We found this circuit in the Radio Electronics Handbook magazine special edition of 1992. The circuit uses an optocoupler as an electronic potentiometer.
This circuit is from a 1969 General Electric manual. The SCR may be the TIC106. Similar circuits...
This circuit was found in a January 1981 Radio Electronics magazine. The transistors are the well...
We found this circuit in a 1991 publication. It is intended for low-impedance microphones,...