>
>> Do external anode tubes have a similar problem of element outgas
>> during lengthy storage? Do they have a getter on the inner surface of the
>> anode which can be activated by arranging to raise the anode temperature?
>> I have several 8877 tubes which have been stored for several years and
>> would like to put them to use.
>
>The gettering in the 8877 is primarily on the heat dam of the
>heater/cathode structure.
>
>It reaches temperature from the normal heater voltage on the tube,
>so a long period of filament activation will getter the tubes. The
>normal problem with 8877's isn't gassing though, it is misalignment
>in the grid causing a short or causing the grid to "hot spot" and
>gold to be boiled off.
See Eimac letter on my Web site. Gold boils at thousands of degrees C.
> Grid wires are located between bands of
>cathode material, so the electrons miss the grid. The electric field
>between grid wires controls anode current, so the grid normally
>doesn't get heavily bombarded with electrons.
>
>If the grid is misaligned, areas of the grid will be struck by
>electrons and the kinetic energy will gradually cause the gold to
>migrate around inside the tube.
>
Not according to the letter from Eimac.
>In severe cases, the grid may touch the cathode.
>
... never seen here. Flakes of dislodged strontium oxide and barium
oxide can short between grid and cathode.
>....
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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