CRT Electron Gun Modification

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
Post Reply
User avatar
Mark Rowley
Posts: 909
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

CRT Electron Gun Modification

Post by Mark Rowley »

Pictured below is the gun assembly (minus the deflection plates) from a 2AP1 CRT. Upon inspection of the gun, I noticed the assemblers used a type of ceramic to "glue" the focus anodes onto their support structure. The ceramic is quite brittle, but appears to have some potential use for future application.

In the picture you can see small globs of the ceramic holding the white support insulators to the focus stack.

Does anyone have any idea what this material is and if it is still available?

Mark Rowley
Attachments
gun3.jpg
Jerry Biehler
Posts: 975
Joined: Tue Nov 24, 2009 3:08 am
Real name:
Location: Beaverton, OR

Re: CRT Electron Gun Modification

Post by Jerry Biehler »

Probably something along the lines of torrseal.
User avatar
Mark Rowley
Posts: 909
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: CRT Electron Gun Modification

Post by Mark Rowley »

Hi Jerry,
Not really like TorrSeal as I dont believe its an epoxy . Its almost like plaster or sheetrock, but harder. I cant imagine it would ever be used to seal anything, but apparently it works good as a temperature and electrically resistant cement.

Mark
Linda Haile
Posts: 230
Joined: Mon Jan 04, 2010 4:28 pm
Real name:

Re: CRT Electron Gun Modification

Post by Linda Haile »

http://www.aremco.com/PDFs/A5_09.pdf

Cerama-dip 538 is used for grid insulators for plasma processing in the semiconductor industry. I think the grids are used in ion etching of silicon wafers (RIE).

I have some to try for feedthroughs but have not tried it yet.

It is a Zirconium Silicate and is a water based paste. Air dry for two hours then bake at 200F for three hours then 300F for one hour.

I imagine this is the best stuff to use as it is what the pro's use.
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

Re: CRT Electron Gun Modification

Post by Doug Coulter »

This looks to me similar to some stuff I've made and used with success. You mix a slurry of talc (soapstone powder, not scented) and sodium silicate. It hardens chemically -- and takes forever before being ready for vacuum (bubbles if you get in a hurry), as it has to cure, and then lose the water, takes days.

Most newer ones I've taken apart don't use that method, they use pieces of soft glass running down the length with the support wires pushed in. Not the right tempcos for an actual vacuum-grade glass/metal seal, but good enough to hold and be very precise -- it's the way the tektronix tubes were made.

You could probably make a good D gun if you put an ion source on there, and upped all the volts by to account for the charge/mass differences.

Space charge defocusing is much worse with slower ions than with electrons due to higher density in the beam for a given current.
Why guess when you can know? Measure!
John Futter
Posts: 1848
Joined: Wed Apr 21, 2004 10:29 pm
Real name: John Futter
Contact:

Re: CRT Electron Gun Modification

Post by John Futter »

Mark
you could follow Dougs recipie or get a lifetime supply from these people who probably supplied whoever made that tube

http://www.sauereisen.com/pdf/HIGHTEMP.pdf
DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 1:13 am
Real name:

Re: CRT Electron Gun Modification

Post by DaveC »

Mark -

Not sure what you're planning to do with this type of electron gun, but....


CRT e guns typically use tri-alkali cathodes, so they aren't really going to work well (or at all) at a high pressures ( P> 10 -6 Torr.) Water, stray gases, hydrocarbons and such will poison the surfaces... Partucularly bad is sputtered metal. Often the metal sputtering happens when the control grid is over driven.

New construction ( the last 20 years) uses the "glass gun" technology... more or less as Doug has already noted.

Dave Cooper
User avatar
Mark Rowley
Posts: 909
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: CRT Electron Gun Modification

Post by Mark Rowley »

Hi Dave,
I built a simple vacuum platform to experiment with electron gun designs. Its similar to one of Steve Hansens old designs I recalled reading about years ago. My first stop was to test several CRT guns I had laying around and then try Steve Sesselmann's idea with the magnetron filament. Eventually I would like to come up with a simple yet effective ion gun design for a basic electrostatic accelerator tube. I have quickly thrown together some designs in the past and have yielded results typical of something "quickly thrown together." I need to improve on this which will require some much needed bench time. Dave, what is a tri-alkali cathode and why are they used in CRT displays?

Anyway, I was mainly curious about the ceramic that I had discovered in the old 2AP1. BTW, I think John hit the nail on the head... Thanks.

The Cerama-Dip that Lyn mentioned is also someting of interest. Do they make a Pb doped version for x-ray shielding?

Mark
Dustin
Posts: 105
Joined: Mon Jul 26, 2010 8:40 pm
Real name:

Re: CRT Electron Gun Modification

Post by Dustin »


http://en.wikipedia.org/wiki/Hot_cathode

under
Oxide-coated cathodes.

Typically is strontium barium calcium carbonates. (I have access to some)
As Dave notes they can be easily be poisoned.

Application is in a solution that you dip the filament let dry and repeat a few times.
It is activated by heating under vacuum.

It increases electron emission current from the filament.

Steve.
Linda Haile
Posts: 230
Joined: Mon Jan 04, 2010 4:28 pm
Real name:

Re: CRT Electron Gun Modification

Post by Linda Haile »

Mark, all I know about Aremco's other products is what is on the data sheet in the link. No mention of a Pb doped version.

