This circuit was found in a Popular Electronics from the 90s. Its purpose is to disable the output of an FM or VHF receiver between stations, preventing the reproduction of hiss.
A circuit for controlling the temperature of a heating element was found in a Mullard transistor manual...
We found this circuit in a 1992 Popular Electronics. The circuit has an optical sensor with LED...
I found this circuit in an old English magazine from 1979, but it can be easily assembled with...