We found this circuit in a Radio Electronics from February 1966. The transistor is from the time and so are the transformers. The circuit is battery powered. Observe the impedances.
This configuration, found in many publications, is from an American book from 1981. The power...
The circuit shown is from an American publication from 1970. It produces a tone that attracts fish...
Found a documentation on PCs from 1996, this circuit can be used as a shield. The relay is rated at...