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building vacuum tubes... some questons

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A kid from Germany and me are going to attempt to design and build our own vacuum tubes, even though he lives across the planet, we will work togather ;) he will design them, and since i have most of the machinery, I will build them, but just a couple of questions...

What kind of glass do I use, and were can i get it locally? I been trying to figure what glass to use, and no web site tells what.

and how hard of a vacuum pump do we need, can i just run 2 fridge compressors in series.

don't even get me started about getters :whacko: can i just buy getters from... say a sodium bulb?
 
There is actually a place somewhere on the web that sells the glass and the metals/filament wires etc needed, Inc I think, Getters....

As to Vac. pumps, I doubt any number of series-connected fridge compressors will achieve the Vac needed for a good tube...

A few experiments with an old tube, a bell-jar and your compressors will tell you.
--But, when you try, with the old tube, keep the heaters at approx 1/2 potential when you let the vac down to air, so the cathode will be above 100 deg. C. Its Moisture from the air that kills 'em when down to air apparently....

You need summit like a Mercury or Oil diffusion pump to get a high enough vac, backed up by a GOOD vac. pump I would think.
 
Scientific American mag. had some Amateur Scientist construction articles a long while back on making a vacuum pump for tubes and lasers etc. They used two fridge rotary vane pumps in series I think. Could also check Ebay for a two stage rotary vane pump specifically for vacuum systems. Varian, Edwards, Welch, Balzers.... Then you need a diffusion pump in front of that. (although a low quality tube vacuum could be reached with just the two rotary vane pumps)

Oil diffusion pumps used to be quite cheap as surplus when they got replaced by turbomolecular pumps in industry. (avoid mercury diffusion pumps, too dangerous) Might look on Ebay for Varian or Edwards or other oil diffusion pumps. You need vacuum gages that can work to these low pressures. (not simple mechanical gauges) Thermocouple gauges are used for the pressure range between the mechanical vane pump and the diffusion/turbo pump, and ion gauges are used for the very low pressure at the input of the diffusion/turbo pump. You'll need some kind of high vacuum valve too since the diffusion pump cannot be exposed to atmospheric while in operation without ruining it and possibly causing a fire. (you cannot turn off the rotary vane pump while the diffusion pump is hot either, so another high vac valve is generally used between them also for emergency shut down) (and the ion gauge cannot be exposed to atmospheric while in operation either)

Obviously, this is not a simple hobby exercise, so consulting one of the text books on high vacuum systems is mandatory. A proper high vac. system will cost you several thousand $ even at surplus prices I expect, so you will want to know what you are doing. I have a full turbopump system in storage, but nowhere to set it up currently.
 
You should get the classic Building Scientific Apparatus by Moore, Davis & Coplan. There's also a Lindsay reprint of an early physics text with excellent vacuum and glassblowing info. Your choice of glass will be determined by the COE of the feedthru wire (Therlo?, Invar, Kovar, etc.) You might be able to steal some feedthru wire from blown out high wattage incandescent bulbs before they become illegal. I don't know of any cheap diffusion pumps. Even a decent oil unit will cost a bit. Once you've used a turbopump, nothing else is tolerable, but they cost quite a lot. Sometimes you can find a cheap one and rebuild the bearings. It might be possible to do a cryopump, but the system needs to be really well sealed. If you're a really good glassblower, there's a complete design for a DIY diffusion pump in these peoples magazine. A rough description is online, but not enough info to build the thing. See here. You can get low cost thermocouple gage heads from Duniway Stockroom. Get the "531" model gage and build a simple circuit from The Bell Jar. IMO, you can build anything if you do enough research and are willing to improvise! Good Luck!

edit- You may want an oil trap for the roughing pump, depending on your setup. The best are molecular sieve types and the cheapest come from Thermionics because they seem to build them for everybody else. Site doesn't seem to be up right now.
 
