troubleshooting tesla coil (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Thu, 14 Jun 2007 19:32:17 -0400
From: Marko Ruban <Marko@xxxxxxxx>
To: tesla@xxxxxxxxxx
Subject: troubleshooting tesla coil

Hello all

I was looking for some help on tesla coil construction, and joined this 
list as a result.  Looks like I came to the right place :)

I'm building my first tesla coil, and could use some help "debugging" 
it.  All of the coil parts have been assembled, according to various 
recipes out on the web, but when put together, the spark gap doesn't fire.

I've got the circuit down to a bare minimum:  5.5KV, 30Khz NST provides 
the power, spark gap connected across the transformer output leads, and 
a capacitor in parallel with spark gap.  Without the capacitor, spark 
gap fires just fine, with it, I just hear humming sound (I think coming 
from the vibrating capacitor plates), but no spark.

Capacitor was home built, consists of 8 copper sheets separated by 10mil 
Mylar insulator, roughly 8"x6" area.  Measured C is 7nF.  When DC power 
is supplied (through a rectifier circuit), makes the gap fire at 
intervals, indicating that cap is storing charge.  I thought this could 
be my problem component, so I built a different type of capacitor (beer 
bottle salt water, 800pF), but that didn't change a thing.  Neither 
capacitor is shorted out, according to my multimeter.

Is there any definitive way to test the capacitor for faults?  Am I 
missing something else?  What could be going wrong?

Thanks, for any thoughts you can provide on the subject.

Marko