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Round vs flattened primary tubing
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From: Robert W. Stephens [SMTP:rwstephens-at-headwaters-dot-com]
Sent: Friday, June 12, 1998 9:07 AM
To: Tesla List
Subject: Re: Round vs flattened primary tubing
> From: Bert Hickman [SMTP:bert.hickman-at-aquila-dot-com]
> Sent: Wednesday, June 10, 1998 11:46 PM
> To: Tesla List
> Subject: Re: Round vs flattened primary tubing
>
> Tesla List wrote:
> <SNIP>
> > > You are absolutely
> > > correct about maintaining the conductive skin area (this
> > > configuration may actually be slightly better in this respect than a
> > > round conductor because the RF currents will tend to concentrate on
> > > the inner side) and how the round edges would be better for corona
> > control
> > > than the sharp edge of copper ribbon, but I think the real advantage is
> > how you
> > > could gain more inductance for a given sized flat pancake while
> > maintaining the
> > > same generous turn-turn spacing. I prefer to make my flat primaries
> > > smaller in diameter than say the length of the secondary or the
> > > diameter of the topload. This allows the coil base to roll through
> > > more doorways than would otherwise be possible, and helps reduce
> > > primary strikes by keeping this component _tucked-in_. My 15-1/2 inch
> > > diameter secondary MTC-1 system rolls through a normal 31 inch wide
> > > man-door.
> >
>
> > Robert:
> > RE the increased inductance for a given sized primary. Since my
> > post, I played around with the Wintesla2 program to see the effect of more
> > compact primary windings. Interestingly, the inductance was about the
> > minimum for wire diameter equal to the turn to turn spacing for 1/4 inch
> > wire or tubing. The inductance goes up a little as turn to turn spacing is
> > either decreased (mutual coupling effect?) or increased (wire length gets
> > longer). However, the change in inductance only amounted to that which
> > would be gained by increasing the total number of turns by a tenth of a
> > turn! (I have no idea if Wintesla2 is producing completely correct
> > results.) Except for fitting through a doorway, the other benefits don't
> > seem worth the effort.
> >
> > --Steve
> <SNIP>
>
> Steve,
>
> There can be a significant advantage! Let's build a pancake style
> primary from 3/8" copper tubing with 1/4" clearance between turns. Let's
> also specify an inner diameter of 10", and a maximum outer diameter of
> 25".
>
> 3/8" round tubing:
> In order to have 1/4" clearance between turns, we'd need a turn-turn
> spacing of 5/8". This limits us to a primary with 14 turns, resulting in
> about 72 uH of inductance.
>
> Flattenned 3/8" tubing:
> Now lets make a primary using the same tubing that's been pre-flattenned
> to form a copper "strap" that's approximately 1/2" wide by 1/8" thick.
> Using this material, we can decrease the turn-turn spacing to 0.375"
> while still maintaining 1/4" clearance between turns. We can now fit 20
> turns in the same space, resulting in a primary with about 201 uH of
> inductance, or about 2.8X the inductance!
>
> -- Bert --
Steve, All,
Bert Hickman has done a terrific job through working an example in
demonstrating what is was I was attempting to say. Thank's Bert!
Robert W. Stephens
Director
Lindsay Scientific Co.
RR1 Shelburne, ON Canada L0N-1S5
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