Failure mode of MMC's

["sundog" <sundog-at-timeship-dot-net> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

  Hi all!


   Well, good news, bad news, and mediocre news...


 The good news is that I got up to 35-37" streamers yesterday evening
(thursday) from my 4" coil (Thanks Dave!).  I changed the electrodes is my
sparkgap to thin brass rod, as well as the stationary electrodes.   The
flying electrodes worked beautiful, but the stationary got waaaay too hot &
burned off some wire insulation from my tank wires....oops...No biggie.  The
bad news is I'm running just over 2kva to do it.  Not too efficient.  The
mediocre news is that I think I may have cooked my MMC or a few NST's.  The
unrelated news is that on the 15th I go in for Lasik eye surgery and get rid
of my glasses!!! WOOHOO!!!

   I added a polycarbonate sheet above the primary, and for the most part,
the streamers ignored the primary completely!  It was great!  I got an
occaisonal strike to the sheet, and it just spread out like some weird vine
on the polycarbonate.  Very cool looking.  I opened up the gap a little bit,
then fiddled with the phase of the disc on the rotor, and believe that I
toasted a chunk 'o my MMC.  My output dropped a lot, and my tuning went out
a complete turn, and the srsg just sounded a lot wimpier.  The next run I
only got ~3" streamers...definately a problem somewhere. Tonight I'll try to
test each string in the MMC (5nf, 17kv), and also the trannies.

if I *did* kill an MMC, it died peacefully.  No pops, no "exploding
caps"...my output just dropped.  What is the normal failure mode for an MMC
in TC use?  In stress-testing mine destructed by popping the red coating and
letting out some smoke/hissing.  I'll be inspecting it later...


My coil...
  4" secondary wound with ~600something turns of 22 ga.
  35nf MMC
  (6) 12kv30ma NST's for ~2kva
  6x14(?) toroid.  Looks about silly-big on the thing, but it makes it rock!
  srsg running 120bps
  tunes ~turn 4 on the primary.
    Best runs were last night,  producing 35-37" streamers and 1 40" strike
to a grounded rod.  I got ~5" by changing the gap electrodes from zinc and
making the stationary electrodes out of brass rod.  Works *much* better.
Also adjusted the gap for best operation between runs.


Ideas?  Comments?  I think this coil can do better.  42" from a 15/60 just
puts this to a bit 'o shame.

									Caio!
										sundog