This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms and excites a load of 16 ohms. The integrated circuit of the time is the PA237.
This useful benchtop power supply uses a single LM350 integrated circuit as a regulator. The...
If the input voltage falls below 12 V the LED glows up. Other voltages can be monitored by...
The circuit shown is only for analog telephone lines. I found it in Popular Electronics (1991). It...