Found in an American publication from the 1980s, this circuit can be found in commercial sound equipment of the time. The list with the component values is given next to the diagram.
Found in the 1991 Electronics Experimenter Handbook, this circuit detects voltage variations in...
This RCA commercial radio had its circuit published in Radio Electronics magazine in August 1959....
This circuit can also use other series operational amplifiers such as MC33172, MC33174, MC35171,...