Why are class A common emitter amplifiers not suitable for use as power amplifiers?

Question

Why are class A common emitter amplifiers not suitable for use as power amplifiers?

Answer 1

efficiency  

Answer 2

Only about 25% of the total power used by the amplifier is actually sent to the load (speaker, etc.).  Which means that about 75% is wasted as heat.  For a large, high-powered PA, this means using excessively large heat sinks and using components that are perhaps unnecessarily large.  Some Class A amps only supply 12.5% of the total power to the load.  The theoretical efficiency limit for Class A is about 50%.

For a 100 W highly linear Class A amplifer (12.5% to the load), this means the rest of the amplifier is dissipating 700 Watts internally!

Class AB amplifers are much more efficient and can approach 50 or even 66% efficiency depending on the bias.  Smaller heat sinks and components can be used to achieve the same power levels as Class A amplifiers.

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