High Voltage Coax
Subject: High Voltage Coax
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Mon, 20 Mar 1995 21:14:00 GMT
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*Forwarded From: Eugene Welcome
*Original Area: FIDOElectronics
*Forwarded By: Richard Quick
As R. Quick sprayed ALL with clouds of Ions, he said regarding coax.
RQ> To say that simply because they are electrically equivilent
RQ> for signal transmission is one thing: we are using the material
RQ> for a purpose for which it was not designed or rated.
There is a Technical information chart in the Belden Catalog that gives
the max RMS operating voltage of coax. Polyethylene (PE) insulated RG-8
= 5000 volts. Foamed Polyethylene (FPE) insulated
RG-8 = 600 volts. Some RG-58 FPE insulated is good for only 200 volts
as 1900 volts for RG58 PE. RG-213 PE insulated = 5000 volts. I worked
with RG-8 PE and RG-59 PE for years for medical equipment that used
several thousand volts for image tube amplifiers, Hi-voltage Ion
getters on the early image tubes to maintain a vacuum and Gamma
Cameras. The higher voltages for the xray tubes used a special cable
that resembled coax. It is about the size of an average mans thumb. I
don't have one in front of me and I have been retired to long to
remember exact dimensions. :) This cable is 100 KV RMS rated and very
flexible. It has a special rubber composition that covers a small
bundle of two stranded wires wrapped with a wire shield. This is over
wrapped with mylar and then the thicker rubber. The outer rubber is
wrapped with a semi-conductive tape and covered over with a braided
shield just like coax. The final cover is either braided nylon or a
soft plastic cover. This stuff is expensive but it is available surplus
and also an Xray service person may have several hanks hanging around
with a blown end fitting. They rarely short within the cable, just the
end fittings that are hand done with potting epoxy and all to often a
human error makes these fittings short lived. It take a half hour per
end fitting by an experienced technician to process. The service tech
will often times replace the cable than repair on the job as the
fitting may have been botched in the first place and the other end may
go next. There is a larger size for ortho-voltage xray (in plain
language, radiation therapy xray). They are rated at 500 KV RMS and are
usually short 10 to 25 ft and very stiff and about 2.5 inches in
diameter. Similar constuction as the smaller cable.
I have seven 0.1 mfd 5000 VDCW extended foil Part# 0F50-104 and two 0.1
mfd 4000 VDCW extended foil Part# 0F40-104 capacitors made by Plastic
Capacitors Inc. of Chicago Ill. They are assembled in glass tubes of
1.25" diameter by 2 inches long for the 5KV and 1X2" for the 4KV. There
is a clear oil and the metal end caps are solder sealed to the glass.
There is a 1/2" X 8/32 thread stud on each end. I have some lower cap
values in higher KV ranges that are built the same except they are 1/2
to 5/8 diameter by 5 or 6 inches long. I have to find them. :( My attic
is my warehouse. The ones discribed were in a box in my shop. Can these
be of any use for your work? I've had them for 10+ years with nothing
now planned. I got them new and I never used them.
Of course it's grounded, See....YEEEEEAAAAAAAAHHHHHHHH....
73, Gene, K7"EEK" !! a Mouse !!! A Non-offensive Signature Line.
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