The sensor used in this circuit is uncommon today, however equivalent types can be tried. The comparator also supports modern equivalents. The circuit is from 80's documentation.
This circuit was found in a 90s Radio Electronics. It is intended to amplify the sound channel of...
This circuit uses a 4020 counter that divides the frequency up to 210, being found in a former...
This circuit was found in a Radio Electronics magazine from May 1967. The circuit has the time...