Differenzverstärker

771,083. Valve amplifying circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Jan. 25, 1955 [Jan. 25, 1954], No. 2209/55. Class 40(6) In a push-pull amplifier of the type comprising a pair of valves with a common cathode impedance, discrimination against in-phase voltages is increased by replacing each valve by two or more in cascade connection. The signals are applied to the grids of the lower valves 5, 6 respectively, the anodes of which are directly connected to the cathodes of the upper valves 12, 13, respectively. The valves 12, 13 have load resistors 9, 10 across which the output is obtained. The common cathode impedance comprises a further pair of valves 16, 17, in cascade connection, having a cathode resistor 11 and with the grids held at fixed potentials by means of potentiometer 18, 19, 20. In a simplified modification, Fig. 2 (not shown), the common cathode impedance comprises a resistor. The grids of the valves 12, 13 are held at a fixed potential relative to that of the cathodes of the valves 5, 6 by means of a gas-discharge tube 14 which is fed through a resistor 15. This resistor may be replaced by a valve system such as that 16, 17 comprising the cathode impedance.