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B139 SP1044

 
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iso
Senior Contributor 200+


Joined: 29 Aug 2011
Posts: 215
Location: Finland

PostPosted: Sun Apr 15, 2012 1:00 pm    Post subject: B139 SP1044 Reply with quote

Does anybody know how B139 was upgraded during SP1044:s quite long production run.

From spec sheets you can see that voice coil former was probably upgraded sometime. Early spec sheets confirm more modest working temperatures than late spec sheets. Colin also mentioned sometime, that late production units after mid 80īs are most consistent in performance.

So if anybody has inside information about upgrades during SP1044 production, please let us know. Most important issue is which units are most suitable for vented box, TL or IB usage... and of course why.

Best Regards,


Last edited by iso on Fri Apr 20, 2012 7:43 am; edited 1 time in total
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speakerguru
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Joined: 18 Nov 2005
Posts: 958
Location: Green Hut, Tovil

PostPosted: Mon Apr 16, 2012 10:30 pm    Post subject: Reply with quote

Sorry I can't help with dates. I have no memory for that sort of thing. I did most of the prep work in reducing voice coil tolerance from +/-10% to +/-5%. To that end there was a change from self bonding (nylon) coated wire to wet wound (epoxy) polyester coated wire. The split nomex VC former gained a nomex tube over the unwound portion at the same time. The material did not change. All versions were nomex, therefore Qm remained the same.

The magnet changed from a bolted design with a staked pole to a bonded one with a pole/backplate forging. This resulted in about 1~2% increase in gap flux density. Not a significant amount as regards box alignment.
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speakerguru
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Joined: 18 Nov 2005
Posts: 958
Location: Green Hut, Tovil

PostPosted: Fri May 18, 2012 7:54 am    Post subject: Reply with quote

There are small pictures of the two different types of voice coil construction, in KEFTOPICS here: http://www.hifiloudspeakers.info/Anatomy/KEFDocuments/KEFTopics/KEFTOPICS_Vol_4_No_1.pdf
It also contains a lot of knowledge on power handling, voice coil temperature and protection circuits.

Thanks to Terry for putting it up.
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