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 found in a 1988 documentation consists of a timer or sequential timer controller. The...
This resistance meter circuit was found in the February 1984 issue of Radio Electronics magazine. It is...
We found this circuit on the internet. The components are current, and the time depends on C1...