Eric,
I had planned on building a few of the units to sell, but just didn't get around to it.
The heart of the unit is a HV module made by EMCO, they have modules from 100v to 12,000v, the output voltage is adjusted by changing the input voltage from 0 - 15vdc. The problem is the cost, if you buy them from EMCO they want around $200 each, I finally found a guy on Ebay who sells the 10KV model for $40. In fact he has a listing right now:
http://cgi.ebay.com/ws/eBayISAPI.dll...category=36323
The rest is pretty much straight forward, a full wave voltage doubler to supply dc from the 6V6 filament connection, and a LM317T adjustable regulator used to adjust the output HV.
Here's another picture of the unit. The regulator should have a heatsink, I added one after this picture was taken.
If you are interested in building one I'll draw up the schematic and email you or post it if there's interest.
Chuck