Radio Broadcast (Nov 1926-Apr 1927)

316 RADIO BROADCAST ADVERTISER At WGN Mica Condensers Prevent Shifting of Frequency Bands BECAUSE the Sangamo condenser is solidly molded in bakelite, mechanical movement of dielectric or plates is impossible. This is one important factor in the permanent accuracy of the Sangamo. No one has greater need for condenser accuracy than a great broadcasting station like WGN. Read Mr. Leverett's comment: "Last June I used Sangamo Mica Condensers in a multiple band pass filter. This has been in use for some time, and has given the best of results, showing no shifting of the frequency band. This permanency I believe is due entirely to the consistency of these condensers, there being no apparent change in capacity nor leakage across them. I cheerfully recommend them wherever a constant capacity is required. (Signed) Geo. H. Leverett, Asst. Engineer" Station WGN Chicago Sangamo Condenser Blocks American-made condensers, wound under uniform tension to eliminate air or ozone bubbles that cause breakdowns. Handy sizes : 12 mfd. tapped 8, 2, 2 mfd. 14 mfd. tapped 8, 2, 2, 1, 1 mfd. 14 mfd. tapped 4 (high voltage), 4, 2, 1, 1, 1, 1 mfd. Also separate condensers; special capacity blocks to order. Sangamo Electric Company 6331-11 Springfield, Illinois -jf RADIO DIVISION, 50 Church Street, New York SALES OFFICES— PRINCIPAL CITIES Built to look perform like Set. Utors ro imMtfwhere:-30 l)a<vs Free! SEND COUPON FOR AMAZING SPECIAL OFFER! NOTEs This offer is mad* to prospective buyers by famous big Radio Corporation, one of America's oldest reliable manufacturers of fine sets— seventh successful year. Many satisfied users in every state. Postal or coupon brings testimony of nearby users and proof Miraco's outperform sets costing up to 4 times as much. Very easy to operate BEAUTIFUL BIG -POWERFUL Users report Miraco Radios eet Drotmms Coast to Coast, olnoCsolbs end Mexico, loud and clear on speaker; outperform $100 to $200 sets. Porrio bavo heard Europe, S. America. Don'tconfOBO Miraco with umall cheap nets. UnlPHH trial proven it Mus i' SKl.1',0 VIVE, CLEAREST TONED and MOST I'OWERKUL DISTANCE-* iETTER arnontf beautiful biff 6tube acta, don't boy it. Every Miraco comes completely assembled, rucidly tested aod fully eanrantocd, ecial Our Factory Prices Save You Up to 1/2S SEND NO MONEY! battc on nrt:i, •prnkara, tnb AMAZING OFKEEt. Ultra-o (not Ulna. J la mm •ousvnluo in a bur Guaranteed 5-tube, 3-dial Save or mnko Uttra-5 " Retail List Hokellt inKpnnulii, hIh bcnntlf till* , cuhtnotti: Con I Hi.ttcry <',il.l.n: f.iitur.u. I too | t t,, mention I , n-h i>ti.'.n! n.-t:. I Send for Amozlng Low"Unltune" Prlco | MIDWEST RADIO CORPORATION, Ploneor.Bullders ot Sets 40b -G Mir.n o Bide., Cincinnati, Ohio WITHOUT ( >HLIi;ATION. u.'nd free literature, AUAZ1NO Si'KCLAL Or-Tf'Eli, toutiwony oX uimlw, etc. R8oo(62i.3i3.73). Mercury Vapor Mercury-Arc Rectifiers. Rectifiers. Radio. Oct., 1926. Pp. 40-41. "An Amateur's Mercury Arc Rectifier," Don C. Wallace. In order to supply plate current to the larger tubes used for transmitting purposes, a mercury arc rectifier can be used. A suitable one is sold by the General Electric Company. It supplies voltages anywhere from 500 to 5000 with practically no internal drop. The circuit arrangement and the layout and construction of parts necessary for such a transmitter are described. R343. Electron-Tube Receiving Set. Receiver, Radio. Oct., 1926. Pp. 29-ff. " Equamatic." "The ' Equamatic' Tuned R. F. Receiver," G. M. Best. Of the various methods used in tuned radio frequency sets to overcome the tendency to oscillate at the higher frequencies and still have a high efficiency, the " Equamatic" system is said to bring about a stable condition more uniform than any other. The principle involved consists in automatically varying the coupling between primary and secondary coils through direct connection with the condenser shaft. The method of constructing and operating a receiver employing the "Equamatic" system is outlined. R344.5. Alternating Current Supply. Eliminators, Radio News. Oct., 1926. Pp. 322-ff. B Battery. "B Battery Eliminators," M. L. Muhleman. The various forms of B battery eliminators now on the market are presented and discussed. Their circuit diagrams, and the principle upon which they operate, is