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Pressure adjustments for smaller tubes

 >>  --Why is it that such a high pressure of gas creates this effect?  Some
 tubes I've played w/ by putting in high gas pressure seem to just create a
well defined, fine line inside the tube.<<

 The snaking is simply a matter of path of least resistance. In a high
pressure situation there is inherently more resistance to begin with so the
arc is always looking for alternate paths. Kinda like the grass is greener
effect.

 >> --What is happening when snaking occurs in other units that are processed
in the "standard" fashion?  And why, if it does occur, does it stop during
aging in? <<

 This is for the same reason that some tubes are not snaking as you described
even in the high pressure situation. I say that this is the equivalent of
weather inside the tube. The fact that there are impurities evolving within
the space sets up different densities of molecules and different resistances
in that same space. This makes snaking easier to trigger. There are other
factors involved such as standing waves and cyclic phenomenon related to the
alternating voltage source frequency but I like the simplistic weather answer
myself. Most people that come into my shop can handle that one. Once the tube
stabilizes snaking does not occur so readily unless the pressure is very high
or impurities continue to evolve from the heat of normal running currents.

 >> --I'm also wondering about the mention of adjusting pressure for smaller
units.  Several
 people on the list have mentioned it & I'm wondering about the reasoning from
diverting from the charts. <<

 I noticed that the only time I had field problems with tubes I pumped was
when the sign contained tubes smaller than a foot in the design somewhere. The
transformers were going bad in these signs and it wasn't until a few of the
short tubes failed did I realize that the normal fill amount needed to be
adjusted somehow. Unfortunately for me, this list did not exist and I learned
most of what I know through trial and error. The fact that there is such a
short distance between the electrodes is the problem with the normal fill
pressure. There is not enough material to slow the electrodes down in this
case and there is a high rate of sputtering at the electrodes. Think of it
like a bullet proof vest. If you can't make it thick enough then make it out
of a material that is denser or at least has more resistance.

 Anyway, the charts are just a guideline for normal case situations. I like
Kenny's little program because it figures out mixed loads (merc and neon)
nicely. I am not sure if he factored in short or longer tube lengths in the
mix but it certainly is useful for the ability to mix transformer sizes to
what you have on the shelf.  Nice job, Kenny!

  E-mail from: Tom Biebel, 05-Apr-1996
 

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