Walter,
Congratulations! Here's something from the MAFCA
sight(http://www.mafca.com) about redoing the horn for 12v.
Question:
I would like to know how to rewire a Model A Sparton Horn
from 6 volt to 12 volt. What size wire? Number of turns?
Answer:
To change the Model A horn from 6 volts to 12 volts, you
must rewind the two field coils. Leave the armature as it is. First
disassemble the horn to remove the brushes and the armature. Unsolder the
two wires at the connector clip ( one from each field coil.) Note the
direction of winding on the coils. The two coils are wound in opposite
directions. The rule of thumb is that when you double the voltage, you use
1/2 the wire size and double the turns. So going from 6v to 12v use 24
gauge wire (original wire is 20 gauge, 1/2 that size is 23 gauge, but
almost impossible to find 23 gauge so I have always used 24 gauge readily
available at Radio Shack). Six volt coils have 45 turns and I have been
using 100 turns with 24 gauge wire with great success. Be sure to use
coated wire, normally used to wind RF radio coils or speaker coils. After
winding the horn coils I usually brush a coat of light varnish to help
insulate. The windings do not need to be real tight or in neat rows. In
fact I found that if I wrapped just tight
enough to form the wire
around the core, and laid about 6 or 7 turns per layer, without being too
careful how straight each wind was, I got better results on horn
operation. In looking at a lot of original horns, some were manufactured
with very precise and straight windings and some were wound
very
haphazardly.
Have fun,
GW
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