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 was obtained in the publication 101 Electronics Projects of 1979. The circuit can be...
With the indicated components, this circuit oscillates around 3.6 kHz. The components can be...
This interesting configuration was found in a 1965s Electronic Design. It makes use of components of...