Complementary Push-pull amplifiers use two “complementary” or matching transistors, one being an NPN-type and the other being a PNP-type with both power transistors receiving the same input signal together that is equal in magnitude, but in opposite phase to each other. This results in one transistor only amplifying one half of the input waveform cycle while the other transistor amplifies the other half of the input waveform cycle with the resulting “two-halves” being put back together again at the output terminal.
In complementary push pull amplifier neither an input nor an output transformer is needed. The main difficulty with this circuit is the if there is unbalance in the characteristic f the two transistors considerable distortion will be introduced.