This circuit was found in an English publication from 1967. The circuit is for listening on a phone. Transistors are types of germanium of the time.
XTAL from 4 to 20 MHz can be used in this oscillator. The XRF choke can range from 10 to 100 µH...
This two-transistor amplifier stage has a feedback network allowing a voltage gain between 10 and...
In the figure we have an interface using an optical coupler and the comparator LM339 or any...