W8JI, Tom, asked ' what is Rocky Point effect?'
It was first noticed in the mid to late 1920's at the (then) new Rocky
Point, Long Island of, I believe, RCA, although it might have been AT&T.
They found that even when biased off, occasionally there would be an
internal arc over in power tubes, especially, apparently, in water
cooled tubes. Similar arc overs occurred when tubes were idling in class
B, and when operating, for no apparent reason. Examination showed that
major damage had occurred at 'high' spots on electrodes, and, I believe,
at points on the plate structure where the water cooling was less
effective due to the flow peculiarities. (G3RZP question: was some form
of local heating involved - possibly a shift towards a local point
running on to the negative slope portion of the Nagayoki curve?) A
'cure' was found by 'flashing' the tubes at very high voltage to induce
an internal, controlled arc while pumping - effectively plasma eroding
the high spots on the electrodes. It was thought the problem was due to
gas occlusion, which was liberated by the very high electric field
strength occurring at the 'high' spots, exacerbated by high temperature
- thus running with a local spot on the Nagayoki curve could make things
worse.
Information from G6JP, who spent his whole professional engineering life
on production engineering and applications of tubes, receiving and
transmitting, up to many kw.
Although the apparent symptoms match those described as parasitic
induced arcs, this is not to say that the parasitics do or do not occur
- after all, the early stages of a cold and of pneumonic plague are
similar!
73
Peter G3RZP
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