no wave -traps. The winter of 1925 come around and the static stopped but KDO and KFY kept right on with their dy- The `Windham " Variable Condenser namiting and what with their blanking everything within twenty degrees of them on the dials there was serious talk A durable, rigid instrument with correct of lynching amongst some of the wilder electrical characteristics and made by minds of the BCL's. skilled mechanics. It is provided with "Just about the time that the twenty- adjustable bronze cone bearings, the ninth petition to revoke KFY's license brake is independent of the bearings and was being started the gang who owned adjustable. The plates arc straight line. the station opened up a new subdivision only forty-one minutes by airplane from h occupies small space, single hole mounting. the Pacific Electric Terminal and col- The price is right. lected enough money Desirable territory open. to add another 5,000 watts to their outfit. And the The Goyer Company, Willimantic, Conn., U. S. A. ink on their license was still wet when (Continued on Page 50)

48 Tell them that you saw It In RADIO

www.americanradiohistory.com RADIO 'KITH M ETI C l."hatteries +73" hatteries +RECTIGON= clear radio reception

HARK back to your old arithmetic and those busy boys "A" and "B". They were forever doing "a certain piece ofwork". They're still inseparable. Nowadays "A" and "B" storage bat- teries are busy with clear radio reception. "A" still depends upon "B" and vice versa. Both need to be kept fully alive to do their best work. Both can be kept alive easily and dependably through the use of one [did you know that?) com- pact, little device - e (stiEghoùs Rectigon Battery

Superiorities no muss or THERE;S u« the fuss when you acids or Rcfligon. 140. do moving 7. chp emicals g- or 6 - Bhcbareejt-to48. no nsiul TO recharge cj azte and or auto- quality cell radio"A" adjust It has high .rSnap..attenea throughout. batteries merely merely insulation mobile L ebo tettn caseÁ s pro- terminals wn inals Even the adjust "snap" bete with Simple Gion %ln «ßed as shown here. acid -resisting maroons to >r can be. enamel. Guaranteed satufy W, eye), RehSo completely

Tell them that you saw rtt in RADIO 49 www.americanradiohistory.com THE BEAT NOTE (Continued from Page 48) KDO called their bet and raised it, coming on the air with 12,500 wags and Spectacularr running occasional tests four or five nights a week on 25,000. "Them was desperate times. Every- thing but the superhets went out of Perlé rm.a nce business entire and with them bringing in KDO in forty fifty places on the and dials nobody got much of anything. Any little two -for-a -nickel crystal set would GrTYFlPEe. 22 Super -Selectivity bring him in on a loud -speaker for fifty miles around and with nothing but a (I)UOFORMER. build the new Duodyne with the Camfield Type steady stream of soprano solos regular 22 Duoformer, and the Camfield Type 886 .00025 mfd. Straight Line Condenser. every night and jazz bands playing up / to 3:30 in the morning radio took big vl This circuit-using either dry or storage bat- a teries-is designed for the new power tubes, slump. Every other station in both Los CX220, or UX120, and CX112 or UX112, and Angeles and the San Francisco Bay re- gives a combination of gion went out of business early in 1927,. being unable to stand this cut-throat Selectivity business of raising the pot and until old Sensitivity Hartz brought out his Fourth Dimen- Volume sion Circuit things were pretty much at a standstill all over the Pacific Coast. Tone Quality "The Fourth Dimension outfit went big. Nobody understood much about it never before obtained in a five tube set. The The closed magnetic field. wavelength range is 150 to 550 meters. except that it had only one control and and special winding of the four funny looking steel tubes without new Type 22 Camfield Duo - Send 25c for "The Duodyne Circuit," a com- former is the secret of the plete descriptive booklet with instructions any filaments. It worked off the elec- selectivity and sensitivity of and the Duodyne Circuit. drawings for building. tric light system and cut out KDO or KFY like the superhets had done before Camfield Duoformers are If your jobber boxed and sold in kits of can not sup- and brought in the distant stations ply you with a complete three. Price $10.00 complete. line DEALERS: of Camfield parts, send us fairly well although seeing as how in his name and your order di- 7fJJ>> \ July 1927 there was only one station "-- r rect. .-rrrrrrrrr:rr- \ , using less than 5,000 watts in the J' 11iUG1l-u4 ß whole 1nitü tü lt n United States it so much /^sns, \JIt1111J111 didn't take of CSTRAIGHT a much to bring them in. At that time LINT LOW LOSS there were only twenty-two stations left, out of the six hundred odd which öNvDENSER had been working the year before. The In the transparent dustpruol case rest . had quit because it wasn't stylish. This condenser embodies a new principle of construction, for people to listen to the low power combining every essential and desirable feature in a single unit. Its straight-line action together with the outfits anymore. 360° dial, absolutely eliminates the necessity of a ver- nier. "Then began the big fight amongst the The Camfield Condenser is The Camfield Condenser is enclosed in a transparent sold in 3 sizes, as follows: Dust -Proof survivors. KDO fired the first shot by Type Case which prevents the accumulation of 886 .00025 mfd.....$6.00 dust between the plates, thus making it PERMANENT- putting in- a bank of twelve 10 -kilowatt Type 887 .00035 mfd..... 6.00 LY LOW -LOSS. Type 888 .0005 mfd..... 6.50 tubes and every Hartz receiver on the Pacific Coast went out of business while CAMFIELD RADIO MANUFACTURING COMPANY he began causing serious interference 807 HARRISON STREET 1268 WEST 115TH STREET with those as far back as Salt Lake Ciiy OAKLAND, CALIF. CLEVELAND, OHIO Factory Representatives: and Denver. They had to move the Baker -Smith Co., Inc., 1270 Broadway, New York City; 30 N. Dearborn St., Chicago station forty miles out of Oakland on A. S. Lindstrom Co., San Francisco, Los Angeles, Portland, Seattle, Salt Lake City the Farallone Islands an account of their burning up nearby houses by melt- ARE YOU A SUBSCRIBER? ing the wiring, and electrocuting people SEND $1.00 FOR A TRIAL SUBSCRIPTION TO "RADIO" FOR 6 MONTHS who got too close to the station. I re- member the night when they overloaded their tubes up to two hundred thousand YOU NEED THE NEW CARTER "Dialite' watts and before their towers melted down they had stopped every street Gar- Can be used in addition as Gives you light right a in and say, where you need it over battery switch - shows you Oakland San Francisco to when the dials. Makes logging your tubes are burning. nothing of wrecking the P. G. & E. simpler and surer. You A quarter turn snap switch, positive in action, operates power lines for can put your set in any on two miles around and either 6 or 41/2 volts. Current ÓIALITE part of the room and al- cons umplion negligible. See setting fire to the Allendale sub -station. ways be able to read the one at your dealer's today. But they were picked up on crystal sets dial marking. Simple to install. Single hole mounting. 01,75 Complete as far away as Johannesburg in South Branch Offices at In Canada: With Lamp Africa and an unconfirmed report from Los Angeles Carter Radio Co., Limited, Toronto. Portland Coast the Samoan Islands stated that they had Seattle Distributors: wrecked three receiving outfits in Tu- Salt Lake City A. S. LINDSTROM & CO. tuila. 274 Brannan St. San Francisco, Calif. "Within a month radio was at a stand - (Continued on Page 52)

50 Tell them that you saw it in RADIO www.americanradiohistory.com ...c t,. Gtn for the home LL one needs to get the est radio results from Su.

Zenith is good musical l and a feeling for exclu tonal values. So far as technical ability is c, cerned, the Super -Zenith L. easily controlled that a child c bring i.I jii -,.s many stati ons-- just a'. -each n ' the Saiïic' cl kyof1-_

cration c? ï'_ make _ i ent the Super -Zeniths are priced at from $240 ct -; to $2,000. Each instrument is sold under a quality guarantee. Above clear, is shown the De Luxe Spanish model. depend tration _i er -Zenith VII . . S 240 ,_)er -Zenith VIII . . 260 ,:per-Zenith IX ... 355 .Also Zenith regenerative sets (non- adiating) licensed under Armstrong U. S. Patent No. 1,113,149 -1_ith 4R ...... 100 lith 3R 175 ;wilding, Chicago, Ill.

ear

4D 1 0

www.americanradiohistory.com (Continued from Page 50) still all over the United States, and for Give Your Tuner that matter, all over North America. Nobody closer than five thou",, id miles aMan-sized Voice to KDO could listen to anyone except him or use anything more sensitive than NOW-you can enjoy loud a crystal set with safety. The sheriff speaker reproduction locked me up soon after that and with- with your favorite tuner. in a few months everyone had nearly Using the "Electrad" 3 -Step forgotten about radio; aerials had been Resistance Coupled Amplifier torn down everywhere on account of the Kit it's easy and economical to fire hazard, while radio sets were selling build an amplifier kit. And for a dollar apiece with no takers. you will get a clarity and fidel- When KFY at length secured a license ity of tone unequalled by any early in March 1928 to work on 150,- other amplifying method. 000 watts there were only ten stations "Electrad" 3 -Step Resistance left in North America with nobody Coupled Amplifier Kit No. 1-C closer than Europe or Asia to listen to -A big $6.75 value. Contains them. KFY was forced to move to the the necessary Resistor Coup- middle of the Mojave Desert to keep lers, Certified Mica Conden- from going broke paying judgments sers, Condenser mounting, Cer- which people won against them for tified Grid Leaks, and Resist- burning down houses or electrocuting ors. Nothing else needed ex- their relatives. cept sockets, rheostat and bus- "KFY was hardly settled in its new bar. location when the Major -General Elec- At all Good Radio Shops or Sent tric Company sold ten of their eastern Direct-Ask Your Dealer, or Write, factories and with the capital thus ob- for Folder on Resistance Coupling tained raised their power to a new un- Amplification. heard of height-300,000 watts, twice ELECT RAD, Inc the power of their only competitor, for 428 Broadway, New York City by that time the remaining eight sta- Also makers of other handy radio essentials-Certi- tions had surrendered. fied Grid Leaks, Audiohms, Lightning Arresters, "KDO opened up with his 300,000 Lamp Socket Antenna and many others. "ELECTRAD" VARIOHM watts the morning of January 1st, 1929 Price $1.25-Gives that much de- and telegrams and cable messages which s rru sired last hair's breadth iÍlnlfffffl i tuning, clears up DX came pouring in soon confirmed their -` ee.J reception. Gives any re- boast of a crystal set range 12,500 sistance from t/4 to of 30 megohms. Mount miles-girdling the globe! There wás "ELECTRAD* ed $1.50. LEAD-IN a delay in the opening, which had been Price 40c scheduled for Christmas Day, 1928, due Fits under locked win- dows or doors. No holes to a lien for unpaid wages which had to bore. Quickly in- stalled. 3000 volt insu- been obtained by a number of workmen lation. Extra water- employed in the construction of the sta- proofing. Meets the quality standard set by tion. The company was fast going to "Electrad" - there is a difference. pieces with the terrific expense of their continual additions in power and the appalling cost of replacing tubes and electrical equipment which was constant- ly being ruined by high -frequency surges. The stock of the company E LECT RÄD. dropped to less than 38 when the ,ale of the eastern factories was announced and within a week it had fallen off ten rÇ HE "Electrad" Certified Fixed Mica points to rise again to an unsteady 32/ Condenser is a revelation in accuracy for a long period. and design. Ingenious, rigid binding and "Despite the best efforts of their fren- firm riveting fastens parts securely at Six zied engineers KFY succeeded in being different points insuring positive electrical heard on a crystal set in but one isolated ONE contact. Impervious to temperature and cli- case at a maximum distance of 10,552 PIECE matic variations. Exerts even pressure upon miles from Los Angeles and the citi- the largest possible surface-can't work zens of that city, forgetting their past loose. Binding strap and soldering lug in grievances against the station rose as one one piece. Accuracy and quietness assured man and overnight subscribed a fund of always. Value guaranteed to remain within $4,429,621.07 for a super -super -station 10% of calibration. Standard capacities, of 500,000 watts to be later increased 3 types. Licensed under Pat. No. 1,181,623, to 750,000 watts if necessary. May 2, 1916 and applications pending. Price "The new station rose apace ; gigantic towers reached toward the clouds in an "claie Six Point 30c to 75c in sealed dust and moisture proof packages. immense antenna system forty miles Pressure Condenser' square, equipped with 750 Johnson energy couplers to allow the radiation (Continued on Page 54)

52 Tell them that you saw it in RADIO www.americanradiohistory.com This Catalogue represents the world's greatest radio store

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Tell them that you saw it in ßA1IO 53 www.americanradiohistory.com (Continued from Page 52) of this tremendous power on a wave- length of 112.7 meters, the exact wave- length of their rival, KDO. etIt was in this manner that they hoped to drown out the signals of their only remaining enemy and drive him from the air lanes, for it was common knowledge that the Major -General Electric Company was on the verge of bankruptcy and incap- able of raising sufficient money to meet this last and greatest increase of power. By March 1929 the new station was well toward completion and on July 4th of that year it was finished and sched- uled to open at eight o'clock, p. m. l-'' Stort 1,1z1 Perfection "The attention of the entire world was focused upon the thrilling climax of this epic battle and dark hints of a counter- plot by KDO raised the odds against W/iere the Oakland station is the difference from 2 to 1 to al- most even money. Feeling ran high in both cities and several men who looked in radio transformers ? like Oaklanders were hanged to .lamp posts in Los Angeles by bloodthirsty THE audio frequency trans- mobs of local patriots. formers in your radio perform "Seven -fifty p. m. that fateful day. a most important duty. They aid Slowly the tremendous banks of motor in increasing the volume of sound generators at KFY started, one after ... in building it up to the desired another; engineers hurried about super- strength. BUT- vising the warming -up of the gigantic When sound is increased, the tubes, the announcer stood at his post, tendency is toward distortion. chronometer in hand; daring citizens of That's where the difference comes Los Angeles dragged out their ancient in transformers. Inefficient trans- crystal receivers, eager to hear the open- formers will give distorted recep- ing words of the announcer regardless tion, just as a defective mirror will of almost certain death by electrocution. show a distorted image. "Seven fifty-five! In the operating room Whether you are building a set, of KDO the engineers labored or buying one, be sure about the franticálly with their apparatus, one transformers. No radio, remem- group busy with a set of wavemeters, ber, can be better than its trans- another making certain dangerous formers. A safe guide to follow is changes in the wiring. In mad haste the Jefferson trade mark. You can they labored toward the culmination of depend on quality in perform- JEFFERSON the horrid scheme which they had ance when the name "Jefferson" evolved, sweating and straining every is on the product. Tube Rejuvenator muscle and sinew, they ran their tempo- Jefferson Transformers are made by Keep your radio tubes like rary connections about ,the vast building new!Rejuvenate them regu- transformer specialists-the world's larly, AT HOME, justasyou that their desperate plot might succeed. largest manufacturers recharge of small trans- your storage bat- Not that there was a lack of formers. There is a very definite reason tery. Jefferson Home Rejuve- time; there why leading nator doubles and trebles were whole days, weeks left in radio engineers specify tube life, quickly pays for it- which "Jefferson." You'll find it in the clear, self. Raises your set'sefficien- they might perfect it to a successful con- sweet, life -like amplification which cy to 100%, and keeps it there! clusion, but the honor Jefferson Completely restores para- of KDO was at Transformers give. Sold by lyzed or exhausted tubes. stake. KFY must never, the better dealers used by leading set Takes large or small tubes- even for the manufacturers. types 201-A, 301-A, UV -199, space of a minute drown out their sig- C-299, 5 -VA. Don't be with- out this long-awaited radio nals. Almost certain death awaited JEFFERSON necessity. $7.50 at leading ELECTRIC dealers. them, but death was a lesser calamity MANUFACTURING CO. than defeat. 501 So. Green St., Chicago, Ill. "At 7.58X p.m., Pacific Time, KDO's signals were heard as the giant station Makers of Jefferson Radio, Bell Ringing and Toy Transformers; Jefferson Spark Coils for commenced its last stand, as usual slip- Automobile, Stationary and Marine Engines; Jefferson Oil Burner Ignition Transformers. ping in a few minutes on the silent period which was even then still ob- served as a matter of custom. Far back in the Gobi Desert of China the ob- servers of KFY adjusted their crystal JEFFERSON sets; another group in a steamship far RADIO TRANSFORMERS to the southward of Cape Horn were ,it their instruments, chronometers in hand, eager to hear the voice of their beloved new station crashing through that of their competitor. (Continued on Page 56)

54 Tell them that you saw It In RADIO www.americanradiohistory.com c_AL11E3) Ra cli o hy wait for to -morrow listen in to -day! WAITING for someone to invent a better radio than Fada Radio is like saying- "I won't buy a car yet-we'll all be driving planes one of these days!" Waiting Time is Wasted Time When Joy is on the Air! "Fada Radio-the Standard of Reception" promises these things and proves them! Splendid clarity and tonal values Absolute control of volume -Ability to get remarkable distances Certainty and ease in tuning in and tuning out -A demonstration of these qualities in your home or at the store, and without obligation -A Fada Service that guar- antees satisfaction. If You Waited Fifty Years You Couldn't Improve on That Call up the local Authorized Fada Dealer and ask him to demon- strate Fada Radio in your home to -night. Try it before you buy it -let your "listening -in" decide!

Most Pada dealers will be glad to arrange convenient terms of payment. Send for the book D, "Fada Radio-The Standard of Reception." F. A. D. ANDREA, INC. CHICAGO NEW YORK SAN FRANCISCO FADA RADIO, LTD.-TORONTO FADA RADIO, LTD.-LONDON Manufacturers ofTUNED RADIO FREQUENCY receivers ruing the highly efficient NEUTRODYNE principle

There is a Fada Radio model for every purse-all 5 -tube Neutrodyne sets for dry cell or storage battery tubes, from $85 to Art Cabinet models up to $300. Illustrated is the Ncutrola-Grand at $225.

Tell them that you saw It in RADIO www.americanradiohistory.com (Continued from Page 54) "The operating room of KDO was an inferno of laboring apparatus. The giant tubes glowed with a red heat, the generators smoked and g. 3wled and spat fire from their commutators under the terrific overload imposed upon them ; up went the needle of the wattmeter - 400,000-415,000. It wavered and dropped slightly and the tense group of engineers before it cursed with one voice. Then upward it staggered again as the operators recklessly sped up the generators and cut out coil after coil of controlling resistances and reactances 425,000 watts! The steel of the tubes had reached all but welding heat and exactly at 8 :00 p. m. when the triumph- ant voice of the announcer at KFY spoke the opening words of his address the wattmeter at KDO had reached the terrific figure of 461,3221 "Far back in the desert of Gobi the ob- servers of the Los Angeles station ex- changed wondering glances; aboard the steamship far below the southern tip of It the"Ractio Traffic" South America the watchers shook their crystal sets and feverishly prodded their you run into a flock of high-powered galena for new points. In that fatal WHENbroadcasting stations, all riding the ether moment thousands of people in far off Africa, in Europe, at the same time, can you pick your way in the frozen wastes through of Siberia frowned in perplexity and to your desired destination without hunted for new points on their detec- getting tangled up in the jam? tors. It was not music which bellowed The Centralab Radiohm will .from their loud speakers, only an in- enable you to sane medley of "ride" through the "radio traffic" whining sound in which with ease - mingled the signals of KDO and KFY. slip past unwanted "locals" and bring in selected Something was wrong! But in the lab- "DX" loud and clear. Smooth variation from oratories of KDO the engineers watched zero to 200,000 ohms. Especially adapted to their fusing tubes and smoking appar- plate circuit control of oscillation. Now used atus and laughed in triumph even in as a their knowledge of the catastrophe so standard unit by more than a score of swiftly approaching. leading radio manufacturers. "A minute passed and one of the oper- $2.00 at your radio dealer's-or mailed direct. ators of KFY detected a subtle move- Write for literature and circuits describing ment of the earth beneath his feet and this and other Centralab patented controls. mentioned it to his companions. Like- CENTRAL RADIO LABORATORIES wise the engineers of KDO felt this 14 Keefe Avenue Milwaukee, Wisconsin vague quaking, and trembled, for they knew the awful meaning of this as yet insignificant vibration. With whitened faces they silently gripped the hands of their fellows. Death before dishonor! "In the far-off reaches of the Gobi Desert the observers of KFY felt this OEntralab motion of the ground and the steamship hove to in the far southern reaches of the Antarctic shuddered with a vibra- tion foreign to its movement as the un- heeding citizens of Los Angeles aboard her prodded their crystals and even BAKELITE PANEL ENGRAVING risked destruction by listening on a one - tube reflex receiver. "It was then that the chief engineer VOLNEY G. MATHISON & CO. of KFY received the first intimation of 660 Twelfth Street, Oakland, California the disaster in a rush cablegram from Wholesalers of BAKELITE PANELS, SHEETS and TUB- China. For a full minute he glared at ING. BAKELITE CUTTING, DRILLING, the fatal message and then wie a wild and cry of horror he leaped to the switch- SUPER-FINE ENGRAVING board as his active brain grasped the Special machine service to the trade; lathe -work, drilling, forming brackets, shields, etc.1 Mfgrs. of all kinds of radio inductance coils, doughnut, super -machine weave, or on bakelite tubing. fiendish plot. One quick pull at the WRITE FOR PRICE LISTS master switch and the giant tubes were (Continued on Page 58)

56 Tell them that you saw it in RADIO

www.americanradiohistory.com .""\c:....,. /%`' .`\ -, . -° \\\,. __-, __ -

ibedv . tind feS with Thordarson Transfor If you were commissioned to explore the polar regions, you too would be very particular to select the best equipment - especially in radio, your sole means of communication. 4S) HORDARSON Super Amplifying that year after year, leading builders I Transformers - the identical of fine sets- makers of fine instru- transformers sold by dealers every- ments especially noted for distance where and used in a majority of and superb tonequalities-use more ref,i9"Ñ6 quality sets-have been the exclu- Thordarsons than all competitive sive choice of MacMillan on his transformers combined. expeditions. Arctic In addition to Thordarson audio fre- P Surely no greater tribute can be quency and power amplifying trans- paid to the actual supremacy of formers in his receiving sets, Mac Thordarson Transformers, product Milian chose Thordarson Trans- (/nw - of the world's oldest and largest formers for exclusive use in his exclusive transformer specialists. broadcasting station, WA P, on GyeißE Faultlessly they amplified programs board the Peary. WA P success- and messages from great distances fully broadcast the weird voices and Derenadyae on the 1923-1924 expedition - and instruments of Eskimo entertainers ADLER -ROYAL came back "as good as new."Equally back to civilization. MURDOCIK successful was their performance more to build the last expedition. Thordarsons cost - MU -RAD on but no more to buy. Dealers every- The wisdom of MacMillan's choice where. Interesting bulletins on Valley is further confirmed by the fact amplification mailed free. Silver-Marshall The Thordarson' utoformer "All Fre- Autoformers are $5 each. Other Thor quencyAmplifiers are our latest develop- darson Radio Transformers: A udio Fre- OZARKA ment. They amplify clearly the lowest quency(subpanel or top mounting types), 'U 11TB DJtE as well as the highest notes of any 2-1, $5; 31/2-1, $4; 6-1, $4.50. Power instrument. An adoption of impedances, r `, Amplifying, $13 the pair. Interstage Ort resistances and capacities. Write for the k t Power Amplifying, each $8. If dealer `l Jew Auto former Hook up Bulletin-it s free. cannot supply, order from us. LEI CH NUNN-LANDON THORDARSON ELECTRIC MANUFACTURING CO. KUSTOMBILTand Transformer speczalzsts since 1895 many others WORLD'S OLDEST AND LARGEST EXCLUSIVE TRANSFORMER MAKERS use Chicago, U.S.A.

