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KEF C55 tweeter revival

 
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shrad
Junior Contributor 10+


Joined: 10 Nov 2015
Posts: 12

PostPosted: Wed Nov 11, 2015 8:40 am    Post subject: KEF C55 tweeter revival Reply with quote

Hi all,

I have a C55 with a burnt out tweeter...

I have tried rewinding the coil with similar wire after cleaning the mess with isopropyl alcohol (burnt out varnish and glue) which turned out not too bad (with a coil winder) but this is not it as I have no idea of the original characteristics of the coil wire and dimensions

Do someone here have access to specifications about the coil and wire used? I heard that former KEF employees were coming here sometimes...

I could also replace the tweeter but I'm wondering if it is best to replace the pair or stick with one... anyway those found on ebay these times are from the newer uniQ version with silver ring and I would prefer to keep the original design

I don't know what would be the best choice for me there... also you have to account that as I'm from Belgium shipping some complete units from US or other far places is out of the question due to pricing

I'm ready to take hi resolution pictures and document the process if you wish

Thanks a lot for those willing to help!
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Wed Nov 11, 2015 9:51 am    Post subject: Reply with quote

From memory (which is often hazy), most 4 Ohm 1" soft dome KEF tweeters of my era were wound with about 19 turns of 0.1mm dia copper wire on 2 layers. The coating was high temperature polyester grade 1 and the wet winding adhesive was a very high temperature rated epoxy.
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shrad
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Joined: 10 Nov 2015
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PostPosted: Wed Nov 11, 2015 12:29 pm    Post subject: Reply with quote

Hi speakerguru

thanks for the tip, however it seems there was only one layer of wire when I first unwound it

I wonder if the heat may have damaged the tweeter assembly in a way that other components may have been altered definitely, as if you say they were coated in high temp epoxy it means the sludge I had to remove is either melted resin, or part of the ferrofluid

I fear I'll have no choice but replace both tweeters... but at 100$ the pair from china it is a pain, really...

do you know of any source other than spare C55 units or even other uniQ based speakers?
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speakerguru
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Location: Green Hut, Tovil

PostPosted: Wed Nov 11, 2015 6:14 pm    Post subject: Reply with quote

Any sludge will be the remains of ferrofluid. If the voice coil was overheated to the point of the voice coil wire fusing to open circuit, then the temperature reached may have been sufficient to destroy the cyanoacrylate bond between voice coil former and diaphragm and also deform the diaphragm itself.

I know of no sources for spare units other than KEF in Maidstone.

I don't recall in any detail what sort of tweeters were used in the C55, so, I could only offer other hints and suggestions if you post some pictures of the units and the damage.

However, it sounds like you have already decided the unit(s?) cannot be saved.
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shrad
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Joined: 10 Nov 2015
Posts: 12

PostPosted: Thu Nov 12, 2015 2:49 pm    Post subject: Reply with quote

honestly I cannot tell as I have never seen some burnt out ferrofluid and can only guess, but according to what you say I guess they are damaged beyond repair... maybe I was trying to convince myself that it was still possible to do something

the tweeters are NT19 units (same as with other uniQ coaxial tweeters)

the rest is pristine so I will try to find replacement tweeters, because I really don't want to loose such nice speakers as the C55

I'll try to post some pictures if I have time this weekend

I have already contacted KEF directly but had no response, I did it again today and I'll see

now I'll have to source some, or find spare speakers to dismantle

are there some users here who would are stocking parts and could help?
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shrad
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Joined: 10 Nov 2015
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PostPosted: Fri Nov 13, 2015 11:46 am    Post subject: Reply with quote

Response from KEF : this tweeter is not available anymore and there is no substitute

guess I'll have to buy the first I find, be it chinese or not
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Thierry
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Joined: 02 Sep 2010
Posts: 72
Location: France - Outskirts of Paris

PostPosted: Sat Nov 14, 2015 10:13 am    Post subject: Reply with quote

Hi,

Maybe before you give up you could try to have your tweeter repaired ?

http://www.wembleyloudspeaker.com/

Good luck.

Thierry
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shrad
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Joined: 10 Nov 2015
Posts: 12

PostPosted: Mon Nov 16, 2015 3:40 pm    Post subject: Reply with quote

Hi Thierry

Thanks a lot I'll contact them to enquire... I guess they will be able to direct me in the worse case scenario Smile
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shrad
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Joined: 10 Nov 2015
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PostPosted: Tue Dec 01, 2015 9:46 pm    Post subject: Reply with quote

Hi all,

Can someone help me deciding if those are worth? they are NT19C and I wonder if they are adaptable to my C55

http://www.befr.ebay.be/itm/331722007250

I hope they can be reduced to the bare tweeter and bolt... that would be nice as I could replace two in a row and have a better match Smile

EDIT: bought them, they seem to be the same units with a shell glued to adapt on other drivers... they are brand new and I have big hopes...
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shrad
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Joined: 10 Nov 2015
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PostPosted: Fri Dec 11, 2015 12:16 pm    Post subject: Reply with quote

Hi there, got the tweeters in perfect shape except a small bump in the protection grid but that's acceptable

I managed to replace the original tweeter but it required a slight modification to match the screws I had in stock which were 5mm shorter than needed... I just had to saw off a small part of the central screw tunnel top of the rear mount

If anyone wants I can post pictures when doing the second speaker
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shrad
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PostPosted: Sat Dec 12, 2015 8:11 am    Post subject: Reply with quote

repair done, flawless sound again...
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audiolabtower
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Joined: 06 Jan 2009
Posts: 544

PostPosted: Sat Dec 12, 2015 12:17 pm    Post subject: Reply with quote

good story, well done Very Happy
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proffski
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Joined: 22 Aug 2003
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Location: Tewkesbury UK

PostPosted: Sun Dec 13, 2015 4:43 pm    Post subject: Reply with quote

Splendid news, pictures would be most welcome!
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shrad
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Joined: 10 Nov 2015
Posts: 12

PostPosted: Sun Dec 13, 2015 9:08 pm    Post subject: Reply with quote

Unfortunately I took no pictures, I can just say that I had to remove the back of the tweeter casing by prying off the sticker around the end part to free the wires, then unplug the protective body to have access to the metal back of the tweeter

The original screw was M5 to the eye, new one was M3.5 or something and as the previous tweeters were having brass spacers screwed on, the new ones wouldn't reach the tweeter back

I found two longer screws but they were short of approx. 5mm which was the height of the screw tube coming out in extra of the crossover mount

I cut the bulge off with a knife by successive cuts in the plastic, to have the screw head at the level of the plastic plane, and I was able to mount them

I had to keep the metal plate originally retaining the tweeter, but replacing them with rubber discs would have been nicer

It is important to use a bit of cardboard to center the tweeter around the woofer winding before fastening so it will not scratch during the cone excursion

Overall difficulty was moderate for someone used to repairs and with a bit of Mc Gyver blood Smile
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