This circuit was found in a 1967 General Electric documentation. Tunnel diodes can oscillate at very high frequencies. These are not currently easy to obtain components.
This is a simple 1-digit voltmeter circuit using voltage comparators. It was found in a 2004...
This circuit is from old documentation, but the regulator may be 78xx series equivalent and the...
This circuit appeared in the November 1995 issue of Electronics Now magazine. The circuit uses...