Hi There,
I've bought a bunch of NSTs from various places on eBay, and I've found that not all vendors are alike, and certainly not all transformers are alike. You really want to find a non-solid-state transformer with no GFI. They tend to be older units. I've found 15,000v 30ma NSTs on eBay for between $20 and $50, depending on how weird the bidding gets. They're heavy, so shipping tends to cost about the same amount.
I recently bought an NST from an eBay source listed as a 15/60 (15,000v 60ma output). I won the bidding at $70 w/shipping, and the guy sent me a 15/30 transformer (1/2 the current output - much smaller unit) with the current rating scratched off the manufacturer's rating panel. Not sure if he anticipated I would notice the difference, but it was pretty clear. As I have several of these transformers I could see the difference, and also, he wasn't smart enough to scrape off the model number or the kVA ratings, so I looked up the data sheet. Sure enough, it's a 15/30 and not a 15/60. So make sure if you get one you only get one where the seller has taken a picture of the aluminum or steel plate that has all the rating info on it. It's kind of hard to tell the physical size from the eBay pictures.
I'm not sure about the transformer in the sale you listed, but most of the NSTs I have bought, come from manufacturers like Franceformer, or Jefferson, etc., and they're potted - that is - the transformer is in a case that is filled with black tarry stuff and you can't get at it without some trouble. The high voltage terminals are attached to ceramic bushings and are far apart from each other. Separation and insulation of the terminals to prevent arcing and corona is probably not so much a problem at 1500V, but it is at 15kv.
Now, there are people on this site who have made tesla coils using DC dry cell batteries. So high voltage and current is not an absolute necessity to create a coil. Coils work on the principle of resonance, which says if you keep giving things little pushes at the right time, you can get a big energy buildup. if you're doing things like using voltage doublers or DC resonant charging supplies you certainly could do it. But they are trickier to build. A 7,9,12,or 15kv NST and a static spark gap might very well be the simplest coil you can make and the results are pretty cool in terms of spark production. And NSTs that I've been mentioning have a built in current limiting architecture that prevents them from drawing too much current if the output is shorted. Don't know about this one you picked. But if you could every call such a thing easier - it's certainly simpler to build a coil around an NST than non-current-limited power supplies built around pole pigs or microwave oven transformers.
Anyway, happy building! Coiling is great fun.
Joe
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