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 sensor was published in Radio Electronics magazine in April 1962. The two-transistor circuit...
Another of the many similar configurations we have in this section. This one is from a Radio...
This circuit like the previous one is intended for 24V x 3W solenoids being connected from the...