Howard,
If you have the original Altette from 1951, it is the worst type of all Altettes to get working. Especially if you don't have a clue how to go about it.
The first thing to do is clean the points and ensure that the resistance across them is as close to 0 as possible.
Check the coil resistance, should be less than 0.6 ohms for 6V.
Next, assemble and loosen the pushrod locknut and back off the pushrod.
Set up the horn on a bracket held in a vice and set up a dial indicator bearing against the centre of the diaphragm.
Apply voltage to horn and read movement.
The movement has to be set to around 0.010" by shimming with paper gaskets under the diaphragm.
Note that there must be an audible "click" as the armature contacts the pole with 0.010" movement.
If you get the movement right without the "click", the horn will sound weak.
Usually the correct movement without the "click" is caused by too much shimming.
After you have got this right, adjust the pushrod in the armature until the horn sounds right.
A front and back picture of your horn will enable me to positively identify which type you have.
If you were in Australia, I could have done it for you.
Good luck!
Trev.
