GB601205A - Improvements in neutralized thermionic amplifiers - Google Patents

Abstract

601,205. Valve amplifying circuits. O'BRIEN, W. J. Oct. 16, 1942, No. 14526. Convention date, Aug. 5, 1941. [Class 40 (v)] In a high-frequency amplifier means are provided to compensate for changes in the internal capacities of the valve produced by changes in grid bias so as to prevent these changes from introducing a phase-shift in the amplifier. Fig. I shows an amplifier in which the input capacity depends .on the space charge effect and variations are compensated by resistance 8. The output capacity will tend to cause a reactive component of the output voltage to produce a voltage across the resistance 8 which would be impressed on the input, but is balanced out by a phase-opposed voltage through a balancing condenser 23. The gridplate capacity is neutralized by a condenser 25 feeding out of phase voltage to the grid preferably through potentiometer 26-28. In a modification, an additional coupling resistance is arranged in series with the input circuit and is traversed by current derived from the output circuit, Fig. 2 (not shown). Alternatively, the compensating resistance may be included in the plate circuit and the voltage across it fed in series with the input circuit to the grid, Fig. 4 (not shown). Fig. 3 shows a neutralizing arrangement with a divided input circuit in which the plate-cathode capacity is neutralized by condenser 35 and the plate-grid capacity by condenser 36, a second compensating resistance 29 being provided.