Abstract: A biasing and control circuit for varying the output power delivered by the push-pull output stage of a power amplifier is disclosed. The biasing and control circuit incorporates both fixed and cathode biasing to allow output power to be varied without introducing distortion. A negative fixed biasing voltage is applied to the control grids of the vacuum tubes comprising the push-pull output stage, while the cathodes of such tubes are varied between ground and selected voltage levels above ground. To vary the voltage levels, the cathodes of the tubes are joined together by a common connection and coupled to ground through a variable impedance which when varied changes the conductivity of the output tubes, and thereby, the output power delivered by the amplier.