We found this circuit in the magazine Eletcronics Now of July 1994. The power supply is according to the relay and the transistor can be any general purpose one.
This electronic Morse Key for telegraph message transmission was found in an American 1980s...
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...
Found in a 90s Radio Electronics, this circuit uses an AD590 or AD592 for remote temperature...