Tungsten Electrode Source
Subject: Tungsten Electrode Source
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Mon, 1 Jan 1996 18:10:00 GMT
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Quoting Chuck Curran <ccurran-at-EARTH.EXECPC.COM>:
> I have been collecting information on rotary spark gaps and I
> have one question you may have the answer for. I don't know
> what the best source for tungsten electrode material might be.
You don't have to use tungsten. There are other electrode designs
and materials that will work. One of the problems with tungsten
is that this material is next to impossible to machine. It is
very hard and brittle. Richard Hull was using threaded electrodes
made of Niobium, which machines like butter compared to tungsten.
On my hot rotor (built after the video was produced) I drilled
and tapped my electrode mounting holes equidistant around the rim
of the rotor. I threaded 3/8 inch screws through the holes and
then cut the screw heads off with a hack saw. The cut end of the
stud was carefully dressed with a file to restore and damaged
threads. This left a threaded stud that extends outward about 3/8
of an inch from both sides of the flat rotor disk.
Threaded Stud> --| |-- <Threaded Stud
I went to a specialty fastener company and purchased a box of 100
stainless steel "acorn" or "cap" nuts with a 3/8 inch thread.
Since I had purchased the nuts beforehand I was able to match the
thread lengths and type to my studs in advance. Two cap nuts are
screwed down, one on either end of the protruding stud. The heads
of the cap nuts form the rotor electrodes.
What I like about this idea was the ease in balancing the rotor
by filing a bit on the threaded studs, and the fact that the cap
nut electrodes are uniform right out of the box and are easily
and cheaply replaced.
With a bit of carefull measuring, you can get the cap nut to
bottom out just as the back side of the cap contacts the metal
hot rotor. This allows a large surface area contact for RF
current flow and heat sinking.
While it is true that the stainless steel cap nuts are not nearly
so long lasting as tungsten in this application (even the
tungsten does not last forever) it has advantages that all the
materials may be found right of the shelf with a mininum of
machining required. Electrode replacements are a breeze, and the
stainless cap nuts do last long enough to be cost effective.
... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12