This circuit was found in American documentation from 1966, but it can be assembled with a modern equivalent transistor. The circuit is based on a mechanical tuning fork with a coil feedback system.
This circuit is from an American documentation from 1975. However, the circuit is still current, since...
This is a very simple continuity tester, powered by one or two batteries of any size. The...
This amplifier for instrumentation with very high input impedance was found in a manual of JFET...