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Misc. Neon Stuff

>>  A job I did in December of 1994 is now turning red when the weather gets
cold. There is 600 feet of glass in this sign and it is on top of a 12 story
building. It will cost thousands of dollars to replace this glass and I don't
even know what is wrong with it. <<

One thing no one else mentioned with regard to merc. migration is the placement
of the tubulation. I've found that when shops tubulate in the middle of the tube
or somewhere along the tube length instead of using tubulated electrodes the
mercury will condense in the tipped off remains. That is because it is out of
the heat zone of the plasma current. The heat of the electrodes also helps to
drive the mercury toward that center tubulation area. While there are pros and
cons to tubulating vs. using tubulated electrodes, this is one reason not to use
them on merc. units.

>>  it was demonstrated that even low levels of UV facilitate the
outgassing of vacuum systems. <<

Interesting! Learn something new every day! Nice find.

Now to get into the grounded electrode on the manifold fray. My opinion on this
is that if I were to ground on the tube side of the main stopcock there would be
a lot of tubes that we could not pump. If you have to put a grounded trode on
the system then the place where I would put it would be right after the main
stopcock and before the pump. This would protect the pump and would still give
the control of the extra resistance that closing the main stopcock would afford.
I find that the stopcock will prevent the flashback just fine. On my system the
branch of the manifold that goes to the gauges and filling area also has a
stopcock which is closed while bombing. This keeps that side clean and it also
doesn't need to be outgassed since it never sees atmosphere (even if a tube
breaks on the pump). This was Mr. Ablon's idea and one I was glad to implement
and I've found that it works well. One other thing is that you don't want to
flash back too long because it is heating the hell out of the tubulation of the
trode or t-joint (in the case of side tubulating) and it will cause it to crack
real quick.

As for metal manifolds, I don't like them because you can't see problems
developing, metal and HV don't get along and you can't easily check for leaks.
Considering how many times we clean our manifold in a year I'd hate to try that
with a metal one (and know that it is clean). Besides, we're glass people,
right?

And finally,
on the diffusion pumps we have this one:

>> ( Sorry for such a quick reply, but I'm on the way out of town) I have both.
Be back 31/96.  I'll elaborate on the preformance of each after living with both
for more than two years.  (In the meantime, I suggest not going out and buying a
metal pump.)  Morgan <<

MC, how can you start something like that and walk away? And when is 31/96
anyway? You better DO some elaborating when you get back... 

So Don, you didn't mention if you were using that pump you bought. Is it
working? If so, do you like it?


  E-mail from: Tom Biebel, 30-Jan-1996

               - Neoman

               - Plasma Graphics Neon