This circuit is from an 80's Electronic Engineering. The base is a common operating and 4 single integrated voltage comparators. The circuit directly drives 4 indicator LEDs.
This interesting adjustable power supply uses the transistors themselves as controllers and...
This alarm from an old 1978 publication uses PNP transistors and driver and output transformers that are...
This is a typical source of the time (1989) using the well-known regulator integrated circuit 723....