We found this circuit in a documentation for radio amateurs from the 70s. The transistors can be the BC548. With it, small speakers of 4 or 8 ohms can be used as microphones.
This configuration, found in many other circuits in this section, was obtained in a 1970s American...
This circuit for incandescent lamps was found in an American documentation from the 80s. The...
Found in old English documentation this circuit can be made with a BF245 or equivalent. Coils are...