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Re: [TCML] 8" Secondary Woes

Have you considered using a concrete former tube, such as Sonotube
product?  They come in an an eight inch size, although I'm not sure if
that is the OD or ID (if the latter, you would be winding on an 8.5" OD

It will obviously take more work, as you need to dry and coat the tube
before using it, and you will probably want to provide a finish on the
exposed parts of it to look nice (maybe use a wood laminate on the
exposed surfaces).


On 09/03/2013 07:29 AM, Greg Peters wrote:
> Hi all,
> Well I've done something stupid. I wound a beautiful spiral primary with a
> 12" diameter inside turn on nice polycarbonate supports. I assumed that I
> would be using an 8" (200mm) secondary and that 8" was a standard pipe
> size. I was aiming for 2" between the primary and secondary. Never assume
> anything! The nearest PVC water pipe OD is either 160mm (6") or 250mm (10").
> 8" OD tube is as rare as hens teeth in Australia. The only exception is 8"
> acrylic tube which is difficult to cut and work with. I'm not a big fan of
> acrylic, as I always seem to get my saw stuck, etc and I can see my
> beautiful former being destroyed.
> I have called nearly every pipe and plastics supplier in the country and I
> am out of luck. No polycarbonate, styrene, PVC, polyethylene, polypropylene
> or other plastic in 8" OD! I even called some of the gas pipeline suppliers
> - I CAN get a length of blue 200mm LDPE pipe for about $500....not ideal
> (expense wise).
> I noticed that McMaster Carr has very cheap polycarbonate tubing in 8" OD,
> and placed an order only to be informed that they will not ship to
> Australia. There are a few other not so cheap US suppliers who may be able
> to assist if necessary though they seem significantly more expensive.
> Anyway, the closest thing I have found in Oz for a reasonable price ($200)
> is a length of orange PVC electrical conduit at 225mm (9") OD.
> So, my question to the list. Do I persist with trying to find an 8" tube,
> possibly even from overseas, or settle on the 9" conduit and tolerate
> having only 1.5" between my primary and secondary? I expect I will need to
> lift the secondary quite a bit to prevent overcoupling and even flash overs
> from the primary which will be running 24kV. Is anyone else running a
> largeish coil with this kind of spacing?
> This was meant to be a museum quality build and the idea of having to
> significantly lift the secondary is frustrating, but realistically it's
> looking like the only option! The coil has been painstakingly designed to
> sit exactly in the middle of my shed space for maximum spark length in all
> directions. Oh well, next time I will be more careful and assume nothing!

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