CD 942 failure tonight

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Original poster: "John Richardson" <jprich-at-up-dot-net> 

Hello,

Copnsidering the recent MMC debate,  I figured that I would share this 
evening's run.  This is a first fire, and tuning was done at partial variac 
setting.  Volt and amp meters are not in yet, so I can't give any real 
numbers.  Also, SRSG was set using a flourescent bulb, as I am still 
waiting on my motor run caps for John's phase controller.

Here are the specs:

Topload: 4x24  Soon to have an additional 4x36 on top of it.
Secondary:  4.5 OD PVC with 36" of heavy build #24, 1481 turns.  Plan on an 
8" with an 8 by 36 toroid in the future.
Primary:  .25 Cu tubing, .25 between turns, 16 turns total, seems happiest 
tapped at 6 and 5/8 turns.
Gap: SRSG
Safety across RSG:  Set at .5"
NST safety gap:  5/8"
Trans:12000/120 NST
Capacitor bank:  4 strings of 9, total of .0667, per MMC chart.

After rough tuning and ramping up variac, I heard one cap blow.  Black soot 
and a hole about a quarter inch deep.  Soldered up a new one, and ramped 
variac up to 120 volts.  Sparks about 4 feet, and gap won't fire until 
variac is above 60%.  After that it will fire all the way down to about a 
quarter turn on the variac.  Checked rotary, and there is no follow around 
with the gap arc.  She fires right on electrode alignment, so I am assuming 
that phase is pretty close.  Started it up again, and tried to fine 
tune.  A half turn either way from the tap point of turn 6 5/8 and 
performance diminishes.  Put tap back at this point and fed the trans the 
full 120 volts.  I stopped things again to check everything out.  First I 
checked the variac, an ancient Ohmite, to see if it was getting warm.  It's 
only rated for 10 amps, and I made a new brush out of a piece of brass due 
to no access to new parts.  Everything looks good and runs cool.  The  lash 
up wiring to the coil primary is 14 gauge, and it is hot to the touch, and 
the primary is warm.  Will go to #8 for final set up.  Looked at cap bank, 
and the new cap looked like a piece of popcorn that had just popped, black 
and all.  The one on the next string over was bulging like you know what, 
but no black stuff.  I can see the foil, however.

Why is this happening?  I am not going to re-fire the system until the last 
portion of the tank wiring is replaced with #8, PFC caps and meters 
installed, phase controller up and running, and new toroid installed.  I've 
put lots of work into this thing, including welding up a nice stand for the 
controller, gap, trans and cap assembly, and want to get to the bottom of 
this cap problem.  Any thoughts?

Thanks,
John Richardson