The distortion resulting from the use of center-tapped transformers in a class B power amplifier

The transformer-coupled Class B amplifier is investigated with regard to harmonic distortion caused indirectly by the self-resonance of the transformer primary. For undistorted Class B operation, the short-circuited flow of even harmonic unbalanced mode currents is essential. When these harmonics are at a frequency at which the transformer primary is close to self-resonance, the flow is impeded and harmonic plate voltages will appear. A slight circuit asymmetry or nonlinearity will permit the harmonic voltages to couple into the load, as harmonic distortion. By a similar effect negative feedback circuits can increase distortion by an amount for which formulas are given.