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Kef B139 6171 rubber surround

 
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doc-do
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Location: Russian Federation

PostPosted: Mon Nov 10, 2014 7:54 pm    Post subject: Kef B139 6171 rubber surround Reply with quote

Hello
I have two kef B139 6171, but the rubber surround looks outside the cones. Is it normally? See the photos, please
Photo 1
Photo 2
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speakerguru
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PostPosted: Mon Nov 10, 2014 11:36 pm    Post subject: Reply with quote

No. Inward roll is the norm. See http://www.kef.com/uploads/files/en/kef_units/A%20History%20of%20Kef%20Drive%20Units%20issue%203.pdf from the KEF site museum.
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doc-do
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PostPosted: Tue Nov 11, 2014 7:07 am    Post subject: Reply with quote

is it possible to rebuild?
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speakerguru
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PostPosted: Tue Nov 11, 2014 9:33 am    Post subject: Reply with quote

No. Firstly, the expanded polystyrene (EPS) diaphragm would break up if you try to remove the rubber surround. Second the rubber surround itself will probably tear if you try to remove it from the chassis. Most solvents would make the rubber swell and also melt the EPS.
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doc-do
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PostPosted: Tue Nov 11, 2014 9:54 am    Post subject: Reply with quote

How did the previous owner could do it & what is the influence for sound?
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speakerguru
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PostPosted: Tue Nov 11, 2014 10:33 pm    Post subject: Reply with quote

I can only assume that in the late 60s, the then KEF Russian agent was supplied with separate service parts and assembled them incorrectly. As the B139 should not be used much above 400Hz, I don't think an inverted surround will make much difference to the sound. As long as the voice coil is centred and not rubbing, don't worry about it.
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doc-do
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PostPosted: Wed Nov 12, 2014 6:58 am    Post subject: Reply with quote

I'm very much doubt that Russia had such dynamics and agents. They were bought in London last year. I'm interested in Chris Rogers TL projects, but can you tell me what mid/bass except B110 & k040 may be used?
Thanks for advice
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speakerguru
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PostPosted: Wed Nov 12, 2014 9:07 am    Post subject: Reply with quote

doc-do wrote:
They were bought in London last year.
My bad assumption then. I only joined KEF in the mid 70s when SP1044 was the only B139 in production. It is possible that some trial batches of 6171 B139s were made with an inverted surround in the 60s. If Malcolm Jones or anyone who is in contact with him lurks on this forum then perhaps they could answer.

doc-do wrote:
but can you tell me what mid/bass except B110 & k040 may be used?
No. Why not use one of the new B110 copies made by Falcon?
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doc-do
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PostPosted: Wed Nov 12, 2014 9:29 am    Post subject: Reply with quote

It costs as a small jet plane. I want to find cheaper
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speakerguru
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PostPosted: Wed Nov 12, 2014 11:17 pm    Post subject: Reply with quote

KEF drive units were very expensive in the 60s and 70s. Now that they are being made in smaller quantities for a niche market, why would they be cheap?
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doc-do
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PostPosted: Sun Nov 16, 2014 11:54 am    Post subject: Reply with quote

Where does can I see the construction of the b139 cone? Can any guru helping me?
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proffski
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PostPosted: Mon Nov 17, 2014 12:35 pm    Post subject: Reply with quote

doc-do wrote:
Where does can I see the construction of the b139 cone? Can any guru helping me?


I have tried for many years, and as far as I am concerned sadly it does not exist... Sad
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