This circuit is from a 1967 Triplett manual. The circuit uses components of the time, the common FET and the general-purpose bipolar transistor.
This metal detector was found in a 2001 Poptronics, but it can still be easily assembled, as the...
This circuit for 6 lamps was found in old American documentation. The supply is of high voltage...
With this circuit it is possible to have a safe indication of the balance point for the signals of the...