Found in a 1949 Radio Electronics, this 4-tube circuit was fed directly from the mains with a half-wave rectifier.
A tap on sensor X1 of the circuit shown in the figure causes the flip-flop formed by the 4 NAND...
This circuit, from Intersil Databook since 1983, shows the use of the ICL7107 in a voltmeter with...
I got this4 circuit from Hands-On Electronics, 1988. The American magazine no longer exists, but...