Class B and AB amplifiers employ 2 active devices to cover the complete 360 deg of input signal flow. Each transistor is therefore biased to perform over approximately 180 deg of the input signal. Class B bias is when the collector current I with no signal is just conducting (about 1% of maximum possible value). Class-AB bias is when the collector current I is about 1/4 of maximum possible value.
The class-AB push–pull output amplifier circuit below could be the basis for a moderate-power audio amplifier. 

प्रवर्धक का एक व्यावहारिक परिपथ

Q3 is a common emitter stage that provides amplification of the signal and the DC bias current through D1 and D2 to generate a bias voltage for the output devices. The output pair are arranged in class-AB push–pull, also called a complementary pair. The diodes D1 and D2 provide a small amount of constant voltage bias for the output pair, just biasing them into the conducting state so that crossover distortion is minimized. That is, the diodes push the output stage into class-AB mode (assuming that the base-emitter drop of the output transistors is reduced by heat dissipation).

This design automatically stabilizes its operating point, since overall feedback internally operates from DC up through the audio range and beyond. The use of fixed diode bias requires the diodes to be both electrically and thermally matched to the output transistors. If the output transistors conduct too much, they can easily overheat and destroy themselves, as the full current from the power supply is not limited at this stage.

A common solution to help stabilize the output device operating point is to include some emitter resistors, typically an ohm or so. Calculating the values of the circuit's resistors and capacitors is done based on the components employed and the intended use of the amplifier.
स्थिर अभिनति या बेस बायस
क्लास-बी तथा एबी प्रवर्धकों की अभिनति
Signal requirements
एमिटर में प्रतिरोध के साथ फिक्स्ड बायस