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 sophisticated RPM counter circuit with discrete integrated circuits was obtained in a 1993...
We found this circuit in an old American documentation. The operational amplifier is not common...
This oscillator can be found in other articles on the site. This is from a 4 MHz documentation, remembering...