SEAS 25F-EW repair and hack

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Disco Volante

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Jun 20, 2021
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The classic 10" driver from Seas, sold truckloads in the 70's. Still reasonably easy to get hold of, at least here in Scandinavia.
A lot of them suffer from loose magnets due to moist storage, the zinc plating on the steel parts of the motor expands and cracks the old (sloppily applied) epoxy.
Well, what better fun on a rainy sunday, let's have a look at what's inside and possibly a way out of the misery;-)
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Disco Volante

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Jun 20, 2021
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The cone and suspension is in the way. After removing the loose parts of the motor, (no longer clamping the VC tight), scalpel and fingers do a great job of removing the soft parts.
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While I'm at it, why not convert these two regular 25F-EW to a pair of unobtanium 25F-EBWX? (Seas for extra magnet and foam surround)...
This is where the machine shop comes in handy.
New larger magnets (120x18x60), watercut steel discs (designed in FreeCad). The center piece can be recycled, with a 2mm shim to account for the thicker magnet.
Did I mention I *love* my lathe?

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Threaded holes in the front plate and magnet gap adjusted. I was able to gain .4mm on the outside diameter after measuring against VC. Hope I can still get the thing centered properly, come that day. But the higher efficiency is worth the extra trouble.
I increased the thickness from to 8mm; the VC is 14mm high which will give an Xmax of 3mm, approximately, and a significant increase in efficiency.
 

Disco Volante

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After coffee break, turned a centering plug from POM. Love this plastic, it cuts perfectly. A bit wasteful turning it from solid stock, but it's Sunday after all...
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Ready for assembly:

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TIG-welded the pole piece to the back plate. It was a press fit, but it needs to be secure. Seas used a sort of riveting technique, but now that I've cut it out of the old backplate, I have to weld it.

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Disco Volante

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Glued it up with epoxy, put a little bit of a rather firm polyester felt in the space inside the magnet. These magnets are made for 2" VCs, so this little 38mm 1.5" thing leaves a big gap inside.
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It's looking up, but the hardest part is still ahead...

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Disco Volante

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Got the basket on the motor, cut three screws to exact length, used a drop of Loctite to keep the screws in place and a little SMP sealant between the parts to prevent resonances.
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The old rubber edge was a royal pain to get off. These drivers are very well made (well, except for the glue on the magnet). Used several sharp blades in my little cutter, strong glasses and just very fiddly business getting the rubber and glue off without cutting into the delicate paper cone.
Foam surround mounted, carefully centered. I use a German brand "Auro" of a less smelly/toxic and somewhat adjustable contact-glue.
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For future hacks on these units, I'll probably just leave the rubber surround on. The idea was to lighten the outer edge of the cone to lessen the inevitable HF breakups associated with the bigger motor system vs a very light membrane. Measurements will show, I might have to coat the membrane with something to stiffen it up a bit, moving the breakups above the point of crossover.

Dust cap needs to go, to be able to center properly. I use various thicknesses of paper. This one took three layers of ordinary office paper to get a tight fit. They need to not overlap, so cut to length. We don't want any excentricities in the VC and centering needs to be as good as possible.DSC01768.JPG
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Disco Volante

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@totoxraymond Thanks, if you ever need any help, PM me. I've wanted a workshop like this since I was a kid, always taking things apart. Drove my parents crazy. Later I learned how to put things together again...
 

Disco Volante

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Ok, it's beginning to look like a speaker again. Smeared glue on the edge of the spider to bond it to the edge where I cut it a while ago. Not too pretty, but it'll work. I use a glue called Rubberfix made by Casco for this. It's also (mainly?) for fixing shoes, and it's the most durable "liquid rubber" I've tried (I don't work for Casco).
It takes a while to harden though, up to 48hrs depending on thickness.
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The second magnesium basket had some patches where oxidation had broken through the paint, so it got a partial blasting with the neighbour's glass-bead blaster, and a fresh coat of matte black paint. Also glued up the second motor system..IMG_3788.JPGIMG_3783.JPG
 
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