The I^2 x R heating of the grid at 144MHz is probably minimal because
gold is a fairly good electrical conductor, and there are over 100
grid-bars to share the current burden of 24Arms. An interesting thing
about my conversation with Mr. Foote is that the frequency of the
intermittent "oscillation condition" (which causes the top layer of
atoms in the grid's gold plating to boil off) had apparently never been
measured by Eimac's 8877 development team - or perhaps they never told
Mr. Foote what it was. My guess is that the frequency thereof is in the
UHF range due to the evaporation pattern seen on the grid in
gold-sputtered tubes. That is to say: If the grid is is acting like a
quarter-wave resonant antenna, then there should be more current near the
low-Z end nearest ground -- which is evident in the pattern of gold
evaporation that I've seen since patches of bare base metal have appeared
only in the bottom third of the grid.
- The mystery remains as to why Eimac's customer rep [Mr. Reid Brandon]
told QST's Paul Pagel that Mr. Foote was not authorized to discuss gold
evaporation with me.
cheerz, Peter.
Was it Murphy who said things are usually more complicated than they look?
>Rich's calculations are interesting. With these levels of grid current,
>how much
>heating of the grid is there because of the effects of skin resistance? I
>admit
>I haven't done the calculation, but intuitively, there must be some
>heating from
>this effect, and surely that has an effect on the allowable dissipation?
>73
>
>Peter G3RZP
>
>
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
end
|