Radio Digest (Apr 1925-Jan 1926)

20 RADIO DIGES T— Illustrated June 6, 1925. A. B. C. RADIO COURSE (Continued on page 19) shown in figure 55. The shunt is a very low resistance and the greater part of the current in the circuit passes through the shunt and only a small part of the current passes through the instrument I. The indication of the instrument I is, of course, due to the current through it, and if the relation of this current to the current through the shunt is known the total current in the main circuit may be determined by multiplying the indication of the instrument I by a constant. The scale on the instrument may be marked to read the current in the main circuit and in such a case there is no need of a constant. In the use of an ammeter shunt the division of the total current between the shunt and the instrument must be known and the division of this current is not the same for direct current as it may be for an alternating current, unless the electrical characteristics of the shunt and the instrument are identical. A voltmeter is an instrument used to measure the difference in the electrical pressure between the two points on an electrical circuit to which its two terminals are connected. For example, in figure 56, the voltmeter V is connected to the terminals of the resistance R and 9 O Q Oi • SHUNT iO Figure 55 will give an indication of the value of the electrical pressure between the terminals of the resistance. The ammeter A will indicate the current in the main circuit, which will be practically the same as the current in the resistance R, provided the voltmeter takes a very small current. A voltmeter depends for its operation upon some effect produced by an electrical current, just as in the case of the ammeter, and the only difference in their construction is that the voltmeter has a comparatively high resistance and the ammeter a comparatively low resistance. The deflection of the moving element of Finer Selectivity Equip your receiv ing set with Apex Vernier Dials. They will greatly increase iM the efficiency of any l| set. Make tuning pos itive bringindistant stations. Your dealer ^7 has them. If not, send W $2.00 for Royal Brass •' Finish— $2. 50 for Satin Silver Finish, or $3.50 for DeLuxe ' Gold Plated (24k). I APEX SUPER 5 J \l This highly efficient jl tuned radio frequency f| receiver is most advanced (S in design ?nd construction. 1|S Ah instrument that meets /^ every critical expectation JKfc of the radio enthusiast. (^ Housed in a highly finished walnut cabinet, complete with Jones Mulri-plug Battery Cable. All settings highlygold plated. Sellsfor $95 complete excepting acce*sor c s. At AilGood Dealers APEX ELEC. MFG. C O. ■': ■':" the voltmeter depends upon the current through the instrument, and, if the resistance of the instrument is constant, this current will vary in value as the electrical pressure between the terminals of the instrument changes, A voltmeter may be constructed so that a full scale deflection of the pointer will be produced by several different voltages. For example, the resistance of a certain voltmeter may be such that an electrical pressure of 15 volts is required to produce a full scale deflection. Now if a second coil be placed in series with this instrument and the resistance of this coil is equal to the resistance of the voltmeter, then a pressure of 30 volts will be required to produce a full scale deflection of the pointer. This second coil may be placed inside of the containing o O o R vvvvwv So O or V PigTire 56 case of the instrument and a double marking placed on the scale, and a double set of terminals provided. A wave meter is an instrument consisting of a variable condenser in series with a variable inductance and some means of indicating the maximum value of the current in the circuit. An instrument of this kind is used to measure the wave length of an oscillatory circuit by adjusting the inductance or capacity, or both, until the wave length is in resonance with the circuit to be measured. The resonance condition can be determined by means of the current indicating device in the meter, the current being maximum for resonance. An ammeter is usually used to indicate the current, although in some instruments a telephone receiver and detector are used, the detector being required to make the radio frequency currents above audibility audible. AVURDOCK ^lcHie^Si Deresnadyne MALONE LEMON MASTER RADIO ADLER-WJYAL ##> HARTMAN AUDIOLA EAGLE GLOBE AND MANY OTHERS SuPer AMPLIFYING TRANSFORMERS Standard on the mgjorih) of quality sets Build or replace with Thordarsons. Dealers every•■'■ere. Hook-up bulletins free. Write Thordarson Elect. ic Mfg. Co., Chicago. The diagram of the wave meter is shown in figure 57. In order that awide range of wave lengths may be measured it is customary to provide several different inductances of different sizes. The condenser is of the variable type with air as a dielectric and its capacity may be varied from zero to' the maximum value, which will depend upon the size, number of plates, and the distance be Fig-ure 57 tween them. The