This circuit appears in several versions in publications of the time and can be modified by changing the capacitors. This one is from Radio Electonics magazine from October 1992.
To operate with high input voltages using a 3-terminal voltage regulator such as the LM340-15, we...
We found this circuit in the October 1988 Radio Electronics magazine. The circuit is still current...
This audio signal relay was found in an American 1980s documentation. The relay is in accordance...