Found in an American publication of 1968, this circuit makes use of a pilot light of the time. It can be replaced with LED with appropriate series resistor. Transistors may be modern equivalents.
Based on the LF256 operational amplifier, this circuit was found in the September 1989 issue of...
We find this circuit in a 1980s documentation. The circuit can be applied to modern operators with...
January 2017 - New ROHM TFZV series of zener diodes is now available from Mouser Electronics. The...