R Super AMPLIFYING TRANSFORMERS Standard on Ibe mcgorie of quality sets

you it in Tell them that saw RADIO 57 www.americanradiohistory.com (Continued from Page S61 extinguishedplRa he wor ke Vital Parts ofleadiizgRadio controls of th.e switcidhbyoard and weoithth a Sets soft slurring of brushes h.tr .Ll the tempo of the \.the cru niai a 4.,k u ria !rare than the lure it nantit!." radio meld. Suu more true than in fia giant dynamos dropped lower and lower is not surprising chat leading manufacturers of radio arts a.-@YaYtlr. far they. hookups choo.e the only diet gaining a lull tnchaical knoNsie.ige of their while ever more pronounced grew the and the trwltà they makeup grue vibrations. Too late had the message in lull c.ubsltirtauwt d ¿lue, the choice of Benjamin Radio P`roducts, above all other., by the been received! u.auuy-1 ul man)an) itie Chimneys began to fall, d tit.. modern radio seta. bbespeaks eloquently nl thou as pea.tl..f ea ..) paru north !!lade by une of the aliter ma..utaaurees of ere-tr.cal souda the frail shack of the Gobi observers Ea:1. F s he- -n noir a 4'..T. r radii, part-to ennuie ism the or net d the we the collapsed like matchwood. A tower aria .rarest Ladle pure...laudeat woken-1. the" total e!bien,, spell. the acme fell lino. .ty, t weed r.Y..a, of at KFY, another and another, the the dutlIìauwt at theurhaamx an,i dt,a,x1t at. and the r1a, l.mao Atari. the 1.ß.:d 'ex:lumens tJ ceiling of tata! *Al these triai. uunhy !eatww ta banal it:lbu" the gigantic auditorium cracked and falling plaster rained upon Benjamin the panic stricken mob which fled for the open. And through all these warn- Electric ings of the approaching holocaust the Mfg. co. strains of a soprano solo from KDO shrieked over the entire globe. The last broadcasting station on earth! "A still more violent tremor of the earth and suddenly the voice of the BENJAMIN singer grew blurred and strange. Then Tuned Radio Frequency Transformers with a flash of incandescent metal the giant tubes of collapsed Lu /iri,tawr -Lau Lhsrnbt.tcJ Capaïir, KDO into ruin and the faithful generators gradually a.r4 .oa, at. pat<1ri .,r ref :La.. -a4 a.L,f eta. (ores ate -i that rf_.le slowed to eternal rest. .a 11.x.1.4 o-. _.i,1 a.1 a t_atL f..2141..1 ,d Greater Tuning 'Lange-Greater Selecti,it% "Still more tremendous grew the vibra- -- tions; the entire globe rocked to its core .. : .. .af`a..r}, xx tLa4 .l .ire.:sai the)m_, .r .>.c t.c t1Ja att.wco '- t_i.r.i A !'.:-i::rB: aita..L4 and 11..a4rr:a1 la Weird as it... at its fundamental vibration, seven . _ ..[ t .a-at.r±>t .a ..as.i torve ttºr rºrea :s.eo C.-.ia air ....,1}1lra1 r _ _..; . - . - cycles per s cond. For the engineers of __ _L _l. tìaccra .i. i.ir A.!. a.arilY iv.a . irv L gf tus iauau and KDO had changed their wavelength on ricnjau4iu L1cRaT.>nc Joàcts Benjamin that fateful evening, changed it a frac- LOW Lone. Lnrg Runge Ca>,otienercrs i"_: _ .. . . e ä., ::, fvr.ee_t the ua3:r tion of one meter to heterodyne with the ,Ití a.tibt Iír.r t e pr: Dee9r.te and lasarlua, .anuasl d carrier wave of KFY and produced a aas xe , te wee a ntiv Sr xe ra>fsa.:l `.ìape cads eke traa.i.,w rame .w 4t.r 4-a¿4ar/ auld brat note of seven 9 cles per second! And ri.íL_z..trs b.a11.-41,t,E 2111 atbtiJl< Lr.tea..ty .d ..:a1...11s an the laar,.t s+dr as they had hoped and prayed the tre- .r :1. a..: .4a, 34.467 .i.....o sua.o..ua N4... al. . eked t', keel- ..t ...:.:..1r.t.areaa .u..,. ab.r...a.u..4 waortIll ...d .Mtge. O.w,. ,;: Nti.'a.y`f. . slow rí.i__.c.re ju.laa mendous force behind this vibra- it te.rv ....vir .a r lu.a ee ..a juan f...... Ueartr aie u,, r.atdxe .arc, ...,...,:u. ..aw ana +ti-... tion had rocked the earth, gradually at bear .a.....ac:,,.a Srtra..a...c h lr,._tr la I:rst, but with ever increasing ampli- -.,..1 .. i.rte.ea l..w..tuc t.t lsr ,_... 1... . . _. L.Jer ..:..t tude until houses fell like matchwood, _>... tt.,..ir l.d, ....r.,, wade,. ... I cities were collapsed like feeble things --...,.r a._ti.k, c 5... t+r a ,,:..a, .,., .. ..w,. of pasteboard and mountains toppled to Y tLe aaan ir.u..a, .... Cú A. Lew yu..,. 1«..443.6.: . ..t ruin. The earth opened in huge ...'.a,ar .4s. a. ia.e a.. _...r..r...,.,c Ht..a h.loWa at .t,.e. ..a chain., it rose and fell like the waves rw.4,, w m.a..um3 .., aa.a.,..,. ..,.,._, M.« of the sea and new mountains were a..an a, Jima., .t e,...... naa- .44... ea.u.. .4414. formed in a minute. Sea bottoms were .,us;w 41 au... 11. :.. _i'fr.ìf9 ..a.. laid bare while vast areas of land were forever sunk beneath the surface of the inrushing waters, huge fires started and burned for months afterward under the impetus of the terrific storms which sprang up at the moment of the cata- ASS the U. S. clysm.. For the two hours the vibra- P Gterataeat tions continued, gradually diminishing in Cauarercìal r A.tn4atritr RLa L- intensity and when they at length ceased omit rua.aaaa! the civilization of two thousand years IJÛN'T WAIT! Th.. litai Mill helr lud vanished. Only a few half -insane Yep t Nub. ii! head 1, I6.t `et S uh y J survivors wandered in a daze about the X -LV atti r4'044 ia ARIO DENSERS ttawraa w ta«tt ten new earth to shortly relapse into barbar- - .. -.. ..r...... e.. -se, aa.a l3. sir ,..,.4 rer, r.L..YH...4* ywr trrp- ¡.weaag, ism." ±,.+...r .ea bb rreraid its a. The voice of interrupted. GERALD M. BEST yam as the l' _ S, Athos F.+4t1.ar «ca1 anal t .c,! 8, ¿Le lore-mu L.t Carole w lrren,a. "Say," he plaintively inquired, "Is this 1{,aJtn Engineer* old windbag gonna carry on all night? artrar.+ ea. a 111.....r sta a awrr t ..s a...Lta..rerawwt 440, Fora l..r 11...,a NUM..: b,. *MY M t, lr.i short C It he is, somebody's got to get me some !titbit \ 1.y.a. ri r.aya t.s te ei atars..aYw" time only teusra, l.a 44.1.a..n. M.a.er,. t.. ttrtlr. v Oc inure parchment." r Wetbitq- thris. il.Muul. . tt+anl*w. !twu,atr,ee tttt/ RADIO INSTITUTE OF AMERICA "Applesauce!" he growled to his a - trrd ..dr. tray.aray .rawwe hraw Ilat rrEL t. Tw .a,rbrj aapp,t. MIMI* to AMU 333 Broadway, New York City sìstant as the carted their* notes to- n1 AMn4l t. Awl ltttwrlar+d.. tut lb* t,.attuy), tan oaL M.r art w.tmutaatr famm....." tart.tg t ward the scribe's home. "The old boy's rtrrtaat+.dfw trd p.aaa.a vet law r osi .rrr. batty-been wandering around with the hue {i.ie ARE VOU A SUBSCRIBER? XI RADIO LNURAT'ORIIS FOR sun shining on that bald dome of his Sas lat.o.1. ..,ra. tytlìAGO SEND TRIAL SUBSCRIPTION ! PPAO FOR SIX MONTHS too long!"

SI rcu thFm teat 'um saw lt ta RADIO

www.americanradiohistory.com bsolute / CCUTCC3/

For the man who demands absolute accuracy ,in radio apparatus, there is no substitute for "General Instrument." Their products have become recognized by the competent radio technician as a nucleus around which can be built a radio receiver. that will perform unflinchingly. Radio engineers use them as standards for comparison. If you are a seasoned amateur, you know the meaning of "Gen- eral Instrument." If you are a beginner just learning the mys- teries of Radio and have the ability to become an expert, you will soon discover the open door to radio perfection is "General In- strument."

9he inimitable heos7at

Without the organization of Gen- eral Instrument back of it this rheo- stat could not be built. Therefore it cannot be imitated. Once you get it you have the real thing-but you must say "General Instru- TYPE 40 ment."

Concentric cYtraght .fine ,9requencc2 Condenser (Pyrex Insulated) f FsequENç Not a trade name but (fj.) GE"A' an. accurate descrip- tion of General Instru- PATENTED ment Type 80.

STATOR OBTAINABLE AT BETTER CLASS RADIO DEPARTMENTS s

14(renteereedil Ingtrumurtenag > u ...Manufacturers f Laboratory Equipment 423 Broome Street New York. City

Tell them that you saw. it in RADIO www.americanradiohistory.com $9 MARIUS LATOUR (Continued from Page 20) 4 in connection with work along these lines in this country. In regard to the question of reflex- KITS! ing, the Schloemilch-von Bronk 8 TUBE patent, now held by the Alien Property Cus- BASEBOARD MODEL, $84.75 todian, has raised an issue which is not 3 Jefferson No. 150 radio frequency transformers, $15, or Remler No. 600, $18.00; 1 Jefferson No. 155 filter yet decided. As a matter of fact, transformer or Remler No. 610, $5; 1 each General Radio Oscillator Coils: No. 277A, $1.25; No. 277B, $1.25; No. 277C, $1.25. One coil mounting, No. 274B, $1. Twelve Coil Mounting Plugs, each 15e. One Bradleystat, scarcely any of these patents have been $1.85. Two No. 631 Remler condensers, each, $5; two, $10.00. Three Federal Jacks, $2.10. Three small litigated thoroughly, and it is remarkable Benjamin Sockets, 5 large Benjamin sockets, each, $1. One Weston voltmeter, $8. One 2 mfd. Dubilier cond., $1.75. One 1 mfd. Dubilier cond., $1.25. Two .00025 Dub. fixed cond., each, 35c. One .002, 60e. that a foreign inventor could come to Two .006, each, 75e. Two .0005, each. 35c. Two 3 meg. Leaks, each, 20e. One .1 meg. Leak, 20e. One 2000 - ohm Federal potentiometer, $2.20. Seven Eby binding posts, each, 15e. Four No. 1-A Amperites, each, $1.10. America and in view of the powerful One No. 112 Amperite, $1.10. Bakelite panel, drilled, engraved, polished, 7x20 inches. $5.75. Baseboard, 35e. interests involved, amounting to the pos- Bus wire, 50e. Screws, 35c. Two Audio Transformers, Thordarson, each, $5.00. Or two Karns Harmonic Audios, each, $7.00, or Lyrics, each, $9.00, or All-American, each, $4.50. sible assessment of royalties of the order Complete kit as above, $84.75. of $110,000,000,-secure an adjust- Karns audio transformera extra, each, $2.00, or Lyric Audio Transformers extra, each, $3.50. ment of claims in view of the above panel, ready -cut Shielded Model Kit, complete with shielding, etc., ready to assemble, $89.50. facts. All Parts Sold Above Separately at Quoted Prices The time is rapidly approaching when the tendency of the radio art, as con- RADIO TUBE MATCHING SERVICE trolled by patents of leading inventors, We scientifically match up sets of tubes especially for use in superheterodyne' and tuned -frequency will be to form "gentlemen's agree- receivers. Price per tube, Cunningham or Radiotron, each, $2.50, postpaid. Furnished in matched ments" to avoid expensive litigation groups of 3, 5, 6, 7, 8 and 9. rather than to tie up b isiness through -di!ç the uncertainty of the results following RADIO OWNERS SERVICE COMPANY indiscriminate merchandising under 660 Twelfth Street Oakland, California these conditions. This has been the his- tory of the lighting and power divisions of the electrical industry and the tend- ency is to bring the same situation about in the realm of communication. D The half -million odd dollars received ER 11°A .S MiD by the inventor for waiving his rights as EROvOI( a plaintiff in patent litigation for up-to- BY-PASS CONDENSER date and future royalties, will do much

CON DENSERS :*1111 COW to clear the industry of the spirit of restraint in regard to future develop- ment. Latour was astounded both at ERovox the extent of the radio industry in this country and the vast improvements for uiccuracy which have been made on his own dis- closures, by American inventors. There is no exaggeration in stating that our audio frequency transformers are being EROv(s perfected to an extent undreamt by him. 2ualiq Latour seems to have neglected no for CAP possible detail in regard to patenting iíPA Mode in all capacities. slight improvements, such as a tap coil, particulars al Write for 'o Oo which is generally used in the rat. ) art, our complete line, inclwt- ERO 1O/ V ing Resisto formers, Rheo- V 006 and coaxial transformers for radio and stats and Grid Leaks. audio frequency circuits. He realizt: fOr Çesults _ the deleterious effects of cross capaci- _ tance in these transformers, and also how AEROVOX WIRELESS CORP. 489 Broome Street, New York City to turn the same to advantage in secur- Chicago Office: 53 W. Jackson Boulevard ing stability. Western Representatives: Rtcs-Htrr Co., SAN FRANCISCO -Los ANGELES All in all, the workings of his mind show a tremendous constructive imag- ination and also a very businesslike op- portunism, qualities which are necessary for any inventor to possess in order to keep on his feet in the midst of the rush i Diameter negotiations any vast improve- 4" Over AU in which The Greatest Name in Radio ment will bring upon him. Latour B. M. S. VERNI-JUSTER promptly capitalized his work in his own The new B. M. S. Verni -Duster gives razor -edge se- country, but, like many Frenchmen, even lectivity. Not just a dial with makeshift vernier an accurate, well -made mechanism. though at one time visitors to America, The Window -pane attaeent, but Posit action - 15:1 gearing. Insulated friction he had very little conception of the Lead-in Connector dutch eliminates body capacity-no tools el whatever are required to attach it. sPP v50 American temperament in regard to na- Sticks to glass without holes. Brooklyn Metal Stamping Corp. tion-wide response to new ideas. Instantly On or off 718-728 Atlantic Ave., Brooklyn, N. Y. It is somewhat amusing to realize the $2.00Atyourdealer Western Representative: or post paid similarity of invention which crops out D 8. DU BOIS F. L. Tomlinson & Co. f'IoIRiNOLES _ 443 So. San Pedro St., Los Angeles, Calif. 1 Td, ts S t. at different parts of the world when /Y YOdM MONBA 152 Security Bldg., Portland, Oregon Portland, Oregon (Continued on Page 62)

60 Tell them that you saw It In RADIO www.americanradiohistory.com Your set at its best always with a SuperDucon -- the 'B"BR ttevq Substitute When guests come in, your set is ready. No run-down "B" batteries-no batteries being recharged. There's the Super-Ducon plugged into the light socket-ready to deliver a steady, silent flow of current. It's the perfect substitute of "B" batteries- equipped with a specially designed RCA tube (Rectron UV -196) that has an average life of more than 1000 hours. It's a thoroughly effi- cient device-made and backed by Dubilier.

And it keeps your set at its best ! TentedDubilier and listed by the National Board of Fire Underwriters. CONDENSER AND RADIO CORPORATION

Price $47.50 Write for descriptive booklet No. L-3 "The Super-Ducon- and how to install it." 4377 Bronx Boulevard New York City

C

Tell them that you saw it In RATIO 61 www.americanradiohistory.com (Continued from Page 60) ideas are "in the air," so to speak. The Sup eradio loading down of an antenna by periodic- Receiver ally distributed inductances, condensers, or other combinations, sees to be a kind of "electrified mood" through which most radio inventors pass at some time or other, and Latour has been no 5 -Tubes exception to this desire for improvement of the characteristics of antennas with 2 Dials "shortened" fundamentals. There has been formed the American Latour Corporation which has sold 80 $56 per cent of its stock to the Hazeltine Corporation for $250,000.00 and his in- terests are no longer directly involved Licensed Under Reactodyne Agreement in the domestic radio situation except through the possible At last-true beauty is combined with scientific design so that results future development never of present patent before expected are now easily achieved. Loose, extravagant claims applications. His good are not fortune in cashing made for this set, which must be seen and heard to be appreciated. in on his early work is a splendid illustration of the fact that Results Undreamed "make haste slowly" is a safe met, -4 of of Now Secured watching the development Operates on radically of a field in new principle-inductive reaction. Housed in a handsome, which pioneer compact, solid walnut cabinet with black claims have been allowed. bakelite panel engraved in deep gold. Selden illustrated Produces full rounded tones with all their color and shading. Oscillations automati- this attitude in the cally controlled. Use of low loss S. L. F. Condensers and highly developed Solenoid automotive industry and Latour has R. F. Transformers results in tremendous power without disturbing squeals, while done so even more brilliantly. simple controls, only two, regulate the thunderous volume to fairylike desired. whispers, if Send for circular giving engineering details why the Superadio is so far ahead of present day conceptions. MARCONI BEAMS (Continued from Page 12) Tested Tubes Now Possible It is not the intention of this article to delve deeply into the theoretical Remember-you can now buy TESTED tubes-where ex- the planation of this phenomenon brought Superadio Dynometer is on the job. This meter is direct about by the presence of the reflector but reading. Measures the amplification factor, plate imped- it will suffice to say that the energy set ence and mutual conductance of any radio tube. Ex. up in A produces oscillations in B; this tremely easy to operate. Tests three tubes per minute. reflector then in turn re -radiates the electro -magnetic waves from A. These re -radiated waves interfere with those produced by the antenna in a definite Jobbers and Dealers and constant manner so that the strength of radiation is increased to a very Write for details on the Dynometer and our liberal marked extent in one direction whilst selling proposition. Be the first in your town to sell Superadio Dynometer equipped in the other direction the waves cancel TESTED tubes. with phones and plug. Price $120. (Patents Pending) each other. With this arrangement it is possible to De WITT-La FRANCE Co., Inc. concentrate all the energy into .a beam 54 Washburn Ave., Cambridge, Massachusetts of 10 degrees convergency so that any Boston Representative: Chicago Representative: Martin, Hartley a De Witt Sales Co., 99 Bedford receiving station lying in the St. William A. Welty 8 Co., 36 So. State St. arc of that beam will be able to receive 36 times more energy than it would if the sa,1ie power was radiated uniformly through- out the 360 degrees, as is practically the 423044Wrie case with existing transmitting stations. LOUD SPEAKER Putting this in another way a 10 kw. station projecting its waves within a 10 With Concert Unit degree beam becomes, so far as the dis- The large size of this Unit gives great range with tone of tant receiver is concerned, equivalent to most pleasing quality, which, combined with the special a broadcasting slifying properties radio transmitter having of the Burns horn, produces remark. a power of 300 kw. able results. A speaker that will add to the enjoyment of any receiving set. Pleases the eye as well as the ear.

