Re: toroid parts...

>>I think you will find that whatever you use to reinforce the center of
>>the toroid will make the entire assembly very stiff. I have used
>>masonite and just plain 1/8" plywood with excellent results. I use a
>>bead of alumunum glue on both sides of the center piece to firmly attach
>>it to the duct and let it dry well. Then I connect the center mounting
>>hole to the toroid using aluminum tape with adhesive on one side.
>>Good luck
>Hi All -
>Has anyone tried to test these duct toroids for capacitance to compare them
>with spun aluminum toroids? They appear to have very low capacitance.
>John C.

What...You're selling spun toroids too? C'mon...;) 

Since all of the charge on an isolated capacitance is on the surface of the
capacitor, assuming uniformity and smoothness, one would think that the
Al-duct capacitors would be slightly *higher* in capacitance than a smooth
toroid, simply because there is a greater surface area on the ducting. It's
not like there are any sharp edges or corners to leak charge from, the only
real possibility might be from the seam, where the two ends are joined. But
careful construction should take care of that. Admittedly, there will be
greater concentrations of electrons at the peaks of all the "ridges" (for
lack of a better word), but as far as the entire electric-field density is
concerned, I can't imagine the difference being more than a couple of
pico-farads, again towards a *higher* capacitance. I supposed the
capacitance could be lower on a really high-power system though...my largest
has only been 3kW.