> Before I put in the new Pride tube, the amp was inspected and found to my
> surprise that the amp cover was still with masking tape ! When Ameritron
> paints the cover it is masked with paper tape where it it supposed to
> contact the amp chassis. It is then normal practice to remove tape before
it
> is used on the amp chassis. Not so with my amp !
> I guess there was a shielding anomality of the RF compartment in my amp,
> that may have contributed to parasitic oscillations.
The tape would certainly allow RF to leak out of the case and cause TVI, but
the amp is unconditionally stable with or without a cover.
Folks in Mississippi, like folks all over the world, are getting sloppier
and sloppier with time, but the tape had absolutely nothing to do with the
zener.
Graphite anode tubes are particularly bad at outgassing from the porous
graphite elements, and even the smallest amount of residual gas will cause a
momentary flash over.
The worse thing about all this parasitic nonsense is it has eroded the
working knowledge base of our fraternity, filling it with all sorts of odd
ideas about very simple problems.
Go to:
http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm
and read about outgassing and HV arcs in vacuum tubes and also about
gettering and anode types.
73 Tom
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