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High Voltage Feedthru, Richards design

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

Re: High Voltage Feedthru, Richards design

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

Re: High Voltage Feedthru, Richards design

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

Re: High Voltage Feedthru, Richards design

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

Re: High Voltage Feedthru, Richards design

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

Re: High Voltage Feedthru, Richards design

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

Re: High Voltage Feedthru, Richards design

Posted: Fri Aug 02, 2019 2:09 pm
by Pascal Mueller
Hi,

where can I find more information about this design? I searched Richard Hull's threads but I wasn't able to find one about a feedthrough design.

Thanks

Re: High Voltage Feedthru, Richards design

Posted: Fri Aug 02, 2019 5:29 pm
by Mark Rowley
Pascal
I don't think there is one thread solely dedicated to the construction of this design. It seems to be scattered about between 2002 and 2004. It's all there, trust me. It takes some effort to data-mine the forums. I never bookmarked anything but found this reference fairly quickly. There's probably around 10 threads which discuss its construction in one form or another.

http://www.fusor.net/board/viewtopic.ph ... irt#p13118

All in all its a fairly basic design. Cut off the old flange and silver solder on a modified 2.75" CF blank. Finding an exact duplicate of that particular insulator may be difficult but the premise of construction should apply to similar models.

Mark Rowley

Re: High Voltage Feedthru, Richards design

Posted: Sat Aug 03, 2019 12:00 pm
by Pascal Mueller
Ah I see, I thought that he wrote it down in a thread somewhere - don't know, just kind of expected it like that. Maybe because a lot of FAQs etc. are from him. Anyway, I'm going to check it out, thanks! :)

Re: High Voltage Feedthru, Richards design

Posted: Sun Aug 04, 2019 9:08 am
by Richard Hull
The photos above show the method I used. No real text beyond look at the image and do it. There is a thread within the last year where one of my insulators was used in this manner. It might be in the construction forum as I sold my last such insulator at last October's HEAS. Check between October 2018 and June 2019. Luke Harrell posted it..

Update found it! Luke put it in the new user forum.

http://www.fusor.net/board/viewtopic.php?f=46&t=12608


Richard Hull