Class-AB Operation

Author: N.H. Crowhurst

Class-B operation Is only really suitable for amplifiers where constant skilled attention is available to insure the conditions are correct. Most practical amplifiers are used under circumstances where they are installed and forgotten, A class-B amplifier would likely give considerable distortion if this were done.

Class AB amplifier operation

For this reason a popular method (called class-AB) consists of splitting the difference. For small outputs, up to about half maximum power, both tubes are conducting current all of the time. When full output is needed, each tube goes beyond the zero plate current for part of the cycle, but for not a complete half-waveform. This design results in an amplifier that is less critical in operation and can Ke used without critical selection of output tubes and adjustment of bias.