Found in a manual of integrated circuits from the 90s, this circuit makes use of that time components. It is indicated to limit the current in 6 V chargers.
This circuit that can amplify signals from 0 to 30 MHz was found in a 90s Popular Electronics....
This circuit makes use of a low impedance microphone. The relay is according to the supply voltage...
This circuit for incandescent lamps was found in a 70s documentation. The circuit uses an SCR...