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I just got a Columbia machine that has a 15 soundbox whith a damaged aluminium diaphragm. Most probably the diaphragm was broken around the central hole (not a big deal) but some muddler thought it was a good idea to submerge everything with glue and see if it could hold the needlebar in place.

I think that, unfortunately, the diaphragm is unrecoverable as it will rip during disassambly because of the glue. Actually, I will be lucky if I will be able to recover the bar and its tyny screw, which is also submerged by glue and as a matter of fact I can't even see.

I tried to search for an appropriate spare aluminum diaphragm on the web but came up with nothing. Is it possible that no one produces replicas of aluminium diaphragms, while mica ones are so easy to find? Do you know anyone that does, perhaps? What would you do in my case?

Also, I never disassebled a no. 15 before, and again with some surprise I couldn't find a tutorial. The closest thing I could find is this thread about the no. 9. Does anyone perhaps know of a good page with some details about the no. 15?

Thanks for helping!



(generic example of no. 15 Columbia soundbox linked from the internet)

The No.15 is one of the easiest soundboxes to overhaul. Take the front and back off, and remove the rubber gaskets.Undo the two nuts at the base of the stylus bar, and holding the soundbox over a tray, slowly undo the screws that are inside the nuts. the stylus bar will then come loose, but watch out for the six tiny ball bearings in each side. (hence the tray!). Dig the bearings out with a wooden cocktail stick, and leave them to soak in a small dish of petrol, thinners, or alcohol. Meanwhile, clean out the sockets of the stylus bar with a small, stiff brush dipped in whatever you are using to wash the ball bearings in. Clean the pointed ends of the two bearing screws. You are now ready to re-assemble. Put a blob of grease in the sockets of the stylus bar, just to hold the tiny ball bearings in place. Replace the ball bearings. Rather than trying to arrange them into a perfect circle, it's easier to drop six in to the socket, and push them into place with a cocktail stick. When one side is filled,turn it over and fill the other side. Hold the stylus bar centrally between the two mounting points and do the two screws up just enough to hold the stylus bar loosely in place. Don't tighten the nuts yet. Cut a new piece of rubber gasket, making sure that the it's a good tight circle, with no gaps, and place it in the bottom of the soundbox body, with the join at the top of the soundbox. Put the tiny stylus bar screw through the hole in the diaphragm, and carefully put the diaphragm in place.Carefully put the blade of a tiny screwdriver in the slot of the screw, and hold it lightly but steadily.Bring the stylus bar up to meet the screw, and when the screw and the hole in the stylus bar meet, tighten the screw. Put a tiny ball of beeswax on the head of the screw, and use either a soldering iron or a small screwdriver heated to re hot to melt the wax, making sure it covers both the screw head and the surrounding area of diaphragm. Now adjust the two pivot screws so that the diaphragm is sitting centrally, and not touching the rim of the soundbox casing. Tighten the nuts, but make sure that the stylus bar is still swinging freely, this is most important. Fine adjustment will be done later. Cut the other new gasket, making the join at the bottom of the soundbox. Place that in, and replace the back of the soundbox.. Now for the "fine tuning". Looking from the front, slacken the left hand nut, just enough allow the screw in it to be turned. Pick a record that's not too worn, and play it. Whilst it's playing, carefully and slowly tighten the screw until any distortion or rattling is eliminated, and then stop. It's very important that the screw is not over-tightened, or the stylus bar will not be free to move and will wreck records very quickly. When you are satisfied with the sound, hold the screw in position firmly whilst you tighten up the nut. (You need three hands) Replace the front of the soundbox, and job done.

If you soak the end of the stylus bar that has the screw in it overnight in paint stripper, that will remove all the glue, and reveal the head of the screw.

New diaphragms are available from here:

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

Barry

Thank you very much for your committed reply, Barry! A lot of informaton in there!

I didn't realize that the soundbox could be opened from the front without removing the needlebar attachment first. I suppose there is a joint somewhere, then; I have to inspect it more closely. I also seem to remember reading somewhere that the gaskets of aluminium diaphragms are made of cardboard, hence they don't need to be replaced. Will the same rubber tubings used for mica diaphragms also fit aluminium ones, in your opinion?

Have you ever purchased and tried out one of those alu diaphragms? How would you comment on their quality? I ask because this soundbox belongs to a reputable Columbia Viva-Tonal, one of the best sounding machines ever, so I'm a bit concerned about using generic parts.

The front is held on by the four screws round the perimeter, and the back in the same way. I collect Columbia portables, so I'm very keen to get the soundboxes back to as - near original condition as possible.

I have used the diaphragms from the suppliers I gave the link to, and they are very good. Not quite as thin as the originals, but as the originals are unobtainable, that's something we have to accept. I've never heard of metal diaphragms using cardboard gaskets, every one I've come across, which number hundreds, all use the standard rubber. Except the HMV No.5 which use thin felt.

Barry

Thanks a lot once again, Barry! Yesterday evening I inspected the soundbox closely and could actually see that there indeed is a joint all around the needlebar hinge. My new concern is that, under the transparency of the glue blob, the tiny diaphragm screw seems to be missing. But of course I have to get rid of the glue before assessing it. Thanks for the idea of the paint stripper, I will try it out and keep you updated (with pictures!). With some luck I might be able to recover the original diaphragm: it has some dents but it doesn't look too bad excepting the central hole and that horrible mountain of glue.

Maybe some help...

Yes Odeon, that helped a lot, thanks: if I'm not mistaken what I have to look for inside the glue blob is not the usual tiny screw but a super-tiny nut! So perhaps it's still there.

Yesterday I disassembled the case and not without surprise I observed that both the diaphragm gaskets as well as the insulator are still soft and flexible. They are both orange and I wonder what compound they are made of, as they appear to be so much more durable than HMV's seals, that I usually find hard as rock.

What a pity that the diaphragm had been so stupidly "serviced" in the past, as the diaphragm is a bit beaten up but not so bad overall and would probably still sound good.

One general question: I suppose that the screws marked 33-35 and 34-35 on the drawing are a safeguard against overswinging of the needlebar in case of clash, is that correct? Is there a procedure to set them, or a recommended clearance towards the needlebar?

I suppose that the screws marked 33-35 and 34-35 on the drawing are a safeguard against overswinging of the needlebar in case of clash, is that correct?

Yes, you´re right!

Tighten the screws that way, that they are barely not touching the needlebar (perhaps 0,5 or 1 mm). Now take a greyed, but really loud record and play it with the box. If there is any rattle, just screw back a half or one turn until there isn´t any rattle. Thats the way I do it.

Regards

Marco Gilardetti wrote:if I'm not mistaken what I have to look for inside the glue blob is not the usual tiny screw but a super-tiny nut!

It would appear that Columbia decided against the tiny nut, as I've never seen one on all the No.15s I've overhauled. Always the tiny screw. A nut would certainly have been easier to deal with though!

Barry

Dear Barry, it seems that at least some early batches were indeed built with the super-tiny nut! And fortunately - as I guessed by inspecting the glue blob under transparency - it was still there!

As a side note, the local hardware store man suggested to try to dissolve the glue with "nitro" paint thinner before going with a paint remover, that is very aggressive and may damage or corrode other parts. It worked perfectly and with one hour of work I could get rid of the glue covering the needlebar end.