If the cone of the loudspeaker itself is damaged or coming away from the frame, it can be repaired with a contact adhesive such as Thixofix or EvoStick. These adhesives dry to a flexible rubbery consistency. Both products are messy and give off fumes, so take appropriate precautions. If it is badly damaged you will probably need a replacement.
If the cone is distorted, so that the speech coil is scraping against the magnet, you may be able to cobble a "repair" by lodging a wad of tissue between the cone and the frame at a suitable point. This is hardly an ideal solution but it may be the best option if a suitable replacement speaker is not available, or as a temporary measure while you are waiting for a replacement to arrive.
I have also heard that spraying a small amount of aerosol lacquer onto the cone has the effect of tightening it, so by selective spraying it is possible correct a distorted cone in this manner. I have not tried this yet, but will do when the opportunity arises.
Leon Crampin offers the following useful suggestion:
Post 1945 Celestian loudspeakers nearly always have a broken glued joint on the cone suspension just next to the moving coil. Repair this with sparingly applied PVA glue, but use a DC power supply to move the cone out about 3 mm to apply the glue, then reverse the connections to preload the joint whilst the glue sets. Check the centering before you leave it to harden.
It is impossible to clean dirty speaker fabric. If it becomes damp the adhesive fixing it to the baffle board softens and the fabric shrinks. I have tried several methods of cleaning it, including car upholstery cleaning products, with no success. If anyone knows a good method of cleaning the speaker fabric, please let me know and I will share it with other visitors!
Normally all you can do is brush it carefully with a soft paintbrush to remove the worst of the dust. Sometimes the shape of the speaker can be seen in the fabric as a dirty shadow, which cannot be removed.
You are very unlikely to be able to obtain an exact replacement fabric since it is no longer manufactured. S.W.Chaplin carries stocks of more modern fabrics and some reproductions, that will act as reasonable replacements in some cases.
The new fabric can be fixed in place with a spray carpet adhesive such as Gripperrods Spray Adhesive. Spray a thin layer on the baffle board only and stretch the fabric across it. Without specialist equipment, you will be unable to stretch it as tight as the original. Place a piece of wood over the top and hold the lot together for a couple of hours, with clamps, bricks or heavy transformers.
A recent visitor, Manfred Mornhinweg, wrote the following in response to my comments:-
You seem to have more trouble than necessary with speaker grille cloth. I usually wash it in almost cold water, using fairly strong detergent. It is really the only way to get it back to look good. And it is impressive HOW good it looks after the washing!
It is true that it can shrink. But you can reduce the shrinking to a minimum by using cold water, and by stretching the cloth slightly while wet, and drying it slowly in that stretched position.
Even if it ends up somewhat smaller, it usually is still big enough to cover all cut-outs of the cabinet. If there is too little margin left, I fix it to a thin backing cloth, cut to the correct side.
This allows me to restore my radios much better than by leaving the dirty cloth there, or by replacing the cloth.
I have not tried Manfred's suggestion yet, but will do when I next encounter this problem. There is nothing to lose, if one was planning to fit a replacement cloth anyway. Another visitor, Gary Tempest, has tried it, and confirms that it works fine:-
I tried that method (posted on your site) of cleaning speaker cloth - i.e.: liquid detergent and almost cold water. It worked just great.
I did not even take the material off the backing plywood board. First a good vacuum. Then, after testing an out of sight corner first, I used the detergent and water sparingly. The adhesive did soften above and below the speaker cut-out. However, I placed a strip of clean material over these followed by two pieces G-clamped wood. After tightening the clamps slightly, I pushed them outwards to stretch the cloth back into position. Finally, I tighten up the clamps and left it to dry. The adhesive has fixed the cloth again, which is clean and tight, with no obvious 'speaker hole'. Thanks.
An alternative suggestion from Chris Roberts:
After reading your tips on cleaning speaker cloth, I tried neat Ammonia (hold you nose!) applied using an old toothbrush, with the grill inverted so that the liquid did not run into the speaker itself. This cleaning method also worked well on Bakelite knobs etc.
This worked very well, and did not leave any residue. My set was Bakelite, I have not checked for the effect of the Ammonia on wooden sets though.
I would recommend removing the speaker and cloth from the cabinet before attempting this. Otherwise, the risk of the ammonia getting where it should not and causing some damage is too great for my liking! Also good ventilation is essential.
Yet another suggestion, this one is from Ranulph Poole:
I don't mind slightly battered wood, but one thing that does look bad is the circle of dirt you get on the loudspeaker cloth. For some reason, the loudspeaker aperture seems to attract dust. The cloth is often of a plastic material (Tygan?) and responds well to being cleaned with washing-up liquid. Obviously, the baffle needs to be taken out from the cabinet and the speaker removed, but the cloth can be left on the baffle.
Finally (for now) John Perata said:
Use Woolite or similar cold water wool product for cleaning grill cloths. Drying rapidly with forced hot air will retain or re-establish original tension.