This alarm oscillator was found in the December 1974 issue of Radio Electronics magazine. The power transistor must be equipped with a good heat sink. The Frequency basically is given by C1.
We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer...
This circuit can be used to power 6, 9 or 12 V devices in your car. The maximum current is 1.5 A....
This simple measuring bridge allows the capacitance m of some pF to microfarads to be measured...