Secondary Coil Forms
Subject: Secondary Coil Forms
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Thu, 14 Dec 1995 02:46:00 GMT
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Quoting Chuck Curran <ccurran-at-earth.execpc-dot-com>:
> Hello Richard:
> I hope this question will not take too much of your time, it
> seems you have been generous in sharing your experiences on
> coil making with many of us! After reading in excess of 500
> e-mails I currently understand that a thin wall large diameter
> teflon tube would be a good choice for a secondary form.
Reasonable assumption, but as you already know, not really too
> However, the only materials that I have found readily available
> are acrylic tubes (6"-at-$8.40/ft., 8"-at-$29.00/ft., 12"-at-$43.07/ft),
> PVC thick walled sewer pipe, or cardboard tubes.
How about a thin wall, gently angled conical section like a
round polyethylene kitchen trash can? Wal-Mart $6.99. Some poly-
propylene containers in large diameters can also be found.
> Many other recommended materials were available, but in 4"
> diameters or smaller.
> There were several posts that suggested that at higher power
> levels a larger diameter coil (10-12"??) would be more
> efficient. However the acrylic tube would be costly in that
> diameter. The reason for the huge cost differential is that
> the tubes are extruded up to and including 6" diameters and
> then cast in larger diameters. I also read that the PVC could
> be sealed with a specific BEHR polyester varnish--would it be
> worth trying if sealed? Has anyone used cardboard tube baked
> in a large oven( got one at work!) to dry it out and then
> sealed with the BEHR material?
I would use thick wall PVC over a sealed cardboard tube any day
of the week. If you can spare the $90.00, a three foot section of
the eight inch plexiglass would be ideal. You can use 30 inches
for the coil form and six inches for a cylinder static gap.
> I have been able to place an order with "The Condenser
> Products Corp." for one of the pulse discharge capacitors you
> recommended and a 10KVA 14,400 VAC pole pig is due to arrive
> If PVC or cardboard, even if carefully sealed, is something
> that more experienced coilers would avoid like the plague, I
> will go for the acrylic material. The specific question is:
> would you suggest I go for larger diameters and acrylics first
> or is trying a sealed PVC or cardboard tube worth the effort?
> (That 6" acrylic tube looks very attractive from a cost
> standpoint.) I haven't seen any comments on the impact of
> the higher loss materials on final coil performance-- does one
> see a 2% or 25% reduction of the final performance level? Any
> estimates available?
Cardboard is avoided like the plague. You simply can't do much
worse unless you wind on wood or leather. PVC is much better than
cardboard, even thick walled PVC. Acrylic is pretty good. The
bottom line resonator performance will range from acceptable to
outstanding if plastic coil forms are used. Thick wall PVC is not
desirable, but this coil form material is acceptable if other
materials are not available (or cost effective). PVC should be
properly prepared by drying and sealing.
I am winding all of my new coils up to eight inches diameter on
thin wall acrylic (plexiglas) coil forms. Over eight inches in
diameter and I would look hard at cheap polyethylene or poly-
propylene trash containers and planters.
Given the power supply and capacitor you have coming, and the
fact that you are looking to build a very high-Q system, I would
go ahead and get the $90.00 plexiglas tube, have the plastics
dealer cut it, and wind the secondary on that. Later you can buy
the plexi to wind the six inch secondary.
Good luck on this project. If you need any assistance please feel
free to ask, I try to help when I can.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12