Found in a 1949 Radio Electronics, this 4-tube circuit was fed directly from the mains with a half-wave rectifier.
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...