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Re: Primary tubing size

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Mike,

I have a 8x36 coil that I power with 1KW and 1/4 tubing is just fine. I plan to go to 2KW with this primary. As the power goes up, Cp goes up and Lp needs to go down (assuming no changes in secondary). This in turn makes the RMS current go up and losses in the primary coil go up. Someone, I believe, said that 1/4 inch was good upto maybe 5KW. I have experienced no noticable primary coil heating at 1KW. I would, however, keep the pancake flat as overcoupling can be a problem with higher power coils. Turn spacing should be sufficient to allow you to tap into the coil and still have no turn to turn flashovers. I use 1/4 inch spacing and tap into it with two 1/4 inch fuse clips soldered together as an assembly. Clip the fuse clips onto the primary coil before soldering as the coil will heat sink the clips and help prevent them from loosing their temper :-)) Keep about 1 1/2 inches clearance from the inner primary turn to the secondary OD (assumes primary will be driven by a two bushing transformer (7500V per bushing).

Gerry R.

Original poster: "Mike Knowlton" <amdx@xxxxxxxxxxx>

I'm planning the primary for my 8-1/2" x 40" secondary.

I think I'll make the primary a sloped pancake @ 25*,
Any better suggestions?

I'm considering 3/8" over 1/4" copper tubing.
Any good reason to use the larger diameter?
Turn spacing provided by 10-32 nylon screws.

Also how for should I start the inner turn from the
O.D of the secondary?

        Thanks for the feedback

                   Step by step
                                Mike