GB458861A - Improvements in thermionic valve systems - Google Patents

Abstract

458,861. Valve circuits. BAIRD TELEVISION, Ltd., WHITE, G. W., and BROWN, A. J., 58, Victoria Street, Westminster, and WILLANS, P. W., Quality House, Quality Court, Chancery Lane, London. May 27, 1935, No. 15455. [Class 40 (v)] In a thermionic amplifier of the " cathodecoupled" type, grid current in one valve flowing through part of the output circuit of the preceding stage is opposed by the anode current in that output circuit. The Figure shows a television transmitting amplifier comprising three cathode-coupled amplifiers 1, 11, 14 and a push-pull modulating stage 15, 16. The grid of valve 11 is biassed slightly positive, the resulting grid current flowing through resistances 6, 7, in opposite sense to the anode current of valve 1 ; the resulting p.d. across 6 due to grid current reduces the negative bias of valve 1 and increases the anode current, and the drop in p.d. across resistance 7 increases the anode voltage applied to 1 from source 8 with the same result. The action of the valves 14 and 11 is similar, the grid bias potentials being obtained by tappings 9, 12 and earth tapping 21 on a floating battery 10. The valves 15, 16 operate in quiescent push-pull, radio-frequency oscillations being injected into the tuned grid circuit 17 from 18. The effect of grid current in these valves on the oscillator and modulation systems is counteracted by a reduction in negative bias of valve 14 and increase in its applied anode voltage due to reduced voltage drop in resistance 19. Specification 457,827 is referred to.