This circuit was obtained from an Electronics Design of 1964. The circuit makes use of tunnel diodes that are uncommon today. The circuit works with very weak signals.
This circuit is from a documentation from the 60s. The circuit can be built with transistors like...
Using a small speaker as a microphone, this 10-LED circuit was found in the March 1992 issue of...
This TTL dice is from an old publication from 1978, but it can still be assembled, as the...