Found in a 70s RCA manual, this circuit uses transistors from the era. Equivalent types can be used such as TIP31 for Q1 and BD135 for Q2.
This is one of many metal detector versions of this type found on this site. This one uses a small...
This circuit was originally designed to measure the gain of two-door RF MOSFETs as indicated by...
Found in a 1967 American electronics magazine, this circuit has an input impedance of 2000 ohms....