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Hi everyone.
I want to unmount the No15 soundboxes from Columbia 202 and 113a portables, but they they won't come. I'm weary of using too much strength. Can anyone give me tips about how I should proceed ?
Thanks.

The soundboxes on these two machines are different versions of the No.15, and are mounted differently. On the 113a, there is a screw on the underside of the arm, just behind the back of the soundbox. The screw has a pointed end, which locates into the tubular extension of the soundbox back. Undo the screw a few turns and the soundbox pulls off. It should be a loose fit, but if it's not, push it off from the back, by pressing on the centre flange. Don't pull it off from the front, or you risk tearing the red rubber insulators, and these are almost impossible to replace.

On the 202, turn the soundbox anti-clockwise until it stops. Then push the soundbox off from the back.

Thank you, I was afraid I might push too hard, but since you confirmed that's what I had to do, I insisted, and the sound box of the 202 came without any problem.
For the 113a, that's another matter, the problem comes from the screw.
Here are some pics.
The first one is what it looks like before unscrewing: The second one, after unscrewing (only the top of the screw comes) : I'm afraid of using pliers to unscrew what's left in place as it might damage the screw.

And while we're at it, the diaphragm looks weird to me...
It seems to be completely flat and totally unlike the one that sits in the other No.15 (from the 202 portable). And it has a brass color matching the tone arm...

The screw has definitely been replaced on the 113a arm. However it shouldn't be hard to make a replacement. You need a machine screw with the same thread, cut to length, with the end filed to a point. Either that, or remove the existing screw thread with pliers, cut it down to a length just proud of the arm, and cut a slot in the top with a hacksaw.

The diaphragm has also been replaced with what looks like thin sheet brass. If it sounds good, then I'd leave it alone, but if not, replacements are available from most spares suppliers, though they will usually have to be trimmed to size.

Thank you very much for these informations.
I'll try and remove the screw with pliers then.
The sound isn't that good right now (not very loud and it rattles quite a bit), but I'll take a look at the gaskets first, surely have to change them. If that is ok, I'll leave the diaphragm as is.

Just opened the sound box of the 113a. The gaskets appear to be in quite good shape, still soft. But the diaphragm is another story, it looks like a strangely bad job to me, though I'm not really qualified to tell. Also, no wax to seal the center area on either side of the diaphragm.

Crikey, no wonder it sounds bad, with that diaphragm, or what is supposed to be a diaphragm!

It should be identical to the one in the 202. Replacements are available from these people:

http://www.medmaw.com/cgi-bin/medmaw/medmaw.cgi

Thanks for the address.

I found this : http://www.m-p.co.uk/muk/parts/chap15/a ... 005115.htm

and that : http://www.m-p.co.uk/muk/parts/chap15/a ... 005515.htm

It seems to me that 55 mm might be a bit too much, and 51 mm not enough, as the one that's in the 202 is rather 53-54 mm.

I use the larger one, and trim a tiny amount off the edge. It's the nearest you'll get to the original as far as I'm aware.