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 is the traditional configuration of a 6 or 12 V source with 7806 or 7812 integrated circuits, for a...
The circuit shown in the figure can act as a home repeater for AM signals from the output of an...
We found this circuit in a 1987 documentation. It is a multi-tester with neon lamp and LEDs...