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RE: MMC partial failure

Nick,

Sounds like you're spark gap may be overheating. I had the same symptoms
last Sunday when I forgot to turn on the SG blower (but I was running way
more power).

Brian D. Basura




-----Original Message-----
From: Tesla List [mailto:tesla-at-pupman-dot-com]
Sent: Monday, July 26, 1999 4:12 PM
To: tesla-at-pupman-dot-com
Subject: Re: MMC partial failiure


Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>

Hi Nick,

	Carefully look at the caps.  Almost always you will see that they
have
swelled up or the case has split somewhere.  However, 5kV should be far
below any voltage breakdown. and three strings should not be stressed
either at this voltage.  I would definitely suspect something else is going
on...  Don't know what but maybe the gap is overheating or the variac is
burning a brush...  I have seen sync rotaries loose sync and do this...

	Terry



At 12:56 PM 7/26/99 -0400, you wrote:
>Hi All,
>         my little coil's mmc seems to be undergoing some sort of weird 
>failiure mode.
>The coil functions normally, throwing nice 18" arcs and drawing 80ma -at- 5kV,

>then it starts to pulse in and out of tune.  
>The secondary discharge stops almost totally and the spark gap makes the
sort 
>of hiss that is does when the coil is very badly tuned.  After a few
seconds 
>it pulses back into tune only to drop out again and repeat what I have 
>already described.
>My theory is that in one of the 3 strings of caps is a cap close to death
and 
>that it is breaking down reducing the capacitance of the string and taking 
>the coil out of tune, then self healing a bit then breaking down again.  
>Unfortunately not having an accurate C meter I can't measure the strings to

>check this.  
>The caps are 1600V 47nF philips 378 series in strings of 10 with 3 strings
in 
>parallel  and the neon is a 6/60 (I said 80ma 5kV because it sags quite a
lot 
>under load) 
>It is not a reso-cap so I don't see how a large enough voltage to damage
the 
>caps is being generated off a 6/60 neon?
>
>Semi-baffled in GB
>Nick Field
>