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 conventional series reducer circuit reduces the voltage of a 12 V battery to the selected value...
In the figure we have a converter that generates a negative voltage from a positive voltage...
This circuit covers the bands from 1.8 to 150 MHz, with plug-in coils whose characteristics are...