This signal injector and tracer (follower) was found in an old American documentation. The transistors can be general use and power is made with one or two common cells.
The circuit in the figure is from a source with the possibility to adjust the output voltage from...
We found this circuit in a 1965 General Electric manual. The circuit applies to incandescent lamps only and...
We found this circuit in an American publication from 1977. The circuit drives two LEDs according to...