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.
CMOS inverters can be used as amplifiers, obtaining a flat response up to approximately 20 kHz....
The maximum time interval of this circuit depends on C1. Larger values can be used to get closer to...
This sonic relay or vox was found in a Popular Electronics from the 90's. The power MOSFET can be of...