We found this circuit in a 1977 factory documentation. The operational amplifiers can be 741 and the symmetrical power supply. Capacitors can be changed for operation at other frequencies.
This circuit was found in General Electric documentation from 1964. It makes use of a PUT, called the...
This mid-frequency amplifier circuit was found in an American publication from the 1950's. The...
The circuit with a common operational amplifier uses a zener as a reference. The circuit is from...