This shield circuit, from a documentation from the 70s, employs an optocoupler with two SCRs to control a small load of 1.5 W.
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...