This simple tone control using two transistors was found in an Electronics Today International of the 90s. Transistors are general purpose NPN types, like the BC549 for greater gain.
This circuit, from the 1990 Motorola Dataar Databook, can use any LM139 series comparator. The circuit...
We find this circuit in a 1980s documentation for amateur radio. The circuit shows how to switch...
With this circuit found in a 1965 Electronic Design, it is possible to read a peak voltage of up to...