Found in a 1965 General Electric circuit manual, this circuit uses SCRs from that time. Modern equivalents according to the power can be used.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...