Material for cathode?

[Sixsmith]

Hi,
We're experimenting with making our own nixie tubes in our shop. I was
planning on making the cathode out of stainless steel, but was
wondering if anyone had any advice about the best material to use.
Would it be better to try to find something rare-earth coated, or
isn't it necessary?

Also, if anyone is in the Boston/Metrowest area and wants to
experiment with us in person, just drop me a line.

Thanks,
Meredith

www.6smith.com

[Stuckey]

As far as the best material goes, I don't know if I could answer that
one. I started experimenting by modifying existing Nixie tubes. I
took a few cheap Russian tubes and broke off the seal. I tried
replacing the neon penning mixture with Argon to change the color.
The biggest challenge I faced was getting the pressure low enough.
Without the right tools to make a good vacuum, you need much more than
the 180 volts to make one of these things glow :)

Good luck - I can't wait to see the results!

Brian

[David Forbes]

That's a good question. I wouldn't know the first thing about the
materials used for the Nixie tube. You can rest assured that whatever
you guess the composition is, it will be wrong.

You might consider, if you're serious, paying a metallurgist to tell you
what the compositions of the metals in a real Nixie tube are.

--
David Forbes, Tucson AZ
http://www.cathodecorner.com/

[will]

LOL.

I seem to remember nickel from somewhere, but I'm probably wrong.
Isn't it in a datasheet somewhere? Maybe some manufacturer has some
old internal memos/datasheets they wouldn't mind giving up nowadays if
you emailed them.

[Unmitigated Fool]

I used to do neon signs so I understand your problem of getting a low enough pressure.  For the best vacuum you need a backing pump and a turbo pump, sometimes called a molecular transfer pump.  Neither are cheep.  Of course neon tubes use a MUCH higher voltage.

[Nick]

On Feb 28, 12:14 am, Sixsmith <phinneusbal...@gmail.com> wrote:
> Hi,
> We're experimenting with making our own nixie tubes in our shop. I was
> planning on making the cathode out of stainless steel, but was
> wondering if anyone had any advice about the best material to use.
> Would it be better to try to find something rare-earth coated, or
> isn't it necessary?

Weston (pp334) says that nickel is ideal but not strong enough, and
recommends nickel-iron alloys or stainless steel. He recommends a h:w
ration of 2:1 for side-view tubes where the cathodes are close
together and 1:1.6 (is that a misprint - does he mean 1.6:1 ?) for end-
view tubes where the cathodes can be further apart.

Note that sputtering increases markedly with decreasing pressure, so
you need the highest pressure you can in your Penning mixture such
that you get reliable striking. If you introduce Hg to reduce the
sputtering, use only a tiny amount as too much will deposit on the
inside of the tube and reduce visibility. In the various books I;ve
read, life of non-Hg doped tubes is generally rated at between 1000 &
1500 hours - with Hg doping this can be many 10s of 1000s of hours and
indeed over 100,000 (allegedly!) in some cases.

With only 0.2W dissipation, the actual cathode temperature can be a
few hundred degrees C, so the cathodes mustn't be stacked too close as
they can distort in use. The recommended minimum spacing is 0.6mm
which allows a stack depth of 0.7mm per layer, i.e. using 0.1mm sheet
metal. Glyphs are either stamped or etched from the sheet. Design of
glyphs is quite cute - many tubes rely on the width of the stroke
changing to try to ensure that each digit has approximately the same
surface area so with a given anode current they have similar
brightness.

The anode is non critical as long as its pretty evenly spaced - the
front mesh is as transparent as possible, and the back plate is coated
matt black to reduce reflections.

Note that some tubes have no anode! They rely on making unused
cathodes into anodes - a neat trick gaining great aesthetics &
visibility at the expense of requiring extra electronics.

I would get an assortment of dead tubes and have the metal analysed -
watch out for the mercury in long-life tubes. Also look closely at the
exact dimensions of each glyph - many larger tubes actually specify
different anode currents for different glyphs (or segments, e.g. in
the B7971).

Cheers

Nick

[Adam Jacobs]

I think that if I was going to go down the road of making homemade Nixies, I'd contact the guy that wrote this:

http://tubedevices.com/alek/pwl/lc1d/homemade_nixie_tubes.pdf

-Adam

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[Nick]

On Feb 28, 6:32 am, Nick <n...@desmith.net> wrote:
> On Feb 28, 12:14 am, Sixsmith <phinneusbal...@gmail.com> wrote:
>
> > Hi,
> > We're experimenting with making our own nixie tubes in our shop.

...

>
> Weston (pp334) says that nickel is ideal but not strong enough, and

...

I should have mentioned that a patent search would be an excellent
place to start - many Burroughs and other patents discuss how to do Hg
doping safely, how to implement "getters" and generally what gasses,
pressures, metals, spacings etc. are used...

Nick

[Sixsmith]

Wow, lots of good advice. Thanks!

It sounds like I should start by testing our shop's vacuum pressure
capabilities on existing nixies and if all goes well then it is
possible to use stainless steel for cathodes. I'll need to experiment
with the placement of the cathode and spacing. And then I will need to
refine for sputtering and longevity.

