High Voltage Feedthru, Richards design

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Mark Rowley
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High Voltage Feedthru, Richards design

Post by Mark Rowley » Tue May 21, 2019 5:27 am

In the final stages of replicating Richard Hull’s ~30kV feedthru design. Just finished machining the conflat blank to accept the HV insulator. A couple minor details and adjustments before silver soldering the two halves together.

As a side note, I believe I bought the beryllium insulator from Richard around 2002 or so.

This feedthru will ultimately compliment a 2.75” four way cross Fusor I’m gearing up to build. I’ll post additional details on that in a new thread in the construction section.

Mark Rowley
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Richard Hull
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Re: High Voltage Feedthru, Richards design

Post by Richard Hull » Tue May 21, 2019 7:06 pm

That is exactly how I did it and the fusor with a ball or toroid field distributing on the top terminal will allow 43kv on my system. In use since 2004. before each use, wipe down the insulator well with pure ethanol to eliminate dust and grime that might break down at extreme ends of its voltage limit.

Those great insulators were purchased in quantities of ten at a time back then at 4 east coast hamfests. I have never seen another since the 2000-2003 hamfest season. Solid BeO you can't beat that!

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Mark Rowley
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Re: High Voltage Feedthru, Richards design

Post by Mark Rowley » Wed May 22, 2019 8:54 pm

Richard,
When you heated the CF to almost red hot conditions, was there a concern of damaging the ceramic feedthru portion of the insulator?

Mark Rowley

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Richard Hull
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Re: High Voltage Feedthru, Richards design

Post by Richard Hull » Thu May 23, 2019 9:26 pm

YES! Absolutely. However I had 12 of these at the time and ran the risk. I did just heat only the CF flange and used lower metling point jewelry silver paste, not silver brazing rod and borax. The paste is sold by Rio Grande and has borax in it. Anyway, I obtained their lowest melting point silver solder paste.

I filled the weld hollow with the silver paste and sat the insulator in the hollow, in the paste. In this manner I just applied enough heat to the CF flange to see the paste turn to a beautiful silver liquid and immediately removed the heat and turned a fan on the finished item to hasten cooling.

The result did not leak at the base of the ceramic. Luck?... or just careful planning and the right choice of materials?

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Mark Rowley
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Re: High Voltage Feedthru, Richards design

Post by Mark Rowley » Sat May 25, 2019 12:35 am

In relation to the maximum shell temperature of the average Fusor, would 550 deg brazing solder be an acceptable choice?

To add a safety measure, a small computer type cooling fan could blow on the insulator during operation.

Mark Rowley

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Richard Hull
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Re: High Voltage Feedthru, Richards design

Post by Richard Hull » Sat May 25, 2019 4:32 am

My fusor never hits 550 deg F! However my fusor is a huge heat sink 8" CF rings and 6" sphere supported on four 12" - 3/4" dia. solid aluminum rods. You are looking at a lot less sink with the little CF cross.
You are in new territory.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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