Large signal amplifier
The early stages of amplifier systems are dealing with small signals. These stages are designed to give good voltage gain. Small signal transistors have a power rating of less than half a watt and power transistors have a power rating of more than half a watt.
The later stages of an amplifier system have much larger collector currents, because the load impedances are much smaller (i.e.: Loudspeaker 1Ω, 4Ω, 8Ω, 16Ω).
Efficiency is most important when large amounts of signal power are required:
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