How to get an Altette horn exchange or repair

[Steverat]

Don't touch that lock nut or adjust the centre screw.
This should be set initially to give the desired armature movement.
The adjustment is done firstly under the dome nut on the front and fine tuned with the small screw on the rear.
This is for this particular model.
However, this is all academic if someone has been there before you and had a play.

Oh heck I played with it on the bench tonight and the first thing I went for was the lock nut and screw. Got it to work too, sounds like an angry bullock. Yes, bullock. Not two of them. Flushed with success I then tried to strip the unit and came to a full stop when trying to unscrew the nut on the front underneath the big dome nut. It won't shift, and I'm a bit wary of forcing it since it sits in the middle of a delicate-looking diaphragm. Now that I have already sinned, I want to go all the way. I'm leaving the central front nut dripping with plusgas overnight in the hope it will yield to my desires in the morning. Which model have I got? Can you tell?

Further to what Trev said, once the nuts around the edge holding the bezel and diaphragm the diaphragm will come out, but has to be slid over in one particular direction first. It helps to know which direction of course, from memory you slide it in the direction AWAY from the terminals. If you look at some pics of ehe internal you will see why, the piece held on by that centre nut “interlocks” with the contact breaker.

Many thanks to you and Trev for the guidance, as you can see I’m up early to try it out in the garage. But 4:30am start is furtive even by my standards - SWMBO will be on warpath if I am found there before breakfast. There will be an interlude for Xmas and I shall post again in January. Once again many thanks for your help. Have a great Christmas! I’m sure you will do better than us on the weather front for starters.

[worntorn]

Oh heck I played with it on the bench tonight and the first thing I went for was the lock nut and screw. Got it to work too, sounds like an angry bullock. Yes, bullock. Not two of them.

That's close, just some fine tuning is needed.
I was told to adjust until it " sounds like a sick cow in heat"
 
Glen

[Steverat]

Thanks Kiwi and Trev,
I managed to strip it as you advised, now I bought some new dome nuts and I'm having the existing bezel rechromed, so with a lick of paint it should look good again. However (like Della Street)_ one thing puzzles me - the threads in the holdng bracket locations are 1/4" BSF, but the other 4 are about 3/16" - of course I can tap the smaller ones out and use 1/4" studding for all of them but I just wonder what the smaller ones should be - a 3/16" tap will go through them with lots of clearance but the 1/4" tap will not go in.

[chaterlea25]

Hi Steverat,
I think the threads are 1BA
Just to add more confusion
Open to correction?
John

[Rex]

When I did my 1936 horn a while back I'm pretty sure they were indeed 1BA. In my experience only manufacturers of electricals ever used odd BA sizes, although there's bound to be other applications.

[trevinoz]

They are definitely 1 BA.

[Steverat]

Yes you are right, it’s 0BA on the mounting stud holes and 1BA on the other 4. So it’s either make up 2 stepped studs or have different nut sizes

[KiwiGF]

Yes you are right, it’s 0BA on the mounting stud holes and 1BA on the other 4. So it’s either make up 2 stepped studs or have different nut sizes

I’m fairly certain you can buy dome nuts with the same across flats size, but having different thread diameter to suit the two stud sizes. See:

https://www.ebay.com/itm/LUCAS-ALTETTE-HEX-domes-USE-with-FLAT-ALLOY-Disc-Lucas-Nuts/362515649325?hash=item54679dd32d:g:a-EAAOxyOalTZ8N~

Also I vaguely remember when cleaning out the threads one of the two ba sizes is same as bsf, or close enough.

[trevinoz]

The large ones are not 0 BA but are definitely 1/4" BSF.
0 BA has a pitch of 1.0 mm and a diameter of 6 mm which is close enough to allow a screw to mate up to 1/4" BSF.
All of the acorn nuts are 3/8" AF as are the two 1/4 BSF nuts which secure the horn to the bracket.

[Steverat]

Thanks, I think I'm close to having it sorted now. got the 2off 1/4" BSF and 4off 1BA nuts and the studding is coming to suit.
One more thing  - the terminal screws. Mine are missing. If they are BA the sockets look like they must be 3BA??????

[trevinoz]

That would be 2BA, Steve.
Special hex head slotted screws. 1/4" AF brass.
Your picture shows one of them in place.

[Steverat]

 
Dont know what happened to it, not there now...
Thanks Trev.

[trevinoz]

You can probably get them from Taff or use a cheese head screw.
While you have it apart, lubricate the adjusting screw in the points, I use Neverseez or similar.