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 1-transistor circuit for currents up to 50 mA was found in the August 1974 Radio Electronics...
This circuit is from 1997 when Camcorder-type video cameras that used powerful batteries were...
This is a commercial circuit for an AM radio with 4 transistors, published in a Japanese magazine in...