This circuit is from Motorola's 1990 Linear Databook. The transistors allow equivalents and the output power depends on the supply voltage. The power supply must be 30 V symmetrical.
I found this simple circuit in an English magazine from 1984. The circuit can be assembled easily...
This circuit was found in a 1958’s publication. It uses germanium transistor, availble that time....
This capacitance or approximation relay was found in an ancient American documentation. The SCR...