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Concerto lack of bass / IMF swap ?

 
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ady
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Joined: 10 Aug 2005
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Location: UK

PostPosted: Wed Oct 04, 2006 10:55 pm    Post subject: Concerto lack of bass / IMF swap ? Reply with quote

Hi..

I've just picked up a pair of nicotine smelling Concerto's. They do not have consecutive serial numbers but are not too far off and both have a sticker showing 1970 as their test / manufacture date.

After a quick test it was clear one speaker had a much richer sound than the other and the thinner sounding speaker had occassional 'scratching' sounds. I took the bass unit out and noticed one of the thin wires from the terminal to the voice coil appears almost broken where it sticks to the spider.

Is this a very easy DIY fix?

I have an early pair of TLS 80's in storage. Could I just swap the pair of B139's over to the Concerto's or are they any differences between the drivers?


Many thanks

adrian
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speakerguru
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Joined: 18 Nov 2005
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Location: Green Hut, Tovil

PostPosted: Thu Oct 05, 2006 9:09 pm    Post subject: Reply with quote

Bad news I'm afraid. It's not an easy fix at all.

Sounds like the leadout braids have or have almost broken due to matal fatigue. It's very hard to work in there with such a shallow diaphragm and both the diaphragm and spider both being very easily damaged by heat.

Even if you are ultra skillfull and the braid is long enough that you are able to resolder it, the whole solder joint must then be glued solid to the coil former so that only fresh unsoldered braid flexes. If the solder is allowed to flex the joint will break again in no time. If any part of the braid where the solder has "wicked" into it is allowed to move it will also break again very quickly.

A recone would be the only reliable fix.

I don't know anything about TLS80s but if the B139s have the same SP(1044) number or 6000 series number then they are interchangeable.
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ady
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Location: UK

PostPosted: Thu Oct 05, 2006 10:57 pm    Post subject: Reply with quote

excellent advice, thanks..

it doesn't seem worth getting it reconed...

I'll swap the IMF B139's over.. I know these are OK.. and since I've no room for the TLS80's in our flat, they might as well be of some use..



adrian
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ColinR
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Joined: 31 Jul 2004
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Location: Staffordshire

PostPosted: Fri Oct 06, 2006 10:17 am    Post subject: Reply with quote

I bet the wire has degraded by the steel staple half way across the spider.
Another case of materials science meets the British climate.

Now if you’re into having a fiddle, get some 5 Amp flex, remove the outer insulation cut a six inch length of one of the inners, remove the insulation and braid the copper wire.
Put a half hitch into the end of the wire, break the speakers’ wire at the spider and tighten the knot.
Add electronic conductive paint to taste.
Put a blob of “Araldite” on the joint to fix.
Solder the other end to the B139A terminal.

Alternatively get both B139’s out of the IMF’s (they may have ventilated pole pieces) and swap.

If you’re near Stafford I’ve an unused KEF reconed (12/81) B139A in the garage doing nothing.
I only have three and four ways that use B139B's Very Happy .
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ady
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Joined: 10 Aug 2005
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Location: UK

PostPosted: Sun Oct 08, 2006 7:54 pm    Post subject: Reply with quote

thanks for the advice all..

i've taken the easy option and swiped the B139's from the IMF's...

for future reference, a closeup of the failure point of the fine braided wire on my B139 will appear here sortly...


I'm really enjoying the sound already... I suspect a crossover upgrade will improve them some more... I think I'm going to use them in place of my normal AR 2Ax speakers.. with my 405-2..

My other concern is child damage! The grille cloths are quite loose, I'm going to order some replacement cloth. Is it easy to stretch the cloth so that little fingers can't make much indentation and possible touch the drivers?


adrian
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ColinR
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Location: Staffordshire

PostPosted: Sun Oct 08, 2006 9:14 pm    Post subject: Reply with quote

Quote:
Is it easy to stretch the cloth so that little fingers can't make much indentation and possible touch the drivers


Fixing grill cloths to frames without creases or wrinkles is a black art Evil or Very Mad .

If the material in natural, dampen it first before attacking the frame with a staple gun and hair drier.

You could always "go disco" and get some mesh grills - I'm thinking about steel mesh (rabbit hutch type) or fine green plastic mesh between the grill frame and the new material, so visit your local garden centre Very Happy before going off to maplin, discodisco or whatever.
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ady
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Joined: 10 Aug 2005
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Location: UK

PostPosted: Mon Oct 09, 2006 9:25 pm    Post subject: Reply with quote

thanks...

found this, just now.. probably looks easier than it is though!

http://www.humanspeakers.com/howto/grill-cloth.htm


i suspect the glue is similiar to the stuff I've used from an excellent US ebay seller ( vintage-ar ) who specialises in AR speaker repair kits and parts.. Very smelly, very strong, easy to use but dries out even in sealed containers after a few months.. Everytime I get around to refoaming one of my woofers I have to send off for some more!
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ColinR
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PostPosted: Tue Oct 10, 2006 8:16 pm    Post subject: Reply with quote

For "acid brush" substitute an old (used for 6 to 8 weeks) toothbrush.

Try a ~£3 tin of Screwfix Contact Adhesive for the grill cloths.
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RGBE
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Joined: 22 Sep 2006
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PostPosted: Wed Oct 11, 2006 12:12 pm    Post subject: Reply with quote

If you have a pair of TLS80, use them! In my opinion, destroying a working TL80 to mend an unkown pair of Concertos makes no sense.

The bass extension and openess of the TLS80 is much, much better.

There is not such a big difference in the floor area required.
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ady
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PostPosted: Wed Oct 11, 2006 1:18 pm    Post subject: Reply with quote

yes, i know, i know.. i'd love to use the TLS80's but we have so little space.. they are safe though and will be used when we move to a bigger place..

adrian
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