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I have an old celestion g12h30 from 1971. MM reads 15 Ohms.
But it seems to have an issue. When moving the diaphragm (equally with right and left hand) there is a rub. Looks like a polling speaker. Maybe the voice coil rubs﻿ against the pole piece.
So, is my speaker definitely dead or is it possible to fix this?
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Good luck!From the "Let's Talk Speakers Q & A" on Weber's site
From: David Knechtges
I recently purchased a '62 Brown Princeton which has a noticeable speaker buzz. I determined the problem is probably a warped voice coil or something in the gap, because I can push in on the cone and hear a rubbing noise as the cone moves. The speaker is an Oxford, dated '62. Should I buy a replacement speaker, have the original reconed, or ?
David, congratulations on the purchase. Nice amp. The noise is definitely a rub, either from, as you suggested, a warped (from overheating) voice coil, or flakes of paper or other material stuck in the gap between the voice coil and pole or front plate hole. There is a way to correct that if it isn't too severe. I'll detail it here, then you can make the decision whether to try it or not. The result is that you correct the problem without reconing the speaker, thus preserving the value of the original speaker. First, since you will be performing this operation without demagnetizing the magnet, make sure your work area is very clean and you have plenty of light. Lay the speaker on its back with the cone facing up and with a scalpel, carefully cut out the dustcap, leaving about 1/16" of dustcap where it is glued to the cone. This is important because the voice coil wires pass through this point and you want to make sure you don't cut them. Next, use a vacuum cleaner or clean, dry pressurized air to suck or blow the dust and other debris out of the gap. If you hold the speaker upside down with the cone facing downward it will probably help getting the dust and debris out. Next, take a 3x5 index card and cut it into a strip that is the correct length so that you can form it into a circle and stick it down into the gap between the inside of the voice coil and the outside of the pole. This will help form the voice coil back into a circle. Next, lay the speaker back down on its back. Take a Q-tip or small paint brush and dip it into a bottle of acetone (finger nail polish remover). Spread a small amount of this acetone on a couple of the rings of the spider, which is the brownish/yellow corrugated disk attached to the backside of the cone at the base of the basket. Next, place a jar lid or other disk on the cone where the dustcap was and let the speaker set overnight. The lid or disk will prevent dust from getting into the gap overnight, and the acetone causes the spider to relax and reposition slightly, thus repositioning the voice coil. The next day, remove the lid and the index card strip and see if you still have a rub. If you do, try the acetone again, same procedure. If, after a couple of tries, it seems hopeless, then professional reconing is the only resolve. I think it's worth trying though, to preserve the value of the original speaker. If it works, contact me with the size of the dustcap and I'll send you one to replace the one you cut out and instructions on how to replace it. As far as using the speaker, if you plan to use it regularly, at high volumes, I would suggest packing the original away and install a replacement speaker. Many speakers would work well in that amp, such as a Mojo MP10R, a Naylor 10, a Kendrick 10, or a WeberVST P10Q. If you want some british tone, you might check out Celestion's new Silver series or WeberVST's Blue Pup and Silver Ten.
Footnote 02-17-97 David followed the procedure outlined above and corrected the rubbing problem, thus preserving the value of his vintage speaker.
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I'd keep it as a memoir, and get a new one
I know - sacrilege, but wouldn't it almost cost as much for reconing ?
I'm a big fan of the G12H-30 and with proper patient break-in they do sound good for new ones IMHO