This circuit is from an old Japanese publication of 1962. The circuit uses two batteries, one for the filaments of the tubes and the other one of high voltage for the plate circuits.
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...