Found in Popular Electronics from the 90s, this circuit detects modulated infrared radiation and serves as a test for remote controls. Infrared sensors equivalent to the one indicated can be used.
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....