Definition
An electronic amplifier biased so that current flows in the output device for less than half of each input signal cycle. Because it conducts only during a small portion of the cycle, a Class-C amplifier is highly efficient but produces a heavily distorted output, so it is used almost exclusively with a tuned (resonant) circuit that restores the signal to a clean waveform. It is most commonly used as the final power stage in radio-frequency transmitters.
Plain English
A type of amplifier that switches on only briefly during each cycle of the incoming signal. This makes it very efficient at producing power, but the output is rough and only useful when paired with a tuned circuit that smooths it back into a clean radio signal.
Context Anchor
Seen in aircraft electronics and avionics maintenance, especially in descriptions of transmitter power circuits in radios or transponders.
Derivation
The 'class' system (A, B, AB, C) was developed by early radio engineers to label amplifiers by how much of each signal cycle the device conducts. Class A conducts the full cycle, Class B about half, and Class C less than half. The letter is simply a category label, not an abbreviation.
Why Pilots Care
Aircraft radios rely on Class-C stages to transmit strong signals over distance while drawing minimal electrical power from the aircraft system.
Analogy
It is like pushing a playground swing with short, well-timed pushes instead of pushing continuously. If the timing is right, short pushes can keep the motion going with less effort.
Intuition Check
Do not confuse Class-C Amplifier with Class C airspace. Here, Class C is an electronics operating class, not an airspace category.
Example Sentence 1
The final stage of the VHF transmitter uses a Class-C amplifier to produce the radio-frequency output sent to the antenna.
Example Sentence 2
Class-C amplifiers are chosen for the transmitter final stage because they deliver high power with good efficiency.