W/NG horn repair

The W/NG has had a rather nice military Altette for years, which I found I think on eBay. It's always worked, but never very well - not very loud and with that strangled parrot sound common to Altettes with shims missing or loose parts.

One idle moment I tinkered around with the adjuster, which is quite easy to get to in these early Altettes being hidden under a big cap nut on the front of the horn. I could get it to sound a bit better, but I was puzzled by the adjuster moving out of position after I had tightened it. I realised eventually that the armature, which is held to the diaphragm by a large nut and which contains the adjuster, was loose on the diaphragm.

No matter! Says I, I will tighten it up. Weeks of soaking in various solvents followed as these are notoriously tight and being out in the weather, will corrode up. I eventually loosened it with a big tube spanner, only to find that it wasn't loose on the diaphragm at all but that there was a nice ring of diaphragm material held tightly by the nut but that was no longer attached to the rest of the diaphragm. A fatigue failure after 80 years of service!

Now, you can't buy these parts. I had another Altette to cannibalize, but I also have a TIG welder. After a few attempts (during which time I realised my Tungsten tip was contaminated, hence the mess on the left) I got a decent weld all around and re-fixed the broken ring in its original position.

The Dremel made short work of the excess weld:

In adjusting the horn, I was messing about with the screws on the back. It's important that the internal contact breaker assembly is level:

The two screws on the right fix the contact breaker; the one on the left adjusts the level. Once you have it level, leave the screw alone!

Here's the diaphragm reassembled with the armature and the adjuster. I assembled the rest of the horn and tested it - it didn't work, but the coiled pulled the armature in. Why? Because the diaphragm is upside down in this picture...

With it turned over, it worked beautifully and sounded better than it ever has.