On Fri, 8 May 1998 13:13:14 -0600 John Lyles <jtml@lanl.gov> writes:
>Hi,
>
>Not to enter the parasitic discussion, I just wanted to pass on the
>advice
>I got from both Econco and CPI/Eimac over the years. When high potting
>the
>grid/filament of big tubes, especially those in hundred KW ratings, be
>sure
>to use pure DC or keep the time on the high pot to a minimum, few
>seconds
>for example. A lot of commercial Hi-potential machines have AC ripple
>at
>the mains frequency, at least the older big units did. Modern high
>freq and
>switching power supplies are exempt from this warning.
John..what would you think about the typical "ham" level hi-pot setup?
It would be a bug zap xfmr with typically a 0.2 MF/10KV filter cap. I
have built one here that will Variac up to about 12.5KVDC but I am
getting the impression that it will not do anything useful for tube gas
testing. It certainly works fine for testing air and vacuum variable
caps.
Low frequency
>resonances can be excited in the structures, causing them to vibrate
>and
>possibly cause a short. I don't know where the bottom end of this
>warning
>falls, such as 10kW, 20, etc. A mechanical engineer with knowledge of
>the
>tube structure would know. I know that the tubes for modulators in big
>transmitters had certain frequencies that they could sing at, if
>excited
>mechanically.
>
>In the Philips paper from 60 years ago, that I posted having found a
>month
>ago, there was reference to the proper amount of energy limiting R in
>the
>plate circuit, to prevent filament bending due to the forces from the
>occassional arc from "Rocky Point" effect in big tubes. While I have
>heard
>this debated constantly for weeks here, the analysis was published a
>long
>time ago by experts in one of the major tube companies.
I remember that posting John...and it should have stopped any further
speculation. Perhaps you would repost that for all to see...again.
73 Carl KM1H
I tried to do
>an
>OCR (optical character recognition) on the TIFF images that I scanned,
>but
>the program (Omnipage) said no, I had not saved it with 300 dpi
>resolution.
>So, I am unable to post the text here, but read it several times now.
>
>John
>K5PRO
>
>
>
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>
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