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.
Found in an Electronic Design from the 80's, this circuit monitors a three-phase line, activating a...
This high impedance step suggested by an English publication can operate up to 1 MHz with 1 V rms...
This powerful high-fidelity amplifier was described in an article in Radio Electronics magazine in...