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Looking for some GLASS high voltage fast diodes.

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Ash Small

Sun Sept 04 2011, 07:08PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I've spent all day looking for some fast (100nS or faster) HV glass diodes.

They have to be glass because they will be inside a vacuum chamber and I want to avoid any outgassing problems.

I can't find any on Ebay, and only found one manufacturer, VMI, and one supplier, RS, which is only offering a couple of the VMI diodes, one for ~Â£5 and one for ~Â£7 each, and I'll need at least 100 10K diodes, maybe a lot more.

VMI website:

Does anyone know of anywhere I can try to get them at a more reasonable price, or any other suggestions?

(I've even considered trying to strip off the plastic/epoxy encapsulation on some of the cheaper diodes to see what's inside. Apperently, according to some sources, they are glass encapsulated inside the plastic/epoxy.)

Antonio

Sun Sept 04 2011, 07:17PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

They probably use plastic insulation because it leaks much less than glass. It's easy to find HV diodes with leakage currents in the fraction of nA range. No glass exposed to plain air would allow so low leakage.

Ash Small

Sun Sept 04 2011, 07:30PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Antonio wrote ...

They probably use plastic insulation because it leaks much less than glass.

Are you referring to the ones that apparently have plastic encapsulation over the glass encapsulation?

Antonio wrote ...

It's easy to find HV diodes with leakage currents in the fraction of nA range. No glass exposed to plain air would allow so low leakage.

I'm assuming that in a vacuum the leakage problem won't exist.

Turkey9

Sun Sept 04 2011, 07:56PM

Registered Member #1451 Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661

If the plastic is the same as the plastic/ceramic of DIP ICs, then there won't be enough outgassing to even think about. Most epoxies don't outgass enough to be a problem. If you are still worried, you can look up the material on the nasa outgassing database: http://outgassing.nasa.gov/cgi/uncgi/search/search_html.sh

Carl Pugh

Sun Sept 04 2011, 08:19PM

Registered Member #1064 Joined: Tue Oct 16 2007, 05:04PM
Location:
Posts: 42

I put some transformer oil (Shell Diala AX) in a metal container under a good vacuum. After 3 or 4 hours the surface of the oil became perfectly still.
Did same test, but put a piece of acrylic in the oil. The surface of the oil never became still.
Could you purchase some diodes manufactured by different manufactures and test them?

Patrick

Sun Sept 04 2011, 08:38PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Carl Pugh wrote ...

Could you purchase some diodes manufactured by different manufactures and test them?

Id test plastic diodes as carl says, long before I pay big $ for a few glass ones. You dont even know if the outgassing problem exists yet.

Ash Small

Sun Sept 04 2011, 08:39PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Carl Pugh wrote ...

I put some transformer oil (Shell Diala AX) in a metal container under a good vacuum. After 3 or 4 hours the surface of the oil became perfectly still.
Did same test, but put a piece of acrylic in the oil. The surface of the oil never became still.
Could you purchase some diodes manufactured by different manufactures and test them?

I may try that, but it will be pretty high vacuum, so I'd expect some outgassing from any plastic/epoxy. (This is the reason I'm using vacuum capacitors).

As I understand it, any outgassing will increase the risk of dielectric breakdown.

The whole idea of using vacuum capacitors and glass diodes in vacuum is to build a multiplier that can achieve ~650kV, therefore, I consider it a priority to avoid ANY outgassing, and to achieve a very high vacuum.

I don't consider that I'm ready yet to start a 'project thread' on this. I'm still doing 'preliminary research'. Some relevant 'background' is in this thread:

Patrick

Sun Sept 04 2011, 08:43PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I dont think outgassing at the sub-single micron ultimate vacuum level will effect dielectric strength, and cantelectrons fly through a vacuum given a high enought V? IE, a CRT or VT?

Proud Mary

Sun Sept 04 2011, 08:46PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

X100UFG 10kV trr 100 ns glass

Z150UFG 15kV 300mA trr 100 ns glass

They won't be cheap.

Pinky's Brain

Sun Sept 04 2011, 08:50PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

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