This source for 50 W amplifiers per channel was found in 1967 Delco documentation. Transistors are from that time, difficult to obtain today.
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...