This circuit is from 1967 General Electric documentation. It uses SUS which are not very common components today. The maximum frequency should not exceed a few kilohertz.
This filter that rejects determines frequency (notch) was found in a Popular Electronics of 1993....
Found in Popular Electronics in 1992, this circuit can generate signals up to a few tens of...
This circuit turns on an old cassette recorder when the telephone rings, thus enabling the...