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Re: NSTs and The HEAT
<SNIP>
> > > (2) If you short the secondary of a neon sign transformer then the
> > > current-limiting kicks in. The transformer will run hot, but
> > > it was designed to do so, and this will not damage the NST in any
> > > way.
> > >
> > > I hope that this explanation helps.
> > > Fr. Tom McGahee
>
> Would I be correct in thinking that running one shorted like this would be
> a good way to heat up and re-form the possibly cracked tar in an old NST?
>
> This could be a good startup technique to reduce the risk of early faiure
> from high voltage breakdown. Similarly (in the distant past dark ages) we
> would slowly apply a DC "forming" voltage to salvaged electrolytic caps,
> to heal the fragile areas in the oxide dielectric, before throwing them
> right into service...
>
> Dave
>
Correct, Dave! However, the amount of melting thus provided is somewhat
limited. A better method is to heat the NST in an oven for long enough
to cause the "tar" to melt and then slosh the NST vigourously for about
15 seconds to a minute. This not only clears the cracks away, but it also
helps remove carbon tracking that may be present. In fact, this method
has been used successfully by many coilers to bring "bad" NSTs back
to full health. It sure beats re-potting!
Note: be very careful if sloshing the NST. Remember, it is HOT!
Also, some "tar" *will* oooze out, so have something under the
NST to catch the "tar". Your wife may frown on your using the oven.
Gary Weaver has successfully rejuvenated NSTs by heating them
on an outdoor grill. Just remember that a slow heating is
preferable. You want to melt the tar, not cook the NST!
Note that heating only works if the NST uses a "tar"-like compound
inside. Some NSTs do *not* use the "tar", but some other resinous
compound that does not melt.
Hope this helps.
Fr. Tom