Horn Rewiring: Model A Sparton Question

I’m interested in rewiring a Model A Sparton Horn from 6 volts to 12 volts. Could you please provide guidance on the wire size and the number of turns required for this conversion?
Answer:

To convert a Model A Sparton Horn from 6 volts to 12 volts, you’ll need to rewire the two field coils while leaving the armature as it is. Here’s how to do it:

1. Disassemble the horn to remove the brushes and the armature.
2. Unsolder the two wires at the connector clip (one from each field coil).
3. Pay attention to the direction of winding on the coils; they are wound in opposite directions.

The general rule for doubling the voltage is to use half the wire size and double the number of turns. In this case, going from 6 volts to 12 volts, you should use 24-gauge wire. While the original wire is 20-gauge, it’s challenging to find 23-gauge wire (which would be half the size), so 24-gauge wire, readily available at places like Radio Shack, is a suitable choice.

The 6-volt coils typically have 45 turns each. To convert to 12 volts, you can wind each coil with around 100 turns of 24-gauge wire. It’s essential to use coated wire, usually used for winding RF radio coils or speaker coils. After winding the horn coils, consider applying a light varnish coat to help with insulation.

When winding the coils, they don’t need to be wound tightly or in perfectly neat rows. Some original horns had precise and straight windings, while others were wound more haphazardly. Experimenting with slightly looser windings and a less structured approach may yield better results in horn operation.