We found this circuit in a documentation for radio amateurs from the 70s. The transistors can be the BC548. With it, small speakers of 4 or 8 ohms can be used as microphones.
We found this circuit in a 2002 documentation. It still uses old type plugs, but it can be adapted to...
This circuit was proposed by a 1965 Electronic Design. Its purpose is to widen the line transients...
The circuit shown can measure currents less than 1 uA and is powered by two 1.5 V batteries in a...