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 preamp with a transistor for turntables with crystal capsules was found in a Japanese...
This variable frequency oscillator generates signals that have a recurrence frequency determined by...
This circuit with neon lamp and unijunction was found in the September 1970 Radio Electronics...