This circuit can work with almost any JFET. The circuit is from an Electronics Now from April 1993. It is powered by a 12 V battery, but can also be powered by 9 V.
We find this circuit in an old documentation, but it can be made using modern transistors. The circuit...
We found this circuit in a spy book from the 90s. Transistors admit equivalents and the coil can...
The circuit shown was found in an American documentation from 1964. The circuit uses transistors of...