Re: secondary coil for pole pig

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Steve Ward" <steve.ward@xxxxxxxxx>

Hi Miles,

I use the concrete form tube on my largest tesla coil and it works
well producing 12 foot sparks from a 45" long winding (though there
has been some flashover when i try to push beyond that, but that isnt
due to the cardboard form).  Anyway, there are some things you must do
before using the tube.  Here is what i did:

Take a knife and score around the edge of the spiraling seam on the
tube (you just want to cut into the outermost layer of paper and no
further).  This allows easy removal of the outer layer of paper, which
usually has lots of black printing on it (which i have hi-pot tested
and found to be quite conductive!!).  Once the printing is all gone, i
lightly sand the tube.  I then put on a layer of urethane varnish,
then sanded when dry.  Repeat this step about 3 times to get a nice
coating and smooth surface (this is important if you want to avoid
trouble with guiding the wire onto the form).  After winding the coil
i put about 8 layers of varnish on it.  I used plywood end caps, which
are secured with screws going into the side of the form and into the
side of the cap.  After the wooden caps are in place, i thoroughly
sealed the ends of the coil form (where plywood meets cardboard).
Dont worry about the small bits of metal, so long as they are properly
placed they will not cause any problems.

I only have 1 issue with the cardboard form, and that is its structral
soundness.  With my large 9.5"x44" toroid up top, the cardboard form
seems to flex a bit, and im worried that the coil form may eventually
be destroyed by this.  So far i cant see any structrual damage to the
form.  I plan to eventually wind a new secondary with the 10" PVC i
found near a dumpster... the quest for more power is on!

Overall, i would say that concrete form tubes make a very decent coil
form.  A bonus is that they weigh considerably less than a PVC form,
though at the expense of some rigidity.

Steve

On 3/14/06, Tesla list <tesla@xxxxxxxxxx> wrote:
> Original poster: "miles waldron" <mileswaldron@xxxxxxxxxxx>
>
> Is it OK to use one of those quick crete card board tubes from Home Depot
> that is 8 inches or 12 inches in diameter to build a 1200 turn #20 wire
> secondary? I want a big secondary to work with my 15KVA pole pig. The card
> board tubes seem to be waxed inside. If this is possible can someone provide
> any advice? If this is not a good idea, can someone please tell me why?
>
> Thanks!
>
>
>