GB684862A - Improvements in or relating to electric wave amplifiers - Google Patents

Abstract

684,862. Valve amplifying circuits. SOC. D'ELECTRONIQUE ET D'AUTOMATISME. May 11, 1950 [May 11, 1949], No. 11799/50. Class 40 (vi). In an intermittently-operated D.C. coupled amplifier drift is reduced by a voltage integrating circuit having its output connected to a bias circuit, and its input switched during rest periods to receive' a potential equal to the difference between the amplifier output and a reference potential while during work periods the input is left free. When relay 29 is in the released position, the amplifier comprising valves 1, 2 and 3 is disconnected from the input and output terminals 23, 24. The potential of the anode of valve 3, if different from earth causes capacitor 14 to charge or discharge and so vary the bias potential on valve 2, the effective capacity of capacitor 14 being increased by valve 12. During the work period switch 30 is closed to operate relay 29, disconnecting the input to valve 12 and connecting terminals 23, 24 to the amplifier. The valve 12 holds the bias on valve 2 constant for the duration of the short work period. Should the permissible drift be exceeded, relay 19 operates to light local and remote warning lamps 21, 22. When some reference potential, other than earth, is used, a battery 37 is added. Negative feed-back is provided by resistor 28, and a further circuit may be connected between terminals 23, 24 and thus disconnected from the amplifier during the rest period. The switch 30 may be operated by the input and a series of amplifiers controlled by multiple connections 31. Specification 620,140 is referred to.