This circuit was found in a RE Experimenter Handbook from the 90's. The components are of the time, rare nowadays, except the 555 and 4017.
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...