I know the Cerama-Dip 538 is used for grid mounts/insulators for moly grids which are used for electrostatic focussing for ion etching of silicon wafers. It therefore should be suitable for holding your anodes in place.

I'm planning to try it on HV feedthroughs though, for bonding them together.
DaveC
Posts: 2346
Joined: Sat Jun 30, 2001 1:13 am
Real name:

Re: CRT Electron Gun Modification

Post by DaveC »

Mark -

A Steven notes below, tri -alkali cathodes start from tri-carbonate cathode coatings... which are usually strontinum, barium and calcium carbonates. After reaching a good vacuum in the -6's, heat is applied to burn off the binder first, and dry the carbonates, then temperature is raised in two stages, if memory serves correctly.... to convert the carbonate to the oxides. Temps are around 1500 K or above for this part.

The oxide blend results in a low work function surface... around 1-1.1 electron volts. Compared to the work function of Tungsten at 4.25 eV and Thoriated Tungsten at about 2.5 - 2.6 eV, the tri oxide cathode surface has a higher current density at lower temperature.

Dave Cooper
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

Re: CRT Electron Gun Modification

Post by Doug Coulter »

In tests here of electron beam generating devices for ionizers and such, we tried the tri-alkali stuff, old tube cathodes and homebrew mix, doing our own activations and so on. It's hard to get right, but not impossible. I have a couple older books on vacuum tube tech that give the process.

The thing is, they won't take post activation exposure to air and live. They form hydroxides that you can't reactivate at all, so you get maybe two shots total out of that type.

Based on some work I read on mass spectrometer ion source design, we tried yttria (Y2O3) and while it doesn't work quite as well in lowering the work function, it does handle air exposure after that, and doesn't fry if you get a little too hot on the filament...so that's what we stuck with from then on. Instead of the dull red you can run the alkali stuff at, this gets closer to orange, but that's still a great deal over yellow hot thoriated tungsten (which also is ruined by air exposure to a large degree, and further by ions hitting it, reducing too much thoria which then evaporates) or the white hot you need for pure tungsten.

A compromise, but a decent one if you make things that have to be air exposed once in awhile.
We got for example, about 10 ma emission off a 6v, 10w filament running on 3.5v coated with it, which was maybe space charge limited (we didn't have a very strong field to pull electrons off).
At any rate, it solved that for us.
Why guess when you can know? Measure!
lutzhoffman
Posts: 188
Joined: Mon Dec 07, 2009 8:59 pm
Real name:

Re: CRT Electron Gun Modification

Post by lutzhoffman »

Hello:

Aremco materials makes a bunch of ceramic "glue type" of high temp ceramic compounds. This stuff is like toothpaste when wet, and it becomes a hard ceramic upon heating. They have many versions, based on MgO, Al2O3, and even Zircoa.

Another common use is for cementing in Xe and halogen quartz lamps, into their reflector assemblies, which have to take a lot of heat. Actually you may be on to something here, this stuff could come in very handy for fusor, and high temp vacuum applications. Enjoy folks, maybe bookmark this one : )

http://www.aremco.com/a4.html
Attachments
Aremco.pdf
(148.21 KiB) Downloaded 799 times
Richard Hester
Posts: 1519
Joined: Thu Jul 05, 2001 12:07 am
Real name:

Re: CRT Electron Gun Modification

Post by Richard Hester »

I looked at the Aremco stuff a few years back when I was thinking of making a spark-plug feedthrough without any organics like epoxy, etc. I never followed through, though.
User avatar
Mark Rowley
Posts: 909
Joined: Sun Dec 29, 2002 12:20 am
Real name: Mark Rowley
Location: Sacramento California
Contact:

Re: CRT Electron Gun Modification

Post by Mark Rowley »

Removing the filament feedthru assembly from a magnetron was fairly easy with a lathe. Unfortunately this time was more of a practice run as the filament was bad. Once out, I noticed a coating on the heater plate. It can be seen in th attached photo. Is this an oxide I should be concerned about?

Mark Rowley
Attachments
MagFil2.jpg
Dustin
Posts: 105
Joined: Mon Jul 26, 2010 8:40 pm
Real name:

Re: CRT Electron Gun Modification

Post by Dustin »

Thanks Lutz
This will be very useful
Steve
User avatar
Steven Sesselmann
Posts: 2127
Joined: Wed Aug 10, 2005 9:50 pm
Real name: Steven Sesselmann
Location: Sydney - Australia
Contact:

Re: CRT Electron Gun Modification

Post by Steven Sesselmann »

Mark,

I have removed the filament from dozens of magnetrons, and I can assure you that you get better with time. I broke a few in the beginning.

Later I actually found a source in China where I could buy them open.

Be careful if cutting or grinding the ceramic plug, many of them are made from beryllium oxide, best to cut or grind under water.

viewtopic.php?f=12&t=5013#p32321

Steven
http://www.gammaspectacular.com - Gamma Spectrometry Systems
https://www.researchgate.net/profile/Steven_Sesselmann - Various papers and patents on RG
Jerry Biehler
Posts: 975
Joined: Tue Nov 24, 2009 3:08 am
Real name:
Location: Beaverton, OR

Re: CRT Electron Gun Modification

Post by Jerry Biehler »

I didnt know that. I took some classes on scientific glassblowing and they had told me the white ceramic stuff was torr-seal. Good to know.
Post Reply

Return to “Ion Gun Design and Construction (& FAQs)”