The 'getter" is the silver coating inside of your tubes. Examination
of the getter is a good way to tell if the tube is in good condition. On a 5692 tube, for example, if the silver getter coating
at the top has a smooth, consistant round edge, then this indicates that the tube has little or no use. If you find "notches"
at the edge of the getter, right above the uprights in the center of the plates, then this indicates usage as these notches
will recede into the getter as continuous heat is applied over time during use. The deeper the notch, the more the use.
The "getter flashing" absorbs free oxygen, nitrogen, carbon dioxide,
carbon monoxide and hydrogen from the tube whether the tube is used or not. You can be certain the vacuum is bad "ONLY" if
the flashing turns chalky white all over. If it is silver, black, rainbow-colored, or even totally gone, the tube might
still work fine. In fact, a "BLACK" getter is MORE effective than a "SHINY" getter at absorbing gas.
Here's a quote taken from "GETTER MATERIALS FOR ELECTRON TUBES" by Werner Espe: "If the getter is vaporized very slowly,
the first barium atoms evaporated will absorb the gas present so that the remaining getter is deposited in a very high vacuum,
exhibiting a "shiny" mirror. If flashing is done very rapidly, however, the getter deposits in a rather high vapor pressure,
and the getter mirror will be discolored (rainbow-like) due to the dispersion of the barium. If vaporization is carried
out in the inert atmosphere of a rare gas, the condensed deposit will be "black", resulting in a "dispersal" getter.
This condition does not mean that the getter is contaminated, but merely that the deposit is finely divided and therefore
absorbs light. Such deposits exhibit "HIGH" efficiency than the bright deposits: i.e. DARKER is better.
The ONLY way to accurately determine the health of a vacuum tube is to test it ELECTRICALLY. PERIOD. Anyone who discards
a tube because its getter flashing is slightly "discolored" is making a sad mistake.
More info available at http://www.svetlana.com/docs/tubeFAQ.html