Horn is of a distinctive design with pyralin flare in several e handsome finishes. NEW RADIO CATALOGUES No. 20511-With ^', Flare...... _...... _.._.._.$22.50 "Radio Vacuum Tube" from the C. E. No. 205D-PdahoganrTintod Flare..._...... -..__. _ _ 25.00 Manufacturing Co. of Providence, R. I., No. 20SP-Mother-of-Pearl Flare _..... _. 30.00 gives a No. 100 -Medium detailed description of the methods Phonograph Ualt._.. ._ 10.00 of manufacture No. 120 -Concert Phonograph Unit_ ..... _. _.__.._..__ employed and of the char- 12.00 acteristics of "Celeo" tubes. At your dealers, or write direct to manufacturers. American Battery Co. of Chicago, has pub- lished a folder describing the construction ,/Qmerréan 6lecÍzc and performance of the Big A®erican B bat- tery charger. This is a chemical rectifier State and Siaty.fourth Street. CHICAGO, U. S. A. which may also be used as a trickle charger for .4 batteries.

Tell them that you saw it in RADIO

www.americanradiohistory.com -1r)(

Carver[ Loop

Bennington Tube Socket Radio tested all insulationsr- and adopted 73a/ielíte Mason Z & T Jr. Detector In the laboratories of radio manufacturers, in actual use in all climates and under adverse conditions, Bakelite has proven its superiority for radio insulation. The reason for this dominance of Bakelite in radio is easily understood. Its high insulation value, so essential to tonal quality, is unimpaired by time, temperature variations or by service. Saal Soft Speaker Bakelite is generally used for exposed radio parts, dials, knobs. panels and accessories, because its color and high finish are per- manent, undimmed by exposure or handling. The use of Bakelite in the set you buy or build will insure you Pacent Knob against inferior reception through defective insulation. It will pay you to make sure that Bakelite is used in the radio set or parts that you buy. Write for Booklet No. 30 BAKELITE CORPORATION 247 Park Avenue New York, N. Y. Chicago Office: 636 West 22nd Street Western Representative: Pathé Dial ELECTRICAL SPECIALTY CO. 443 S. San Pedro St. 75 Fremont Street 1041 Sixth Ave., ao., Los Angeles San Francisco Seattle

Bakelite is anexclusive trade mark and can be used only on products made from materials BAKELITE manufactured by the is the registered trade Bakelite Corporation. mark for the phenol It is the only material resin product manu- which may bear this factured under p a t- famous mark of excel- ents owned by the lence. KELI Bakelite Corporation. T H E MATERIAL O F A THOUSAND USES

Tell them that you saw it in RADIO www.americanradiohistory.com 63 CALIBRATION LABORATORY (Continued from Page 21) and B battery eliminators, as well as the proper design of filters for B eliminator circuits. A precision capacity bridge giving ac- curate readings for any capacity desired 235-49 Elizabeth .%ve., is included in the equipment. This en- ables the measurement of condenser re- sistance at any frequency desired. The scale of fees required for Calibra- tion work represents less than cost of labor, particularly in the plotting of curves of the results, and no part of the charge includes anything for the cost of apparatus. The following list gives the type of work which we are prepared to do at once. Other services will be added as rapidly as new apparatus can be secured. CALIBRATION FEES Wavemeters: $1.00 for first tw coils, $.35 for each additional coil; $.5G extra for each curve. For buzzer type the cali- bration covers 100-3000 meters; for vac- uum tube type 25-25,0C^ meters; tube MOZART-RAUIOCI EV E type to be accompanied by actual tube SUPER HEADSET, and statement of filament, plate and grid voltage to be used and anticipated range $5.00 of each coil. MOZART UPRIGHT Variable Condensers: $1.00 for capac- ity curve drawn from 10 tested points, SPEAKERS including maximum and minimum. Fixed Condensers: $.25 each for cali- bration at either radio or audio frequency THE STANDARD - - $ 8.00 as specified. Grid Leaks: $.25 each for d.c. resist- THE BLACK BEAUTY 10.00 ance. THE 12 -IN -B - - - 12.00 Inductances: Fixed or variable; $.50 each up to 100 millihenries; $.75 from THE 14 -IN -B - - - 14.00 100 millihenries to 1 henry; $1.00 above 1 henry. I. F. Transformers: $2.00 for matching with specified tuned transformer; $1.00 for frequency characteristic curve. A. F. Transformers: $1.00 for curve of frequency characteristic from 60 to 5000 NOW it is neither nec- cycles; $.50 for impedance or inductance essary to buy an in- measurement at any desired frequency. Vacuum Tubes: $.50 for measurement different "loud speaker" of amplification constant at any one PHONOGRAPH UNIT or audio frequency. to use headphones un- All TYPE A, $4.00 equipment should be securely suitable for amplifying packed in wooden box with screwed lid TYPE B, $6.00 service. so as to be usable for return shipment. Fees do not include return express or These speakers-true insured parcel post charges, which reproducers provide should be added. Stamps not accepted in - payment. No responsibility is assumed highly satisfactory en- for breakage during shipment. tertainment - and the In addition to this calibration service, low cost makes them facilities have been provided for testing available all kinds of transmitting equipment. to all. They These include phantom and real aerials will give results far su- for tests from 5 to 1500 meters, direct perior in tone and vol- current power from 12 to 2000 volts, ume to other instru- a. c. at 110-220 volt 60 cycle single ments at, or, near their phase, 2 kw. 220 volt 500 cycle single price. phase and 220 volt 60 cycle three phase. Transformers are installed to give 1100, These speakers are 2200, 3300, 4400 and 6600 volts, which correct, and, only a dem- may be rectified by a high tension mer- onstration is needed to cury arc. Proper meters are available BABY GRAND prove with all this apparatus. their unquestion- Owing to the special nature COMPLETE of these able quality. tests no quotations can be made until WITH full details have been arranged by cor- TYPE A UNIT, $9.00 respondence. TYPE B, $12.00 More important than the equipment available is the fact that th,. men on RADIO's technical staff are competent and experienced in making the tests, Their reports may be relied upon. 64 Tell them that you law It in RADIO www.americanradiohistory.com THE PERFECT, UNION - OF ART AND SCIENCE rain*

DE FOREST AUDION is the world standard ln tubes. De Forest created the first successful radio tube, and his invention made broadcasting possible. The De Forest policy of a specific type tube for each socket Insures finer reception and greater distance. Price, $3.

DE FOREST F5 AW A compact, powerful set in polished walnut that will bring Joy to many a household. Gives rich volume, and has the capacity to separate stations positively so that you can pick the broadcast gems without interfer- ence. Extremely easy to operate. Price (minus tubes, loud speaker and batteries) $90.

DE FOREST F-5 M A superfine 5-tube set in two color mahog- any cabinet, with built-in loud speaker and concealed compartments for "A" and "B' ' batteries. A great distance -getter, with un- canny power to tune in and out stations at will, and gifted with splendid tonal quali- ties. Extremely simple to operate. No howling or hissing in tuning in. An unsur- passed value at $110. De Forest Radio Sets can be bought at prices ranging from $85 to $450. De. Forest Genius now Humanizes Radio! is Not eXARVELOUS new circuit, just dance,. ripple and sparkle . . clearly, dis- But Tonal Supremacy All- perfected, reproduces flawlessly tinctly... musically! Those brooding low notes, Elbert McGran Jackson, renowned sculptor, the mellow, soft modulations of never caught in average reception, are heard architect and painter, put into this hand - distinctly-as though from the next room. wrought, hand -carved cabinet the spirit of the human voice and captures the In the reproduction of orchestral music the radio, in design, in motif-it is not an adap- hitherto elusive overtones of the full importance of the De Forest achievement tation of a phonograph. An image of charm- musical register .... tuning sim- stands out. For the first time you get the over- ing individuality, it harmonizes with the set- as well as the middle tones the ma- ting of any home. plified . . a new ease in opera- tones ... tion all embodied in the new jestic roll of the kettle drums, the crooning One unit, everything self-contained-not a .... of the bass viols, the strident crash of the wire in sight, nothing to connect ... and and beautiful De Forest W5 or W6 brasses and the piping heraldry of the cornets portable; move it any place! Only charm and Radiophones. and trombones. A symphony orchestra heard beauty for the eye. over the De Forest W5 or W6 stirs the soul. The artistic conical reproducer is an insepa- No incoherence, no oscillating jumble of and its tonal mecha- The voice of radio is no longer flinty and me- in its rable part of the cabinet noise-every instrument, every octave, nism peerlessly attuned to that of the Weagant tallic, but mellow, human and musical- true value. A magic achievement! development Roy A. Wea- circuit. There are just two controls for tuning, thanks to the by To the lover of dance music the De Forest which makes gant, Vice -President and Chief Engineer of and these operate on one dial, W5 or W6 brings more sprightliness, more in" De Forest Radio Company, of a new and the normally perplexing task of "tuning the beauties of syncopation you should hear marvelous circuit. ... extremely simple. There are special power Vincent Lopez, Joseph Knecht, The Night tubes in the fifth and sixth sockets which can This ingenious circuit, and all the joy it Hawks, or any others over either of these in- give you volume to flood an auditorium, if means to radio lovers, makes its first public struments! you desire it. And, at your fingers' tips, the appearance in the De Forest W5 and W6 Radio- All the tenderness of song, every shading of means to tune in a far -distant station you phones, masterpieces of cabinet art worthy the soprano's voice, all the pathos of the folk want no matter how powerful nearby stations onlyof a scientific development so outstanding. song-exquisite but elusive elements so much may be. So wonderful is the reproduction in of tone desired but lost in practically all present-day See the incomparable De Forest W5 and W6 the De Forest W5 or W 6 that only the presence reception, are captured by these De Forest at your De Forest dealer's or write for an in- of the lovely instrument dispels the illusion masterpieces. booklet describing these master- rooms. teresting that the living artist is in the To everything that is broadcast, the De pieces in detail. Piano chords come to you with their full Forest Radiophone gives animation, life and rich resonance-true piano tone. High notes humanness. DE FOREST RADIO CO., Jersey City, N. J. Jhe qyeatesrt E S .Name in7Zadio DE ALEfì5FORE ALL CITIES AND RADIO COMMVNITIES IN HE EPOCH-MAKING ACHIEVEMENT WHICH MAKES ORDINARY RADIO RECEPTION A THING OF YESTERDAY

Tell them that you saw it In RADIO 65

www.americanradiohistory.com ¡7f.öö"äèE'0 AFTER THE LICENSE (Continued from Page 22) merchant marine officers were given com- Ruild Quality Into Your missions. The civilian operator who succeeded a "gob" after the war had no, Receiver If You Would easy job regaining lost prestige. Get Quality Out of I t ! Perhaps a great many operators have themselves to blame. It may be what HAMMARLUNI) we were taught, but more than one of Precision Products Have Never us has gone aboard ship fully convinced Been Excelled that if ill befell the skipper the rest of the crew would immediately pay hom- Alfred J. Koenig, the age to the wireless man. "boy wonder" of radio as he appears today. More than one radio man who has felt at peace with the world has boarded a ship to find himself the heir to a gang of enemies. Why? Just because his A Radio predecessor refused to acknowledge any authority other than the master's, and in many cases not even the captain's. Straight Avoids Operator Then, again, it Line Critical nettled many shit' of- Frequency Tuning ficers to see a landlubber step righ Zhto The New their class, Hammarlund Straight-line Frequency Con Fifteen! or to read how heroicey denser -at distributes stations equally over the dials. It has all the familiar Hammarlund low -loss feature, were-the operators-when the rest of plus many new ones-the perfections of advanced ALFRED J. KOENIG the crew deserved ast much, perhaps engineering. Made in all standard capacities. worked as an office boy by day and more, praise. studied radio at the Radio In- In our own case we have found that stitute of America by night. At life aboard ship is just what we make the age of fifteen he received it. We once had conferred upon us what his First Class U. S. Govern- was considered-at that time-a com- ment Commercial Radio Oper- pliment. A mariner, with more than ator's License. Today he is en- the usual amount of intelligence, con- gaged in the transmission and descended to confide to us that we were receipt of photoradiograms at the "most rational" wireless man he had the Radio Corporation of Amer- sailed with. ica's station in Hawaii. Just what comparison our friend was Thousands of our graduates are drawing we don't know. He may have now holding successful posi- known the radio man who nailed the tions in radio. And YOU can skipper's shoes to the bridge-and got attain success in radio, too. away with I he Hammarlund Space -wound Coil is supported by it,-or the other who invited a mere filin of transparent dielectric. Its inductance animosity by going to the engine room le high and its losses are extremely small. Made for the "Roberts," Tuned Radio Frequency, and Study radio in spare time skylight and yelling at the chief who other standard circuits. "Hammarlund, Jr.," is a stood on the top grating, "Hey! Let's Even though you may be em- have the juice, will ya?" ployed at present, the Radio Institute of America's Home All these digressions may seem to have Study Course in Radio can give nothing in common with commercial you all the knowledge you need radio operating. On the contrary they to be able to pass your radio are essentially worth knowing, are sel- license examination - to be dom taught, and learned only through ready for your first radio job. experience. This is the world's oldest radio One thing a radio man soclearns is school-conducted by the Radio that the practice of keeping secret the Corporation of America. For contents of messages will hold him in further information, address the good stead, for very often he is made the confidant of all classes on board; and if RADIO INSTITUTE he relayed some of the stuff given him, - distinctive precision midget condenser of many uses. It is similar in construction to the larger Hammar- OF AMERICA it would be the stirring up of a hornet's lund models, and requires only one hole for mount- nest ing. Circuit diagrams of uses sent on request. Formerly Marconi Institute Established in 1909 for fair. When the sea is rough or men are out of do Write for Descriptive Folder sorts they say and 322 Broadway New York City things they would not do ordinarily. Hammarlund Mfg. Co. -CUT HERE- - - Talk about old women! There is no - seafarer who cannot find a thousand and 424-438 W. 33rd St., New York Radio Institute of America Pacific Coast Representatives: 322 Broadway. New York City one things to grumble about if he wants ATLANTIC AND PACIFIC AGENCIES CORP. Please send nie full information about your Home to. Study Course of radio instruction. 383 Brannan St., San Francisco I am interested in the complete course, includ- The radio man should fie a diplomat aQ tt hL -R dio ing code instruction, which qualifies for the U.S. like the skipper, who, confronted by an Gov't Commercial or Radio License. Amateur irate crew, reprimanded the steward be- J-tammarIund Name fore them. "Steward," says he, "didn't P R E C/ S/ O N I tell you to give these men all the po- PRODUCTS Address tatoes they want? Give the n all they want!" Meanwhile, the exact amount l (Continued on Page 68) o Tell them that you saw It In RADIO

www.americanradiohistory.com Illllllllllllllllmllilllllllllllllllll IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII .l2adio pparatus"'

scHMANS FILTER CONDENSERS Specified for the Helium Tube Rectifier ("B" battery eliminator) Mr. Edwin E. Turner, in his interesting arti- cle "The Helium Tube Rectifier" in this issue, specifies the following TOBE con- densers ;-3 type 711, 4 MFD. ; 1 type 709, 2 MFD.; 1 type 707, 5 MFD. ; 2 type 705, 1 MFD. Any "B" battery eliminator circuit depends very largely for its operating efficiency upon the filter condensers used. TOBE con- densers alone possess all the following favorable characteristics : Will operate at voltages up to 700 D. C. without breakdown or eee. overheating. High megohm resistance-indicating perfect insulation. .5 MFD. Type 707 $ .90 Capacities guaranteed to be within 5% of accuracy. Extreme heat or cold has no effect on TOBE condensers. .1 MFD. Type 705 .70 Compact and handsome in appearance. Current consumption practically nil. 2. MFD. Type 709 1.75 TOBE condensers are distinguishable by their silvered finish case-"A better condenser." Ask your dealer for them by 4. MFD. Type 711 3.75 name "TOBE." Manufacturers, dealers, and Jobbers write for informative 4eiri circular. The Leading Collapsible Loop! f cr Super Het. or any circuit

ELECTRICALLY SUPREME ; large size-27 inch sides-gives great pick-up. Genuine Litz with spacing permanently assured. Very low R. F. re- sistance. Unique system of taps with jumpers to divide loop without dead ends, adapts it to center tap and loop regenerative sets and allows tuning at low wavelengths without change of condenser. Graduated circular plate at base gives compass set- tings. MECHANICALLY SUPREME; constructed of beautifully finished hardwood, structurally rigid with minimum weight. Folds instantly for storage or transportation. When open all looseness in wires is immediately taken up-appearance always per- fect. MADE TO LABORATORY STANDARDS FOR A LIFETIME OF EFFICIENT USE K\,

IIIIPaTmsuumnnwu ; 820 Market Street, San Francisco, California DeutschmannCo. 052 'obeCORNNILL BOSTON MASS.

Tell them that you saw it in RADIO 67

www.americanradiohistory.com (Continued from Page 66) was indicated by the skipper's wagging index finger. Once away from the dock we begin to feel that we are somebody. As we watch the receding coastline we begin to real- ize that "pounding brass" at sea is far different than in our cosy home surround- ings. No quitting if we want to; no hanging the message on the hook until the next night. We are responsible for maintaining communication with land, the sole connecting link with the rest of the world. So, when you hear your station called and try to pick your mes- sage through what seems to be an im- penetrable barrier of signals, you begin to feel that you were not fully justified in criticising from your favorite corner at home. Commercial like THE KODEL MICRO- traffic, any other traf- PHONE LOUD SPEAKER fic, depends upon the class of station and is an exact replica of the the power of the egts:pment. The larg- transmitting microphone er passenger vessels with their 500 and used in broadcasting. 1000 -watt continuous wave transmitters The effecient Kodel reproducing unit, with an ingenious new have, of course, a great volume of traf- snail-shellhom, mounted inside the microphone case, produces $1500 fic. They maintain constant communi- a remarkably clear, full -toned cation with shore. from volume. Non -vibrating tone They have three chamber eliminates distortion. to seven or eight operators. An opera- The $15 model incorporates the tor for such a craft does not necessarily new Kodel, Jr. unit; with the large Kodel unit, $20. have to be a speed artist. He must be Radio dealers everywhere Gage them able to transmit and receive consistently THE KODEL RADIO CORP. at an average speed of 25 words per so? F Pearl St.. Cincinnati. O. minute. There must be no lost motion, for the number of ship stations is far in excess of the number of shore stations, Design and there is always some one waiting to Patented work the fellow you are in communica- tion with. KKODEL The practice of calling up the nearest coastal station and notifying him of leaving the dock, also of giving him a QRU? or QTC? has not been encour- aged since radiocasting became so popu- lar. A minimum of harbor traffic seems to be the order of the day. Many coast- al stations send out QST's every two 14f1(ROPSPEAKER hours or so with a list of ships for whom it has traffic. Such schedules will be fur- nished the operator by the cor -:;any as- signing him. On cargo vessels having but one operator it is not compulsary to stand a continuous watch while along the coast, if these schedules are adhered to. 7Andrews Once away from the coast, the cargo vessel operator's time is practically his own. The DeresnaRADIO RECEIVING BET e only watch he must observe almost religiously is for the time signals, Combines Tone Quality and Selectivity With Distance weather forecasts Price $165 Without Accessories and press dispatches. ANDREWS RADIO CO., Tribune Tower, Chicago The volume of traffic is small on a cargo F. L. TOMLINSON CO., Los Angeles and San Francisco ROBINSON SALES CO., Seattle vessel, much of the work having to do with bearings while along the coast. In the handling of any kind of traf- ilLaáoretor;/ fic an operator will save nimself a lot of Produce,_ r v\rBerr time and trouble at the end of the voy- LA i ARE YOU A SUBSCRIBER? Be age if he abstracts, as soon as possible, /be Dlsloetllaitlewr Ampepcerllara Send for Trial Subscription what traffic he handles. These abstracts Used ow the U. S. N. Dirigibles are handed into the radio operating com- Made all capacities, 12,000 ohms and up. pany at the completion of e ich voyage. Litt prices $1.50. Special sisee to order. $1.00 for Six Months Write today. Discounts to dealers. Each company has its own forms and CRESCENT RADIO SUPPLY COMPANY 3 Liberty 8t., Jamaica, N. Y. (Continued on Page 70)

