GB450036A - Improvements in electric circuits comprising thermionic amplifiers in push-pull - Google Patents

Abstract

450,036. Valve amplifying circuits. GENERAL ELECTRIC CO., Ltd., Magnet House, Kmgsway, London, and MACFADYEN, K. A., c/o General Electric Co., Ltd., Wembley, Middlesex. May 8, 1935, No. 13586. [Class 40 (v)] The grids of a pair of push-pull power amplifiers are fed from a previous push-pull stage with voltages arising across a centretapped impedance in the cathode circuits of the previous stage. As shown in Fig. 1, signals are fed by a centre-tapped transformer 10, 12 to the grids of push-pull valves B1, B2, the cathodes of which are connected to each other by a choke 19. The centre tap 18 is connected through a grid-bias source to the centre of the choke 19. The centre of this choke is also connected to HT-, and its ends to the respective grids of the power amplifiers A1, A2. The cathodes of valves A1, A2 are connected to each other and to HT-, and their grids are biassed by a battery 20. Output is taken from valves A1, A2 by a centre-tapped transformer 5. In a modification shown in Fig. 2, separate chokes 21, 21<1> and self-biassing resistances 25, 25<1> are included in the cathode leads of the valves B1, B2 ; and the cathodes of these valves are connected through condensers 23, 23<1> to the grids of valves A1, A2. A divided choke 22 with a single core has its sections connected between the grids and cathodes of the valves A1, A2, each section including a separatelyadjustable bias source. The circuit is designed to reduce distortion due to the flow of grid current.