We found this circuit in a 1967 American documentation. The diodes are general-purpose and the input frequency can be between 80 and 800 Hz.
We found this circuit on Radio Electronics from July 1990. It triggers a relay with a touch of the...
These three circuits have different treble responses. We found them in the February 1970 issue of...
This photoelectric cell light relay was found in Radio Electronics magazine from April 1958. The...