This 1965 Philips circuit uses old company transistors like the BFY51 and BFY50. The circuit is powered by 12 V and the power gain is 8.9 dB.
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...