The idea of this circuit found in a Radio Electronics from January 1966. The idea of the circuit is to improve the reception of audio signals, mainly telegraphy, working as a filter.
This simple circuit can use any general-purpose transistor. The power supply must be isolated. The circuit...
This is a configuration much explored by assemblers, being found on this site in dozens of similar...
The frequency of this oscillator depends on T, which for the audio band can be a common output...