Radio Digest (July 1924-Apr 1925)

RADIO DIGES T— Illustrated July 12, 1924 NEW UNIDYNE RECEIVER (Continued from page 1) such tubes have been confined only to the laboratories of a very few large firms who have offered little information relative to any experimental work they may have carried on. This possibly may be explained by the fact that the sale of three electrode tubes has been very profitable so why detract from same by introducing a few more new tubes that would require .Filament Normal Qr\p P\.ACTE Figure 1 expensive machinery for production, and other numerous items which would materially effect the profits of the year. The Fourth Electrode The effect of the third electrode or grid in the vacuum tube has been repeatedly described so that all should be well acquainted with it. If, as shown in Figure 1, the inner grid around the filament is positively charged by connecting it to the positive terminal of the filament battery it accomplishes the same thing as increased filament heat would, namely accelerate the departure of electrons from the filament. The result is a more pronounced flow of electrons to the plate. From tube curves it is known that increasing the positive potential on the grid has the same effect on the plate flow as increasing the plate battery. Another way of saying it would be that the equivalent internal resistance of the plate circuit has been reduced. This first inner grid then simply becomes an accessory to the filament in providing an increased flow of electrons. The second or outer grid performs the same functions as the grid in the normal three electrode tube, that is, as the incoming oscillations change from positive to negative, it assists or resists the flow of electrons to the plate. What Amplification Depends On It is obvious that this increased flow of electrons from the filament through the use of the extra or inner grid is equivalent to the same increase through use of plate batteries, hence there should be no difference in tube life. The suggestion might be made that by using a plate battery in addition, an even greater plate flow will result. Depending on the characteristics of these new tubes, this may be true, but it must be remembered that the amplification power of a tube depends on the effect of the normal grid on this plate current. Regardless of how great this plate current may be, the variations in the potential of the normal grid will be no different from the usual tube and hence the plate current fluctuations correspond closely to those in the present tubes in use. It must be kept in mind that the purpose of this tube and its circuits is primarily to eliminate the necessity of the B battery. Research will undoubtedly create further development which as yet are unthought of. TJnidyne Circuit The circuit used in conjunction with this four electrode tube is shown in Figure 2. On examination, the circuit will appear normal with the exception of three points. 1 — The extra grid. 2 — No B battery. 3 — The transformer. The extra grid is the one connected to the positive A battery lead. The plate circuit runs from the plate of the tube, through the tickler coil, then through the primary of the transformer, through the receivers and back to the filament circuit. The secondary of this ten to one ratio transformer connects on one side to this inner grid and the other side to the plate Gl?ID WITH PEWWtKT Positive Charge For that Summer Portable You Want Efficiency and Compactness VARIOMETER VARIOCOUPLER Pat. Pending Ffanstiehl Variometer, P-301 $4.75 Ffftnstiehl Variocoupler, P-300 5.00 PFANSTIEHL RADIO SERVICE CO. Highland Park, 111. Chicago: 1001 W. Washington St. Haymarket 8010 The GREBE CLARIFIER THE first practical, workable solution of the problem of radiation from regenerative receivers. Unlike the "wave-trap" it increases signal intensity. $30 Increases Selectivity Increases Signal Intensity Improves Quality Prevents Radiation And— Is Easily Connected Ask your dealer or write for literature A. H. GREBE & CO. Richmond Hill, N. Y. Western Branch — 4 51 East 3rd St., Eos Angeles, Cal. L-lOO tOTOl RAXNO AF.TR.A.ns Figue 2 Q Phoncs Q circuit. The theory of this transformer is, that the rectified current passing through the primary of the trasformer in the plate circuit develops a stepped up induced flow which is fed back into the inner grid producing what might be called an additional regenerative feature. Undoubtedly this makes the circuit very difficult to control because in further circuits the (Continued on page 8) BUILT BY RADIO ENGINEERS FOB THOSE WHO DEMAND THE BEST Great selectivity — no static — quality reception Write for Catalog Many Advantages Lincoln Collapsible Loops offer many advantages, appreciated by Radio Engineers and Radio enthusiasts. Wave length range with 23 plate condenser is 3 60 to 600 meters. H. F. Resistance at 400 meters — only 7 ohms. Wire is stranded, flexible and of great tensile strength and high conductivity. Inductance .2 millihenry. At your dealers. Tapped Loop $8.00 Without taps $6.50 If your dealer cannot supply you, order direct, giving us his name. Lincoln Radio Corporation 224 N. Wells St. Chicago, Illinois IT HAS been the tradition of the Federal Company, over it's 25 years in manufacturing Electrical Communication Equipment, that it must give its users the highest refinements of the art. Federal tradition will not permit the manufacture of a radio set just for radio noises. Each and every manufacturing necessity to produce a harmonious set is known to Federal Engineers, and no Federal set is produced without them. Federal radio sets are built with two thoughts in mindfirst: simplicity of operation, but three controls being necessary— second: special controls for refinement if the user is interested -in reproducing all the beauty of tones that fill the air. "Lovers of good music" know why Federal is better, and know the real value of the refinement placed at their command to make it easy to obtain the clearest tone reception. FEDERAL TELEPHONE & TELEGRAPH CO. Buffalo, N. Y. Boston New York Philadelphia Chicago Pittsburgh San Francisco ^federal St^dardJ^DIO1*0*™*8 Look for this sign Several > ' RADIO '<«••"> Bridgeburg Canada London England