HV Feedthrough Build

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HV Feedthrough Build

Postby Tyler Christensen » Thu Dec 22, 2011 2:24 am

Thought I'd share my new feedthrough that I'll put to test in a few days (flying home tomorrow for winter break). It is basically a copy of Doug's design. I'm using 1"OD 0.157" Wall Pyrex, with an inside 5/8"OD 0.094" Wall Pyrex slip-fit.

I found a nice way to make the end plug go in and out forever without any need for lube and without ever damaging the o-rings (diamond chamfering helps but didn't fully solve the problem from what I tried). I just put the tube in the lathe, and torched the end for a minute or two and it, and it flared out adding probably 0.1" to the diameter (forgot to measure it, now it's all packed up for the flight home tomorrow). Just enough to let the o-ring not touch the glass as it first slides in, but be in full contact after sliding in an inch. As long as you do this to only one side it doesn't interfere with its use since you can always put the quick-coupling on from the other side. Although if it really bothers you to have it only single-side access on that, you can carve off the excess from the outside of the tube until it fits into the coupling. I did that on a few of my tubes then realized there's really no point and just left it after flaring.

I'll post back hopefully next week with how it's working, excited to use this with my feedback-regulated power supply and hopefully get a few million n/s at a stability that I can just sit back and activate stuff forever. Never really had good stability in my fusor.
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Admittedly, I got a bit carried away with spare parts... just want to have lots of sizes of everything since my lathe access and fusor are 3000 miles apart.
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Re: HV Feedthrough Build

Postby Tyler Christensen » Mon Dec 26, 2011 8:48 pm

It works great! I've been running 45kV 17mA as my standard setting and it seems to do it indefinitely without trouble. Stalk stays below glowing temperature and heatsinks down the 3/8" shaft very well. I haven't had any arc over issues at up to 60kV testing, and the edge of the glass nearest the grid seems to be giving absolutely no troubles and no cracking. I have the glass terminate about an inch before the grid begins.
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45kV 17mA
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Re: HV Feedthrough Build

Postby Doug Coulter » Mon Dec 26, 2011 9:00 pm

Keep an eye on it - I've had issues with hot D hitting the glass and making silicon (reducing the glass chemically), which can act to attract sparks. Usually happens if I run the snot out of the fusor for long enough to get everything really hot.
The fact that it's all pyrex may have an effect here, depends on the potential the glass end tends to reach whether it attracts its own doom - or that's the current theory. Pyrex is pretty conductive as glasses go...it might stay close enough to ground to be fine.

And oh, by the way, great work man! These things rock at my place - if you break 'em, you can make 'em again.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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