wrote in message
...
On Oct 15, 2:36 am, "N_Cook" wrote:
Anyone aware of a site of such tips for renovation.
About 50 years old. Looks as though the card of the cone hase weakened
with
age, probably like the paper of books goes brown and crumbly over time.
Looks as though the central cone area probably has failed to resist the
returning force of the periphery and the spider and has buckled
torsionally
but not split in that inner zone ,one or so inches, from the voice coil
join
and radially out.

If it actually works, and just the paper is going bad, try spraying
the cone with an aeresol(sp) spray varnish, a little at a time until
you get the stiffness that you think it should be. If the flexible
portion around the perimeter is going, a very thin layer of spray
adhesive may hold things together.


+++++

This is a 12 inch Jensen speaker of about 1960. I suspect the periphery
corrugations that should flex, had hardened up over the decades. Owner not
overdrive abusing , I removed the central dome to check how much rubbing
there was, no obvious scoring but did brush in some silicone oil. The VC
showed through the gap in the former , as the original unusual green
enamelling (not copper carbonate), looked fine. I covered this central area
with a silicone bakeware cupcake mould and blasted the worst cockled areas
with hot air on a low setting and pushed back wirth a spoon. In the end
perhaps 50 percent of the original cockling. Then some spray adhesive in
that cockled area
Next time I may try hotter temp or try chemical to soften the card , water?
diluted paint stripper? a small test patch initially whatever chosen. I
think next time it would be a hotter temp of hot air and a matching cone of
wood as a former , pushed in place, while cooling. There was some small
cracks in the cone near the outer edge, 1mm hotmelt string "soldered" in
those. After all that, here was still some very slight rubbing at the core,
flexing the cone in by hand, perhaps the VC former needs remoulding as well,
but it seems to work well enough to reduced power levels without distortion.
Do the electromagnetic forces , form the former into more of a circle during
powering?