This battery-powered 3-valve circuit was found in American documentation from 1947; Two batteries are used, one high voltage and one low voltage for the filaments.
This circuit was found in an ancient American documentation. Used integrated circuits are uncommon...
This circuit operates at a voltage of 1.3 V from a single mercury cell. We found in an old...
Found in American documentation from the 90s, this circuit uses common FETs. It has a range drift...