This transistor tester with different gain ranges was found in documentation from the 1980s. The circuit can still be implemented with more modern components and used with general purpose transistors.
This circuit, from ancient French documentation, produces a rectangular pulse from input pulses...
This timer for small intervals, but which can be increased with the increase of R1, was obtained in an...
Found in a 90s Radio Electronics, this circuit can supply currents of a few amps, according to the power...