So I found another great trick on Andrew Seltzman's website
He shows how to remove the potted NST from its case and insulate the center tap from ground. If you ground one terminal, this gives you the full voltage between the other terminal and ground. Even better, you can use bridge rectification and still ground the case.
For demo fusors, this could make using cheaper 9kv and even 5kv transformers a possibility. For those who already have 15kv transformers, they could greatly increase power they can supply.
Even modified this way, the transformer would only produce 2/3 nameplate current and voltage, so you couldn't quite get 30kv@10mA required for fusion with a 15kv 30mA NST and 2 or 3 stage CW multiplier, but you could with a rarer 15kv 60mA NST. Also you could place multiple transformers in parallel to get more current as Jack Williams thought of. One note however, the large 15kv capacitors needed to avoid huge drop and ripple voltages would likely exceed the cost of the transformers themselves.
As high voltage goes, this is a pretty safe way to 15kv at a usable currents. Other than x-ray transformers, I can't think of amateur power supply that is as simple and as powerful.
