Richard W. Ehrhorn wrote:
>Eimac engineers referred to the cause of the flashovers as "barnacles," but
>your description is much more descriptive.
I've heard of both gas inclusions and surface imperfections that might
be the same as Eimac's 'barnacles'.
>These flashovers usually
>occurred very early in tube life - more often than not during factory
>checkout of the amplifiers - and were self-clearing after two or three
>flashes. We also experienced frequent new-tubes-in standby flashovers in
>early 8877s and 8874s through the late 70's, but in the last 15 years or so
>they seem much less common.
>
Whatever the cause, improvements such as pure, gas-free metals and
better processing can certainly help.
>Proper fault current limiting
>resistors tame the phenomenon to the point that many times the plate
>overcurrent relay or breaker doesn't even trip.
I think that's the main point: don't worry too much about the reason
why, but do expect that it will happen, and protect accordingly.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.demon.co.uk/g3sek
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