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.
We found this circuit in a 1988 documentation, but all the components used are still common today....
This variable high frequency oscillator circuit was found in an old English documentation. The...
This crystal fundamental frequency oscillator can operate at frequencies up to a few tens of...