RE: 6" Coil Problems

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

Original poster: "Ted Rosenberg by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Ted.Rosenberg-at-radioshack-dot-com>

Jonathan:
I recently went through a similar experience which I related last week in a
post entitled Setting the Safety Gap.
If your safety gap on the Terry Filter is too wide and it never fires, any
over volting by the NST due to a wide main spark gap could backfire and
overheat the MOV array to the point that the solder on their leads melts!
And, of course, if one MOV goes, they all do.
I cleaned off the filter board, reset the SG according to the step-by-step
info in the archives, replaced the MOV string and all is well once more.
My main gap, a t-gap, is set differently, of course, than a static gap.
When I had a static gap, the total "gappage" of the 9 tubes was about .0312
or so. As I recall, the total of all the gaps was .25 and .25 divided by 8
was .03125 And that was with a 15/60ma NST.
Hope this helps.
Safety first

Ted


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Monday, September 23, 2002 11:28 PM
To: tesla-at-pupman-dot-com
Subject: 6" Coil Problems


Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Kidd6488-at-aol-dot-com>

Hello everyone,  (forgive me for this being long, there is a lot to include 
:-\   .)
      
       I've had my coil put away for a while, and recently brought it out
for 
some tests. 
       If you don't know, my coil is as follows:

- 12/60 NST
- Terry Filter
- Multi - Pipe Static Spark Gap   ( 12 gaps, each at .025" )
- .017 uF Geek Cap
- 10 turn, .25" Cu pipe primary coil
- 6" * 30" (Wound) secondary coil, #20 AWG wire.
- Controller consists of just a switch/light combo, and one outlet.

Max sparks to date were 22" Ok, for my first coil, but a 12/60 should
deliver 
more. The problem during the first runs was that the spark gap would only 
fire at 3 or less gaps! That is only .075 total gap! And never once did the 
properly set safety gaps fire.

Yesterday, I had just my NST, filter and spark gap hooked up, to see how
many 
gaps that would let me use.  Suddenly there was smoke coming from somewhere,

which later turned out to be a MOV in the filter. :-( While investigating
the 
smoke, I noticed a piece of what I think is soldier, stuck under the leads
of 
the MOV array, making contact with at least two of the MOVs. I removed it
and 
tryed again. I guess MOVs fail closed, because I let the smoke out of a 
second MOV.

I believe the soldier shorted out one half of the MOVs, which lowered the 
voltage at which they clamp. This level was under half of my NSTs voltage,
so 
they were sitting there, dead short to ground. I guess the 60mA for a while 
burned it up.  When the one failed, the same scenario occured, and the
second 
MOV failed. Does that make sense to every one?

After that I connected the NST straight to the Spark gap, with no filter,
cap 
or anything. It let me use all 11 or 12 (I forget the total) gaps. Pleasing,

that my NST was still OK, I took out the actual filter, but left the power 
resistors, and the safety gaps in circuit. That gave me max of 7 gaps, any 
more and the safety gaps would fire. Sounds good to me.

Now that makes me wonder, how long has that short been in the filter? Could 
that have been giving me the less-than-satisfactory performance before? I 
would like to try the coil now, but I am a bit worried about the filter not 
being in there. I still have the safety gaps (which seem to work now) and
the 
power resistors in place, and I know that some people use NSTs with out any 
protection at all. But hey, I'm 14, and poor; I have built a Tesla Coil and 
just bought an electric guitar, so I dont feel like burning up this NST. 

Would it be ok to run the coil the way it is?

I thank you for reading this, and hope to get this working right...

---------------------------------------
Jonathon Reinhart
hot-streamer-dot-com/jonathon