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Tech Help -
Technical Sheet HR1.
Helium Rinse During Processing
Masonlite Electrodes.
The
use of a Helium rinse
as part of the process serves two purposes. Firstly, any minute
residual gases remaining in the tubes after the initial bombardment
will be diluted by a factor of several thousand. Secondly, the
rinse will indicate, if for any reason, the bombardment was
inadequate by a visual deterioration in gas colour from a straw
yellow to a blush white discharge.
Method
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Once the
initial bombardment is complete and the tube temperature has fallen
to approximately 100ºC and a vacuum between 10-2 and 10-3
[1 - 10 microns] has been achieved. |
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Induce 5
millibars [4 torr] of Helium gas. |
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Switch on
the current set at 500mA. This current setting is the same for
all ratings of electrodes except the 20mA type which should be run at 200mA. |
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Allow the
tubes to burn for at least one minute. If over this period the
gas discharge remains a consistant straw yellow colour, a clean,
sufficiently bombarded tube will have be indicated. |
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Open fully
the main valve. |
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Allow the
tubes to cool to 50ºC and fully evacuate 10 10-3 [1 micron] |
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Fill
the tubes with the required amount of rare gas and seal off for ageing. |
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At the
end of the one minute runnung time, if the gas discharge colour has
deteriorated, a second bombardment can be performed using the Helium
gas in the tubes as follows.
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Increase the
current to between 700 and 900 mA to effect full heating of the tubes
once more up to 250ºC keeping the main valve closed throughout.
When this is achieved :-
Switch off the current.
Open the main valve.
Allow the
tubes to cool to 100ºC and achieve a vacuum of between 10-2
and 2 x 10-2
[10 microns].
Repeat the
Helium rinse process to achieve a straw yellow gas discharge colour.
Continue
through the rare gas filling process. |
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Note: |
Helium neon
mixtures so called cleaning gases can be used, the discharge colour
should be a bright orange. Helium is recommended because it is
cheaper and more readily available. |
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