For what portion of a signal cycle does a Class C amplifier operate?

A Class C amplifier is biased well beyond the cutoff point. As a result, the amplifying device remains off for most of the input signal's cycle and only conducts during the highest peaks, which amounts to less than 180 degrees. Because the device is off for the majority of the time, Class C amplifiers are highly efficient, wasting very little power as heat. However, this very short conduction angle heavily distorts the waveform. Due to this distortion, Class C cannot be used for linear applications like SSB or AM. Instead, it is used for constant-envelope modes like CW or FM, where a tuned tank circuit acts like a flywheel to smooth the short pulses back into a full sine wave.