What is a push-pull amplifier?

[FAQ Team]

Name for the configuration of the output stage. We saw in another FAQ answer that Class B operation is efficient, but suffers from the disadvantage of outputting an amplified, half-wave rectified version of the original signal.

This won't do for Hi-Fi!

Fortunately, we can get around the problem by doubling up on valves. One valve is fed with the signal to be amplified and the other is fed with an inverted signal. During the first half-cycle, the first valve conducts and during the second half-cycle the second valve does so. If we now invert one of the outputs and add them together, we have neatly reconstituted the original waveform. This is the basis for the push-pull amplifier. The first inversion is carried out by the phase-splitter and the second by the output transformer.