>
>I said:
>
>>>Speaking of glitches..
>>>None of my 8877's have been hot for some time now. (6 months to
>>>2-3 years, depending on the tube) I seem to remember reading here
>>>that someone recommended 4-5 hours on the filaments before
>>>applying B+ . Does that sound right?
>
>And Rich answered:
>
>>There is no such statement on the tech spec sheets. If a seal is
>>leaky, the tube is history.
>
>Ah. Then the tales of heating the tubes for a period after
>extended storage are just that.
// On the surface it sounds like a helpful tip. With some
multi-hundreds of kWs, 22kV electron-tubes that have been in storage, it
may be a good idea to run the ion-pump for a while before blastoff. For
tetrodes with handles, as well as 3-500Zs and the like which do not
generate X-rays and don't have an internal ion-pump, I found that there
is no such thing as disappearing gas, except possibly when the operator
uses Beano® anti-flatulent tablets. ------- Also: If heat is helpful,
normal operation should be better than running the filament.
- The first time I butted heads with the disappearing gas theory was
during the Grate Parasitics Debate. This theory was used to explain
"big-bangs". However, when I said that I had high-potted a number of
grid-filament shorted tubes from kaput HF amplifiers that had experienced
a big-bang, and found over 95% of them to have good vacuums, the
gettering /disappearing gas theory was used to "explain" my finding good
vacuums. Apparently, the gas that had really and truly caused the
big-bang had simply disappeared because self-gettering had gobbled it up
- apparently before the operator could switch off the filaments. Also:
¿Could an arc in a near-vacuum be heard as a big bang outside the
envelope?
- Weird Science.
>I have no reason to believe
>any seal is leaky, but I had heard that the potential for a
>startup glitch could be reduced that way.
>
// The World of Ham Radio is not immune to techno-blather and old wives'
tales propagated by recognized experts.
cheers, Jim
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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