This circuit was found in the August 1993 Electronics Now magazine. It is for telephones used on common old-style analog lines.
With a strong positive feedback (via a 10 M resistor) we can get the trigger setting for the...
The critical component of this circuit is the transformar. We found it in an 1980s documentation....
This old oscillator using germanium transistors has a high impedance headphone as inductor to...