Each of these devices uses a hand-crank magneto generator (from an old telephone) to generate an AC electrical current. These magnetos are connected, in parallel, to 2 or 3 light sockets which are then connected to two terminals. The more light bulbs screwed in, the more resistance is present in the circuit, so the less current to the terminals. The light bulbs do light up if they are screwed in. With all light bulbs screwed in the resulting current is very mild. Without the light bulbs in the circuit the current coming straight from the magneto can be quite “shocking”. Some of the stronger devices also have a potentiometer to adjust the output. Others have a switch that engages a working bell.

The screw terminals used on these devices also function as “banana plug” connectors. All units also have a mini-phono jack.

Each mag produces a slightly different wave form. Some are “spikier” than others, some are smoother, and some are stronger.