66R Tell them that you saw it in RADIO

www.americanradiohistory.com .4 SMÌ SILVER SIX

FACTS THE "WHY OF THE SIX" BOOMERANG CRITICISM Ad Described in Radio Broadcast of November and December. The Silver Six is at once the most satisfactory and the most unusual SELECTIVITY is such that out of town stations broadcast receiver ever devised. It is the first practical receiver with may be brought to Chicago through twelve powerful Sensitivity, Selectivity and Tonal Quality which cannot be surpassed. local stations. Selectivity can be regulated at will, This can only be understood by a careful study of the receiver's charac- from a degree satisfactory for ordinary reception, up to the surprising limit where side -bands are cut. teristics as analyzed under "FACTS." SENSITIVITY is so great that nothing will sur- pass the "Six" except special laboratory -built The Silver Six was put through its paces for a prominent Editor, an super -heterodynes. Either coast may be brought Engineer and an Executive just after it was perfected. How did they in to Chicago during the summer months on a small react? The Editor asked to have the tuning broadened ... The Engineer antenna-in many cases on a loop. in FLEXIBILITY permits the use of antenna or loop was astonished at the uncanny ability to bring in DX Stations daylight with either detector, ono or both stages of radio ... The Executive objected to the intensity with which notes low on the frequency amplification. Interchangeable R. F. musical scale were reproduced. Why did these men react this way? Transformers, with adjustable antenna coupler, per- was not receiver" of merit mit operation on all waves from 50 to 550-or higher Simply because the Silver Six "just another if desired. easily recognized in comparison with existing standards ... But because VOLUME is so great as to paralyze any but the it was an accomplishment so far in advance of the commonplace that these best loud -speakers. Yet it may be adjusted to any three authorities had to revise their standards in order to appreciate ideal degree by a single knob. performance-not merely in theory-but when the "Six" actually demon- QUALITY cannot be excelled due to resistance amazed senses. coupled amplification. It is the only receiver that strated it to their will bring real appreciation of "cone" speakers. CIRCUIT consists of two stages of R. F. amplifi- These men were unable to demand and the "Six" fail to produce. Selec- cation with special oscillation control uniformly tivity was at their command-ease of control theirs for the asking-one, effective et all wavelengths, grid -biased detector and by a single knob from three stage resistance coupled audio amplifier. two or three dials as preferred-volume adjustable EASE OF CONTROL allows use of one, two or a whisper to a roar without a discordant note-rather, with a perfect three dials at will. harmony that enthralled the listeners. TUBES may be either dry cell or storage battery, with 11V201 -A's recommended. "B" Battery Con- WHAT WAS THEIR VERDICT? UNQUALIFIED APPROVAL! sumption at 135 volts is below 10 milliamperes-less than one-third that of other six -tube receivers. WHY? BECAUSE SEEING IS BELIEVING! ASSEMBLY requires but a few hours, using only parts supplied in kit. TYPE 600 KIT, including all parts necessary to build the $53 00 complete "SIX" Mail this Coupon TYPE 610 KIT, essentials only, including 3 condensers, 3 inductances and 3 inductance sockets $27 75o Silver -Marshall, Inc., Chicago, Ill. SM Products at Your Dealer's Getlemen: Please send me: See These and Other A-Complete building data on the Silver "Six," for which I am enclosing 50c. B-Descriptive circulars on S -M Products. i1ver4farska11 Name 106 South Wabash Avenue CHICAGO

Tell them that you saw it in RADIII 69 www.americanradiohistory.com 'IZED DIST r, (Continued from Page 68) OF IeG methods and instructs the operators in -04 the use of them. There are three important classes of messages handled by commercial stations. Electrical Research laboratories (,tChec Private paid messages using the prefix "P" if sent direct, the prefix "X" if to al$taE RADIO be relayed ; Captain's service messages, e i. e., messages pertaining to ship's busi- ness, using the prefix "MSG"; Dead- head or franked messages using the pre- fix "PDH". These latter are usually enjoyed by the captain, officials of the steamship company and of the radio company, and by the operator. These frank privileges entitle the above to a ' certain number of free words within the lines of the radio company operating the Mid. under Lowenstein station. Patents, March 5, 19,8. The wavelengths in common a for commercial work are 600 meters for Fwd. calling and 705 and 875 for traffic, and Space Gives Ideal also the band 180') to 2400 for C.W. traffic. Bearings are handled on 800 Tuning at meters. Some ships are tuned to 450 meters for bearings in foreign ports only. Spreads low wavelength Modern ship installations leave little stations without crowding those to be desired. Not so a decade ago. from 50° to 100°. Lightweight and compact in style. Then most of the radio rooms were con- verted staterooms. What had been the HERE is a new con- Equi Space is small and upper bunk supported the apparatus ex- denser that surpasses compact, requiring cept the motor all present-day types. The Special Erla Features little generator, which was space. Very light but hav- stuck in the remotest corner beneath the conventional straight line Minimumcapacity only 10m.m.f. ing extreme rigidity be- lower bunk upon frequency condenser Ratio of maximum to minimum cause of four riveted cross which the operator spreads stations on the capacity 35 to 1. members. slept. low wavelength Total resistance of only 3 ohms propor- at 1.W cycles. In our own experience we have tions on the dial but it also Go to any radio store Four riveted cross members sup- more than once brings stations between porting stator plates provide ri- and see this amazing con- awakened to find 50 and 100 too close to- gidity unapproached. denser today. It will make the 1 K. W. "coffin" on our chest. Single -hole mounting makes it a gether. On the higher easy striking difference in any When occasion demanded that a new and quick to attach. set. wavelengths are many high- Light weight plates of special brush be put in the m.g. we either in- powered stations that are spring brass appreciably reduce Send your name bulk and weight, and tremen- and curred the enmity of the steward by extremely difficult to sepa- dously reduce tendency toward address today and we will rate. misalignment from rough usage. mail free, news of the ruining the bunk, or jeopardized some The Erla 'Equi Space latest radio discoveries vaudeville performer's job by enacting makes allowance for this. and inventions. the role of a contortionist. It gires maximum spreads be teem stations *Trade Mark Registered Modern equipment and the rooms over the entire range of the d 'al. Specially Electrical Research laboratories into which it is placed seem to have been designed plates make this possible. CHICAGO, U. S. A. designed by men of vision. T What re- Now all stations, low frequency as I -BÌ well as Electrical Research Laboratories. pairs that are necessary to make can be high frequency, are spaced on 2500 Cottage the dial insure Grove Ave., Chicago, IIl. done without wrecking place, to the best results. Tun- Tell me what's new In radio. the In ing is made far sharper. Sensitivity is this respect it is wise to keep in with greatly increased, reducing losses to an Name the engineers. Not all ships carry spare unprecedented minimum. Plates of spe- cial spring brass are scientifically spaced Address armatures for the generator. If you and give maximum conductivity. Scien- City should be so unfortunate as to burn out tific tests show a resistance far lower an armature coil, if it is at all possible even County State... than costly laboratory types. to repair it, the engine room is the logi- cal place to do it. Other necessary re- pairs can usually be taken care of by the operator. These can be kept at a mini- mum by the proper care and inspection of the apparatus. Most companies re- SCORES AGAIN! quire an apparatus report of tii i i at the end CZ1r A complete Radio Receiver each voyage, and send inspectors aboard ' ÄviA to check up. f $2.00, List Should an operator experience serious Pyradiolin Panel, Key to the Air Low Loss Coil, Clever and Sharp Tuner, Westinghouse Type Biudin Pons, Key to the Air Permanent trouble at a time when being able to Detector. (No eat -whiskers). The losest priced Reretter in the world equipped with this standard transmit is a matter of life and death, and Detector. A real little wonder. he is literally up against it, he must re- Usual Key to the Air Guarantee. sort to his own ingenuity. A couple of STAFFORD RADIO COMPANY years ago two operators fafitd them- 2R, Medford Hillside, Mass. ****eieries selves in such a predicament. With Jobben and Dealen, Send for Sample Receiver. their generator "shot" beyond repair et AI Represeasetire: A. S. Lindstrom Co., 274 Brannan St.. Sen I,anri.ro. Cal. (Continued on Page 72)

' 70 Tell theist that you saw It In RADIO www.americanradiohistory.com .a`";,Äe

Anew era in radio delight BEAUTIFUL to look at-thrilling to operate- superb in tone-the Super -Thompson Duo -Tone SUPER-THOMPSON Console inspires pride of ownership. DUO -TONE CONSOLE The Thompson laboratories have built into it the Model C-61 List Price $360 during 16 years' expe- Stations come in sharply one after wide knowledge acquired the other by simply moving the rience. Over 116 different Thompson -built types of single master control. Equipped with newly developed Thompson radio apparatus stand back of it, sponsors of its Duo -Tone reproducing system-two performance, its trueness of reproduction, its power, separate built-in speakers reproduc- ing bass and treble tones distinctly. and its ability to secure distant stations. Creates a sound perspective and a range of tonal reproduction never This instrument gives its owners a new under- heretofore attained. Has improved standing of the charm and fascination of present- volume control, graduating from loud to soft without change of tone day broadcasting. The Super -Thompson Duo -Tone or pitch. Beautiful mahogany Queen Anne Console Cabinet provides is built especially for those whose home equipment space for all batteries or battery is of the best. Other Thompson Receivers from $125. eliminators. An improved Neutro - dyne operating on three UV -201A Thompson and Thompson -Fuller Speakers, $28 and and two UX-112 power tubes. In $35. All prices slightly higher west of the Rocky tonal reproduction, ease of opera- tion, volume and distance -getting Mountains and in Canada. Sold by the better dealers ability, the Super -Thompson is the finest receiver to come from the fa- everywhere. R. E. Thompson Manufacturing Com- mous Thompson laboratories to date. pany, 30 Church Street, New York City. CDO(DPSOD Built by makers of army and navy apparatus used by leading nations HADIO Tell them that you saw it in RAI)In 71 www.americanradiohistory.com (Continued from Page 70) they contrived an apparatus for interrup- f WE SOLD 4000 SETS ting the direct current by taking an Had 4000 ordinary electric fan and providing Favorable Reports brushes for the same. These were placed in the direct current circuit. In this Before We Felt Justified to Say way they were able, by making the fan blades act as a motor and make contact with the improvised brushes, to give a pulsating current through the trans- former. This improvised emergency set made it possible for them to communi- cate up to 1400 miles, and earned for them commendation from the Depart- ment of Commerce. The fellow who gives everybody the impression that he can get along with- out them had best be careful. Some Quality Radio Apparatus night, when the wind is high and the moon and stars are as visible ti Now we invite you go as an- to to your APEX Dealer who will be glad to nouncer at a distant station, although make a personal demonstration for you in your home or in his they store. A demonstration will may never have heard of Joseph prove to you that APEX Radio Re- Conrad or Captain Dingle, the boats- ceivers will give you everything you can possibly wish for in a radio receiver from wain and his gang will give the haughty the standpoint of selectivity, clarity, volume, person distance and attractiveness of design. every opportunity to imperson- ate one of these author's characters while The APEX Super Five $95 The APEX Utility Radio he tries to fix the aerial. Without Accessories Table $75 But what does it all lead to? A The APEX De Luxe $135 The APEX Entertainer (Loud sea- going operator has as much, if not more, Without Accessories Speaker) . $22.50 The APEX Baby Grand Console $225 The APEX Console Enter- opportunity for sightseeing as any per- Without Accessories tainer $27.50 son on board ship. If he is wise he will Upon Request We Will Gladly Mail You Descriptive Folder make this a profitable pastime. A cam- era is an invaluable aide. A prolific 141 West St. APEX ELECTRIC MFG. CO. Dept. Chicago writer can always find a market for Prices West of Rockies Slightly Higher. Canadian Prices Approximately 40% Higher travel articles. Operators have had all Western Representative: A. S. LINDSTROM CO., San Francisco, California sorts of "side lines." We know of two, Branch Offices: Seattle, Portland, Los Angeles and Salt Lake City both of whom are at present editing Northern California Distributor; two UNITED RADIO SUPPLIES CO., San Francisco very prominent radio magazines, who had very diversified lines. One wrote newspaper articles and stories, the other sold beef -tea tablets. Very often an operator becomes en- amoured of the fickle sea and decides to make it his lifework. Shifting over to the deck or engine departments is the next step. Or, if the shipping business ap- peals to him, the job of freight clerk and so on up to purser are steps to a position ashore. Again, he might get interested The Climax of Our Achievements in the huge profits made by shipchand- lers and break into that game Since the beginning of broadcasting B -T apparatus and circuits have set new stand- via the ards of efficiency. The first 3 circuit tuner, the first vernier Condenser, the "Nameless" steward's department. -all B -T triumphs. But, if it is the operator's intention The B -T "Counterphase-Six." Three stages of radio frequency,-only two tuning to stick at radio, and he tires of ship dials,-sharp, selective, sensitive,-requires only a short indoor aerial for distance work, in order reception,-the to land a trick at a shore "Counterphase-Six" is truly the climax of our achievements. station we suggest here and now Complete that set and kits for the home builder are both available. he get himself assigned See your dealer. Send for Illustrated Circulars. to a vessel that gets him back to headquarters very often. Flewelling Big companies have a way of forgetting Indorses B -T Sockets seniority and giving the man close at This noted radio authority says: "The standard tube sockets of your manutne- lure have so met the approval of my laboratory staff that we have decided to use hand a crack at the job. them practically exclusively." With the daily increasing volume of 'The only socket made that takes all Navy base and both large or small UX tubes without an adapter. Prive, 75c. Send for Circulars. traffic a coast station operator must not only be able to copy an infinite variety BREMER-TULLY MFG. CO. of fists, but must also be capable of ex- 532 S. Canal Street Chicago, Illinois erting his imagination. A knowledge of Morse telegraphy while not imperative is very often a valuable asset. The high-powered trans-oceanic sta- ARE YOU A SUBSCRIBER? . tions require operators who have special SEND $1.00 FOR A TRIAL SUBSCRIPTION TO "RADIO" FOR 6 MONTHS training and are usually recruited from (Continued on Page 74)

72 Tell them that you saw it in RADIO www.americanradiohistory.com 6 -VOLT "A" BATTERY Here is the rugged, good- looking Exide 6 -volt "A" Battery. One-piece case.

2 -VOLT "A" BATTERY Compact Exide for low - voltage tubes. Also made in 4 -volt size.

24-VOLT"B" BATTERY In glass cells, 6000 milli. ampere capacity. Also in 48 -volt size.

THE EXIDE RADIO POWER UNIT (Combination "A" battery and charger) RECTIFIER This unit is kept connected to your electric light socket as well Exide Rectifier for econom- as to the radio set. Raise the small switch on the end and the re- ical recharging of "B" Bat- ceiving set is ready for use; lower it and the battery is automatically tery from your own house placed on charge. Finished in rich mahogany color, the Exide current. Radio Power Unit is furnished in two sizes - one, for sets using 4 -volt tubes; the other for sets using 6 -volt tubes; retailing at $28 and $38 respectively- slightly higher west of the Rockies.

Range far and near with your radio set BRINGING in the distant stations, selecting the choice num- bers from local programs - in short, getting the most enjoyment from your radio set-is largely a matter of proper current supply. All the distance, volume, and clearness that an ample, uni- form supply of current gives to radio reception are yours when current is supplied by Exide Radio Batteries. There are Exide "A" and "B" storage batteries for every requirement, and a rectifier for recharging "B" storage batteries. xiôe See the complete line at any Exide Dealer's or at your favorite RADIO radio store. BATTERIES THE ELECTRIC STORAGE BATTERY COMPANY, Philadelphia Exide Batteries of Canada, Limited, 153 Duff erin Street, Toronto FOR BE, ER RADIO RECEPTION, USE STORAGE BATTERIES Tell them that you saw it in RADIO 73 www.americanradiohistory.com (Continued from Page 72) ship and shore stations. Limited com- mercial stations, such as employed by Radiola Portable large industrial concerns in communicat- ing between offices in different cities, Super -Heterodyne usually require an experienced operator. They handle a certain OWNERS : type of traffic, and a knowledge of typewriting is essential. -send for special No. 109 circular This is a valuable asset in any case and and get our sug- is often demanded of operators. gestion for protecting your Commercial tubes and operating has its oppor - watching your bat- unities. Ship operators are broadened teries. Good reception is by travel, and have what you ample time for self- want. improvement-or for losing money play- The Jewell No. 109 High ing poker if Resistance they disagree with Dr. El- Volt Meter Panel iot's fifteen minute a day theory. was designed for Radiola Many prominent Super -Het radio men started in owners. We make as "brass pounders," not the least known other instruments that can being the youthful vice-president be and easily mounted on other general manager of sets. the Radio Co, 'Ira- Order from Dealer tion, David Sarnoff. Broadcasting has opened up a new field for the commercial Send for 15 B Radio operator, but we regret Instrument Catalog the decline in w operators and the increase in engineers Jewell Electrical when this step is taken. Instrument Co. All in all it's a great game. Salaries 1650 Walnut Street - Chicago have never been princely for several reas- ons. Who can blame a student-even if he doesn't need the money-for spend- ing his holidays in this profitable man-' ner? It has often been referred to as a woman's ,Jvs,'Pu6/;shed trHOv.zD BE/NEYERY job. Some intrepid females have taken a fling at it, but they were Our New FA/VS L/BRARY few and far between. 56 Page If you want to make radio your life A'6'oioto/DE EEYóRB kihi work, don't for a minute think that the commercial end of the game is not worth a "Chockful" of data a n d ;t. Complete parts for latest trial. It affords a splendid take-off valuable information for model BEST SUPERHET- in soaring the heights RADIO ENTHUSIASTS. ERODYNE, new 8 -tube loop of this intriguing Trouble shooting chart. . 1. model, covering the range art. Latest released list of from 50 to 600 meters. \VR5 BROADCASTING STA prices for this circuit, includ- TIONS, and hundreds of ing ALL standard, exactly as RADIO VALUES specified by the inventors. THE LIFE OF A "B" law Be sure to get our prices WRS Prices Are Lower! Lt',t-sol*,iQit>A1 BATTERY WRS FIRST-you'll save money, Service Is get better value and better (Continued from Page 33) PROMPT, EFFICIENT, service. COMPLETE! Consequently it is safe to assume a life of EVERYTHING IN RADIO! RADIO $71.50 100 hours for GET OUR PRICES Wt1SALË5TRat three cells in series. Much OGNURGM WRS is headquarters for FIRST! All Standard Parts, Kits and greater life, proportionately, is actually You'll Save Money! Sets. Every Approved Cir- secured at the ampere so Be sure to write for cuit! / rate, that it Everything Fully Guaran. is true economy to Catalog CR10 Note that word "service" in our name. connect two cells in It is SATISFACTION INSURANCEI teed. Money -back Basis! your parallel for each 1 Everything you buy here-from bus bar / volt duty, giving a to the finest multi tube set le guaranteed with "money-baakl" You eceire one battery of six cells in series-parallel hundred cents' worth of value for EVERY dollar you invest at WRS. connection for sets using four or more such tubes. A.CHURCH S Except for portable sets, a storage bat- WHOLESAL T tery R.nOiO SE,Q vicE CO %new YORK, N Y, will be found more satisfactory as a source of filament supply for the larger tubes. This is also true, in the long run, in the case of B batteries.

In cutting off the power from a set, Notice to our Readers a "two pole" snap switch is advan- tageous, as it can be used to break one We have a few copies of the August, 1925 issue of "RADIO" side each of the filament and plate bat- tery, on hand. This issue contains Best's Super -Heterodyne fea- respectively, thus rendering the en- tire set "dead," if any work is to be ture. done on it, and as a good safety precau- Send 25c for a Copy tion, as well, when not in use. Worn out, or weak dry cells can be easily revived for short service by punch- Pacific Building "RADIO" San Francisco ing full of holes, and soaking in strong salt water for a couple of hours.

