# Re: Stainless steel tubing for primary?

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• Subject: Re: Stainless steel tubing for primary?
• From: "Tesla list" <tesla@xxxxxxxxxx>
• Date: Sun, 17 Apr 2005 22:37:32 -0600
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Original poster: Kurt Schraner <k.schraner@xxxxxxxxxxx>

Hi Tom, all,

while it would probably work, I'd not give away loss of energy, due to ferromagnetic properties of the material. Sometimes it may be forgotten, skin effect resistance not only depends on frequency, but as well on permeability. And you would expect a much higher primary coil RF resistance, which would need to be related to the gap loss. I'd just not torture myself for making a stainless-steel minor quality primary, when 1/4" soft copper tubing can be bought everywhere. Here the formula for skin-depth:

(sorry no greek letters in plain ASCII):

Skin-depth  d = SQRT( 2 / (omega * uo * ur * k) )

resonant frequency      f
at resonant frequency   omega = 2*Pi*f

permeability constant in SI-System:
uo = 1.25664E-06[H/m] =1.256637061[uH/m]

relative magnetic permeability ur [-]
(Ferromagnetic materials - even some stainless steels - having a much higher number here, ... some 10 to some 1000), meaning the skin-depth going down by the square-rooot of the proportion. .

Example Copper:
rel. magnetic permeability     ur       1       [ - ]
specific resistivity (20C)    rho  [[Ohm*mm2/m]  =0.01786 for copper
conductivity of conductor      k    [m/(mm2*Ohm)]=55.99104143

Cheers,
Kurt

Tesla list schrieb:
Original poster: "Coyle, Thomas M." <tcoyle@xxxxxxxxxxxxxxx>
So I'm all ready to wind a nice flat primary today, and, lo and behold,
I'm out of 1/4" copper tubing. I have a bunch of 1/2", but don't feel
like getting arm-exercise today. I do, however, just happen to have
about 1000ft of 1/4" stainless steel tubing in a continuous spool laying
here.
Any thoughts on using this for a primary?
Performance considerations aside, I think it'd look quite cool.
Tom