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 circuit was obtained from an article in Radio Electronics magazine in October 1966. It...
This circuit uses a feedback system that latches the relay when closed. The circuit uses an...
This circuit was obtained in a 1976 English magazine, and can be assembled with equivalent...