This circuit, found in a 1964 US documentation, consists of a selective amplifier that lets only 10 Hz pass around a 400 Hz center frequency with the indicated components.
This circuit is designed to activate an automotive alarm after 8 minutes of activation. Of course...
This is one of the channels of an amplifier suggested by Westinghouse in 1970s documentation. The circuit...
This astable multivibrator, well known to all, was found in the Raytheon transistor application manual of...