This simple audio signal tracer or follower can be made with a BC548 instead of the original transistor. The output is made in a small crystal phone. The power can be from 5 to 9V.
This remote listening device was found in documentation from the 50's. The transistors used are...
Found in a 2005 Linear Technology application manual, this circuit provides outputs from a current...
Found in the September 1992 issue of Radio Electronics magazine. This circuit generates pulses that...