This circuit works like a solid-state contactor. We find it in General Electric documentation from 1965. SCRs can be modern equivalents according to the controlled load.
This oscillator with crystal for overtone operation was found in an old American documentation. The coil...
This test consists of a simple Hartley oscillator using a transformer of the type found on older...
We found this circuit in an American 1980s documentation. The transistors can be equivalent as BC548...