"jasee"
Phil Allison wrote:

Actually I was rewinding the voice coil. (I've done this succesfully
before, but not with this tweeter). It seems that the enamelled
copper wire that was used was not standard enamelled copper wire as
the total length of the dual layer coil was about 2.84metres which
in 40SWG gives a dc resistance of about 3.7ohms. However the
original which appears to be the same gauge measures about 7ohms. So
that is that, unfortunately, as far as I can see. :-(


** KEF's data on the T27 says that the voice coil is rated for
continuous operation at 130 C.
It also says that it can withstand 220C for 5 seconds.
Suggests that the enamelled wire is not low temp ( self fluxing)
grade.

Thanks for your reply.
The standard stuff I've got has a 'rating of 155C'.
I wasn't aware that there were any other grades!
Having had a quick look around, there are loads of types! Colour is no
guide (you can have any colour you want!) I must have been just lucky the
first time!
SWG in standard enamelled wire seems to define an overall diameter and a
depth of insulation. The measured diameter was the same. If it is
standard copper then it would have to be significantly thinnner to make
the dc resistance (which it doesn't appear to be). So, still a bit
puzzled.


** My calces give 0.1 mm dia *copper* as having the appropriate
resistance value for you given length.

That could translate to 0.2mm overall and maybe = 40 SWG.

155 C grade enamel is in the middle of the available temp range - 220 C is
the highest IIRC.

It could be that KEF actually used 220 C enamel, but the adhesive to hold it
on the former is only 130C safe.

BTW:

Rewinding tweeter voice coils must make brain surgery look easy.





....... Phil