This diagram was found in the November 1972 issue of Radio Electronics magazine in an article describing benchtop equipment. The transistors are of the time and the frequencies are given by the coils.
This circuit is from an old American documentation, from 1977, but it can be implemented with more...
This circuit was found in a 1970s American documentation. It can be applied to almost any...
This circuit generates an accurate 1 Hz signal controlled by a crystal. The circuit is from 1995...