GB225579A - Improvements in or relating to thermionic valve circuits - Google Patents

Abstract

225,579. Grimes Radio Engineering Co., Inc., (Assignees of Grimes, D.). Dec. 1, 1923, [Convention date]. Thermionic amplifiers. - Reflex circuits for wireless reception, of the kind described in Specification 204,301, in which radio-frequency currents and audio-frequency currents traverse the valves in reverse order, are modified so as to prevent howling owing to audio-frequency capacity coupling between the coils of the radio-frequency transformers. Fig. 2 shows a two-valve reflex circuit similar to that described in Specification 204,301, except that the telephones or speaker 30 are connected between the anode 8 of the first valve 6 and the radio-frequency primary coil 9. With this connection, the coil 9 assumes a minimum of audio-frequency voltage and is therefore ineffective in transferring audio-frequency potentials to the grid 14 of the second valve 13 through the inter-coil capacity 31. Transfer of audio-frequency energy through the capacity 32 of the second radio-frequency transformer 17 is minimized by connecting one end of the transformer secondary to the filament lead 46. In an alternative arrangement, the telephones 30 are connected in the usual position between the battery 28 and the coil 9, but the secondary 23 of the audio-frequency transformer 21 and its shunting condenser 16 are transferred to the grid side of the coil 12. In a further alternative, shown in Fig. 4, the audio-frequency coil 23 and the radio-frequency coil 12 are connected in parallel in the grid circuit of the valve 13. A condenser 36 blocks audio-frequency currents from the radio-frequency coil 12, and a radio-frequency choke 37 may if necessary be provided in the audio-frequency branch. Similar parallel connections may be arranged for the telephones 30 and the radio-frequency coil 9 in the plate circuit of the first valve. In all cases, the telephones may be replaced by the primary coil of a transformer, the secondary of which is connected to the grid of a power amplifying valve, having a loud speaker or telephones in its plate circuit.