We found this circuit in Radio Electronics Special Projects from 1992. The circuit turns on the power when the microphone plug is inserted into the input jack.
This low-power circuit for small lamps according to transistors was found in the January 1959...
This dimmer for the 120 V (117 V) network was found in the magazine Electronics Now of August...
This old amplifier uses germanium transistors from the time. The circuit is from a Mullard...