The expected answers were:
(a) The difference between class B push-pull amplifiers and Class A amplifiers in terms of the three specified parameters are as follows:
- Operations: Transistors utilized for Class B push-pull amplifiers are biased to operate during only half of the input cycle; for class A amplifiers, the transistors are biased to operate over complete input cycle.
- Output power: Output power obtainable from class B push-pull amplifier is about twice that available from a comparable Class A amplifier for the same power input.
- Efficiency: Class B push-pull amplifiers are much more efficient (maximum efficiency of about 78.5%) than class A amplifiers, for which maximum possible efficiency is 25%.
(b) Most amplifier distortion types can be reduced through negative feedback, whilst others will improve with choice of transistor operating input.
This question was on amplifiers. Many candidates could not answers recall question correctly.
