Building a homemade SGTC part 2: The Tank Capacit

In order for a Tesla coil to operate correctly, the tank capacitor must be matched to the transformer. An online calculator is a useful method to calculate the correct capacitance. According to this calculator, my 9kV neon sign transformer requires a 0.0176uF capacitor (17.6nF).
To find the voltage rating of the capacitor, multiply the rated output of your transformer (in my case, 9000 volts) by 1.4 to get the peak voltage. 9000 x 1.4=12,600 volts. I'll round that to 13000 for a little extra safety. Since the capacitor in a Tesla coil is often charged to twice the transformer voltage, you must now double the peak voltage of your transformer. 13,000 x 2=26,000 volts for the capacitor. So, for my transformer, I will need a 26,000v, 17.6nF capacitor.
There are a few options for tank capacitor of a Tesla coil. The first is a single, large high-voltage pulse capacitor. Though they may be effective and not take up too much space, they tend to be rather expensive. They also MUST NOT BE POLARIZED, as current is supposed to oscillate through the tank capacitor. Polarized capacitors would probably explode.
The second option is a MMC (multi-miniature capacitors), which is a bunch of smaller capacitors wired together in series-parallel configurations to get the correct values. These are probably the favorite of many Tesla coilers nowadays, but once again, buying all these capacitors can get rather expensive.
That leaves the final option: build your own. This is definitely the cheapest method, but it is important to understand that homemade capacitors are extremely "picky" and may not always work on the first try.
One style of homemade capacitor is a basic stacked plate type. A dielectric is placed between two conductive plates, and another is stacked on top of that. This pattern repeats until the correct values are attained. Another online calculator is useful to determine the size of the plate capacitor.
Another type is a rolled capacitor, which is similar to a plate capacitor except that it is all rolled together and (often) submerged in mineral oil to keep it cool and reduce corona. I, personally, don't recommend this, as it is quite messy and tends to fail in Tesla coil applications.
I chose to go with the final option: the classic beer bottle capacitor. This method uses several bottles (often beer bottles) with aluminum foil on the outside and filled with saltwater. The great part about the beer bottle capacitor is that you can easily get most of the parts for free from a recycling center. At this point, I have two banks of six bottles. This is what they look like:
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The first photo is just the overall look of the capacitor. In the second photo, you can see the long screws I am using to make contact with the water in the bottles. Everything is held together by the two scrap pieces of metal that are sitting across the mouths of the bottles. The "base plate" is a piece of metal used to connect all of the foil parts of the capacitors, and the "top plates" connect all the screws. These serve to be the two high-voltage contacts.

The next part of the Tesla coil: The Spark Gap.