74 Tell them that you saw it in RADIO www.americanradiohistory.com NATIONAL Velvet Vernier Dial

National Condenser B National Type DX Type Velvet Vernier Dial Straight LineWave Length Type A (Patents Pending)

Recognizing the demand In addition, a new and ex- for a Velvet Vernier Dial clusive feature has been in- which can be readily mount- cluded. A variable ratio ed on any variable conden- having a minimum- reduc- ser, our engineers have tion of 6 to 1 and a maxi- developed this new design mum of 22 to 1 may be

embodying the ' same me- obtained instantly by simply chanical drive as the con- shifting a small lever. Thus ventional Type A Velvet the user may select the par- Vernier Dial (Patents pend- ticular speed best suited to ing), and retaining its vel- local conditions. vety smoothness of opera- tion and freedom from back lash. '29r

National Velvet Vernier enthusiasts now have the option of the more conventional type A dial or the new Type B. List price of either A or B, $2.50

Use genuine NATIONAL Dials, Condensers and Tuning Units for they give supreme satisfaction

Write for Bulletin 107R

NATIONAL CO., Inc. W. E. READY, President National Tuning Unit 110 Brookline St., Cambridge, Mass. National Tuning Unit Type BD -2 Type BD -1

Tell them that you saw it in RADIO 75 www.americanradiohistory.com COIL EFFICIENCY (Continued from Page 24) degree. The coil has a comparatively AMPLIFIES! BEAUTIFIES! CLARIFIES! high distributed capacity and a high natural wavelength, and hence it is not Burns 66MEIL-0-7I°®NE99 Loud Speaker suitable for circuits in which a wide "Floods the Home tuning range is required with a given with condenser. This coil is a mean in all Mellow -Tone" 10 Days Trial respects between the single layer sole- Absolutely FREE noid and the three -banked wound coil. The Single Layer Solenoid Great Acoustic This case has already been considered in the illustration above. The L/1 ratio Achievement found was 142.5, the radius of the coil was 4.77 cm., and the number of turns required was 38.8. The diameter of this coil is very nearly equal to 3.75 inches. Super- The advantages of this type of coil are Sensitive that it is easy to design and to vind, Unit that it has a fairly high inductance to resistance ratio, and that it has a com- paratively low value of distributed cap- acity. The disadvantages are that it re- Send quires a large space and that its external 75C.i_.; ari t magnetic field is large. NO Plug I The Lorentz Coil (Basket weave) Money This is the particular type which has been given the name of "low loss." The L/1 ratio of it will show to what extent it ARVELOUS Super -sensitive Unit. Famous electro -magno coil construction with PRECISION adjustor to is entitled to the appellation. There are regulate reception from faintest whisper to thunderous VOLUME that will fill an auditorium. Stands 22 lnehes high. Bell is 14 inches and made of lustrous jet black Pyralin, in graceful flower petal design. different modes of winding this coil, What a beauty it is! Worthy of the finest homes! The sound conduit is polished almsi- and all look very much alike unless the num, non -vibrating, non-resonating-eliminates hush, raspy sounds. Mounted on swivel 50 -swings smoothly in all directions. A $50 Speaker in construction and appearadce. $ windings are examined very` closely. OUR PRICE For the purpose of obtaining the L/1 Send NO money! Pay NOTHING to postman! 10-daytrial FREE! ratio certain assumptions as to the mode 7 wo Generations We want you to SEE! to HEAR! to ENJOY it!-before pay - of winding were made, the coil was re- of Honorable Dealings ing a cent. If satisfied after 10 days' trial, you may pay cash, or on our Nationally Famous Charge $ A duced to the equivalent single layer sole- Account `$1 Payment Plan WEEKLY or_ 4 Month noid, and this was given the best shape. ASHINR TO OWN the Burns "MEL-O-TONE" Loud Speaker is to first 1 give friends and family real ENJOYMENT when listen - The assumption made was that lug to Importers and National Mail Order House broadcasts. It amplifies CLEARLY, FAITHFULLY, the coil was so wound that three turns I SWEETLY, the beautiful strains of the violin; stirring airs 365 Washington St., Boston, Mass. of bands; snap and pep of jam music; thrilling notes of occupied the axial space that two turns Largest Distributors of "MEL-O-TONE" opera singer; natural inflections of the orator; delightful would have occupied in a single layer Loud Speakers 1 richness of concert music. We have sold hundreds to "fus- For prompt attention address Radio Dept. 110 siest" Radio Fans-and they are delighted with the Burns solenoid; that is, that the turns per centi- "MEL-O-TONE" Speaker! Gentlemen: Please send me $22.50 Burns meter was 15 instead of 10 and that "MEL-O-TONE" Loud Speaker with 75e Eminent Radio Scientists endone the Horn plug included FREE. I enclose NO money, Type Loud Speaker. The curved throat and there was no change in the conductivity and pay NOTHING to Postman. If I am NOTE wide mouth produce concentrated volume. di. satisfied after ten DAYS' TRIAL, I have ruction's( volume, greater volume, than the per turn. It was also assumed that the the privilege of paying cash or at the rate Nonhon type which diffuses volume. Try the Burns and meshes were such that the angles were of $4.00 monthly. Otherwise, 1 shall re- test the truth of this FACT yourself. turn it. 150° and 30°. The kinking of the w: e NAME _-...._...._ Yours Today! Send increases its length and hence decreases ADDRESS ORDER NO Money! This the L/1 ratio, and the amount of vari- Amazingly Liberal Offer ation in the length of the wire depends Please write PLAINLY! Tear this coupon for Limited Time Only! on the angles of the meshes. out NOW! If you wish to tell w something Send Coupon Now! about yourself, it will be appreciated. The value obtained for the L/1 ratio Radio 11-25 was 155.8. This, however, neglected the decrease in inductance caused by the sep- CARDWELL TORO -IRAN aration of the turns in the meshes. This decrease is considerable, but is too dif- The ideal inductance FREE Radio Catalog L aride ficult to calculate: The ratio is there- Allen D. Cardwell Mfg. tuft of newest Ideas, over 100 latest hook- fore larger than it should be and it is Corp. uppee laves you as much as half on a set. Shows standard radio parts, kite, sets at 81 Prospect Street big savings. Be sure to get this thrifty probable that if account were taken of book before you buy. Also please in - Brooklyn, N. Y. elude name of radio fan. this decrease in the inductance that the BARAWIK CO. Icetco°o'o ssk: L/1 ratio would be reduced to equality with that of the single layer solenoid. The number of required was You Can Get turns 4.43 RADIO from Factory to YOU Greater Redea or Cr,.isl and the radius of the equivalent sole- Set Reception if you use noid was 3.64 centimeters, or the di- Get our list price on Parta also the Knocked Down 1 and 3 Tube Sets BROWNLIE ameter required was 2.75 inches. Compare List Price with others then The advantages of the I *rentz type to per Cent Your Price Vernier Detector Deduct 20 50 of coil, if any, are low cap- A. C. HAYDEN CO., Brockton. Mass. $2.00 at Your Dealer or Direct distributed ROLAND BROWNLIE & CO. acity and the absence of solid dielectric 22 Saunders St. Medford, Mass. in the field. The disadvantages are dif-_

76 Tell them' that you saw it In RADIO www.americanradiohistory.com ficulty of winding, lack of mechanical strength, and inconstancy of inductance. The Spider-Web "Low Loss" Coil Increased Sensitivity, Selectivity This coil is about the same as the Range previous "low loss" coil except that it is and Distance wound in pancake instead of cylindrical fashion. The meshes are assumed to have the same angles, the number 01 HAYNES R. F. UNIT turns per centimeter is the same, 15, and amplification to any the shape factor is the one which gives Now you can add radio frequency greatest inductance for a given length of set with positive assurance of a marked gain in sensi- wire. In this case this is given by the tivity, selectivity, and distance. relation c=.75a, in which c is the radial depth of the winding and a is the mean COMPLETE PARTS FOR A New System radius of the coil. The L/1 ratio is THE R. F. UNIT $10 of R. F. Amplification 156.7, the number of turns required is 1 Haynes -Griffin DX Condenser .00023.-$ 3.50 Simple, practical and highly efficient. The 42.7, and the mean radius is 3.8 cm, or 1 Haynes -Griffin Socket 1.00 is and inexpens- nearly 1.5 in. 6 Hard Rubber binding new Haynes R. F. Unit easy Posts .30 in the original The properties of this coil are about 1 20 Ohm Rheostat .75 ive to build. No changes 1 .002 Fixed Condenser .40 required. the same as those of the Lorentz coil. 1 Special R. F. Choke wiring of your set The L/1 ratio seems to be slightly larger Coil 1.20 1 Special Antenna Regarding the results obtained with the but in view of the fact that some of the Coupler .. 3.15 1 3 -inch Dial.. .. .50 R. F. Unit, Mr. Haynes says: assumptions are only approximate it ma) 1 7 x 10 -inch Hard Rubber Panel (Drilled) .95 be regarded to be the same. As in the Bus Wire, Solder, Lugs, "Stations which are absolutely inaud- Lorentz coil, the ratio is a little too Etc. .20 the ordinary set alone, come Total ...... $11 95 ible on high for the same reason. 'Phis coil has in clearly and distinctly when the R. F. Special $O the additional advantage of greater com- combination price Unit is used ahead of the receiver." pactness, and it is also possibly mort rugged. Mr. Haynes' New Booklet The Flat Pancake Coil on the R. F. Unit In this case each turn is a perfect Discusses the R. F. Unit and radio fre- circle and all the turns lie in the same quency amplification thoroughly in simple, plane. The turns are wound 10 to the non -technical language. How to build and centimeter in the radial direction. Tht operate the R. F. Unit ahead of the super- L /1 is 141.8, the mean radius is ratio Browning Drake, Roberts, and 3.32 cm, and the number of turns 37.3 heterodyne, sets. An ideal method of There is practically no difference be- other popular / tween this coil and the single layer sole- coupling the "Super" to an antenna, // noid, except that it ocupies less space. giving a distinct increase in ampli- / R-11 fication and selectivity. / The Standard Coil HAYNES- Complete with schematic and / GRIFFIN This is the single layer coil wound RADIO pictorial wiringdiagramsg / SERVICE, Inc, on a regular twelve sided form such as / and photographs. Send / 41 West 43rd Street is used for the standard coils at the foryour copy now. Use / New York, N, Y. II l S. Clark St., Chicago Bureau of Standards. The turns are Price the handy coupon. j I enclose 20e. Send me a not spaced, however, like these turns on Per Copy 20c copy of Mr. Haynes' new book- the standard coils, but are close wound /let on the R. F. Unit. The inductance has been calculated on HAYNES-GRIFFIN RADIO SERVICE / Incorporated the assumption that the inductance o' / Name the polygonal coil is equal to the induc- 41 West 43rd St., New York, N. Y. // tance of the circular coil which has a 111 S. Clark St., Chicago, 111. //Addrert radius equal to the mean of the inscribes and circumscribed circles of the polygon, the turns remaining constant. It is this THL mean circular coil which has been given the shape ratio of 2.46 to give greatest ntennáphöïïë, ZILTRA--LOiTiLOS5 inductance for a given length of wire. IMPROVES RECEPTION LO cop CONDENSER wonderful results witii dives PLAT ES DISTRIBUTE THE STA- The length of the wire is the perimeter set. Not attached to, but mere- SPECIAL CUTLASS any radio EVENLY OVER THE DIAL SIMPLIFIES of ly placed under the telephone. Price One TIONS the twelve sided figure multiplied by insulatedY wire and 'TUNING. CAPACITY 0005 MED Dealer or the number of turns. The calculation simplesi instr1thAtouructions ss.00 Mailed C.O.D. on 3 days approval. gave a value of 141.7 for the L/1 ratio, ANTENNAPHONE CO. PHENIX RADIO CORP., 116-F East 25 St.,N.Y.C. New York Ctty which is only slightly less than the ratio 90 West St. for the single layer circular solenoid. The radius of the circumscribed circle is 4.85 cm and the number of turns is 38.8. & BACK COPIES OF "RADIO" Single Layer Coil of Square Section AUGUST With Best's Super -Het. Articles. In this case also the mean cylinder Both for 50c. between the inscribed and the circum- SEPTEMBER "RADIO" : SAN FRANCISCO scribed was given the best shape. The inductance was calculated by two dif-

Tell them that you saw it in RADIO 77

www.americanradiohistory.com ferent methods, both of which gave sub- stantially the same results. The first was by considering the mean cylinder and the second by employing the formula for a square coil. The L/1 ratio was 125.0, the length of the side of the square was 6.9 cm, and the number of turns was 50.5. The D Coil Much praise has been given this coil from time to time. It is usually stated that its inductance is 50 per cent greater than the inductance of the single layer solenoid of the same number of turns and diameter of tubing. The infer- ence is that the coil is 50 per cent more Why Resistance Coupled Amplification? efficient than the simple coil. This is not true, for the D coil is about 25 per cent less efficient than the single layer solenoid. This is due to the fact that the increase in the required amount of wire is greater than the increase in the inductance. In the single layer solenoid the length of one turn is equal to 3.1416 times the di- ameter. In the D coil the length of one turn is two diameters greater, since the wire crosses over from side to side twice for each complete turn. There- fore the length of each turn in the D BECAUSE this method of amplification is the only way to procure quality of coil is 5.1416 times the diameter of the tone without the slightest distortion. The Haven Super Amplifier can be con- winding form. This makes the total veniently put into any existing set. Use it also in the new set you are going to build. length of the wire in the D coil about To increase volume 50'c and have no distortion use Haven High Mu Tubes in 64 per cent greater than thg length of resistance Coupled Amplifiers. Prices-High Mu -20, $4.00. Mu -6 (for last or out- the wire in the simple solenoid. But the put stage), $5.00. .Hail the coupon for complete information inductance of the D coil is never more than 55 per cent greater than the in- !le i2tte o/ llevi ductance of the simple coil, and there- Th fore the percentage is against the form- .DAVE Ni \,RÀpf lfi^\C 0 P 0' \A'ti/Ú er. The 55 per cent increase is for very s/ot Spoc ale short D coils; for coils of approximately 'es ils the same length as is required for Newark Reg. C. S. Pat. Or. New Jersey the best shape ratio in the single layer sole- DA\EN RAUCO CORPORATION A -11 -TS 1St Summit Street, Newark, N. J. noid, the percentage increase in the in- Please bead me the following: ductance is only about 33 per cent. A Re...tor 30e a Get the Hand. Manual, i. enclosed. practical D coil would fall somewhere Complete Catalogue (tree). beak of Resist- between these two values. Coupled ance Name In the coil calculated the shape ratio Am plif i cation - At Dealers. S. Addict. was 3.33, giving an inductance increase By mail, 35e. of 46.5 per cent. This gave an e/1 ratio of 111.7. The required number of I w /l vale e. "eud lour Irttrrbead and we w tl! ha. e our nears t Ji.tnbulor eemmuu.eate w.th lou. turns was 29.4 and the required radius was 4.9 cm, or a diameter of 3.86 in. THE BIG LITTLE THINGS OF RADIO The main advantage of this coil is that it has a very small external magnetic field. The main disadvantage is the Vrrmiu' difficulty of winding it. 5TUBE Get a The Astatic Pair of Solenoids An astatic pair of solenoids are two Phonograph Unit single layer coils of equal inductance .411 placed side by side with their axes paral- Before Neu deride ao a radie et any kind at any pries. FREE lel and connected in series aiding, or so bee the new Premier S Tubs ta.emble. A templets Ensemble of genuine Premier part. I not a kit) already fields With only one subscription to that their in space are in opposite attached to panes of genuine black walnut grained directions; that is, so that the external Bakelite. selectivity! Dt.tanre! Superb ;mepsion ! Does "RADIO" for one year-$2.50. anything any bet at three r four times Unit is made by The Union field of the one is in the same direction its price ran do. It i. today'. uu- Fabric Company. as the internal field of the other. No matehed radio value. See your deal

78 Tell them that you saw it in FtA131O

www.americanradiohistory.com mutual inductance between the two when placed about 1/8 in. apart was Every Precise Instrument is a Laboratory Product equal to one twelfth of the inductance of one of the coils. Measurement of the mutual checked this result very closely, more closely, accidentally, than the ac- curacy of the measurement or the as- sumptions warranted. Nevertheless it gave two legs to proceed on. The re- sults will, of course, be somewhat dif- ferent when different shape ratios and PRECISE separations between the two coils are Supervize No. 480 used. Two cases will be given, one Audio Transformer which more nearly represents the theor- etical result and the other which more nearly represents the measured coils. In the first case each of the two sole- noids was given the best shape ratio, and the inductance of each was taken as 76,200 centimeters. This gives an inductance of 165,000 centimeters when the two are properly connected in series. The L/1 ratio obtained was 119.1, the A PRECISE Transformer required number of turns on each half was 30.0, and the radius of each was for every ratio 3.68 cm, or the diameter was 2.9 in. This coil is more efficient than the next THE Precise Line includes the most complete one, but it requires too much space and is line of transformers in the world. There is a not convenient. It requires a baseboard Precise transformer for every ratio and purse. space of 2.9 in. x 6 in. The second case was a pair of coils The new No. 480 Supersize Audio Transformer is each of which had a shape ratio of unity, the latest addition to the Precise Line. It is de- that is, the length of the winding was signed to bring forth with magnificent volume and equal to the diameter. The same sep- perfect shading of tones, the deep toned bass or aration between the two coils was used, the high, clear soprano. Mr. James L. McLaughlin, and also the same mutual inductance R. E., the noted superheterodyne authority, specifies was assumed for lack of something more the Precise No. 480 for his new One -Control Re- definite. The L/1 ratio obtained was ceiver. Ask your dealer to show you the complete 112.7, the number of turns on each half Precise line. was 48.3, and the required radius of each half was 2.42 cm, or a diameter Ne. 285 of 1.9 in. Although this is not quite COMET The Original Type 285 so efficient as the previous coil, it is Ratio 3% to 1 Transformer much more convenient and requires less Price. 83.25 Ratio 4% to 1 baseboard space. The shape of this coil Price, $5.00 was very nearly equal to the shape of Rochester, New York the measured coil. Branch Offices: 126 Liberty An astatic pair is much easier to make St., New York City 454 Builders' Exchange, Minne - than a D coil, and it appears to be some- 53 W. Jackson Blvd., Chicago, spolia, Minn. Illinois 1127 Pine Street, St. Louie, Mo. what more efficient. Like the D coil it 821 Market St., San Francisco, 701 A. O. U. W. Bldg., Little has a small external magnetic field. California Rock, Arkansas Canadian Distributors: PERKINS ELECTRIC, Ltd., The Toroidal Coil of Circular Sec- Toronto-Montreal-Winnipeg tion This is the doughnut coil. It is the most efficient of the toroidal coils for ARE YOU A SUBSCRIBER? SEND $1.00 FOR A the reason that each turn is a circle. TRIAL SUBSCRIPTION TO "RADIO" FOR 6 MONTHS There is an accurate forinula for the inductance of this type of coil, namely, t L=47rN2 R2-r2) RASLA in which L is the inductance in centi- FIXED meters, N is the number of turns, R DETECTOR the mean radius of the ring, and r is the radius of the cross section, or of each turn. The length of the wire is -given by 1=27rrN. mot FROST -ammo PAN-TAB This coil has a best shape, 12 OR louder, clearer reception with that is, a your reflex set, go to your near- JACKS ARE BEST shape which gives the greatest inductance est dealer and ask for the RASLA for YOUR RADIO sep, Fixed Detector. Lists at only $1.25. SET for a given length of wire. The condi- The finest radio jacks panelhung made, for either tion is that r=.5205R. When this con- Write to the Davidson Radio Corpo- assembly or usual Installa- ration, 222 Fulton Street New York tion. At your dealer's 65e to 90e 1iet. dition is put into the formula for in- City, N. Y., for the FREE ductance this becomes 1Rasla Book of Hook-ups e HERBERT H. FROST,Inc. 314.324 West L 3.53rN2=165,000 cm. Superior Street Chicago

