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 protects the speakers in case the amplifiers have problems. With a continuous voltage...
We found this circuit in an American documentation from the 60's. The transistors are made of...
This circuit provides a signal when dialing occurs. The circuit is powered by the telephone line...