This circuit was obtained in an old European publication on FETs. The FET admits equivalent and the feed must have good filtration. Signal input cables and output cables must be shielded.
This circuit was found in a 1975 documentation. Current general-purpose transistors can be used,...
We found this circuit in a publication for radio amateurs in 1974. The bipolar transistors can be...
This conventional humidity or water alarm circuit was found in an English documentation from 1974....