Tell them that you saw it In RADIO 79 www.americanradiohistory.com The number of turns on the coil is There's Economy given by N=2irn(R-r)=57.8r, since n=10, being the number of turns per Bare Necessities and Satisfaction centimeter. Solving these equations, in these Valley units the L/1 ratio turns out to be 78.3, the number of turns required 139.3, the You will find both economy and satis- radius of the cross section 2.41 cm, and faction in the use of the Valley B - the radius of the ring 4.63 cm. This Eliminator and the Valley Battery coil is not very convenient since the Charger. overall diameter is more than 5.5 inches. Economy in the B -Eliminator because The Toroidal Coil of Square Cross it stops forever the expense of buy- Section ing new B batteries. . . This coil is similar to the doughnut the charger because it coil, is not quite so efficient. The HOYT z inch Economy in but A er B Battery recharges your own storage battery formula for the inductance of a toroidal Voltmeter Type 17 at home overnight at one -tenth the coil of rectangular cross section is L== Moving Coil cost of service station charging. . . 2hN2logR/r, in which h is the axial Action And satisfaction in both because, by length of the coil, N the number of a turns, R the outside radius, and r the car will run without an using them, you need never miss Your program on account of low or worn- inside radius. Of all the toroidal coils ammeter, oil gauge or speedometer. out bat- having a rectangular cross section the one But would you care to run it in that teries. having a square section is the mist ef- way? At any moment electric cur- ficient. In order that the sectic f be a rent might fail, bearings burn out, square the value of h must be equal to As in the case of the dough- gasolene give out, all without warning. (R-r). nut coil, the rectangular sectioned coil set with- When you run a radio has a best shape. The condition is that out the positive knowledge of its the ratio of the outside radius to the condition and operation, that can inside be equal to the square root of the be given only by the use of meters, base of natural logarithms, or very this con- you are taking just the same nearly that R=1.649r. When dition is put into the formula for induct- kind of a chance. You may damage THE VALLEY B -ELIMINATOR operates from ordinary light socket; provides ance it becomes simply L=hN2, or if your set and its accessories irrepar- a steady, noiseless flow of B current the section is square, L=(R-r)N2= ably without a moment's warning. at a constant voltage all the time. .649rN2. The first automobiles were sold With it, there can never be any de- The length of the wire in the coil without full equipment - because crease of signals or frying noises due is given by 1=4hN=4(P -r)N. Hence the public had not been educated to to low B batteries. Volume is main- the L/1 ratio is simply equal to N/4. good. of turns that can be put demand it. tained. Reception is uniformly The number on the form is given by N=207rr. Solv- Radio sets have been similarly For receiving sets of from one to eight tubes. Costs less at the start ing the equations for the unknowns gives sold. But as the public becomes and than wet B batteries. Costs less in L//.63.0, N=252, Rí.61 cm, demanding di- more educated it is the long run than dry cells. Much 7=4.01 cm.This coil has an overall in., and is meters. more sat- ; ameter of approximately 5.25 therefore about as inconvenient as the KEEP AHEAD OF THE TIMES isfactory coil. TROUBLE IN YOUR than doughnut AND external characteristics of these HOYT METERS. both. The RADIO WITH two coils are alike. They have no ex- magnetic field, and that fact is Our book " HOYT METERS FOR RADIO" shows ternal the complete HOYT line of Radio Meters. Send for it. their only advantage. This makes it possible to use these coils in crt vded of undesirable Burton - Rogers Company places without any danger between the several coils, or be- 26 Brighton Ave. - Boston, Mass. coupling the coils and other parts of the National Distributors tween circuit. Taken by themselves these coils half as efficient as the THE VALLEY BATTERY CHARGER 1S are only about it is con- the only charger needed for all radio single layer solenoid, but when eddy currents storage batteries. Its correct 6 -am- sidered that losses from are practically pere charging rate makes overnight in adjacent metal parts of an external M M LowLoss charging a possibility. eliminated by the absence efficiency in a crowded set The Valley Charger also functions field, their INSULATORS is more favorable. Eddy current losses on any lamp socket. It takes about be considerable in an open coil like a dime's worth of current for an may hpl!I!19!e19UU!NmNie the single layer solenoid when this is Perfect your entire instal- average charge. Quiet in operation. your placed in a wrong position with respect lation by insulating Valley wows. antenna ground system. Most radio dealers handle the to shields or condenser plates. No Your set is not responsible B -Eliminator and Valley Charger. posi- for energy lost thru a poorly insul- special arrangement of angles or Use M & M Low -Loss Any one of them will be glad to ated aerial. tions is necessary with the toroidal coils. Lead-in and 'Wall Insulators. show you these units and explain Lead-in Insulators-d in., 50e; 10 in., The D coil and the astatic pair come 80; 20 in., $1.50. Wall Insulators - their advantages. ' about half way between the toroidal 5 in., 60e. Radio Division Dealers: If your jobber can not sup- the open type of coils, both with re- ply you write us direct, giving us VALLEY ELECTRIC CO. ST. LouIs, L'. 8. A. and your jobber's name. Send for catalog. Branches in Principal Cities spect to efficiency by themselves and with respect to the intensity of the ex - The mil Co Valley Electric ternal field. CLEVELAPID.OH10. Tell them that you saw it in RADIO 80 www.americanradiohistory.com In the accompanying table the induct- ance to length of wire ratios of the sev- eral coils have been arranged in the order of their values. The first column gives the name or type of the aril, the second WEBTON the L/1 ratio, the third the percentage of efficiency based on the the L/I ratio for the single layer solenoid, and the FOR RADIO fourth the percentage of efficiency based The Famous Instant Champs on the L 'i ratio of the three banked Radio Part, bOc. wound coil. This 2 -inch vo'tmeter for acc;i- rate co.itrol of tul)e and bat er s ai Ituw YostN i06 rro-.ncA Radios voltages as ure.: mos effectuc et c. O Passer Yotswssr :f operafon an I longe -t hoe fro.: 1 the equipment. Because of its high internal re-istance, 125 ohms per volt, the drain on the "A" batery is !.J insignificant. This is a specially important 3 feature si when dry cell tubes are used. The Instant Change Plug Three Rank Wound .206.0 144.7 100.0 gives rapid and sure shift from headset to loudspeaker. Two Rank Wound 178.0 125.0 86.5 Spider Weh Low Loss 156.7 110.0 76.0 Send for a cotnplimentary copy of Lorentz Low Lose 155.8 109.3 75.6 "Weston Radio Single Layer Solenoid 142.5 100.0 69.2 Instruments" dc - Pancake Circular ... 141.8 99.5 61.8 scribing the Weston Radio line. Standard cod 12 sided 141.7 99.4 61.7 Square Single layer.. _ 115.0 17.7 60.6 WESTON ELECTRICAL Asiatic Pair Short...... 119.1 13.6 57.1 Asiatic Pair Long...... 112.7 79.0 54.7 INSTRUMENT CORPORATION t) Coil Medium length..._ 111.7 71.4 54.2 156 Weston Avenue, Newark, N. J. Torus or Doughnut .... 71.3 55.0 37.0 Pacific Coast Office: 682 MISSION Sr., Toroitl of Sq. Section...... 63.0 44.2 30.6 SAN FRANCISCO

STANDART) THE WORLD OVER A concealed loop can often he mounted on the back of the frame of a picture, hung on a wall. This can't he swung tl*round, but sometimes help when WEST will (9ionccrs srnce 1888 fnrq tnetr and concealment is a factor. Hurd ('nmte----.- t wnt! Splits a Single Degree Into Hair's Breadth Divisions

You'll never know how much difference a dial can make until you get this new MARCO dial in your set. Without the least suggestion of backlash, it responds instantly to your slightest touch. Smooth -working, handsome, supremely accurate, it's typical of MARC() And you keep a record of dial settings in the two slots -right on the dial

itself I

Nickel Plated. $2.50. Gold Plated. $3.00 Martin -Copeland Company Providence, Rhode Island TAIs Is the dial apn-«s 411 Ise McLt+risAlia sdnRle-eoMrol supsA.rwodTwa dtreribed M Mu tiare.

www.americanradiohistory.com BUILDING FOR THE FUTURE (Continued from Page 28) denser should be kept as far apart as pos- sible and away from the audio trans- former. Since this is a regenerative set, a sen- sitive detector tube must be used. The this grid return of the detector in Fig. 1 is season shown to A Plus as is usual with "hard tubes" of the 201-A and WD -12 type. With the grid return to A-, a loss of sen- DURHAM sitiveness may be felt, but 'a much smoother regeneration control may be Variables had in many cases. With a soft tube, and the Sodion D 21, used for detector, Panel Mount Bring control of the grid return should be to A-. Some $1.00 writers stress the necessity for removing detec Fr but Standard high resistance the bases of tubes used for the necessity does not seem apparent in 75c to the panel a set of the construction in this article. Trumpets A fixed grid leak, usually 5 to 10 meg- ohms, with the hard tube for a detector, I_TrirI _ - rosww, 10- tef _I should be chosen in preference to lower Timbre of brass and as a rule. Short lead Note values, thunder of trombone! to grid patent A first-class ground connection is es- Out over mountain and plunger sential for the set, otherwise "hand ca- Both types in be abominable. One three softest pacity effects' will prairie, through storm Always a one -finger control is to tune in a e100-1000 finger ends test of a "good" ground is car- to 100,000 and now at your set, then and sunshine, it ohms. -that's the new DURHAM faint signal on a regenerative ried on the waves of the e101-0.1 Variable. The familiar ease touch the ground post with a moistened megs. to 5 stand- mega. and accuracy of these finger ; if a perceptible change in tun- air from the steel towers e201A-2 ard high resistance units in needs improve- megs. to 10 may be ing occurs, the ground of the broadcast station. megs. their latest form more es- placed anyhere on your ment. A good ground is even And in your home it panel, preferably near the sential with the short wave set than wit1 rings out clearand strong tube they control. Only a a 200-550 meter set, since the tuning lvt hole required. For most the low wave set is very much sha -held fast to all the hook-ups, you'll need two glues DURHAMS-detector and With a poor ground, if hand capaci purity of the original by audio. fects are present, one must sit "jus an,da the marvelous power of or a signal once tuned in will be Look for the plunger a dial. Rauland -Lyric. when the hand is taken from the Either a "grounded rotor" type v The patented DURHAM the combination of sliding plun- able condenser should be used, or ger and non -wear compound variable condenser should be shielded in is your protection and guar- the usual manner, by sticking foil to the high re- antee for accurate inside of panel and connecting this foil sistance control. This style to the ground post. The foil must be fits any around the m_ anting Clipped Dealers: Get This cut out generously condenser screws and shafts of the variou,instru- 75c or Order from jobber now ments. DURHAM type, panel variable con- Bases, specifying Note that rotor of the 30c -45c mount and standard. denser is connected to filament. Con- as indi- DURHAM ed CO.,Inc. necting this filament to ground 1.936 Market St., Philadelphia cated by the dotted line in Fig. 1, thus making "conductive coupling" is gener- ulullnlnit ]alalllllaltllllalllllllelaaaaaatlalduaalt7Y1lllpAltlllaalllBlt as Rauland -Lyric is a laboratory. ally better than "inductive coupling" grade audio transformer de- by omitting the dotted line con- signed especially for music made l overs. The price is nine dollars. nection. Descriptive circular with am- iöjäo Dealers, or plification curve will be mailed A "straight line wavelength" on request. All-American / line frequency" variable con- Radio Corporation, 4201 Bel- ANTED "straight mont Ave., Chicago. If you are the type of dealer who hustles denser has many advantages over the who isn't content to wait type, after business, to more usual straight line capacity for trade to come in but who takes sets out demonstrate, can talk and sell quality merchandise, in that the tuning range is more spread and knows Radio values, we have a big proposition that dealer? out on lower dial settings. for you. Are you of the 50% Discount to Dealers Since this is modernized version of high-grade re- the tuning \V a manufacture a complete line "standard regenerative set," .eivers and sell to dealers at 50% discount. We are The variable condenser is distributors for more than 225 Nationally advertised is the same. Pte,- lines. varied throughout its arc, while the ro- Write today for amazing offers, new t. rued with the AMERIC44, 112 -page catalog and regular monthly tor is simultaneously TRANSFORMER catalogs quoting below - the - market other hand so that a rough hissing sound prices on latest merchandise - all "grunting," The Choice of Noted Music Critics free. Everything in Radio for less. just short of a more violent American Radio Mfg. Co. "clicking," or "squawking" sound is 1422 McGee Street Kansas City, Mo. heard in the phones. It is regrettable www.americanradiohistory.com that this method of tuning is bound to cause some interference to others receiv- e clear tone ing on the same wavelength, but with of 9he Amplion so few using low wave sets as compared comes from to those using 200-500 meter sets, the 30years' experience interference is almost nothing. When ting loud speakers distorted music is heard, turn back tickler and make small adjustments of dials until music is clear. If a coupler which does not permit full rotation of the rotor, or a so-called 180 degree coupler be used, care should be taken that the connections be made of rotor leads as shown in Fig. 1; with . all windings in same direction, maximum regeneration is then had when the rotor windings are turned to parallel those of the stator. An infrequent source of trouble in "home made couplers," is the winding of the two halves Distinctvoicing ofcommands at of the rotor sea is vital! At left, one of the winding in opposite directions. If the naval loud speakers produced by the Amplion organization windings are all properly made, a raising and installed on over 12,000 or lowering of A ships of leading navies and ship- and B voltages, in- ping companies throughout the crease of turns on the rotor, a different world. detector, or a different grid leak may produce the desired regeneration. LL who hear the Amplion are won by its wonderful clearness and deep, full, EXAMINATION FOR life -like tone -qualities which have made JUNIOR RADIO ENGINEER it the world's largest -selling loud speaker. The U. S. Civil Service Commission an- The explanation is that nounces that applications for an examina- The Amplion was evolved tion for the position of by the actual originators and oldest producers of junior radio engi- Clarity is also essential to full neer will be received at Washington until loud speakers.* Long before radio attained general enjoyment of radio. Thirty years' November 14th. The entrance salary popularity, experience in creating loud speakers, is Graham loud speakers had been unrivaled for clearness of tone, $1860 a year with advancement to $2400 without adopted-because of outstanding excellence-by evolved The Amplion. Ask to hear change of assignment. The examin- the exacting the improved new Amplion Dragon, ation is to fill vacancies in various branches British Admiralty and naval experts AR-to, illustrated above of the Government service throughout the of other nations. The Amplion, introduced in 1920, United States. Appointments to positions was based on thirty years of successful experience. formerly known as "radio inspector" in the The supremacy of The Bureau of Navigation of the Department of Hear The Amplion in comparison with any or all Amplion has won world-wide Commerce, will be made from this examina- other radio reproducers. Let your ears tell you recognition and leadership in tion. why sales. Partial list of nations in The duties of this it is so widely known as "The world's finest position consist of such loud speaker." which Amplions are ruling work as routine testing, performing field Amplion Loud Speakers, $12 up. favorites among music -lovers: work, assisting in conduct of experimental Phonograph units in two sizes. Interesting litera- research - UNITED STATES tests, compiling reports, handling ture and dealer's address on request. DOMINION OF CANADA technical correspondence, and other related ENGLAND work. Competitors will be rated on general THE AMPLION CORPORATION OF AMERICA SCOTLAND WALES physics; pure mathematics; practical ques- executive Offices: Suite 0, 280 Madison Ave., New York City IRELAND tions on radio engineering, Canadian Distributors: Burndept of NORWAY SWEDEN including ap- Canada, Ltd., Toronto DENMARK plied mechanics; "Alfred Graham & Co., London, England, Patentees and education, training, HOLLAND BELGIUM and experience. FRANCE SPAIN Full information and application blanks SWITZERLAND may be obtained from the United States Civil ITALY JAPAN Service SOUTH Commission, Washington, D. C., or AFRICA; the secretary of the NEW ZEALAND board of U. S. civil ser- AUSTRALIA vice examiners at the postoffice or custom- house in any city. AMPLION The 1926 Model &he?PJorldsStandard ud Speaker Radio World's f DIAMOND of the AIR Brand New Audio Hookup, by Herman The "Windham" Wire Former Bernard. See it in A Handy Tool for RADIO WORLD Electricians, Radio Fans and Mechanics 1I,e Fri al Notional Radio Weekly This rugged little tool not only makes accurate loops or 15e a copy All Stands eyes for No. 4, 6, 8 and 10 screws but will make either See Current Issue: sharp or easy radius right angle bends and the sharp Save,. Day.' Programs-Complete List of Stations cutter will cut the toughest wire as well. -Radio University: A Great Question Department-Newsy and Answer It is drop forged Trade Department-Service Ar- of the very best steel and carefully tem- ticles, With Diagrams, by Eminent Authorities- pered in oil. Everything for Novice and Expert. trued. Profusely illus Current Prices for Standard Sets and Parta. Retails for $1.25 $6 per year Dealers and Jobbers send (52 numbers) ; $3 six months; $1.50 for full information. Desirable territory still three open. months. SPECIAL: Send $1 for 8 issues. RADIO WORLD THE GOYER COMPANY 1493 Broadway New York City Willimantic, Conn., U. S. A.

Well them that you saw it in RADIO www.americanradiohistory.com 83 t.11L1+1 ¡MY"-JT:-v Tr ,jr VACUUM TUBE (Continued from Page 31) of any circuit for generating oscillations, that during that portion of the cycle of the output current when the grid is posi- tive with respect to the filament as a re- sult of the voltage induced in the coil Ls, the voltage drop between the plate and filament connections (across the CIIELSE coil Lp) is such as to oppose the voltage of the plate battery and hence to reduce hes ew eea the voltage acting between filament and ,,, plate e in the tube. During the other part of the cycle when the grid is negative with respect . ^: dl ' Il oilie to the filament, the voltage ti acting between plate and filament is in- i::6'.cYw,t creased above that of the steady voltage II Q11tnÌ INIÌ-141tiIV of the plate battery. During the portion e II{ of the cycle when aa the grid is positive Areec7uhe with respect to the filament, c ,frent RECEIVER i flows within the tube between the grid 526.º a and filament, and this current increases It \ as the grid becomes more positive. The Licenesd finder direction of the current flow is in the Armstrong Patent No. 1113149 direction of the emf, that is, from grid to filament inside the tube and from filament to grid outside The only genuine Arm. of the tube. trong circuit 3 -Tub e Further, as the grid becomes positive Set, at this low price, with respect to the filament, there is a with a dust -proof, fool- resultant increase in proof inside 1 the current flow panel. between the plate and Cord connections to 111i111, filament of the I. III batteries, no binding 1illIII tube, even though the plate voltage on posts and many other the tube is being reduced. This in- refinements. Op e r ates crease is limited when the stable oscil- on all standard tubes. lating condition For distance and real hás been reached, by tone quality, the equal the saturation effect, which may occur of many $100 sets. Super-)ive 1:50.2 at lower values of plate current than that corresponding to the total filament emission, owing to the loss of electrons Added There's no place like home with a to the grid. Chelsea. After supper, dishes done, Features The plate current wave is distorted the family gathers round the living Both of these at the other extreme of the cycle-that New room to enjoy the radio wonders of Chelsea. possess per- is, when the grid is negative-by recti- forming features and the air-never more delightful and refinements of design fication effects; moreover, the grid cur- only found in the satisfying than with the New Super- most rent is always pulsating, and may be expensive models, Each Five. Here, power and perfect living Chelsea is a manufac- zero for a considerable part of the cycle tured product-not an tone quality are combined with easy assembled while the grid is negative. Consequent- job-and is operation. Dependable, fully guaranteed. enjoyable re- Send for Folders ly, the waves of current suppl'-d to the sults are always assured. Describing AU Latest Chelsea' circuit between F and P, and 1' and G. Chelsea Branches Fig. 8, are each composed of a direct New York, Philadelphia, or average constituent, a fundamental Cleveland, Detroit, CHELSEA RADIO COMPANY constituent corresponding in frequency Chicago, Los Angeles 179 SPRUCE STREET CHELSEA, MASS. to that of the output current, and a num- 4Q3ere-1r%%':%%%%íii ber of higher frequency or harmonic con- :i1`-7icit`1v7 stituents. Speaking only in terms of the useful current constituents, a sinusoidal alter- ' ` AGENTS nating current flows in the grid circuit 110 t - = N E in phase with the alternating voltage =ir WA T D 5 Tube Demonstrator FRE E across the coil Lg, and therefore repre- Earn $25 to Itou e week, pert or full time. Potter Everyone sents a withdrawal of power from the a prospect. Complete line standard sets and accessories, BY- PASS $5 to $90. Write today for illustrated catalog and ex- output circuit, which power is expended clusive selling plan for live dealers and community CONDENSERS within the tube. agents. 20TH CENTURY RADIO CO., 1011 Coca Cola On the other hand, a Bldg., Kansas City, Mo. -Prevent "B" voltage fluctuation sinusoidal alternating constituent of -Allow undistorted amplification plate current flows in opposition to the -Make possible full bass tones voltage across the coil 1,0; this means -Improve reception with "B" that power is being supplied to the out- ARE YOU A SUBSCRIBER? Supply Units. put circuit from the plate circuit of the Send for Trial Subscription Made in /1,1-,i,1,2,3 and 4 Microfarad sties tube. The impedance of the output cir- At Your Dealer's $1.00 for cuit to all frequencies tha are har- Six Months POTTER MANUFACTURING COMPANY monic multiples of the fundamental is North Chicago, Illinois (Continued on Page 86)

R3 Tell them that you saw it In RADIO

www.americanradiohistory.com Radio Never Hada Tube Equal to EMPIRE -TRONS Every tube is a model of perfec- tion; finest me- chanical construc- tion, unequalled for clarity, sensi- tivity and perfect reception. Has been tested for 1200 hours' contin- uous operation. The Famous Truly Portable Satisfactory Performance TELMACO P-1 Receiver Guaranteed Four Tubes Do the Work of Seven Comparative tests The peer of portables in size, weight, ease of tuning, invited ---ask your selectivity, distance, volume, workmanship and price. dealer for an EM- Aerial, loud speaker and batteries self contained. Type '99 also PIRE-TRON and Complete with tubes and batteries, $125.00 Made in U.S.A. Receiver only . . supplied w i th hear the difference. $141.50 '01 base (all Superior Quality Tested in PI Kit Saves Yon Money: Bakelite). Priced Right Factory Our offer of the Telmaco P 1 Receiver In kit form has Our met with enthusiastic reception. This contains all parts, as built by us including case, drilled and en- Distributors and Dealers Wanted graved panel, and illustrated Instructions. $80.00 Some Choice Territory Still Complete kit Open dealer or write us. Descriptive folder free. Write for Circular and Particulars Ask your 'Radio 'Division: Telephone Maintenance Co. 20 So. Wells St. Dept. A Chicago, Ill. LOW LOSS jjality "Radio Exclusively oe Established 1918 LOW WAVE COILS In the Lead Again!-"REV" Basket Weave Coils now equipped with Plug-in Mountings-Quick, EMPIRE efficient coil changing-Five interchangeable units in each outfit-Triple cotton covered paraffined SPEAKERS wire-Chocolate color, won't soil-For any low - loss, low wave circuit-Covers 10 to 110 meters MODEL A and effielently-Inexpensive-Rugged-No increase in Bell 10 in. Price! Height 22 in. UNITS Price $4.50, including mounting. A beautiful line of At your dealer's, or order direct Speakers made of unbreakable compo- RADIO ENGINEERING sition handsomely LABORATORIES finished in rich dark brown, crystalline ef- 27 Thames Street New York, N. Y. fect. Very graceful "THE LOW LOSS COIL PIONEERS" and an ornament to any home. Brings out tone perfectly. Model "A": Bell 10 in., height 22 in., You Can Make $100 fitted with EMPIRE Adjustable Unit- retails at $13.50. Weekly Selling Radio Model "C": Bell 14 in., height 22 in., fitted with EMPIRE Adjustable Unit- retails at $16.50. MODEL C EMPIRE Adjustable RATIOS 314 TO 1-5 To 1 Bell 14 in. Unit; constructed Height 22 in. with greatest seien. No set is better than its parts and no tific care. Guaranteed one part is more important than the to bring out the full volume of any set- Audio Transformer. That's why you true and clear -toned. should insist upon Supertrans in your Retails at $6.50. set---they are by test, the best trans- "The Home of Empire Products" formers on the market. They speak for themselves. Distributed by Write for circulars and prices. L. W. Cleveland Co., Portland, Me. Demonstrate once-results c. P. Denham, Seattle, Washington Waite Auto Supply Co., Providence, R. I. mean sure sales! Sell what American Interna tiona 1 Trading Co. Gray Sales Co., Philadelphia, Pa. everybody wants-radio at low 59-61 Pearl Street, New York Rice -Hitt Co., San Francisco, Calif. prices. Coast to coast reception '. B. Darmstader, Chicago, Ill. -4, 5 and 7 -tube instruments. Cable Address: "Stanmarks, N. Y." 12 Whiting Radio Co., Bridgeport, Conn. Selling i 'aterson Radio Co., Paterson, N. J. Lessons i¡ R E E Buffalo Radiophone Co. Inc., Buffalo, Y Establish a business of your own. N. Start in spare time-evenings. The Jack L. Hunch Co., Denver, Colo. Sales course in 12 lessons and 10 FORD RADIO & MICA CORP. radio service lessons teach you 111-113 Bteerker St., N. Y. J. Matheson Bill, Pres. everything. 3100 Men Are Now Doing It! RADIOCAST Success with over 3,100 men proves merit of our proposit ion. $100 week I y not unusual-many Ozarka men make more in spare time! WEEKLY me personally-tell me Free Book! aboutWrite yourself. I'll see that my Forty-eight Pages of Programs, 64-page book, Ozarka plan No. 100, is sent you with- out cost. Please mention the name of your county. Photos, Humor, Re- Mail the coupon! Musical views, Schedules, Tables, Edi- i/YCORPORATEA t Z':t_ 120 Austin Avenue I.. Chicagollllinoia torials, Etc. r Gentlemen: 10-26 Per Radiocast Weekly ARE YOU A SUBSCRIBER? I am greatly interested in the FREE BOOK "The 5C Ozarks l'ion" whereby 1 can sell your radio instrumente. Copy 433 Pacific Bldg., SEND FOR TRIAL SUBSCRIPTION Name Address City SAN FRANCISCO $1.00 FOR SIX MONTHS L rotor State

