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more gas
Al, ther reason that any tube will stay lit at a colder temperature (all
other things being equal ) is due to heat the tube generates internaly as it
operates. This is why 60 mA is much better in this respect than 30mA. But
we're not talking transformers, we're talking about gas. Due to it's
molecular structure neon generates more heat when running than argon.
Therefore a tube filled with a greater % of neon is going to operate at a
higher temp. This higher operating temp keeps the Hg vaporized longer and
therefore the tube brighter at lower ambient temperatures. Having said this,
helium (again due to it's molecular structure) operates at an even higher
temp than neon, but it is my opinion that having small amounts of helium in
a tube does not do any good for the long term brightness of the tube. Even
though it may start out running hotter, there is some evidence that this
small amount of helium gets cleaned up by the electrodes pretty quickly (just
as Ne gets cleaned up (or trapped, or imbeded, or whatever term you want to
use) ) - maybe as quickly as 2 or 3 months. After the He becomes trapped in
the electrode shells, you are left with whatever your base gas mix was -
75/25 or whatever.
As you go to higher % of Ne in the mixes, your footage can drop some for a
given transformer. Since the tube is running hotter, you also would not want
these mixes when running very high mA transformers - like what you would use
on cold cathode.
As far as I know, Transco is the only one selling it in glass flasks, but any
one who sells SIGN GRADE gasses in SIGN GRADE tanks for the for the industry
can mix them to whatever you want; Spectra, Transco, whoever.
Morgan