Radio Broadcast (May 1928-Apr 1929)

The "Chronophase" for A* C> Tubes T E. SMITH Aero Products, Inc. IN RECENT issues of Radio Broadcast, data have been published outlining the development of the new " Chronophase " system of radio-frequency amplification, and describing the construction of a screen-grid receiver using this circuit. Some kit builders are not particularly anxious to use screen-grid tubes, because of their tendency to amplify microphonic noises and also due to the fact that their filaments are so delicate. Others feel that the storage battery is an unnecessary evil and are anxious to construct a receiver which can be plugged directly into an electric-light socket. For these fans another model of this receiver has been designed which makes use of alternating-current tubes throughout. In this article the a. c. model of the "Chronophase" receiver is described. The construction of the a.c. model of the "Chronophase" receiver is in many details similar to that of the screen-grid model which was described in last month's issue. The assembly of the set is simple, and complete instructions are supplied with the kit of parts. The circuit diagram, given in Fig. 1, shows that the leads to the last stage of audio amplification are independent of other parts of the set. Therefore, if the proper power supply is availble, a 210 or 250-type tube may be used in this stage, simply by applying 75 volts to the red and black terminals of the Yaxley cable connector and four to five-hundred volts to the brown lead. In the event that a 250-type tube is used, a resistor capable of dissipating at least forty watts should be connected between the green lead of the cable connector plate and the Bminus wire. A resistor of 2000 ohms is approximately correct for all types of tubes. No output device has been incorporated in this receiver since many of the loud-speakers, particularly of the dynamic type which are now very popular, are provided with transformers for coupling the output of a power tube to the actuating windings of the speaker. Several methods of coupling the speaker to the final tube are given in Fig. 2. Many owners of radio sets have phonographs of a more or less obsolete type. In this connection it is interesting to note that a first-class audio II * 4 mid To Speaker J 0 B+ Id) FIG. 2. OUTPUT CIRCUITS frequency amplifier, such as is used in "Chronophase," will, with a good loud-speaker, amplify phonograph music equally as well as the finest and most expensive up-to-date phonographs. Therefore, many users may gain a great deal of pleasure by purchasing a phonograph pick-up unit and attaching it to the audio amplifier of their A.C. "Chronophase" receiver. The audio-frequency amplifier used in the "Chronophase" is ideally suited for use with phonograph pick-up units, particularly in the a.c. models where a 210 or 250-type tube may be used in the last stage. The Aero transformers are designed so that they have a very flat amplification characteristic up to above seventhousand cycles and above that point almost no amplification whatever is obtained, thus reducing the "needle-scratch". The changes required in the receiver for the reproduction of phonograph music are exceedingly simple. A regular phone jack may be inserted in the set or tip jacks may be used. If tip jacks are used, attach one tip jack to transformer post labeled P and the other to transformer post labeled B as shown at the point marked X in Fig. 1. If this last method is used, the detector tube must be removed from the socket when the phonograph pick-up unit is used. The following are the parts included in the "Chronophase" A. C. Five Receiver kit: Ci, C2, C? One Aero triple-gang condenser, .00035-mfd., type AE II 2 1 55; C4 One Aero Midget condenser; C5, C6, C7 Three Aerovox moulded mica condensers, .001-mfd. ; Cs One Aerovox moulded mica condenser, .00025-mfd.; Li, L2, L3 1 Aero coil kit, type U-203; L4, L5 Two Aero r.f. choke coils, type C-60; Ri One Special Centralab resistor, AE-250; R2 One grid leak, 3-meg; R3 One Yaxley resistor, 2000-ohm; R4 One Yaxley resistor, 600-ohm; Ti, T2 Two Aero audio transformers, type AE77o; Y One Yaxley cable connector and plug, type 669; One Aero A. C. "Chronophase" foundation unit, including No. 400 cabinet, escutcheon plate, base unit with sockets mounted, wire, solder, and all other parts necessary for mounting and completing set, such as machine screws, bushings, etc. One National dial, type "E"; Three Kurz-Kasch special knobs; Three Eby "Junior" binding posts; One pair Yaxley tip-jacks, type 422. Total cost of kit as supplied by Aero Products Company, $74.50. t^"l-Brown>220 v> It 'Speaker or Speaker Coupler FIG. I. SCHEMATIC DIAGRAM 126