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104ab repair - advice needed

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Joined: 11 Apr 2013
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Location: London

PostPosted: Tue Apr 16, 2013 5:42 pm    Post subject: 104ab repair - advice needed Reply with quote

Hi, I recently came into possession of a pair of 104ab speakers, having never owned a decent set of speakers before in my life. Unfortunately not really knowing what I was doing, I pushed them too hard at my birthday party, and blew one of the tweeters, one of the bass drivers and one of the capacitors in one crossover.

I need some advice on repairing them. I've managed to find a replacement b200 sp1039 on ebay, but I'm quite poor and can't stretch to the price of an original t27 (they seem to go for at least £50 from what i've seen) - so I was wondering if anyone could advise on alternatives.

I saw this advertised as a t27 replacement on ebay but wondered if anybody here had any thoughts on how good it is?


Also I need to replace the capacitors, as one of the ones in the crossover has visibly exploded...i found a replacement set on falcon acoustics site but wasnt sure what the difference between ALCAP 50V low loss 5% or 2% was, and which I should choose?


Many thanks for your help!

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Joined: 06 Nov 2010
Posts: 108
Location: Northamptonshire

PostPosted: Tue Apr 16, 2013 7:37 pm    Post subject: Reply with quote

Hi Paul, this is what I did with mine.....

I was advised to replace all the caps in the crossovers as even if they werenít leaking their values would have drifted after nearly 40 years, I did this with a kit of same value caps from Falcon Acoustics, I opted for the slightly dearer Solens (2%).

I then coated all of the inside un-damped parts of the cabinets with 2mm of floor grade epoxy resin (doesnít go brittle). I rewired them internally with silver plated OFC and added some nice gold plated binding posts.

I by-passed the contour control switch and the fuse. There is a substantial brace holding the bass/midrange (B200) speaker at the back (inside) that had shrunk, so I made some wooden shims and reinstated the brace. I also removed the lose wadding inside to make the ABR (B139) work better and it did on my concrete floors but Iím not sure this would be a good idea on wood floors.

The results were very pleasing, if you want to keep them reasonably "true" I would try and find a T27, they do occasionally go cheaper than your quote on Ebay, also try Gumtree and preloved.

Best of luck
Still learning ......
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Junior Contributor 20+

Joined: 18 Nov 2011
Posts: 22
Location: Tring, UK

PostPosted: Tue Apr 16, 2013 9:04 pm    Post subject: Reply with quote

That's bad luck blowing a tweeter. it sounds like the fuse was the wrong rating (or bypassed) I assume you have checked it! Even if the unknown replacement for the t27 works well it will be different in some respect so you will have a mis-matched pair.
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‹ber Contributor 1000+

Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Wed Apr 17, 2013 8:32 am    Post subject: Reply with quote

Bad luck with the 104aB incident, I did the same to mine in a monitoring situation back in the late 1970s! Smile

Gareth is quite correct, you will have mismatched loudspeakers so the best option is to change both if you can, I doubt if the crossover will be a proper match but better than nothing.

Also note that the machined rebated cutouts are for 108 mm diameter.
The replacements are 96.5mm... you would need to make a sub-plate mounting arrangement rather than butchering the cabinet.
T27 cutout for magnet is 84mm replacement is 71mm.
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