This circuit uses a feedback integrator. We found it in Ferranti's transistor manual from 1974. Transistors are general-purpose types at the time.
This circuit, which combines a bipolar with any JFET, was found in the April 1993 issue of...
This simple metal detector was found in a 1960 Sylvania transistor manual. The phone must be high...
Found in documentation from the 90s, this circuit was used in communications receivers of the...