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Kef 104ab

 
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Streamz
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Joined: 22 Jan 2007
Posts: 3

PostPosted: Sun Feb 04, 2007 11:34 pm    Post subject: Kef 104ab Reply with quote

Hi recently aquired a set of these speakers, and I have to say they sound amazing. Unfortuntely one tweeter was dead, so I ebayed a replacement. But I'm now paranoid about blowing another tweeter, as the fuse does not seem to blow in time to save it. Is there something I can do (i.e. a different rated fuse) to better protect the tweeters?
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ColinR
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Joined: 31 Jul 2004
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Location: Staffordshire

PostPosted: Sun Feb 04, 2007 11:40 pm    Post subject: Reply with quote

KEF 104's were fitted with 500mA anti surge (slow blow) fuses, replace with a smaller (400mA) quick blow fuse or do a "google" on polyswitch.

Malcolm Jones at www.falcon-acoustics.co.uk has an information sheet on his web site and can supply them.
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Streamz
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Joined: 22 Jan 2007
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PostPosted: Mon Feb 05, 2007 1:44 am    Post subject: Reply with quote

Thanks for the help. Would this do the trick?

http://www.dse.co.nz/cgi-bin/dse.storefront/45c67d0900f4107e273fc0a87f3306bc/Product/View/P9342
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Mon Feb 05, 2007 9:16 am    Post subject: Reply with quote

Round about 1975-6 a KEF engineer called Chris Moore had a rig which blew fuses and measured their rupture point and time constant. After blowing hundreds of fuses he determined that a 400mA T (delay) fuse from a certain German manufacturer had a time constant which most closely matched the thermal time constant of a T27 voice coil and blew before the vc temperature exceeded its rated maximum. It was not 100% certain protection but no other fuse came even close.

That German source, of course, has long stopped producing that fuse, so there is no suitable replacement. The safest thing to do is have a smaller fuse but then you may get annoyed when it blows too often. Better than having to find another tweeter though......
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Streamz
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Joined: 22 Jan 2007
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PostPosted: Mon Feb 05, 2007 11:16 am    Post subject: Reply with quote

How low a rating would I need to ensure that the tweeter was safe?

I would much rather change a cheap fuse than hunt down another tweeter.
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speakerguru
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PostPosted: Mon Feb 05, 2007 12:07 pm    Post subject: Reply with quote

A 400mA F (quick blow), as Colin suggested, will probably be safe but may blow quite often if you like to play loud.

A 315mA F will be even safer but may be very annoying.

The choice is yours.
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