Class AB Amplifiers

Author: J.B. Hoag

When the C-bias voltage is of such a value that the tubes of the circuit in Fig. 23 I are operating at a point in between the cutoff and the center of the straight section, small signal voltages will be amplified as in a Class

A circuit and large signal voltages will be amplified approximately by the Class B method. This so-called Class AB amplifier (Fig. 23 L) offers low distortion for small signal intensities and high efficiency at high signal levels.

Fig. 23 L. The principle of operation of Class AB amplifiers

Class AB₁ amplifiers draw no grid current and Class AB₂ amplifiers draw grid currents at the higher input signal levels.