This circuit was obtained in a Popular Electronics from the 90's. The gain depends on R4 and R3. Transistors are general purpose types.
This ohmmeter can be made with a scrap milliammeter used for continuity tests or even resistance...
This circuit was found in the November 1992 issue of Radio Electronics magazine. The circuit has...
Found in an English Maplin documentation from 1983, this circuit generates separate frequency...