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.
This circuit without sensors in series triggering an SCR was found in volume 5 of the 1995...
We found this circuit in an old documentation, but the circuit is current due to the components it uses and...
This circuit is from an old manual of linear integrated circuits. The LM185 is not a common...