Conversion efficiency in Power amplifiers....

This classification is concerning "Operation Point of Transistor". I can not understand conversion each other??.

If the matter is power amplification you must use a large portion of characteristic curve of transistor that will not be linear!

The class A amplifiers must be operate a linear region so that to get a duplication of input signal. Input (base line) resistance is essential about this linearity. You might have to work even graphically on transfer curves to get a non-distorted output. Their power efficiency is low. For this reason they are used as driver for B or C class amplifiers or stand alone if low power rates are enough. Their usable frequency band is wide opposing B and C.

Class B amplifiers are biased so as to no current flow via collector during input signal value is zero and used almost always as couples. One component for positive going inputs and other for negative going inputs. Efficiency is 80% maximally.

Class AB is a special form of class B with reduced "transition distortion" and used for sound / video power stages.

Class C amplifiers have very high power efficiency if they are used narrow band or fixed frequency amplifiers. (Radio transmitters for example).

Search in wikipedia using "Electronic Amplifier" to find related shematics.

I hope these are useful, bye...