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Fixing R105 mk 2's

 
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quadrantfour
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Joined: 16 Apr 2009
Posts: 4
Location: Cheshire UK

PostPosted: Fri Apr 17, 2009 4:38 pm    Post subject: Fixing R105 mk 2's Reply with quote

Hello Everyone
Nice to be on your forum, and to see so many people who appreciate KEF speakers.
I was looking for some advice on the internet and found your forum - I have a pair of R105 mk 2's, they are 27 years old and showing signs of age, but still functioning, all with original parts.
I hadn't used them for several years and one of the bass units had developed a buzz - I gather that this is fairly common with large, heavy-coned drivers like the B300, and can be alleviated by rotating the driver periodically. However - and as KEF lovers you might wince at this bit - there was an accident involving a bass guitar, which fell on one speaker and split the B300 cone. I repaired the split by gently opening the seal around the outer edge, enabling me to apply a strip of black insulating tape on the front and rear surfaces of the cone. This seems to be ok, but having re-sealed the outer edge, the buzz just will not shift. I have rotated the driver, tried to gently coax it with finger pressure, re-opened and re-sealed it again, but to no avail. It definitely seems to be the voice-coil which is out of alignment, and not the taped joint flapping about, the sound can be heard louder toward the central dome. I fear that the blow from the guitar has permanently knocked the coil out of kilter.
So, any advice? Or better, any spare B300's?
I have searched the web for a replacement, but as you very probably know, B300's are very rare, although there was a pair for sale a little while ago on a used hi-fi equipment site - of course, someone beat me to it.........
Hence my eventually finding this forum, I would think that if anyone would be able to help, it would be someone on this site!
There are alternative bextrene-coned units available from Wilmslow Audio, but I'd prefer the genuine article - after all, when you win the lottery and buy your cottage in The Cotswolds, you are NOT going to replace the proper traditional wooden window frames with PVC, are you?
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Fri Apr 17, 2009 9:40 pm    Post subject: Reply with quote

For repairs

http://www.wembleyloudspeaker.com/


http://www.audioloudspeakers.co.uk/boultons.shtml

Regarding replacements, I get lots of "spam" from Serbs and Croats who have the plans for the Skyline and want drive units, I know of no sources.

If you find a pair of Constructor Series B300Bs expect to pay an unreasonable amount for them.

A Peerless drive unit will fit in the hole, but that's all it will do if you look for alternatives.
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speakerguru
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Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Sat Apr 18, 2009 12:08 pm    Post subject: Reply with quote

ColinR wrote:
If you find a pair of Constructor Series B300Bs expect to pay an unreasonable amount for them.


I wish I'd known that when I designed it. I'd could have stashed a few away to ease my retirement Twisted Evil

If you don't have any luck with repairs and reach a point where you have nothing to lose you can try to dismantle and re-assemble. It is possible with a lot of patience. You need to very carefully pick off the dustcap and put it to one side for later. Next you peel off the outer surround from the chassis. The card ring will de-laminate and be very easy to re-stick later. Next, and most difficult, you need to loosen the rear spider's grip on the rear chassis platform. You will need to source some vicious solvent like Inhibisol or methyl-ethyl-ketone (MEK). Do this outdoors. Apply the solvent to the outer edge of the cloth suspension, aka spider, and after about 10-20 minutes start to pick at the outer edge. Keep applying more solvent. Eventually the spider will start to lift and then you can peel it free from the chassis. All adhesives are weaker in peel. Peeling will minimise the damage. You need to reuse everything so take your time to avoid tearing. If you want, you can unsolder the leadouts and remove the whole cone assembly to repair the split properly. If not you need to re-assemble, re-centralising as you go.

Assuming the magnet has not gone off centre on the chassis from the blow and the top plate and pole are still concentric, you will need some 0.010" (ten thou) thick plastic shim material (shirt collar stiffener?). Clear out the magnet gap with folded masking tape and insert the shim all around the gap with no overlap. You can then re-insert the diaphragm assembly. Try it dry for fit and practice then apply solvent adhesive to the spider and water based adhesive to the card ring, then go again for real. Leave overnight then remove the shim and test for rubbing. Reglue the dust cap if all is OK.

I just remembered there is an aluminium stiffening ring in the neck of the coil. This complicates the shim business somewhat. You can't use a continuous shim in the gap to keep things central. You will have to use 4 or 5 strips spaced around the gap instead.
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quadrantfour
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Joined: 16 Apr 2009
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Location: Cheshire UK

PostPosted: Sat Apr 18, 2009 1:06 pm    Post subject: Reply with quote

Thanks ColinR for the addresses.
Thanks Speakerguru for your instructions - in fact I'm a lab technician, obtaining a suitable solvent will be ok, so I'll have a think about sending it for repair or having a go myself.
Regarding your not having stashed away any B300's, I'm trying to imagine a method of how they might have been liberated from the workshop, they're not the sort of article which can be slipped casually under the coat.....!
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ColinR
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Joined: 31 Jul 2004
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Location: Staffordshire

PostPosted: Sat Apr 18, 2009 1:42 pm    Post subject: Reply with quote

Quote:
B300Bs, they're not the sort of article which can be slipped casually under the coat.....!


Indeed not, but if "Speakerguru" had taken a leaf out of John "Ozzy" Osbourne's book of methods of importation he might have Very Happy .

When living just up the road from me in The Cottage, Ranton the Osbourne's had a quadraphonic Sony setup using the big 70W TAN rear amplifier which just had two knobs on it.
The four speakers were by KLH "allegedly" Wink smuggled into the country in PA bass bins following a tour.
Daft thing was because of the exchange rate and time delay he "allegedly" Wink paid more in US$ than he would have done had he bought them new in the UK Shocked .
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