>
>I have been waiting patiently for someone to mention Rocky Point effect
>in connection with "big bangs" in linear amplifiers. Tom finally brought
>up the subject with a very interesting post. I first heard of it in one
>of Bill Orr's columns in Radio magazine. About 1 or 2 years ago it was a
>topic of discussion on Amps. I keep files on about 20 topics of interest
>which are composed of extracts from postings which are cut and pasted to
>the files. One of my files is on Rocky Point effect and I thought there
>might be interest in 2 notes from that file. Unfortunately, I do not
>always note the author but I am almost certain that the first note was
>posted by Dick Ehrhorn of Alpha fame and the second came from a posting
>by a British ham. Here they are.73, Dan, N5AR
>
>"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)."
"Rocky Point" was 1932. The explanation sounds a bit like guesswork. No
photograph of a "Rocky Point" arc-mark is shown to the reader. In 1935,
G. W. Fyler's "Parasites in Transmitters" makes more sense. . There are
plenty of diagrams to help the reader understand why visitations from
parasites occasionally take place. . . Congrats, G. W.
Murphy was right. Things are more complicated than they look at first.
later
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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