This circuit provides a high intensity pulsating signal to a speaker. The circuit is from an American 90's documentation. The power supply is 12 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....