From: "Terrell W. Fritz"
Date: Sat, 29 Jun 2002 23:30:02 -0600
Subject: Re: [TSSP] Re: Top V Probe Design
Hi All,
I got the Jennings JP-325 60kV voltage divider today and posted pics at:
http://hot-streamer.com/temp/Jennings-JP-325/
Some of these picture are sort of big but I thought it needed to preserve the
detail.
http://hot-streamer.com/temp/Jennings-JP-325/P6290001a.jpg
Shows that the voltage divider is in three plug in parts:
The top terminal which is an odd aluminum/plastic assembly whose
construction defies belief.
http://hot-streamer.com/temp/Jennings-JP-325/P6290003a.jpg
It is not at all obvious how they made it or "why"... Seems far too complex
for such a simple task. They were probably trying to limit the stray
capacitance effects to preserve bandwidth.
The "tube" is a rod / pickup / shield design. Much like we have been thinking
of but the vacuum allows very small clearances. They have maybe 500V/mil
spacing in the very high vacuum.
http://hot-streamer.com/temp/Jennings-JP-325/P6290004a.jpg
http://hot-streamer.com/temp/Jennings-JP-325/P6290005a.jpg
http://hot-streamer.com/temp/Jennings-JP-325/P6290007a.jpg
A classic testament to Jenning's bazaar ability to make such vacuum
components! The vacuum seals and such are perfect! Much very high quality
hand work in a very low volume device.
The label tells that c1 = 2.786 pF and C2 is 916.0 pF. I guess that give a
0.00303226 division ratio.
http://hot-streamer.com/temp/Jennings-JP-325/P6290008a.jpg
I don't know how old this thing is but even the "typewriter" font is "old"
:-)) The label is crumbling fast...
Inside the base we see the additional base capacitor which is physically made
instead of a discrete part.
http://hot-streamer.com/temp/Jennings-JP-325/P6290011a.jpg
They have two small cylinders with a plastic material between them. Note the
hand soldering and custom "bending to fit" of the SO-239 connector. The base
is painted over copper. Both Jennings and Pearson seem to love working in
copper. All the contacts are silver or silver plated but they have serious
tarnish. No big problem to clean though.
http://hot-streamer.com/temp/Jennings-JP-325/P6290012a.jpg
So there is one of the most advanced super-high voltage probes around that is
older than I am :-))
http://hot-streamer.com/temp/Jennings-JP-325/P6290013a.jpg
The use and advantages of high vacuum here really stand out. It allows very
small clearances for very high voltage. I will have to "spot knock" test the
heck out of this old thing but it looks like it is very serviceable.
Cheers,
Terry
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.