A sidetone oscillator is a special audio astable multivibrator. Keying is accomplished oscillator that is turned on and off with the by applying a positive dc potential, developed transmitter. The oscillator is rf-driven and bat- from the rf signal, to the reset terminal of the tery operated
It uses a 555 IC timer as an 555.
Electronics: Introduction to LC Oscillators circa 1974 US Air Force Training Film