brought out in detail for every instrument shown. R387. Shields. Shielding. Radio News. Oct., 1926. Pp. 336-337. "A Perfect Static Shield." V. G. Mathison. The use of solid metal shielding is considered to be out of the question when looking for amplification of weak signals in receivers, according to the author. Too much energy is lost. In this article, the use of copper rods or copper wires is substituted for the solid shields, with the result that no energy is absorbed from the set, but the set is totally shielded nevertheless. Coils may also be shielded by this method with considerable success. R132. Amplifying Action. Amplification, Radto News. Oct., 1926. Pp. 342-ff. Radio Frequency. "Radio-Frequency Amplification," E. T. Flewelling. Attention is called to some common errors frequently made in the construction and the connections of tuned radiofrequency amplifier sets. Parts must be balanced and wires so placed that they do not cause disturbances in neighboring parts. Every measurement from stage to stage should be made with precision in order to be able to tell what to expect of a set before it is assembled. R375. Detectors and Rectifiers. Rectifier, Radio News. Oct., 1926. Pp. 343-ff. Raytheon BH. "A New Rectifier for A, B, C, Power Units." A new Raytheon tube, capable of delivering enough current and voitage to replace A, B, and C batteries in a set equipped with 199 tubes and a power amplifier, has been developed. A circuit diaeram showing how this new tube may be used for the above-mentioned purposes is presented, and discussed at some length. Variations from 10 to 85 milliampeies are possible, the tube having a very good regulation over this range. R342. Amplifiers. Amplifiers, Radio News. Oct., 1926. Pp. 353-fT. Audio Frequency. "A New Amplifier and B Supply Unit," A. H. Lynch and R. R. Mayo. The requirements for good audio output are said to rest with the following: 1. An r. f. amplifier which does not cut off side bands. 2. An r. f. amplifier which does not produce excessive gain and bring in local disturbances. 3. An r. f amplifier which does not overload the detector. 4. A straight frequency-line characteristic for the audio amplifier whether under or over-loaded. 5. A loud speaker with good reproducing qualities. An audio frequency amplifier, operated from the lamp socket, and giving exceptional reproduction, is described, and the method of construction outlined. It is a resistancecoupled instrument with a B line power-supply device. R343. Electron-Tube Receiving Sets. Receivers, Radio News. Oct., 1926. Pp. 362-363. Loewe Tube "A Five-ln-Two Receiver," C. J. Fitch. The writer presents a receiving set built around the new multiple tubes made by Loewe of Germany. The internal construction and arrangement of these new tubes, and the apparatus necessary to assemble a neat and compact receiver, are points discussed and presented. R210. Frequency Measurement. Frequency Bureau of Standards. Letter Circular Measurement. Z.C-171. "Methods and Apparatus for Measurement cf the Fiequencies of Distant Radio Transmitting Stations." It is the purpose of this circular to outline several methods of measuring frequencies and to describe the apparatus needed foi this purpose. A schedule of standard frequency transmissions from wwv and 6 xbm, is printed, the range of frequencies covered being from 12s to 6000 kilocycles. The zero beat method and the resonance click method may be used, the former being the more accurate, as stated. Both methods are discussed at some length. In constructing a frequency meter, of fundamental importance is said to be its mechanical ruggedness. The condenser should meet with certain requirements, its range being covered through small variations. It should be shielded and have a low r. f. resistance. As for the lesonance indicator, it may consist of several devices, the thermo-galvanometer being preferred. The testing of this frequency meter is accomplished most satisfactorily with a low-power generator described here. In an accompanying table (No. 1 ) are given the coil sizes of various frequency ranges. A ;-watt generator for setting up the i.f. currents is outlined, with diagrams of hook-ups appended. The method of procedure in making all the measurements is explained in great detail. .xaminea am approved by Radio BROADCAST if