This variable oscillator with power step for alarms was found in an American documentation from the 90's. The power transistor must be equipped with a heat sink.
This circuit was found in an Experimenters Handbook of the 1990s. The purpose of this circuit is to...
This source, from a 1982 documentation, uses a triac to control the power and voltage applied to...
This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit has...