This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
We found this circuit in the May 1972 issue of Radio Electronics magazine. Its purpose is to teach...
This circuit is from 1985 documentation. The integrated circuit used is not very common today, but...
This circuit consists of a simple continuity test with two transistors forming a relaxation...