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Re: Question about Primary Inner Diameter

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Bill,

At 07:55 PM 5/19/2001 -0400, you wrote:
>I just built a new primary for my new (first) coil.  I'll explain why
>Due to the way I constructed it, I couldn't precisely control the inner
>diameter.  Now I have a secondary with 6 5/8" diameter, and the primary
>inner diameter is about  8 1/8" (whereas it was previously 9.5").  Will
>this be work?  I'm using three 15/60's as power, and want to add a
>fourth (if that's relevant).

Sure.  I try to leave 1 inch between the primary and the secondary but your
spacingshould be fine.

>Will it help if I raise the secondary somewhat?  Structurally, what
>works best (easiest) is for the lowest turn of the secondary to be about
>1.25" above the top of the primary.  I could lower it a bit.  I will
>also have a plexiglass sheet over the primary, below the level of the
>bottom turn on the secondary (again, if that's relevant).

I would not worry with it unless you get racing arcs along the secondary
coil.  In that case you may want to rasie it some but I think you are fine
as is.



>	Thanks again,
>	Bill Vanyo
>For the curious --- Why I rebuilt the primary, and how (in such a way
>that I couldn't get the exact inner diameter I wanted):
>First, my coil worked pretty well, but it was heavy as hell (with
>secondary removed, and no power supply) - a 19 turn primary on a heavy
>home-made deck, with space underneath that was originally going to
>contain the power supply.  Most of the weight was wood.  As I grew power
>hungry (adding more NST's), the power supply came to require a seperate
>cart, and the primary and supporting deck didn't need to be so big
>(primary tapped between 5.8 and 7 turns, depending on toroid).  So I
>decided to rebuild, for portability (I can only run it outdoors).
>Now, as for how I constructed it: The primary supports are 8 pieces of
>6" square, 1/2" thick HDPE (cutting board), with 11 holes drilled in
>them.  These are UNCUT.  That is, the tubing passes through the holes -
>it is not laid in notches with something holding it down.  It's quite
>beautiful, but it was a bitch to construct.  Basically, I wound the coil
>on a big board with pegs in it (arranged like eight radial spokes, pegs
>spaced 1/2"), then slid the HDPE supports around the coil, turn by
>turn.  This sliding caused some sort of shifting that resulted in a
>smaller diameter than intended.  Perhaps I'll make another, with the
>diameter larger to start, so as to compensate.  But the end result is
>nice - the coil is essentially embedded in the eith supports, and quite