Tell them that you saw It In RADIO 85

www.americanradiohistory.com (Continued from Page 84) very great, hence there are no appreci- able multiple frequency constituents of the current circulating in the output cir- effairCee cuit, and the alternating voltages across the coils Lp and Lg are in all cases prac- tically sinusoidal. Consequently the useful power sup- plied by the tube can be determined in terms of the alternating voltage across L0 and the fundamental constituent of plate current. If we could neglect the Tone Clarity grid current, this would be the power available for dissipation in Elektron Tubes have proved Beyond Expectation the resist- ances. As the output current increases, to be the finest receiving Just pull the switch and note the clarity the amplitudes of the amplifiers and detectors and richness of tone any Am - alternating volt- peri te -equipped set gives you. Amper- ages across the plate and grid coils in- that money can buy. Reli- ite is the automatic rheostat which does away crease proportionately. The alternating able and highly efficient. with hand rheostats and filament meters. No guessing. No un- grid current increases more and more Satisfaction guaranteed. certainty as to correct tube current. Tubes last longer. Makes any novice rapidly, as the amplitude of the pl 4e There's an Elektron a master operator. Insist upon Arytper- voltage becomes larger. On this ac- (201-A, 199, or 199-A) ite when you buy or build. Price $1.10. count the power loss to the grid in- for every type of circuit Write for free hook-ups and creases. The power supplied by the battery equipment. RADIALL COMPANY DEALERS! Some excellent plate increases with increasing plate Dept.R-16, 50 Franklin St., N.Y.City territory is open. Write voltage, but as the grid voltage in- for our proposition. creases, the effective saturation current PERITE is reached when the grid is positive, and the plate " lie "SELF ADJUSTING "Rheas -tat current becomes zero for an appreciable part of the cycle when the grid is negative; consequently a con- 1bV3H BHL tinued aRni increase in the amplitude of the s....nnmvK output 021.1.).N»-t,3 current results chiefly in an in- RADIO MAPS crease in the POSTPAI D harmonic constituents of CLEKTaOp ANYWHERE plate current without greatly increasing a+rsvrae`-. the fundamental. Obviously, then, a condition of stability ensues when the power supplied by the fundamental of 10e plate current minus the power dissipated i4CUVI`i by the fundamental of grid current is TUBE just equal to the power dissipated by PACIFIC RADIO PUB. CO. NE fi the output current in-Rg, Rp, and Re. EAR? Pacific , Of Bldg San Francisco GRID POTENTIAL AND COUPLING. RADICI In the Hartley circuit of Fig. 7 the instan- taneous u+rw+crvstolr grid potential is determined by Takes the mystery the potential across Le. This potential LECIRODIO CORP. LvNN,MAss. is a function of Lg and the current out of Radio flowing in this coil. Here, Lg and Lp JUST OUT -514 PAGES are not mutually coupled. Referrir , to Compiled by the circuit of Fig. 9, it will be seen that HARRY F. DART, E.E. Formerly with the Western Electric Co., and U. S. Army Instructor of Radio. Technically edited by F. H. Doane NO MORE need you turn from book to book, hoping to find what you want. It is all here, in 514 pages crammed full of every possible radio de- tail. Written in plain language, by engineers for laymen. 100,000 sold. IT EXPLAINS: Electrical terms and circuits, antennas, SAVE MONEY batteries, generators and motors, electron (vacuum) tubes, many receiving book -ups, radio and audio frequency am- plification, broadcast and commercial transmitters aid liot uR the press-latest Radio Catalog & Guide brimful of new Ideas, over 100 special receivers, super -reg ion, codes, etc. Fig. 9. Generating Circuit With Coupled hook-ups with Information-all free. Shows Send $1 today and get this 514 -page 1. C. S. Radio savings as high as 50% ou sets and supplies. Handbook-the biggest value in radio today. Grid and Plate Inductances. Be sure to get this thrifty Illustrated book befo -e you buy. It means money In your t- pocket. Standard guaranteed goods. International Correspondence Schools Writ. ¡.0., ar end es,.. dl.a please ¡aetnde Box 8262-D. Scranton, Penna. BI RAWIK Co., lu-Iui S. canal St. ChIcago,U.S.A. I enclo-e One Dollar. Please send me-post-paid-- the operating grid potential is obtained the 514 -page I. C. S. Radio Handbook. It Is understood that If 1 am not entirely satlstled I may by coupling Lg to L0. Here, Lg is not return this book within live days and you will BIG MONEY FOR RADIO refund my money. a part of the oscillatory circuit. By the mutual inductance Demand for high pay radio men is so great that a big Name definition, Kansas City wholesale concern is now fitting men free to coils such as Lg and Lp of Fig. get into of two the radio business for themselves and make $60 to $200 a week without any capital invested. Select Address 9 is the number of interlinkages rf mag- territory open. Send l ('trek here enclose today for free catalog and amazing Q and $1.50 tt you wish the I netic flux from coil Lp with Lg per ab - offer. Write direct to Mr. H. J. Salaow, Standard Radio edition bound in Leotherold. Co., 1422 Walnut St., Kansas City, Mo. (Continued on Page 88)

86 Tell them that you saw It in RADIO

www.americanradiohistory.com THE TUBE WITH A SENSIBLE GUARANTEE ade with recision .1 $39.50

Right from the start at our factory each SUPERTRON is produced with PRECIS- MARWOL ION as the dominating factor. The material, each process, the triple test, and the final inspection, are all guided by The Line of the most exacting PRECISION. The unit of PRECISION called SUPERTRON is serial numbered and wrapped in a certificate All MONEY MAKERS bearing a corresponding number. Types Thus giving you a means of identi- $2.00 the MARWOL BABY fication to assure full satisfaction. FROM GRAND at $36.50 to the MAR- Pacific Coast Offices: Canada $130, $2.75 WOL CONSOLE GRAND at LOS ANGELES-Pacific States Commercial Co., 3208 Glendale Blvd. SAN FRANCISCO-American Commercial Co., Rialto Bldg. the MARWOL line holds the greatest Branch Offices Thruout the United States sales and profit -making opportunities this SUPERTRON MFG. CO., Inc. year. HOBOKEN, NEW JERSEY is the outstanding line of Export Department, 220 Broadway, New York MARWOL the season, from every standpoint-qual- ity, performance, appearance and range SUPE RT R O I\I' of models and price. GUARANTEE : SERIAL NUMBER MARWOL Dealers know from past experience that MARWOL will hot cut prices-that there is no Summer dump- ing of MARWOL-that MARWOL

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Write or wire today direct to us or to the Sales Branch nearest you for catalog of the KEbo.STER complete line, discounts and = Rosin Core full information. Radio SOLDER / Sure is Safe and Simple MARWOL RADIO CORP. 546-548 BROADWAY I ^`! Approved by -- FACTORY No. 2 Radio Engineers 85 MERCER STREET, NEW YORK CITY Pacific Coast Representatives: C!IIC:AGO SOLDER C0AiTANY In California: In Oregon and Washington: MA/ UANK SALTS COMPANY C. E. GAT 4254 WeiahtwoodAve., Chluso, U.9. A. 926 Insurance Exchange Bldg., 166 Lownsdale Street. urmmawrr Los Angeles, California Portland, Oregon L.rr Y.rl Al,rnu(u'rur,r, .V In Idaho: 54/ tl.ain(Sddr, R. T. CARP YVUCDIALtfl CAN SUPPLY YOU 906 Sprague Street, Spokane, Washington

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www.americanradiohistory.com V (Continued from Page 86) solute ampere change of current in coil L9. The voltage set up in coil Lg is -13.` %. ibllf- Sensation dependent directly upon this mutual in- ductance and the rate of change of cur- br rent in coil L9. k;71ä4t Suppose the circuit of Fig. 9 is gen- e Season erating oscillations of maximum MODEL 5-F -S strength. If the mutual indictance be- 4°, tween Lp and Lg is decreased by separat- v \ e and Improve d ing the two coils the alternating poten- tial induced in Lg is decreased. By vir- tue of the controlling action of the grid, N!1FRSHM A this decrease in coupling results directly in a decrease in the amplitude of the plate current wave and a decrease in the c e variation of plate potential across Lp. This results further in a decrease in the strength of oscillations until a condition of stability ensues for the par 'cular value of coupling between L, and Lg. As the coupling is further decreased the oscillations will become weaker ar-d weaker and finally stop at a particular value of coupling which is determined by the condition that for oscillations to ex- ist, the mutual conductance of the tube must be at least equal in numerical value to a factor depending upon the constants A five -tube tuned radio frequency of the external plate circuit and the par- receiver, ticular value encased in as fine of mutual inductance be- a heavy 5 -ply solid gen- tween Lp and Lg. uine Once oscillations are mahogany cabinet as ever graced any stopped by decreasing the coupling, they radio set. will not again star until the coupling is increased appreciably beyond the pre- vious stopping point. Every part Slightly Higher embodied is newly constructed Denver and The condition for strongest oscilla- resulting in greater efficiency and finer Wert tions exists when the quantity involving tone quality. The illustration shows our the constants of the external plate cir- new straight line wave length, low loss cuit and coupling between L, and Lg is condenser and vernier device, permitting such as to operate the tube over the por- the reception of stations over a wave tion of its characteristic corresponding to minimum length from 290 to 550 meters. mutual conductance for the tube itself. If the coupling is increased beyond this point, the oscillations will For Sale By ºAuthorized Freshman 'Dealers Only again decrease in strength. There is, therefore, an optimum value of coup- Chas. freshman fo.lnc. ling between Radio .Ñecelveey oaò ,halts L, and Ls for mo-: desir- FRESHMAN BUILDING able operation. 240-248' ST 40 -rH ST -NEW 'tt)RK. N Y CHICAGO OFFICE CONDITION FOR MAXIMUM OUTPUT. - 327 S. LA SALLE ST. The output of a tube and its circuit can be increased by increasing either the ARE YOU A SUBSCRIBER' plate current or plate. potential. We SEND $1.00 FOR can increase the plate current by in- A TRIAL SUBSCRIPTION TO "RADIO" FOR 6 MONTHS creasing the filament temperature. The detrimental effects of excessive filament temperature do not often make this a "The Elixir of SET Life" desirable method of increasing the out- Ju.t as the heart is the mort vital organ of the human body-the tube is the most vital part of the put. We may, however, increase the radio set. The SIMPLEX SUPER POWER TUBE Simlé#C plate potential providing at the same performs its function in the radio set with the same /uwcR ' sensitivity, accuracy and regularity as a healthy heart time we make the grid more negative by in the human body. REJUVENATE an amount equal to the quotient of the YOUR SET WITH THE SIMPLEX increase in plate potential and .-he amp- SUPER POWER TUBE, IT MEANS LONGER LIFE lification factor. Safety hinges upon AND BETTER RECEPTION. adequate insulation and the maintenance GUARANTEE: Your dealer Is authorised to exchange or return money for any defective S. S. P. Tube, within ten days. of the necessary negative grid potential. PRICE: Silvered Tube - - $2.00 If output is plotted against external Blue Tube - Typa: S. S. P. $230 plate circuit resistance, other conditions ZOIA, 199. S. 9. P. ASK YOUR DEALER FOR 12. Silvered and THE SIMPLEX remaining constant, it will be found Blue. SUPER POWER TUBE that maximum output is obta.ned when TITANIA MANUFACTURING COMPANY, 105 \Ve.t 40th St., New York the external plate resistance is equal to the internal plate resistance.

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www.americanradiohistory.com Precision This Tells the Inducto Chart Coupler Success Story of the Price, $1.85 Signal Spiral Cam McLaughlin Recommends It James L. McLaughlin, the author- ity on superheterodyne design, rec- Condenser ognizes the superiority of Precision Coils. He says: "The Precision In- The Signal Spiral Cam Condenser is the only ducts Coupler is the only coil condenser on the market equipped with this recommend for use in my new One unique and highly efficient control. The dis- Control Superheterodyne. tinct advantage of its construction is best illustrated by the chart reproduced above. The Inducts Coupler has been de- Note the even distribution of stations over the complete 360° of the dial as compared signed for use where a split wind- to typical condensers of other types. It's all in the cam! ing coil is desired. Made of the best moulded hard rubber, which insures lowest losses. Other Important Features The Cockaday 4 -Circuit Coil is the The Signal Spiral Cam Condenser operates with only coil ever specified by Laurence velvety smoothness and with a complete elimi- M. Cockaday, inventor of the fam- nation of backlash, permitting easy'and accurate ous Cockaday Four -Circuit Tuner, tuning. The electrostatic field is concentrated for use in his set. Double silk cov- within a small area and the dead dial shaft is ered copper wire results in in- not connected to either set of plates. It is com- creased volume and greater selec- pact, being no larger than the old semi -circular tivity. type. It is die cast throughout, insuring abso- lute uniformity. It is designed for either single Cockaday or three -hole mounting, and air core transform- 4 -Circuit ers can in turn be mounted directly on the con- denser. Signal Spiral Cam Condensers are built Coil in three sizes with unusually low minimum Price, $5.50 capacities in all sizes, giving a high tuning ratio. One price for any capacity-.00035, PRECISION COIL CO., Inc. .00025, .0005-$4.00. See one at your dealer's. 209 Centre Street, New York, N. Y. NOW-A BRACKET TYPE LOOP AERIAL Cut out that extaa piece of apparatus by attaching a Signal Bracket Type Loop Aerial right onto the end r.f your radio cabinet. This aerial will turn a complete 360° in a space no greater than the width of the average cabinet. This new aerial has all the advantages of the famous Signal Table Type Loop. Constructed of solid walnut with third tap for sets requiring them. See both types at your dealer's.

SIGNAL ELECTRIC MANUFACTURING CO. Dept. 3-K, Menominee, Michigan Western Representatives: Coil Set No. 24 for Browning -Drake Circuit Don E. CAMPBELL RADIO DISTRIBUTING CO. SICKLES 1216.17 Hearst Bldg., San Francisco, Calif. 408 San Fernando Bldg., Los Angeles. Calif. DIAMOND WEAVE Branches in all principal cities (Trade Ma.k Registered Aug. 4. 1925) COILS For Browning -Drake Roberts, Craig and Hoyt Circuits (Patented Aug. 21, 1923) Get a RADIANT CONDENSERS Sickles Coils for the famous Browning -Drake For Real Radio Reception Circuit are the latest Sickles achievement in Phonograph Unit HEATH RADIO AND ELECTRIC MFG. CO., efficient design for a particular use. They are 208 First Street, Newark, N. J. priced at $7.50 a set. The New No. 18A Coil, for any Roberts Cir. cuit are absolutely standard equipment. They FREE are priced at $8.00 per set. to Coil Set No. 20, at $4.50, is for use specifically With only one subscription with the new Reflex Receiver designed by Al. "RADIO" for one year-$2.50. bert G. Craig using the Sodion detector. Unit is made by The Union Coils for the Hoyt Circuit at $10.00 a set for the Knockout Reflex Circuit at $4.00 a pair, and Fabric Company. the Tuned Radio Frequency coils at $2.00 each MA-ALO are other standard Sickles Coils. Wo manufac- SUBSCRIBE NOW ture also for manufacturers' special requirements. Na-ald DeLuxe Sockets are the only Send for descriptive catalog ones with these 3 exclusive features- " RADIO " lowest loss, lowest capacity and posi- Pacific Building, San Francisco tive side -scraping contact. Send for The F. W. Sickles Co. booklet and laboratory test. Alden Big. 138 Union St. Springfield, Mass. Co., Dept. G9, Springfield, Mass.

saw it in RADIO Tell them that you 89 www.americanradiohistory.com STATIC MITIGATION (Continued from Page 18) ing different makes of a.f. transformers were used, and then a balance between the impulses would be difficult. The antenna -ground circuit of each receiver must be coupled to the first tube circuit as in a neutrodyne receiver, and the connection which joins the A bat- tery to ground must be removed to avoid the possibility of short circuiting any of lhA illance the batteries through the common ground connection. Of course, separate Constant vigilance A and B batteries must be used on each receiver. In case loop receivers are used, is the price oÇ the two loops should be pointed in the same direction, since static from differ- uniformitg ululem ent directions is different in character. and The method of operating the two re- constant vigil- ceivers is as follows : The outputs of the two are connected as shown Fig. ance is maintained 2, using only a single loud speaker. They are then both adjusted to a station, over Magnatrons. the filaments of one being turned t;f That is why Magna.. while adjusting the other. Then both sets of filaments are turned on at once, Irons are uniÇorm,and and the intensity of static and signal ad- justed by filament control until both are uniformly good.voma. reduced to practically zero in the loud cn,arRON speaker. This is a test for the identity of characteristic of the two receivers. The Magnetron DC -201A, DC -199, and DC - the Enew One receiver is then tuned sufficiently 199 (large base) now list for only $2.50 each tube for d batter off of the station wavelength sb that Connewey Electric Laboratories tiimin,tto Magnatron Building, - Hoboken, N. J. s the signal is lost on it and only the Pacific Coast Representative: static remains. e filaments of the Pacific Radio Laboratory other receiver should be turned off dur- 256 So. Los Angeles St., Los Angeles, Calif. ing this procedure. The detuned re- ceiver should not be tuned so far off that it picks up some other station. It should have merely static on it and should be as close to the original signal MACPATRONS wave as possible, without containing any of the signal energy. For this reason sharply tuned receivers such as the neu- trodyne or super -heterodyne are desir- able for this test. After the condition of static on one Good Company receiver and static and signal owl the sec- ond is obtained, it will probably oe neces- MAKE YOUR TUBES KEEP GOOD COMPANY sary to increase the static intensity on the first slightly, since it will not be Bad tubes in your set spoil the good ones quite as strong as on the second, in which REFORM your backsliding tubes with the the signal tends to accentuate the static impulses. By careful adjustment of the BRINGS BACK filament currents of the two receivers, Bum4iBEAGERS BAD TUBES the intensity of the static on the two $7.50 F LA S fri E R can be equalized. Due to the fact that the two receivers are tuned to slightly different waves, only that type of static One model for For tubes with will be balanced which is substantially D.C. or A.C., thoriated fila- the same on all waves. The sudden all cycles. ments. sharp click variety is most nearly equal on all wavelengths, and it is this type Utmost simplic- Results will on which this system is most effective. ity of opera- exceed your ex- It should be remembered that this is tion. pectations. not a static "eliminator." If it did any- thing as final and definite as that, the author would be getting out a patent Send for our booklet "Save a Life" and selling stock. However, if sufficient care is taken in the adjustor nt of the BURTON & ROGERS MANUFACTURING CO. receiver, a definite improver.,ent in the 755 BOYLSTON STREET, BOSTON, MASS. ratio of the static to the station signal can be obtained.

