Re. Aluminum foil toroids (fwd)

---------- Forwarded message ----------
Date: Tue, 7 Jul 98 10:29:08 EDT
From: Gary Lau  07-Jul-1998 1006 <lau-at-hdecad.ENET.dec-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re. Aluminum foil toroids

>From: Dsurfr-at-aol-dot-com
>Help from anybody out there!!
>I have checked an even dozen hardware/builder's supply stores in the area &
>can't find any dryer duct that is all aluminum foil & wire. All they seem to
>offer is solid aluminum (perforated), foil w/ a nylon mesh imbedded in it
>(both good choices for dryer duct) or plastic (which I thought was illegal).
>My olnly other thought was to go to the black corrugated drain pipe or a
>plastic "slinky" wrapped in plastic strapping tape & then wrapped in Al foil
>tape. My one experience w/ this type of toroid ( a small child's toy ring
>wrapped in foil tape) seemed to give off a lot of corona loss from the
>"overlaps" of the tape. Does anyone have any tips as to the correct wrapping
>procedure or any "brand names" of foil ducting on the market?  Thanks, Jim

I'm not aware of any brand names on corregated aluminum ducting, there were no
markings on mine except for the UPC bar code label.  I can't imagine that it
would be hard to find this though.  Any good hardware store or Home Depot-type
of store has a good variety of sizes.

As for wrapping procedures, depending upon the ID of the toroid, precut the
aluminum foil tape into 1" or 2" wide strips just longer than the circumference
of the ducting.  Don't try to wrap one continuous length.  Place the midpoint of
each strip on the outermost OD of the toroid and wrap the tape so that the ends
just overlap at the ID of the toroid.  The point where each strip's midpoint
lays on the previous strip should overlap by about 1/16".

Gary Lau
Waltham, MA USA