Re: CD 942 Failure

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

Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org> 

The 9 I have do not seem to have such defects, though I can only check 
about 75% of the surface area of the soldered caps.  I would be interested 
in Terry's analysis of the potential defect, if Terry is willing.

For some reason (like the fact I've been hlding onto those caps for about 9 
months now), that bump you describe sounds eerily familiar.

Terry, for the uninitiated, what are those two pictures of, and what is the 
scale?  Is that more or less real color, or did the flash (or scan) alter 
the coloring?

John mentioned tapping at 6 turns, what is the inductance at this tap 
point?  Or give dimensional info and we'll calculate it :)

This is certainly interesting.  I wonder if some sort of HF resonance is 
being set up on those really long transmission lines?  When we performed 
the destructive testing on one of our secondaries a few years ago, we 
removed the topload at one point and tapped at about 2-2.5 turns (about 
2.5uH).  Running just over resonant value capacitor and about 12/180 NST 
input (4 strings of 9 .10uF caps for .044uF) the primary got fairly 
warm.  The blown static spark gap a la Marc Metlica (which is still used) 
got hot enough to melt the PVC housing.  I don't believe the caps got warm 
at all, but I personally didn't test their warmth.  Peak currents would 
have been on the order of 1900A peak assuming Vfire ~16kV and ~4ohms tank 
resistance.  Then again, the .10uF caps have a higher peak current rating, 
and have more strings in parallel.  This was the most aggressive test we 
could come up with using the MMC in a TC - perhaps we should have used 15 
foot long wiring from the cap to the primar!
y?

Mark Broker
Chief Engineer, The Geek Group


On Mon, 08 Mar 2004 12:13:35 -0700, Tesla list <tesla-at-pupman-dot-com> wrote:

>Original poster: "Harold Weiss" <hweiss-at-new.rr-dot-com> Hi All,
>
>I had just done a trade for some Geek caps with Mark Broker.  When I was 
>looking them over I found one with what looks like a grain of something 
>under the wrappings.  I'll bet that might be the cause of the recent 
>failure.  Probably some contamination got into the winder and started 
>causing problems that CDE didn't know about.  But whatever it is, it's a 
>sand sized dark lump of something.
>
>Mark, you may want to check your MMC, as these might be of the same batch 
>as the failure.
>
>Terry, do you want a look at it?  Please get me a mailing address so I can 
>get it to you.
>
>David E Weiss
>