7/10/00 - Thinking about the primary capacitor. Obviously, it would be easier and faster to purchase a commercially available high voltage unit, but we have to take expense into account. I will research this to see how true it is. Meanwhile, the American Radio Relay League (ARRL) has a really good capacitor primer here (you will need Adobe Reader for PDF).

After a little research, I found the dielectric table (on the right) for some common materials. Optimally, we would use window glass for its dielectric constant but it breaks down at 250 Volts/mil or less, worse than air! Mica has the highest breakdown voltage which is very desirable for our application. It is also among the highest for dielectric constant. The big drawback is cost and availability in the voltage/capacitance ratings that we need.

I think we will settle on polyethylene film. It has a really good breakdown voltages, reasonable K, is inexpensive, easy to obtain, and is easy to work with. Now all we have to decide is if we want plate or rolled configuration. I am leaning toward plate style as we won't have to deal with stray inductance.

     I just found out that a cap I won the bid for on EBAY contains Pyranol which contains PCB's. Legally, I think I can't even buy this cap. Let's see what the seller has to say. (Click on picture for larger image) This is too bad as the cap looks to be in real good shape. Exercise caution when buying used parts - be aware of what you are buying!
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