This circuit operates from 25 to 65 kHz depending on the transducer used and the settings. We found it in the Radio Electronics magazine of July 1985. The 9V to 12V power supply is not given.
This circuit is from an old 80's linear circuit manual. The configuration can be implemented with modern...
This detector with ultra-low deviation was found in an American documentation from the 90s....
This circuit was found in a Signetics documentation from the 1980s. Next to the figure are the...