This simple audio and RF signal tracker was found in a Japanese publication in 1967. The transistors are made of germanium and the headphone is made of crystal.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...