NST unpotting

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ben Ziegler by way of Terry Fritz <twftesla-at-qwest-dot-net>" <crossguy-at-hotmail-dot-com>

  I recently acquired seven broken NST's for free. I have:
3 4kV 30 ma Jefferson Magneteks, a 7.5kV 30 ma Magnetek, a 9kV 30ma 
Franceformer, a 12kV 30 ma Jefferson (not a Magnetek), and a 15kV 30 ma 
Franceformer.  All have center-tap-grounded secondaries, and all but the 
9-30 are outdoor enclosure type.
  They have high (6 to 10k Ohms) resistance across the secondary terminals, 
low (~0 ohms) resistance across the primary, and no primary to secondary 
continuity, although some have secondary to case continuity. Only the 15-30 
appears to have life in it, drawing a 1" arc over a spark gap (straight from 
120VAC, no caps, etc.)
  Question: Are the resistances within acceptable range?  I am considering 
de-potting them.  From the archives, I set each NST in a ~250 oven until the 
black insulation gunk melts out, then I can add my own insulation, say, 
submerge in a tub of mineral oil.  Would this work?  Anything different 
about the Magneteks? I seem to recall cautions about depotting Magneteks 
from previous threads.  What kind of ohms/continuity should indicate a good 
NST?  What kind of sparks will I get directly off the secondaries?

ben