Re: NST filter failure?

["Gomez ADDams" <gomez-at-netherworld-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Mark, Terry,
 I think this may have been said before, but I'll repeat it just in case it
hasn't been said in a while.

 I believe that a major contributing factor to NST longevity is the quality
of construction of the NST itself.  Having purchased NST's by the pallet
load for small table-top coils at DiaboliCo, and having also scrounged many
of them from neon sign shops, surplus stores, etc, etc, I have found that
all NST's are _not_ created equal.

 Keep in mind that NST's are not intended to be run at their nameplate
secondary voltage for long periods.  When used in their intended
application, neon signs, they essentially act as _ballasts_, that is, they
start at the nameplate secondary voltage, the neon tubing fires, drawing
lots of (well, milliamps) current, the NST's current limiting kicks in, and
the voltage across the tube (and the secondary winding) drops significantly.

 No, I haven't measured typical secondary voltages with neon tubing
connected, but several sign makers have told me the above, and it makes
sense.

 So, what it comes down to is: how conservatively was the NST made, so that
when we abuse it by putting it in Tesla service, it survives anyway?

 I'm not sure what constitutes a well-made transformer.  I know that some
are made in Mexico and some are made in the USA.  Sign builders have
suggested that off-shore built NST's don't last as long in regular neon
service, so there is an implication that they'll last even less time in
Tesla service.

 I have seen Jefferson transformers fail left and right, and yet a friend of
mine has been running an older one for years in a small Tesla coil putting
out 14" streamers, and he's got no protection network! (it's got a
way-oversize capacitor of .1uF, however)

 At DiaboliCo, we bought many Allenson transformers straight from the
manufacturer, and never had any problems unless we failed to allow for
ventilation around the NST and it got so hot the tar melted!  (oops)

 I have an old, old Franceformer 15/30 that I have abused in every way
imaginable, in many Tesla coils, running it in a Jacob's Ladder for hours at
at a time, and it still lives.  It's probably older than I am (38) so it may
have been very well made.

 Food for thought.  You may not get what you pay for, but you almost never
get what you _don't_ pay for.

 - Gomez

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