On Jul 30, 2006, at 1:24 PM, Tom W8JI wrote:
>>>> When the Chinese were making 3-500Z tubes with regular
>>>> glass
>>>> and holes were sucking in the sides, Rich concluded it
>>>> was a
>>>> VHF parasitic that couldn't be seen or measured. This VHF
>>>> oscillation supposedly caused dielectric heating of glass
>>>> at
>>>> VHF.
>>>
>>>
>>> Correct. Rus Healy at QST was the first who told me of
>>> this
>>> phenomenon. However, it took Eimac a while to come up
>>> with a glass
>>> recipe that would not melt at VHF, so I was not surprised
>>> that the
>>> Chinese initially encountered the same difficulty.
>> Do you know when this was? I'd like to know which date
>> codes to avoid.
>
> Steve,
>
> The Chinese tube problem was NOT VHF heating as Rich
> claimed. The Chinese used regular glass and the tubes melted
> even with no RF applied.
So why didn't the entire envelope melt, Mr. Rauch?
>
> What I said was Rich **concluded** it was a parasitic.
correct. The symptoms sounded familiar.
>
> I'm not aware of Eimac ever having that problem or any
> similar problem. It makes no sense at all to think they
> would.
Why is the 7034 (glass anode insulator) rated at 150MHz when the guts
are good for 500MHz?
>
> The Chinese tubes are long gone. They were early Chinese
> tubes.
Correct, Tom. The glass fluxing agent was optimized to minimize D-
factor.
>
> 73 Tom
>
>
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>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
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