We found this circuit in a 1965 Electronic Design. The transistors are from the era, and modern equivalents can be tried out.
This simple metronome, from 1985 documentation uses only transistors and has two settings. For...
We found this circuit in a 1988 documentation. The circuit uses a conventional complementary...
This circuit was found in a 1990 publication. The sensors are electrodes placed in the water tank...