This flip-flop circuit with general purpose transistors was found in American documentation from the 1980s. The maximum operating speed depends on the transistors. Diodes are commonly used.
The figure shows how to use an LM3914 with a variable range moving point. The circuit has an...
This circuit was found in a 90s Popular Electronics. It uses a varicap that admits equivalents. The...
This circuit is from an Electronics Now from 1998 and can be easily assembled with other JFET...