condenser is provided with a dial which will give an accurate indication of the position of the variable plates of the condenser, and also its capacity. Now for each particular inductance there will be a range of wave lengths which may be measured by varying the capacity from its maximum value to its minimum value. A chart or curve usually accompanies each instrument which gives the relation between dial reading and wave length for each inductance. The inductances are most generally mounted outside the containing case of the instrument for ease in changing. (Different types of 'batteries, their construction and special uses, will be taken up next by Professor Moreton. Primary -cells, those which generate electrical energy by chemical action, are the subject next week. — Editor's Note.) The Reader's View Be Harmonica Contests I noticed on the front page of the Radio Digest of May 2 that a harmonica contest is to be waged at Station WBAP. The challenger, Mr. Wright, I have not met, but Mr. McBeth I met in Dallas winter before last, where the writer won first money at an adults' harmonica contest at Kieths, when my friend Borah Minevitch played. Mr. McBeth was there, but for some reason did not play. T am glad to see this spirit of rivalry now, and hope it will be all good natured. When I was a boy we sat on the rail fence and always featured the harmonica to help out the glee (?) club. I would like the addresses of about four or five of the best harmonica players (aside from Mr. Minevitch) and would like to have them write me In care of Radio Digest. I want only ones who have played a number of years and are able to render jazz or classics. — I. J. Lockwood. Tune Him Out I was glad to see the article by Robt. Whitfield of Texas regarding those pests of the air, the telegram readers. Certainly, if anyone has a just cause tocomplain, Mr. Whitfield has, as the chief offender is located in his state. I agree fully with Mr. Whitfield that the main object of these laudatory gushers is to hear their names announced over the Radio. Dike him, when they commence reading the telegrams my hand invariably and instantly reaches for the dials; we have that satisfaction at least. — Thomas D. Farley, Thomaston, Ga. klJCJJ up your set f J with good tubes COME radio fans don't expect much "pep" ^ from their portable sets. "Oh well, only using the small tubes," they explain. But they have quickly revised their ideas when they switched to MAGNATRON DC-199 tubes. You'll never realize how important tubes really are until you adopt MAGNATRONS. Your dealer has them! % CONNEWEY ELECTRIC LABORATORIES Hoboken, Ty.J. ■BUD The Three Curses of Radio Power Noises, Static, Reradiating Squeals absolutely eliminates all power noises, cuts real "static" and reradiating squeals The Kane Antennae The Kane Antennae at least in two. The Kane Antennae enables you to get the full benefit of your Receiving Set All Summer Long. Another of our many satisfied customers proves our claims in the following letters. "HE SUFFERED GRIEF AND PAIN" Gentlemen: — April 14, 1925. Referring to your Ad in "Radio Digest" in regard to your Antennae, I have a six tube Super Zenith operating on wet "A'* llatt., and am troubled with power noises and static, being located within 75 yards of a 50,000-volt power line. Located in two-story building and have set on second floor. Depot is between two railroad tracks. Kindly advise if you think your Antennae would help me out under the above circumstances Kindly give dimensions of Antennae, that -is, length and distance from ground lowest wires would be. It is almost imperative for me to run Antennae across railroad track. Hoping to hear from you soon. (Signed) Yours truly. B. n. Beaver, Agent ATSF RR Co., Johannesburg, Calif. "THEM DAYS IS GONE FOR EVER" Gentlemen: — Johannesburg. Calif.. May t>, 1925. I have installed one of your Antennae which you recently shipped me, and find that it has eliminated all power induction from 50.000-volt power line within 150 feet of Antennae's location. Several stations that I could not bring in at all on account of this power induction I now bring in clearly. Needless to say it has improved greatly reception from all stations. Thanking you for promptness in filling order and wishing you success, I am, (Signed) Yours truly, B. H. Beaver, Agent ATSF RR Co. See for Yourself Just What This Wonderful Antennae Is We will sell you working drawing with instructions for erecting this wonderful Antennae for a dollar bill. If, after looking over the drawing, you decide you would rather have a factory-built Antennae than build one yourself, we will take back the drawing and allow you full purchase price on an order for an Antennae. 6.50 The Special Kane Antennae for Radiola Super-Het's The Regular Kane Antennae for all other sets that use a ground 1 Q A/j connection IJiUU Working' Drawing1 with Instructions for Erecting, $1.00 (Stamps Not Accepted) Postpaid to any part of the United States or sent C.O.D. when 25°b of purchase price accompanies ordar. "HEAR AS YOU HAVE NEVER HEARD BEFORE" THE KANE ANTENNAE COMPANY, Aberdeen, Wash.