Abstract: An audio amplifier in which an output stage is coupled by a driver stage to an input stage which includes two antiphased sources of alternating current. The output stage includes two pentode vacuum tubes each having a cathode, a plate and a screen grid located between the cathode and the plate. Each tube has a control grid connected between the cathode and the screen grid and a suppressor grid connected between the screen grid and the plate, with the control grid and the suppressor grid being shunted to their respective cathodes. The driver stage includes a pair of transistors connected in a push-pull configuration with their emitters connected to the screen grids of said tubes to supply a relatively high value of alternating current to the screen grids which function as control grids for their respective tubes.