Metal parts for nixie tubes

I got a sample of etched parts today, the quality is absolutely outstanding! Sharp edges, no etched spots, no under-etched places. I cant wait to put it all together! Sorry for quality of the photos, all were made in a hurry, as usual 😉

Hexagonal anode grid

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Another update: digits for nixie tubes

It has been some time since my last blog post, don’t be afraid, I am still working on nixie tube project! Around 2-3 hours a day in average. I am building a shed on the garden where I will place all the workshop. I hope it will be finished in one month.

I am also parallely working on the last parts of the whole nixie tube project. One of the most important things are the inner metal parts, I originally planned to etch them myself, but that project became so complicated that I try to outsource as many processes as I can (as I can afford 😉 ). So I found a great local company making etched parts for model makers, we agreed on a test etching and there are the results:

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Stainless steel foil finally arrived

I finnaly got a stainless steel foil (316 type) I orded a few months ago from US. I don’t understand why such a primitive thing is impossible to get (or just find) in EU 🙁 The thickness of it is 0.1mm, I was afraid it would be too thin, but it exactly what I need.

I plan to make all electrodes (digits as well as anode mesh) from it, using photo-etching method. It should have nice results..

Some tubes to scavenge..

I got some old non-working tubes to disassemble as Ron Soyland does. There are some nice pieces of material that are I could hardly find else as a molybdenum sheets, nickel sheets and pipes, getters, tungsten electrodes.. It is also nice stuff to study for possible working techniques.

Argon arrived

I’ve finally got an argon bottle, 1.3m³ of pure argon (99.996%) pressed in 8l bottle. It is pretty heavy 😉 The argon was chosen because it is has similar features to neon, but is much cheaper and – the most important – it is available..

File:Paschen Curves.PNG

This image comes from Wikipedia. The argon compared to neon has a little lower voltage needed for discharge, that’s useful..

This bottle + argon cost $100, refill costs $20, argon valve costs $25. Neon nonrefillable bottle with 12 atmospheric litres of neon (compare to 1300 litres of argon..) costs also $100, simple valve without gauges costs $150, evacuable valve costs $250 🙁

The argon discharge is pink-blue, but is much dimmer than orange neon, that is the reason why neon is used in most of dicharge tubes.. I noticed only some bargraph and dekatrons filled with argon.

 

Reduction valve..

My dog 😉 and a bottle with argon at the background..

Reduction valve mounted..

Borosilicate glass

As I mentioned before, I am going to use a borosilicate glass in combination with tungsten wire. This glass is used in labs for scientific glass blowing, so the first place where I started to look for that glass were e-shops with lab supplies. There ale lots of suppliers, but all want some minimum quantity to order – tens or hundreds tubes of each diameter. But I had a luck, I found a 60% sale on 1500mm tubes, diameters from 12 to 20mm and a some 42mm, there were no minimum quantity needed. The glass brand is Simax, it is czech manufacturer.

Now I am looking for 6mm tubes, I will probably have to buy huge amount of tubes 🙁 ..

Tungsten wire

I started searching for material by looking for tungsten wire.. I found several expensive offers on eBay, too much money for several inches of wire 🙁 Then I wrote several wire manufacturers, there the price/length ratio was much better, but the minimal quantity I had to order was 10kg of wire ($1500) 🙁 Finally, I tried to search for the tungsten wire as a “Wolfram wire” and found one seller in UK, who offered a wire for a reasonable price – 300cm/$5..

It is 0.6mm diameter wire, quite hard and thick, 0.2mm in diameter would be better choice.. The tungsten wire has quite high melting point (3422 °C), so it is fire resistant, I don’t have to be afraid of exposing it into the fire during glass working. That is difference against the copper wires.

Glass to metal seal

The essential matter when making vacuum tubes is good contact of electrodes and glass case, it is called glass to metal seal. It looks simple – just to melt glass, place the hot wire electrode in and wait until it cools down. But there is a problem of different thermal expansion coefficient (TEC), what causes the glass near the connection to crack. So You must use glass and metal with similar TEC.

Soda-lime glass + copper wire

One way is to take ordinary soda-lime glass (TEC 8.5) and choose metal with similar value of TEC, it is often copper (TEC 17) or Dumet wire (I think it is also based on copper). The advantage of using soda-lime glass is that it has lower melting point, so it is easier to form it in proper shape. The main disadvantage is high TEC, so the glass tends to crack easily. Alek zawada is going this way, he mentioned a lots of cracks when dealing with soda-lime glass and copper.

Borosilicate glass + tungsten wire

Borosilicate glass is glass with lower TEC (3.3), it is more resistant to cracking when cooling. A tungsten wire (TEC 4.5) could be used in combination with that glass – it has similar TEC, so it should theoretically produce no cracks 😉 Disadvantage of the tungsten wire is that it can’t be welded to tube’s insides, I haven’t solved that yet.. Tungsten wire is also very hard and the work with it is no comfortable like with copper. But You can expose it directly to the fire when glass forming, it won’t melt unlike the copper. I chose this combination..

 

 

 

Thermal expansion coefficients

 

Material Linear coefficient, α, at 20 °C
(10−6/°C)
Aluminium 23
Brass 19
Carbon steel 10.8
Copper 17
Diamond 1
Glass 8.5
Glass, borosilicate 3.3
Gold 14
Invar 1.2
Iron 11.8
Kapton 20
Lead 29
Magnesium 26
Mercury 61
Molybdenum 4.8
Nickel 13
Oak 54
Platinum 9
Quartz (fused) 0.59
Rubber 77
Sapphire 5.3
Silicon Carbide 2.77
Silicon 3
Silver 18
Stainless steel 17.3
Steel 11.0 ~ 13.0
Titanium 8.6
Tungsten 4.5

Source: Wikipedia

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