ORIGINAL MESSAGE: (may be snipped)
On Wednesday, December 4, 2013 10:51 AM, peter chadwick <g8on@fsmail.net>
wrote:
If one is to believe Philip H. Smith in 'Electronic Applications
of the Smith Chart', McGraw-Hill 1969, page 6, Fig 1.3, the maximum
voltage
appearing on a lossless transmission line with an SWR of infinity is twice
the voltage when matched.
REPLY:
I find that hard to believe but I can't actually disprove it.
However I guarantee that if you transmit high power into an unterminated
coax, the Tesla Coil effect in your output tank will cause some extremely
high voltages to appear across the load cap (and everywhere else in the
tank).
And that is what the discussion is about.
73, Bill W6WRT
If the amp was correctly loaded into a low VSWR antenna and the path
suddenly went open there should be no problem with the rather common 1500V
spacing load variable most companies use.
Common sense says to have adequate fault protection to protect tubes. There
may be a Tesla effect in the tank causing switch damage or arcing of the
tune cap.
All common problems with slow, worn out, or poorly sequenced relay
switching.
The only benefit I see in a vacuum variable load cap is higher current
rating as many cheap variables have poor current handling due to wiper
design.
Carl
KM1H
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