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White belly B110 fact or B.S?

 
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ColinR
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PostPosted: Fri Nov 17, 2006 11:10 pm    Post subject: White belly B110 fact or B.S? Reply with quote

The only "white belly" B110's & B200's I know have some damp / water damage such that the PVA based dope has parted from the Bextrene.

The effect can be reversed with a little rain water (mildly acidic), gentle pressure and a greenhouse!

For those still into "white belly" mythology.

PVA is transparent when it dries Cool .
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Thierry
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PostPosted: Mon Sep 06, 2010 1:41 pm    Post subject: Reply with quote

Very interesting indeed.

Can someone explain what PVA is ? Is it an acronym for PolyVinyl Acetate ?

If so, is PVA easily available and where ? I assume there are several trading names for this polymer but I can't find any.

Thanks,

Thierry
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ColinR
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PostPosted: Mon Sep 06, 2010 1:52 pm    Post subject: Reply with quote

Very Happy
Quote:
Can someone explain what PVA is ? Is it an acronym for PolyVinyl Acetate ?

If so, is PVA easily available and where ?


PVA - aka white woodglue.

Evo-stik from Evode now owned by Bostik is 3.5km from me, useful for cabinet making.

However.

For speaker repairs the cheaper the better i.e. it smells slightly fishy because of the amine impurites.

Wharfedale used a thinned down version with added catering eggwhite to dope their cones.

KEF just used a thinned down version Sad .
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Thierry
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PostPosted: Mon Sep 06, 2010 1:56 pm    Post subject: Reply with quote

Hi Colin,

Thanks a lot indeed !

Does your description mean that a B110B could be rejuvenated if some of the PVA has gone to heaven like here http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=1131 ??

More I spend time studying my newly acquired 105s and more I find KEF solutions very smart, elegant and well engineered. A true example of good engineering, really.

Thierry
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ColinR
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PostPosted: Mon Sep 06, 2010 2:05 pm    Post subject: Reply with quote

Quote:
Does your description mean that a B110B could be rejuvenated if some of the PVA has gone to heaven like here http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=1131 ??



In theory yes, but experimenting with various >90%-80%< solutions of PVA glue will take a lot of spray gun time and test pieces made of Bextrene.
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Thierry
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PostPosted: Mon Sep 06, 2010 2:22 pm    Post subject: Reply with quote

I understand the try and error process. I have old B200s to play with, I may have a try.
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speakerguru
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PostPosted: Mon Sep 06, 2010 7:16 pm    Post subject: Reply with quote

ColinR wrote:
KEF just used a thinned down version

Bextrene cones had one coat of AD7 (which did stick to bextrene) and 2 coats of AD18 (which had the required damping properties but did not stick to bextrene) on the back. The front had only one, more or less cosmetic coat of AD18. It clung on but did not really stick. You could peel it off and recoat if required. The stuff on the back did the real damping and could be controlled by weighing the coated cone as you applied it. The front coat became thinner and thinner as years went by but was never left off because "you had to see" that there was damping compound being used. AD18 had various other internal KEF AD numbers as different thinned versions were used.

Although AD18 was a type of PVA, trade name "Plastiflex", it was a bookbinding adhesive. It was not a regular white glue wood adhesive nor was it made by Evode or Bostik. I'm sorry I can't remember who made it or what it was replaced with when it eventually became unavailable.
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ColinR
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PostPosted: Mon Sep 06, 2010 7:44 pm    Post subject: Reply with quote

Quote:
was a type of PVA, trade name "Plastiflex", it was a bookbinding adhesive


Made by Henkel, however as they sold and swapped several chemical works sites with Dupont, ICI, Great Lakes and BASF and what information Google gives as to who owns and does what these days is most likely not relevant for this type of application.

The clue is cheap "fishy smelling PVA" the amines allow better dispersion in water increasing a spray gun's ability to lift; in bookbinding they're biocides.
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proffski
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PostPosted: Tue Sep 07, 2010 9:14 pm    Post subject: Reply with quote

On a visit to the NAIM factory in Salisbury many years ago I saw the drivers for the SBL? being coated by hand on some sort of a turntable with a brush.

Later the cones were graded and weighed before they stuck those dampening metal pads onto the rear of the magnet (aluminium) and (brass?) to the stamped metal chasis.

Anyway I meander, when the cones were being weighed I was amazed as to ho accurate and repeatable this was being done by a human being and a brush!
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MGM
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PostPosted: Sat Dec 27, 2014 9:56 am    Post subject: Reply with quote

If you have your LS3/5as calibrated by Derek Hughes, he will often add some damping to the B110s cones as well as any adjustments to the crossover.
I was informed by a former BBC employee that some early LS3/5as ( before commercial production began) had PVA added around the B110's dust cap to tame resonances.
My 'own build' models ( with early B110s ) may require it when I get around to shipping them to Derek Hughes.
M Miles.
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