A tank circuit drives the output of the amplifier during the short conduction times of the transistor. The remainder of the time, a constant square wave from the transistor's conduction pulses keeps the oscillation of the output going until the next time the transistor conducts. Can someone enlighten me on how a transistor in a tuned class C can put out a square wave? Original Quote from a website: "If you parallel a capacitor and an inductor you form a tuned circuit. If you pulse a voltage across a tuned circuit, it oscillates as magnetic fields in the inductor and electrostatic fields in the capacitor transfer energy to each other. The constant square wave pulsing from the transistor maintains the oscillation to produce your output waveform."