This circuit was found in a 90s American publication. The same configuration appears in several places on this site, obtained from different sources. The lamps can be replaced by LEDs.
Found in an Analog Devices documentation from the 90s, this circuit uses a component of the time,...
This circuit was found in Philips documentation from 1965. No information was given about the...
This circuit was found in the June 1990 issue of Radio Electronics magazine. Integrated circuits must...