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.
Operating at just 1.35 V this circuit was found in a 1969 Electronic Design. The circuit makes use...
Found in European documentation from the 1980s, this circuit was originally designed for computer...
This grid-dip meter was found in a 1956 documentation from Sylvania. It can be implemented with...