90 Tell them that you saw it in RADIO

www.americanradiohistory.com Introducing "SUPER UNIT JUNIOR" A little brother to the stand- ard Type A and Type B "Super - units." He measures 5x10" and he consists of a stage of tuned R.F., the detector and two stages of Thordarson audio. He has plug-in coils and the standard set of coils which he uses will tune from 170 to 570 meters when used with the S -C Capacity Element to make a one dial set. Other coils for other wave lengths. He makes the most efficient set for use with an aerial and there are just 11 connections to complete him. YOU SHOULD MAKE HIS ACQUAINTANCE! Price, complete with instructions $37.50

MATERIALS NEEDED FOR A COMPLETE SET 1 "Superunit, Jr." NO BACKLASH Is Possible In This New Dial ! 1 S -C Capacity Element or so 2 .0006 condensers. In the new Fynur dial there are no gears to mesh, 1 Front panel, size 7x10 or there can be no lost motion ; no backlash. Forward or larger. backward, the movement is always smooth, free and 2 Bradleystats. without the slightest break or interruption. 1 Double circuit jack. 1 Single circuit jack. Traction (beveled wheels) makes this new Vernier Con- Note: No baseboard is re- trol the most accurate tuning dial on the market. It is quired. simple in construction and beautiful in appearance, and owing to a special automatic compensation adjustment for wear, it will outlast the set on which it is placed. If $3.50 Hanscom Radio you want the utmost accuracy in reception, use Fynur Devices Dials. Ask your dealer or write to us Mfgrs. of the S -C Capacity Element, August Goertz & Co., Inc., 270-286 Morris Ave., Newark, N. J. the one dial control for two control sets. Woonsocket, R. I., U. S. A. Pacific Coast Representative: S. A. WINSOR ARE YOU A SUBSCRIBER? SEND $1.00 FOR A TRIAL SUBSCRIPTION TO "RADIO" FOR 6 MONTHS 1221 Venice Blvd., Los Angeles, Cal. RADIOCAST POWRPEP" WEEKLY A brand new device for eliminating the antenna. Simply place burly -eight Pages ut l'rogranls. POWRPEP under your telephone and listen -in. The results are amazing. Order one of these novel devices today. They are selling Photos, Humor, M u s i c a l Re- fast. views, Schedules, Tables, Edi- torials, Etc. ONLY 35 Cents --Postpaid Per Radiocast Weekly Dealers and Jobbers' Prices on Request Copy 433 Pacific Bldg., ATLANTUS MFG. CO. SAN FRANCISCO 74 Front Street Port Jervis, N. Y.

Tell them that you saw it in RADIO 91

www.americanradiohistory.com CALLS HEARD (Continued from Page 44) By 608W, 2330 Hillhurat Ave., Hollywood, B Calif. laao, lace, laep, lahg, lalw, lang, lbgl, lbgt, lckp, lcmx, aka, 1p1, luw, lxu, 2afp, ELIMINATORS 2agw, 2bbx, 2buy, 2by, 2cty, 2dx, 2gu, AOPV°9SOIN 2gy. 21u, 2nf, 2mk, 2qw, 2xaf, 3awh, 3bta, 3bva, 3cjn, 3jw, 3kg, lot, 3vx, 4ac, day. 4fg, 4f1, 4jd, 4jr, 4oa, 4oi, 4r1, 4rm, 4sa, now offers the Assured Success with 4s1. bann. 5adt, 5afd, 5ahw. bald. 5akI. bamh, Saph, 5aav, 6pu, Sqs, Sad, Suj, 5va, New 5. a, gaff, fibuc, Gait, Best, 6dcf, fxi, 8bgn, Type Tubes 8biq, 8bkq, Bbgt, 8brc, 8byv, Sbal, Seed, 8ckm, Styl, Sdea, Sdme, Beb. 8eq, sjj. Sjq, 88f. and Sul, 8zm, 9adr, 9aed, 9aef, 9afx, 9a11, 9aon, Mocking 9aot, 9atq, 9aud, 9bcx, 9bdw, 9bck, 9bmv, 9brk, 9brq, 9ccb, 9ccs, 9cty, 9cdo, 9cuo, 9daw, 9dbq, 9dkv, 9duc, 9dum, 9dwz, 9hp, 9pn, 9pz, 98e, 9zd, 9zk, 9zt. Canada: 3aa, Bird Unit 4aa, 4cr, 4gt, 4hz, 5ba, 6bf, Set, 5go, bhp, Patented Set, 9ck. Mexico: laa, laf, lax, lb, lg, lx, 9a. Australia: 2bb, 2bc, 2cm, 2da, Elj, 2x1, 3bd, 3bq, 3et, 3ju. N. Z.: lao, lax, lac, 2ae, Transformers 2xa, dag, 4ak, dal, 4ar, Bpi. Chile: leg, ?ld. 9tc. Argentina: bal, afy. P. I.:1hr, $7.50 List Misc.: nas, nedj, nkf, npu, nrrl, numm, nugg, wap. kfuh. jbc, cards answered. 266.? QRR? All All fans remember the pio- By R. C. C. McCabe, 71 Holloway Road, neer of adjustment units - New Zealand Morrison Model C. For 3 U. 8.-lxu, laep, laao, lcx, lbge, lmy, lang, lea, lare, 2xaf, 2a1u, 3bva, 3hg, 4rr, years this unit was a stand- bog, 5aav, 5atv, 6ea, 6eb, 6aav, 6rw, Obst, 6xad, 6cso, Scott Oip, Eno, 6te, Sao', 6avj, ard of comparison. In trend Oawt, 6atf, Obhz, 6cdy, 600, 6bc1, 6cub, 6ja, with radio's Bajm, 6bec, 6b1h, 6cnd, Oche, 6bur, 6dah, great growth, 6bqb, 6bmw, 6chz, 6agk, 6a1j, 6awo, 6fa, Morrison now offers the Gail, 6ctn, 6qd, 6cgw, 6bgo, 6cgw, 6cgo, Gbde, 7ayy, 7aek, 7nt, Tgj, 7uz, Schc, 8apw, Mocking Bird Unit, the peer Seed, 9adm, Btx, 8bgn, 8gz, 9akf, 9bht, 9uq, of all 9ek, 9bn, 9wo, 9ado, 9xn, 9p1, 9ff. Miscel- units. laneous: wiz, nkf, npg, npm, aryl, gbe, wap, nve, mumm, cxl. You cannot equal the tone Designed especially for operation with fly 64.8D, 2347 Lucerne Ave., reproduction of the Mocking the new Filament and NonFilament California. Loa Angeleno Tubes, Dongan Transformers and (40 band)n Bird Unit attached to the Chokes are most essential parts of lang, lany, lare, itx, the lzm, 2act, (qra?), lte, phonograph. Radio assumes remarkable new BEliminators. These 2bxl, 2afp, 2ahm, 2aim, 2bbx, 2bur, 2cgj, 2dx, 2gy, 2kr, 21a, 2np, 3bv, new delights -purity of tone new Eliminators are thoroughly in- 3bce, 3btv, 3bva, lchg, 3eu, Sot, 3xb, 4ave, 4bv, 4eg, 4fg, 4gt. 4js, and the remarkable volume dorsed by Cockaday and other author- 4tn, 4km, 4rm, 481. ities. Saaq, bade, bado, bagn, Said, Sall, (adjustable) are marvelous. 5akn, 5akz, balj, Same, 5apa, Sapm, Saga, barn, 5ary, bask, 6aav, bba, 5ce, 6co, 5ms, Names famous in the industry are Sox, Spa, Sae, buk, 5ux, Ova, Swa, bxbh, The Handsome Mocking found on these new type tubes. Like- Szal, 7aek, 7ald, 7dt, Tgj, Tit, 7kg, 7nx, lux, 7ya, Salt 8aly, Bird wise Dongan-long a leader Sby, Siren. 8bhm, 8bpl, Cabinet at $30 list is a in the Seed, Bey!, Sdal, Sdkk, Bdno, 8eq, 8gi, real musical masterpiece. production of quality transformers- Sgz, Sp1, irk, Stk. Btx, Buk, Szz, 9ado, shares in this achievement. 9aef, 9adr, 9aek, 9aep, 9aey, 9apn, 9atq, Morrison Mocking Bird 9bcx, 9brg, 9bpb, 9bvh, 9bwo, 9c.a, 9ccs, Cabinets Order 9cjw, Seld, 9cvn, Sczz, 9dac, 9dbb, 9occ, and Units at most by Number 9dkv, Sdpx, 9ouc, 9dvr, 9dwn, 9dwz, 9dzn, good dealers or send your Puts AM) Srscortcasioas: Sete, Seta. geht, Sek, Off, 9hp, Soo, 9pn, Ne. S09 Full Wave gum. 9wo, 9xn, 9yav, 9zk. New Zea- order to factory. Absolute Fer Raytheon Tube. land: flak. Canada: 2aa, 4aa, 4gt. Hawaii: 6afr. Mexico: lb, money -back guarantee if not No. S37 Full Ware UX213 lk, Sa. Naval: nkf, npg. Fer R. C. A. Tube. nrrl. Com.: wir, wiz. Unknown: hjd, xaE, satisfied. Ne. S37 Full Ware CX3I3 rat. For Cunningham Tub«, By J. G. Tinney, Set hlanu/acturers: No. S33 Ralf Ware 1X216-13 7.00 74 Kaiaal RL, Hataltal, For R. C. A. Tubes New Zealand .4areetts.e grmatìey price. ow tutu so braid No. SU Hall Ware CX316B (For July and August (40 to 46 meters) mus your Sate. Detector only. For Cumineha a Tubas lag, Imy, lsf, lte, Iza, lang, lare, lbgo, Dialers: Iblu, 2g -y, ihn. ilu, 2nf, 2xg, 2xi. lyt, Ezv, Yerinm Ism ahrteya been wsrAarduu,, CHOKES 2afn, 2afp, 2bbx. !bee, 2brb. 2bur, 2buy, lesibir. Nor asAedale e/ diesausu reed. L., lcty, 2xaf, lbs, 3hg, lauv, 3bva, Sckg, 4cu, two or ssue.. Ne. 514 _ ---- _-. --.SO henry 4tu, don. 4o1, 4r1, 4rm..dsa, 4v1, 4afu, 4ask, No. 506...-. ------_ 10 henry $500 Set, Sew, 6fh, 5kc, hjd, bnj, bnq, boa. Soi, Ne. 5.39 _. -- .---_._- SO haar, buk. Saal, Saks, Bali, fiat'. bzas, Get, 6dh, Morrison Laboratories 6dn, 6dq, 6ea, Sta, 6jp, 611, 6nx, 6q1, firm, Other Speridd Traailorwer. and Choke. for Binh 6rw, 6sb, fitz, Oxg, 6zd, 67h, 6agk, 6a1j, Inc. A and B óliwinotsr Regrire.ets Galy, 6aji, 6ajm, óakz, Galt, 6apk. 6aav, 6avj, Gapw, 325 E. 6awt, 6bap, Gbbw, 6bcl. 6bhg, Jefferson Ave_ Detroit, Mich. Build your B-lJtminater with Donlan sbih, 6bmw, 6bsc, 6bur, Sbve, 6cbb, 6cdy, Transformers sud t:ioke.. yce your Sego. 6cgw, 6che, Ochs, 6cmu 6cmq, 6cno, dealer or send rberk er money order 6csa, Seas, host, Seto, 6avj, 6dab, 6dah, Pacific Coast Distributor,: Now. Shipment. made same day ender 6dcf, 6ets, 6mgk, 6xad, Tay, Tnt, Tut, lus, connived. lack, 7xat, Seq, Ber, See, 8gz, Bjj, Ske, D. S. Spector Co. ink, Bpi, Bry, Ssf, Sxn, Badm, iamb, 8apw, Dealers! Manufacturers! iayy. 8bgn, Beak, Scau, ices, Schk, 8xyz, Rialto Building, San Francisco 9bn, 9dx, Sed, 9ek, Shp, Ont, Sog, lug, 9xh. Cet year share of this We ran sane you on Sin. 9ado, Sall, 9akf, 9aod, Sapm, 9bac, twiner.. Full details any quantity. Prier, 9bek, 9bht, 9bpb, 9ccb, 9ded, !Mac, 9dpx, upon request. ea request. 9dqu, 9duc, 9dvw, 9dwj, Seht, 9yav, 9xq. Alaska: 7de. Algeria: Balg. Australia: !bb. 2bc, tbd, 213,4, 2cm, 2dj, !de. 2gq, 2ij, OONGAN ELECTRIC MANUFACTURING CO. arg, leo, las, 2tm, !via. lyi, Zan, 3ad, let, 3bq, 31m, 31r, 3pm. 3ry, Sui, 3yx, tan, 4rb. 2981 Franklin Si. Detroit, Mich. 6am, 7gh, 7pf. Argentine: cb8. Brazil: Tieaderaars el 31«,, fur Idices Veer, lab, Pal, lap. Canada: 4gt. Chile: leg, Ste. Cocos: 99x, (gra?l. England: Ecc, Psr4 c Cesar Repwaatti. e. Pkf, 21a, lnm, bid, Yea, 51f. Snn, firnt, 6tm, phone lnm. France: 8co, Bet, Seg, Btq, Sae Francisco- Bqq, Stok, Swag, Syor. Hawaii: Safi, fil. Industrial Sales Co.. 171 Sacend >o eel Holland: o-ba, no-ev, pcuu. Italy: ler, Los Angeles -- imt, lno, lrg, lrt. Mexico: lea, lb, lx, Oa. W. A. Breeiman, 443 5e. Sae Pedro Street Miscellaneous: aga, bbvp, cxi, fix, kfuh, ..sf°ou Portland. Ore. - kfvm, m52, naj, nrj, nve, npg, nph, nppm, d cfpcakc- C. B. Coy, 166 Lew.dale npn, npo, npu, napg, asan, nedj, atri. Street nrrl, numm, pot, wir, wqn. North Polar 444114. Wash. - Region: wap, wnp. Samoa: 6zac. Sweden: 6. P. Denham. 272.6 4Stb Avenue b. S smyy. (Continued ow Page 96)

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www.americanradiohistory.com Smallest Uniform Frequency Condensers made easily fit This new unit makes itpossibleto use a light socket for"B" voltage, without any into present sets troublesome hum from alternating current. Supplies the constant voltage necessary for perfect reception. No acid to spill. No mov- ing parts. Requires no attention. Semi- automatic in operation. The least expensive type of unit because of low first cost, mini- They are half to a third the size of others, are only in diameter mum current consumption and long life. 2/" In handsome walnut case. Price $35. with plates fully extended, so will easily go into your set. (-McAndrews Hq Do away with crowding of station readings -85 out of 100 come below cerkieettemil 50 on dial using Pats, Pend. with ordinary condensers-by For best results in home - built sets it is safer to use equipment employed in the best commercial Samson receivers. Here is a su- Uniform Frequency perior coil used in such high grade receivers as t'ondensers Price the Deresnadyne and to 1/10,000 inch, silver plated $3.00 Buckingham. It can be These condensers are built all over used in any hook-up requiring a high type and-in addition-have gold plated plates to prevent oxidization. inductance. Grounded rotor type-minimum capacity 12 mmf. losses lower than Has exceptionally high ratio of inductance to resistance with minimum distributed capa- most laboratory standards. .500 mmf., $7.00; 250 mmf., $6.75; 250 city. Improves tone. Increases range,volume mmf., $6.50. and selectivity. Blue prints of tested hook- ups employing this coil are available. Our Technical Dept ivi!! i answer inquiries. SAMSON DmigSwiral ELECTRIC COMPANY °blding eop CANTON, MASS. Handsomely finished Price in silver and mahog- $8.50 Member RMA anyto harmonize with the Lombard J. Smith, 24 N. San Pedro St., Los Angeles, Calif.; A. S. finest home Lindstrom, 274 Brannan St., San Francisco, Calif.; Mr. H. A. Killam, furnishings. 146% N. Tenth St., Portland, Oregon; Mr. G. H. Maire, 95 Connecticut St., Seattle, Washington; Jennings & McCollom Co., 407 Dooly Bldg., Salt Lake City, Utah; Jack L. Hunch Co., 1641 Stout St., Denver, Colo. Manufacturers of Quality Electrical Products Since 1882. Sales Representatives in Thirty Leading American Cities. Western Representative: A. S. Lindstrom Co., San Fran- c,:ì fab _rem. cisco, Los Angeles, Portland, Seattle, Salt Lake City. Easily portable. Has insulated handle and Practically uniform high amplification over entire au- graduated dial. Reduces static and other in- dible range with minimum distortion is obtained by terference. A special model for every circuit. using Samson Helical Wound Transformers. Ratios- See these standard units at your dealers 6:1, 3:1. $5.00. or write for complete information. 'elioUaziev 1303 First Avenue Maywood. Illinois Perkins Elect. Ltd., Montreal, Toronto, Winnipeg i RADIOCAST WEEKLY Electric Forty-eight Pages of Programs, Photos, Humor, Musical Re- Soldering Tables, views, Schedules, Edi- SEND FOR TRIAL SUBSCRIPTION IRON- torials, Etc. $1.00 FOR SIX MONTHS FREE Per Radiocast Weekly LOOK! Subscribe to "RADIO" for one year Copy 433 Pacific Bldg., Radio Mileage Chart, 10x16 inches. Not a map. ho 110 scale necessary to get your mileage. Mailed on re- -$2.50-and get a -volt MAR- ceipt of VEL Soldering Iron FREE. 50 cents. Address: SAN FRANCISCO "RADIO," San Francisco Graph & Chart Service P. O. Box 945 Waterbury, Conn.

Tell them that you saw it in RADIO 93 www.americanradiohistory.com SHORT WAVE REFLECTORS frame so the center of the bakelite in- (Continued from Page 13) sulator will be over the point for the LABORATORY 3/4 meter is 29.51 in., / of which is reflector wires. The insulators for the 7.38 in. This will be used later as the aerial -counterpoise are the same except focal length. On a large sheet of paper that they are 1 x 4/ in. This allows SERVICE draw line AB near one side.. Line CD for the coupling coil in the center. The By M. BEST is drawn perpendicular to AB at its reflector wires are cut from No. 14 G. center E. On the line CD 7.38 in. bare copper wire. They are exactly THE complete laboratory from E a point is located at G. This 16/ in. long and should be as straight of the Pacific Radio Pub- point is the vertex of the parabola. An- as possible. The ends of the wires are lishing Company is at your other point 7.38 in. from G on line CD slipped through holes in the insulators service. We make tests --- is located at X. This is the focus of the and twisted back around itself. calculations --- give you ex- parabola. A number of lines, KK', LL', pert advice on your radio Mill', NN', 00' are drawn perpen- problems. Gerald M. Best is dicular to CD as shown. They cross in charge of our own labora- CD at points P, H, Q, I and J. Take tory. We have an assort- a compass and with distance EP as a ment of the finest testing radius strike an arc from X on KK' equipment available. making points UU'. Then with the dis- Use this service. Let us answer tance EH as a radius, from X strike your radio questions for you. We arcs on LL' making points YY', then give you expert advice on your taking the distance EQ do the same on radio problems. Our service is most accurate --entirely dependable CC'. Continue until the parabola i, and PROMPT. finished or in other words until the We will answer ten of your opening in the parabola is the right size, radio questions if you subscribe to or in.this case until the opening is 59 in. "RADIO" for only one year. With The distance from the vertex to the cen- your subscription to "RADIO" you will receive ten coupons, entitling ter and perpendicular to the line join- you to answers to ten radio ques- ing the sides of the opening or line GD tions. is 30 inches. The regular cost for answering ten The construction of the reflector needs questions is $2.50. Save this money! little explanation. It is made of finished Subscribe to "RADIO" and get pine. your answers without cost. white The top and bottom frame is made from 1 Use the coupon. Attach your re- x 4 in. material. They mittance of $2.50 to it and mail are separated by posts 2 x 4 x 163/4 in. now. Your investment of $2.50 will long. The whole frame is nailed to- pay big dividends. The coming is. gether securely. A full sized drawing sues of "RADIO" will surprise you. of the parabola is made on some wrap- - - --COUPON -- - - ping paper. Nine equidistant points are located on the curve of the parabola on "RADIO," Pacific Building, Fig. 4. Tuning Mechanism. the drawing. By laying the drawing San Francisco, Calif. on the frame these points are transferred Here is 82.50. Send me "RADIO" for one The transmitter is placed directly be- year and 10 free coupons entitling me to an- to it. These points are where the re- hind the reflector and is coupled to it swers to ten radio questions. flector wires are to be t_ocated. by a link coil. The end coupled to the The insulators shown in Fig. 3a con- coil in the reflector is separated about Name sist of / in. bakelite, 1 x 1Y2 in., with in. and held by two small insulators in. hole in. from one end, which / Address / / made like porcelain cleats, as shown in is screwed to a wooden block 1 x 1 x 2 Fig. 3b. City and State in., which in turn is screwed to the (Continued on Page 96)

MOLL1FORMER "EV UNIT REPLACESalso), BATTERIES complete description of this SEND FOR powerful "B" Unit that you ran build in an hour at most reasonable cost. Uses the current from the light socket-Excellent for Supers and all TRF Sets-Assures greater Clarity- DX and Volume-Noiseless-No Tubes nor Acids- r Utilises full wave rectification. Guaranteed to Give Complete Satisfaction or Your Money Refunded PRICE Complete Kit- 60 Cycle Unit $22.50 Complete Kit- 25 Cycle Unit 24.50 Kits include Rectifiers. /11a4.5 Ar. ta/res Parts sold separately if desired. Tile DEALERS-Write for our proposition. C. E. JACOBS, Sole Mnfr. (b)\ 2808 N. Kedale Avenue CHICAGO Fig. 3. Insulators.

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