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Kef 104aB Resurrection

 
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p1lyp
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Joined: 05 Jun 2014
Posts: 5
Location: Cornwall

PostPosted: Sat Jun 07, 2014 11:52 am    Post subject: Kef 104aB Resurrection Reply with quote

I was fortunate enough to pick up a pair of 104aBs locally for a tenner. Not quite the bargain it might have been given that when I initially hooked them up they sounded dreadful. Very muddy and muffled. BTW, the cabinets are rough too but it's the sound that I'm interested in, not so much the aesthetics.

It was immediately apparent that one of the tweeters (T27) wasn't working. A look on eBay and I was quickly up to speed on how much they fetch. Slightly deterred, I started off with a new set of capacitors for the crossovers. These have drastically improved the sound I'm pleased to say. However, on pulling out the woofers I discovered that one of them has been replaced by an SP1022 at some time in the past. It has the same dimensions as the proper one - SP1039 - but has a smaller diameter coil.

As it stands, I'm waiting for a single T27 and SP1039 to come up for sale. I could replace the T27s with modern equivalents for the same cost but I'd rather stay with the originals. Can anyone help with sourcing these? Quite happy to pay market price.

You'll see I'm a newbie and apologise if asking for help in a first post is bad form.

My first speakers were a pair of Coda IIIs mail-ordered fro Sevenoaks Hi-Fi in the early 80s together with a Marantz PM310 amp and Dual CS505 T/T, all long since passed on to friends.
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martin
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Joined: 25 May 2014
Posts: 17
Location: UK

PostPosted: Sat Jun 07, 2014 5:29 pm    Post subject: Reply with quote

I know it sounds silly but before replacing the tweeters have you checked the fuses?
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p1lyp
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Joined: 05 Jun 2014
Posts: 5
Location: Cornwall

PostPosted: Sat Jun 07, 2014 6:35 pm    Post subject: Reply with quote

It's a good question - sometimes the obvious can be easily overlooked. The fuses had blown but they'd been bridged using sweet paper in one and kitchen foil in the other. The duff tweeter is open circuit.

Has anyone tried opening up a T27? I've got nothing to lose and I'd like to see the damage. The metal diisc on the front through which the wires pass looks to be spot-welded in two points to the faceplate.
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martin
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Joined: 25 May 2014
Posts: 17
Location: UK

PostPosted: Sat Jun 07, 2014 6:59 pm    Post subject: Reply with quote

Ah right I see. The fuses saved my tweeters on few occasions, I use my 104aB's in my small project studio and mistakes can happen when I monitor. Last time I accidentally pushed up the wrong fader resulting in very loud feedback and instead of frying my tweeter it blew the fuse.. phew

For vintage KEF parts these guys seem to have them in stock and also refurbish pushed in domes on the T27
http://www.retrotechaudio.co.uk/classic-kef-spares.html
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SaSi
Senior Contributor 200+


Joined: 24 Aug 2008
Posts: 223

PostPosted: Tue Jun 10, 2014 9:04 pm    Post subject: Reply with quote

p1lyp wrote:

Has anyone tried opening up a T27? I've got nothing to lose and I'd like to see the damage. The metal diisc on the front through which the wires pass looks to be spot-welded in two points to the faceplate.

The diaphragm along with the faceplate disc around it are glued to the metal plate using two sided adhesive tape or something like it.

A couple of decades ago, when there were still spares for these, I obtained two diaphragms (that come as a unit with the voice coil) to fix my T27s that were the victims of a wild school ending party. Pretty easy to fix as the "rods" that you describe as spot welds are acting as guides to affix the new diaphragm where it should.

Only problem, you can't find spares any longer.
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p1lyp
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Joined: 05 Jun 2014
Posts: 5
Location: Cornwall

PostPosted: Tue Jun 10, 2014 9:33 pm    Post subject: Reply with quote

Thanks SaSi. What a shame it isn't recyclable. Throwing away a plastic moulding comes naturally but an aluminium casting will hurt a little.
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SaSi
Senior Contributor 200+


Joined: 24 Aug 2008
Posts: 223

PostPosted: Mon Jun 16, 2014 8:06 pm    Post subject: Reply with quote

But if you want top performing, fresh T27s, you are in luck. Falcon Acoustics have started small runs. Along with B110s.
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p1lyp
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Joined: 05 Jun 2014
Posts: 5
Location: Cornwall

PostPosted: Sat Jun 28, 2014 10:20 pm    Post subject: Reply with quote

I got around to opening up the duff tweeter to have a look at the damage. The coil had become detached from the diaphragm and had dropped into the body of the driver with only one wire attached. It was really tricky getting the coil out and I unwound six inches of copper wire from it in the process.

Testing the resistance it showed 5.1 ohms so I decided to have a go at putting it back together. I used Ronseal floor varnish to stick it back onto the diaphragm positioniing it as near to the end of the 'tube' as possible ie closest to the magnet. I cheated a little with the tails not taking them to the outside which would compromise the dome's attachment, bridging the gap straight to the terminals instead with a little insulating tape on them to avoid shorting with the body. There was enough sticky left on the plate to just squeeze it back together satisfactorily.

The result - sounds perfect! I would have given it 10% chance when I opened it up.
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