Rewinding speaker voice coils?

[skodajag]

Is it possible to rewind o/c voice coils on vintage radios? I’ve always assumed not because these speakers look as if they can’t be disassembled. But is this right?

[GrimJosef]

I imagine it'll depend on the individual speaker and I wouldn't be surprised if most of them can't be disassembled unless you're prepared to cut or tear the paper somewhere.

A speaker cone assembly is made of (up to) four parts i) the voicecoil and its former which is glued to ii) the paper cone which, at its outer edge, has iii) the ring-shaped surround (paper corrugations in cheaper speakers or a separate glued-on rubber or foam shaped ring in more expensive ones) and finally iv) the 'spider' which is a structure attached to the outside of the cone close to where it meets the voicecoil former and is used to centre the voicecoil in the narrow cylindrical magnet gap.

If you want to rewind the voicecoil then you need to be able to remove the cone assembly from the speaker's metal structure, sometimes called the 'basket'. The two are fastened together at two points - the outside of the surround and the outside of the spider. On most speakers these joints are glued (I have some vintage Tannoys though where both those joints are held together with clamping rings and can simply be unscrewed, as I did when the surrounds on mine rotted away and I had to fit whole new cone assemblies, bought from Tannoy). This is where you have to decide whether to try to separate the glue joints or just admit defeat and cut the paper. If you cut then you'll need to re-make the joints after you've fixed the voicecoil. A range of surrounds in different sizes and profiles can be bought online for repairing hifi speakers and if you're lucky you might find one that fits. The spiders might be more of a challenge though. That said, some speakers don't have spiders. They just use the surround to centre the cone and rely on a large magnet gap to accommodate any misalignment.

One thing that I should mention is that overheating of voicecoil wire can deform the former away from its cylindrical shape. If this has happened then it'll be a struggle to get the speaker to work again as the coil will tend to 'rub' in the magnet gap.

Another is that stage performers quite often manage to blow speakers and there are professional speaker repairers out there who have experience of fixing them. An online search should turn up some names. I have to say some of them have had mixed reviews, so if you were thinking of going this way then it would be worth doing a bit of research before you decide.

Cheers,

GJ

[joebog1]

New voice coils are available quite cheaply in a variety of diameters, lengths and impedances. I don't think you will be successful in rewinding an old one.

Joe

[PJL]

I can't imagine how a domestic valve radio could blow the speaker voice coil as the output is transformer coupled and the winding low resistance. The only exception would be the high impedance speakers used in some German radios. Are you sure it is not a fault in the solder joints?

[retailer]

It is do-able I have done it quite a few times, getting the cone assembly out of the frame is not all that easy, a solvent is used to soften the glue around the edge of the cone where it is glued to the frame and also where the spider is glued to the frame near the voice coil. This can take some time applying solvent with a small brush every few minutes and is no fun working with solvent fumes around you constantly probably best done out doors. If all you want to do is get the speaker working then probably easier to just cut the cone out.

I recently re-wound a Goodmans 12" Triaxiom voice coil, quite unpleasant standing around waiting for the glue to soften enough to be able to lift the cone out, the glue holding the voice coil in place on the coil former had let go from age and the wire had just fallen off the former into the gap, made it hard to determine the number of turns as the wire broke as I was trying to get it out of the magnet gap. The voice coil was 15 ohms which is not that common these days, most of the replacement voice coils are either 8 or 4 ohms and I had no luck sourcing a 3inch 15 ohm voice coil, so I had a go at making a new voice coil my self here are my first and second attempts, the second one was going to be used but I thought I might try a rewind first as the coil former was in perfect condition. I measured the total length of the wire and calculated the turns at 100 which meant 2 layers, I turned up a 3inch former and fabricated a hand cranked winding spindle, watched a few youtube videos on voice winding (very important !) and ... first attempt was a failure, the first layer was easy the second was not.
The second time round I wound the coil in 2 stages, first layer - waited for the glue to set and then wound the second layer, this time success. The rest was easy using shims to keep the cone assembly central in the magnet gap while the glue set.

[joebog1]

A three inch coil would probably be doable. I read that the required coil is from a radio, it might be as small as 1/2". That is very scary.

Joe

[skodajag]

Thanks for these replies - interesting, and encouraging.

[McMurdo]

I know a speaker repairer who winds all his coils on a standard coil winding machine. Mind you he does it for a living if you know what I mean.