Found in a Popular Electronics from the 90's, this circuit is used to recognize the frequency of a modulated infrared signal. The LM567 circuit must not be supplied with voltages above 9 V.
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....