GB579685A - Improvements in or relating to thermionic amplifiers - Google Patents

Abstract

579,685. Valve amplifying circuits. MANSFORD, H. L. April 24, 1944, No. 7623. [Class 40 (v)] In an amplifier cumprising a number of pairs of valves, the cathodes of each pair being connected to a common point, and the anodes to a common point while the grids are fed in push-pull, connections are made between the common points to which anodes and cathodes of different pairs are connected such that the anode circuits of the pairs are effectively in series across the power supply. A push-pull input, applied to the grids of a valve pair 1, 1a causes amplified voltages to appear at the anodes, the current passing through the pair remaining constant so that the potential of the cathodes of valve pair 7, 7a is unchanged.' The grids of valves 7, 7a are fed in push-pull from the anodes of valves 1, 1a and, in a similar manner, the output pair of valves 12, 12a are fed from the anodes of valves 7, 7a. Potentials applied in-phase to valves 1, 1a cause changes in the total anode current of the pair, the amplifier gain thereby being reduced to that given by a valve 1 feeding into an anode load, tapped to provide an output voltage. Since later pairs of valves may pass larger currents than the earlier stages, the difference in current may be passed through resistances 24, 25 which may be replaced by further amplifiers of this type. A potentiometer 21 supplies bias to valve 1a and also through the input circuit to valve 1. The grid of one of valves 1, 1a may be earthed, the input being applied to the grid of the other valve, the feed to the first valve being supplied over the common cathode lead 20. The grid of any valve in the chain may be resistance opacity coupled or transformer coupled to the anode of the preceding valve or. cross-connected to a preceding valve in the opposite chain. To provide the correct bias, a resistance may be connected in the grid lead to a valve, a second resistance being connected to a point of constant potential. A resistance may also be connected in the common cathode lead of any pair to adjust the bias. The resistance 20 may be replaced by a pentode, the bias being varied to alter the current through valves 1, 1a and the gain of the amplifier. Further valves may be similarly connected to valves 1, 1a with a pentode in the cathode lead and the anodes connected to the anodes of valves 1, la. Accordingly as one or other of the cathode load pentodes is rendered conducting, signals applied to valves 1, la or the additional valves will be amplified.