Questions about the construction of the high voltage feedthrough

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Miles Duncan
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Questions about the construction of the high voltage feedthrough

Post by Miles Duncan »

I have tungsten wire and a stainless steel stalk feedthrough but am really unsure about how exactly to put it all together. In images of constructed grids, I see the alumina insulation which I will get when I build the grid but also a piece of what appears to be black metal at the end. I know I need to thread the end of the steel rod and need to use a continuous piece of tungsten because the solder won't hold up, but I'm just not sure how to put it all together or what that black piece at the end of the stalk is. Any help would be really appreciated.
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Richard Hull
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Re: Questions about the construction of the high voltage feedthrough

Post by Richard Hull »

What image are you looking at and referring to?

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: Questions about the construction of the high voltage feedthrough

Post by Dennis P Brown »

I wrap the extremely rigid wire I have around a metal pipe (diameter I want my grid size to be) and then slid it off. Next, I take those loops and bend them (using needle noise pliers) into various angles to create a 'sphere' like cage. All rather easy. I place one end piece that I kept straight, snip it to length and place that tip into my steel rod. I use a bolt to lock it into place.
Matt_Gibson
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Re: Questions about the construction of the high voltage feedthrough

Post by Matt_Gibson »

I don’t think that alumina is used by many anymore.

-Matt
Miles Duncan
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Re: Questions about the construction of the high voltage feedthrough

Post by Miles Duncan »

The image I am using as a reference is from Nathan Marshall's fusor. (
Screenshot 2022-10-19 164221.png
) I have a couple of questions: if not aluminia, what insulator do people usually use? Also, when you say you use a bolt to fasten the wire, how exactly do you do that? Also, if some of the negatively charged steel stalk is exposed is that ok as long as it isn't arcing with the chamber?

More questions: I am working with a 2.75-inch t as the main part of my chamber. How large should I make the inner grid?

Any help with this would be really appreciated.

-Miles
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Richard Hull
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Re: Questions about the construction of the high voltage feedthrough

Post by Richard Hull »

There is a rod exiting the large porcelain insulator. This rod no longer has alumina around it for most folks. It is left bare.
The big black thing you speak off is an adapter collet that allows the hollow that runs through it to clamp to the rod with a set screw. The other hollow end receives the bundle of tungsten wire that make up the base of the grid. A set screw usually also secures this bundle within the collar.

His setup in the image is just one way to work a grid onto a stalk rod. If it works, it passes muster.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Matt_Gibson
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Re: Questions about the construction of the high voltage feedthrough

Post by Matt_Gibson »

Here’s what I use. No need to insulate the stalk/connection to the cathode. I used SS tubing that fit snug to the SS stalk from the insulator.
BC3381AC-4502-444D-BFA8-E13165261D8D.jpeg
-Matt
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Dennis P Brown
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Re: Questions about the construction of the high voltage feedthrough

Post by Dennis P Brown »

Using a large diameter steel rod to deliver power to my cathode, I drill a hole in its end, then thread that hole. I drill out a small threaded bolt (that matches the threaded hole I drilled in the post), insert the end of the cathode rod through the hole in the bolt. Bend a very small section over (very small so the bolt and rod go into the drill hole in the post.) Tighten the bolt/cage system into the post. This method holds very well even with lots of thermal cycling.
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