Now thinking about the secondary of the TC. Most of the information that I have been able to find, on the web at least, says that on larger coils (diameter > 7") the secondary winding (not the coil form) should be three times the diameter of the coil. I am assuming that this only works if you have not yet calculated your desired resonant frequency since the length and diameter of the wire, and turn spacing, in conjunction with the circumference of the form will determine the wound length of the winding.

As for the coil form material, Chris Hill (who also has a very informative site) has this to say:

The secondary form of a tesla coil should be made of a material of low loss in the 50 to 1000kHz range. Materials such as polyethylene, polystyrene, polypropylene, polycarbonate (Lexan) or acrylic (Plexiglass) are suitable. Usually, however, PVC is used. PVC is a high-loss material. The coil form should be as thin as possible, but must have sufficient strength to endure the winding process and to support the toroid terminal.

7/15/00

Today I nearly fell on the floor from sticker shock! I priced 12" Lucite cylinders to use as a coil form. Depending on wall thickness, this stuff costs over $300.00 per linear foot! Now I see why coilers use PVC. Even 10" with 1/8" walls costs about $65 per foot. I think I will stick with an 8" or 9" form.

I just received my first item from EBay! 10 pounds of #20 wire. I am still waiting for the caps and 100KV diodes. I have been experimenting with laying out my coil using AutoCad 14. Steep learning curve, but I feel it will be worth the effort. This lets me try stuff before buying expensive materials. To the right, you can see an early rendering. Notice the 'upside down' primary tank coil. I did this for extra insulation (shielding). You will notice that I broke a rule, the one about secondaries not being more than 3 times as high as they are wide. I will have to fix this. Can anyone tell me the reasoning behind this 'rule' and the consequences of breaking it?

I have also been looking into more theory of how a Tesla Coil works. Cavity resonators and transmission line theory seems like Voodoo. I have been getting some good ideas, though. I just realized that I can use my Ham radio as a signal source to 'sweep' the coil to determine resonance and to dynamically see how the coil functions. I also won a bid on a Racal-Dana 1.3 gig frequency counter. This may help, as well.

Now that I have my wire, I'm getting ready to start building the secondary (Thoughts and Details Here)

My major problem at this point is finding a suitable secondary coil form. The best that I have been able to come up with is 12 OD green PVC sewer pipe from a local plumbing supply house. My concern is that it is too thick. The wall thickness is over 1/4", possibly 3/8". The guys that work there say that your hair stands on end when you walk near these 13' pipes! I would guess, from this, that these are real good insulators but that there is a high dielectric value too. 

Finally! I have a form to use for the secondary. I will have to be happy using a 10" PVC form (green, I don't know what schedule it is) Now I can post pictures of the actual construction and testing.

The form I got for free is not long enough. It's OK, though, I just had to bite the bullet and buy a new one. I finally ended up with a gray one that is 5 feet long, 10 3/4" outside diameter with 3/16" wall thickness.