This static switch or triac contactor was obtained from Philips 1969 documentation. The SCR is from the era, but modern equivalents depending on the load can be used.
This circuit was found in documentation from the 70s. We can try current JFET transistors....
This is the power supply circuit for the amplifier in the previous circuit. The source is...
This bridge circuit is designed for 8-ohm speakers delivering a few watts of power. The circuit is from...