I think we're ok for voltage, and where we usually use a bombarder for
neon, we'll use our digital kiln for the nixie. I don't have a glass
lathe, so I'll have to make due with parts I can find and re-work.

In the meantime I'll research the patents and datasheets I can find.

Thanks to everyone for all the information. You've helped me figure
out a strategy to start my experiments.

Best,
Meredith

[John Rehwinkel]

> We're experimenting with making our own nixie tubes in our shop. I was
> planning on making the cathode out of stainless steel, but was
> wondering if anyone had any advice about the best material to use.
> Would it be better to try to find something rare-earth coated, or
> isn't it necessary?

I don't think you need barium oxide or the like for emission, but I do seem to
recall that nixies generally have something coated on the back of the digits
to suppress the discharge there, to concentrate it on the fronts.

I had been toying with this too, but had trouble sourcing insulators for the
digit stack.

http://www.vitriol.com/images/tech/nixies/cathodes.gif

- John

[Phinneus Baltic]

Good point. For some reason I had thought that there was a ceramic component to the cathode, and that was part of its purpose. But I may be way off. It may just be there to help with the aesthetics of the display.

 

Hmmm. Sounds like more research is needed.

 

-Meredith

 

 

[Dirk Sleutjes]

Hi,

It is totally not nixie but still one of my oldtime favourites:
http://translate.google.com/translate?u=http://paillard.claude.free.fr/&langpair=fr%257Cen&hl=en&ie=UTF-8
He's french... (but with google translate the site is readable) and he
makes his own vacuum tubes like triodes. He made his own equipment to
do so like vacuumpomp, welding-device, heater for settling the glas
after blowtorch welding it, etc....

You really have to watch his movie on his page! The craftsmanshift is
incredible! I wish I could do what he does ;-).

Cheers,

Dirk

[Dieter Waechter]

There was a discussion some years ago at the old NEONIXIE-L.
There was a book recommended but I forgot the name.
The book contained data about the gas, pressures, and so on.
I had a copy as pdf, but can't find it in my archive....
Can anyone recall the name?
DIETER
http://www.nocrotec.com/

[marcin]

Somebody already mentioned Alek http://tubedevices.com/alek/pwl/pwl_e.htm
Somewhere from his vast web archives I dag out a paper describing the
first polish nixie LC-1. Can't recall the exact link though. And, this
article is in polish ;)
Shortly: material used for the cathodes was steel, anode was made from
NiFeAl alloy. The gas mixture: 33T neon, 40mT argon. They tried lower
pressures but got excessive sputtering. The argon addition was to
lower the striking voltage. There is more useful data there too.

[Dieter Waechter]

Hello Marcin,
yesm I know Alek of course.
But the document I had was a US book. (Or maybe an English one?)
Dieter

[Nick]

On Feb 28, 6:46 pm, "Dieter Waechter" <i...@nocrotec.com> wrote:
> Hello Marcin,
> yesm I know Alek of course.
> But the document I had was a US book. (Or maybe an English one?)
> Dieter

This does sound like the Weston book.

Nick

[Dieter Waechter]

Thanks Nick!
That's it!

Cold Cathode Glow Discharge Tubes
Author: G F Weston
June 1968
ISBN-13: 9780592027753
ISBN-10: 0592027759
Pages: 374

http://en.wikipedia.org/wiki/George_Weston_%28physicist%29

And:
there was another article:
"The Effect of Current and Pressure on the Impedance of Cold Cathode Glow
Discharge Tubes"
Author: G. F. Weston

"The variation of the impedance of glow discharge tubes with direct current
and pressure has been measured in the audio-frequency range. Providing the
glow completely covers the cathode, the reactive component at any one
frequency varies inversely as the current, whereas the resistive component
varies inversely as the square root of the current. No such simple laws are
found for the variation of impedance with pressure. However, if the
impedance is expressed in terms of ' self-inductance ' and ' degression time
' according to a theory proposed by van Geel, then simple relationships are
obtained both for pressure and current variations. The effect of cathode
material has also been investigated."

And here the old Neonixe mail from 2002 (9 years ago - but I was right):
http://www.neonixie.com/neonixie-list-archive/2500.html

it was from Jan - he had a copy for sale once.

I also had a copy as pdf, but I can't find it anymore.... ;-(
Dieter

[Dieter Waechter]

another interesting link:
http://www.worldlingo.com/ma/enwiki/en/Penning_mixture
Dieter

[threeneurons]

> ... I do seem to recall that nixies generally have something

> coated on the back of the digits to suppress the discharge there,
> to concentrate it on the fronts.

NO-O-O-O !

Don't coat them cathodes at all, so the glow is even all around ! Use
a mesh anode, both front and back, so you can see the cathodes, at all
angles. That way, if you decide to do something like Johm Smout's
clock here:

http://www.clock-it.net/nixie_clocks/infinity.html

The digits will repeat at half the pitch; front, then back
alternately. They'll still be oriented the same way. Work it out on
paper. I've done it. Plus I cheated, since I have a few nixies that
are constructed as I just described. The cheating part is that I lit
it up, and stuck it in between two mirrors.