What is the boiling point of molten gold in vacuum? I assume it is lower in
vacuum as with any liquid in a vacuum.
It may be even more complex than that!
73
Bill wa4lav
At 10:11 AM 4/7/2005 -0700, R.Measures wrote:
>On Apr 7, 2005, at 3:26 AM, Ian White G3SEK wrote:
>
> > R. Measures wrote:
> >>> No, I'm simply saying that the Eimac tube guys that I knew and worked
> >>> with said a lot of what passes for "truth" is a bunch of nonsense.
> >>> In their experience, every case of "parasitic problems" in 8877 amps
> >>> could be resolved by properly grounding the grid
> >>
> >> Did the 8877 design team use improper grid-grounding that resulted in
> >> the "oscillation condition" they observed that caused gold to
> >> evaporate
> >> from the grid of the DUT?
> >>
> > That seems to be conflating two different stories, on the basis of
> > information from an individual Eimac employee which the company
> > subsequently said was incorrect.
>
>Eimac's Reid Brandon told Paul Pagel, the *QST* Technical Topics
>Editor, that Mr. Willis B. Foote was not authorized to release the
>information on the finding about gold-sputtering in the 8877 during
>testing at Eimac.
> >
> > The "oscillation condition" in question was not a VHF parasitic as we
> > know it,
>
>Agreed since the pattern of gold-evaporation indicates that the RF
>current was in the UHF region.
>
> > but can only arise in extremely large tubes that are big enough
> > to have their own internal VHF resonances.
>
>It's obviously not VHF. Since the resonance of a 3-500Z's grid
>measures c. 90MHz, my guess is that an 8877's grid probably resonates
>above 600MHz when it is grounded by an Eimac grid-grounding collet.
>*Has anyone ever measured the grid resonance of an 8877? - (my dipper
>craps out at 300MHz)
> >
> > What causes gold evaporation is overheating - that much seems obvious.
> > What caused the overheating in any particular case is entirely open to
> > question.
>
>The grid's base metal is Mo (molybdenum), which melts at 2617ºC. The
>grid is plated with Au (gold), which boils at 2966ºC. If the entire
>grid structure was overheated, why isn't the Mo melted in tubes with Au
>boiling-blisters?
>
> >
> >
> > --
> > 73 from Ian G3SEK
> >
> >
>
>Richard L. Measures, AG6K, 805.386.3734. www.somis.org
>
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