GB545827A - Improvements in and relating to amplifier coupling circuits - Google Patents

Abstract

545,827. Valve amplifying circuits impedance networks. BRITISH THOMSON-HOUSTON CO., Ltd. April 4, 1941, No. 4542. Convention date, April 5, 1940. [Classes 40 (iii) and 40 (v)] A coupling for a broad band of frequencies between two terminals comprises three resistances connecting the terminals to points of fixed potential a point between the second and third resistances being also connected to a point of fixed potential through a by-pass condenser and between the terminals large and small condensers connected in shunt, the stray capacity to earth of the larger condenser being prevented from attenuating the higher frequencies by providing a decoupling resistance between it and each of the terminals. Fig. 1 shows a coupling comprising anode resistance 19 with series inductance 18 and grid resistance 29 with condensers 27, 38 in parallel decoupling resistances 37, 39 which may be of equal values obviating the loss of high frequency which would otherwise occur due to the stray capacity to earth shown as capacity 40. Gas discharge voltage regulators 26, 36 are provided in the screen grid circuits in addition to the usual byepass condensers. To avoid phase shift and to maintain the gain constant throughout the frequency range the ratio of the resistance 29 to resistance 19 is made equal to the ratio of the capacity 22 to capacity 27 and also to the ratio of resistances 37, 39 to resistance 20. At the highest working frequency the magnitude of the resistance 19 is made equal to the impedance of the stray shunt capacity across resistance 19 while inductance 18 is given a value in Henrys of 1/4# f times the value of resistance 19 where f is the maximum frequency. The Specification gives response curves and numerical data of components for an amplifier operating from 20 cycles to 3 megacycles.