Dick said:
>#####
>From our experience over 25 years and many thousands of tubes, it's
very >clear that in the vast majority of cases, after one or two BANGs
early in life, >the tube continues on for a normal lifetime of normal
performance, just as if >nothing had happened. If the cause wasn't gas
or some other physical >anomaly that is basically eliminated by the arc
- if in fact it was parasitic in >nature - what killed the parasite
during the BANG? Especially if parasitic >suppressor R increased as a
result? Would seem that gain at the parasitic >freq would be higher, not
lower....?
>#### Also, it's much more common in our experience for a new tube to
>BANG when in standby with full cutoff bias applied rather than when
running >RF, keyed or key-down. How to explain that? Seems like most
these are >most unfavorable conditions for spontaneous start of a VHF
parasitic - or any >other sort of oscillation. #####
G6JP, who spent his whole working life in tube manufacture, told me that
this was known at one time as the 'Rocky Point effect', so called
because it was first noticed at the Rocky Point, LI, station of, I
believe, ITT ( but it could have been RCA) on the 150KW long wave SSB
transmitter.
Classical 'Rocky Point' effects are seen with the tubes in cut off. It
was beleived that the phenomena was caused by ionisation at sharp points
on the electrode structure, presumably by ion attraction as in the gas
ion pump, but with enough ionisation to cause a flash over. The cure was
apparently to run the tube in cut off with a very high plate voltage to
allow the arcs to batter the points off! (Current limited, though).
Now, whether you would see ionisation after this had all happened is
another matter................I offer a piece of evidence, which was, I
believe, documented in the Journal of the IRE.
73
Peter G3RZP
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