This circuit is from an 80's Radio Electronics. It triggers a load powered by the power grid from the audio signal captured by the microphone.
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...