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Diff pump

I honestly think this is about an imposable task but if you are going to do this you should start with a diff pump. I have seen some DIY diff pumps for neon work on the web. Another option would be to buy a diff pump from ebay, I have also seen a ton of them at University surplus stores. Dunaway.com has all the supplies and rebuild kits, basically it is a heater boiling oil so there are no moving parts to break. For the roughing pump I have seen a 2cfm pump at harbor frieght. Watch for air leaking into a hot dif pump all can go horribly wrong. Vacuum is not cheap or easy. Clean everything twice with IPA and then clean it again. Stay as far away from water as you can after the IPA.
 
Filiaments are most of the time tungsten, getters are usually barium. older tubes used phosphorus, harder part is getting it flashed onto the glass without it getting eaten up by atmosphere on the way. They put them inside high melting temp containers and then used rf heaters to release it in there after evacuating and sealing the tubes

You can salvage tungsten from light bulbs
 
I believe one of the books on Pete's site goes through materials of vacuum tubes and why you would use different materials. For example, it explains advantages and disadvantages of carbon coating the anode and materials choices for all tube elements. I just can't remember the name of it. I think it might have been an RCA publication (not RDH).

Edit: Aha! it is "Electron Tube Design," apparently an internal RCA publication.
 
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lets talk basics

uhhhmmm here we go.

oil difussion pump , coupled to a turbomuleculair pump . NEED to be leak proof

couple of blowtorches .
lot of fine tooling pilers stuff like that . pincer magnyfying glass . stuuf like that
some sort of LATHE would be great to make bulbs .

spot welder , can be made from a microwave transformer and a few peices of solid copper

OHH i almost forgot some kind of oven would be great for heat treating all the parts before closing the bulb . semiconductor vacuum oven would be perfect . BAKE BAKE BAKE YEesss get rid of that oxygen

OHH and some sort of "clean box " for fillament threating .

i suppose your talking DHT ?

il brainstorm what comes to mind next :scratch1:


also . you need a tidy workplace around 50 square meters . gloves need to be worn during any part of the production and stock up on medical alcohol .
 
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the materials

this is my materials post


PLATE MATERIAL
workable iron 0.1-0.05 MM CAN be used , hard to outgass not very pretty .
nickel is better probably VERY thin . as close to 99% percent purity you can get the better .

optional are titanium . carbon
sources are : you gona want to have nickel sheet metal in strips of 3/4 CM
* CTR material . if you ever dismanteled a CTR you know the beam guns are made of PURE nickel . you could try and sample a role from a big producer .
* battery weld tabs . are pure nickel 99.9 cheaper than specialized CTR stuf google will help you out . :rolleyes:

you gona need to make a die to form the plate . best to have two half size "bracket" halves that are spot welded on the stem in the last stage .

okay you will need to determene the material yourself . what works best for you you can use WAY thicker plate material than some old tubes used , BUT AT A PRICE . will take ages to outgass . higher emission grid dissipation . alowable bulb temprature . plate material and blackening work towards a higher maximum dissipation . thicker plate material will need more heat to deform .

GLASS& DUMET
your going to need glass stems witch fit your exhaust system and glass whit a outside diameter of around 28mm you can blow MUCH bigger bulbs depending on the amount of glass avalable EG wall thickness
and you need dumet whit matching expansion figures .
you also gona need to be able to make a STEM . or "PINCH " where all the wires come out .
teralabs.org is a good website about glasswork .

cathodes ""emitting surface " EDIT barium strontium and calcium need to be in their carbon bound state EG barium carbonate strontium carbonate calcium carbonate . when evacuating the device you flash the heater during pump out before you flash the getter , when flasing tunsten heaters you flash them at a few 100s degrees above normal operating temperature to turn the carbonates into OXIDES you then flash the getter to remove the last traces , then there is the burn in period to get the emission stable .
directly made cathodes can be made by heating barium strontium (calcium) mixes on a (host ) EG cathode / heater wire . needs to be applied in an alcohol / solution and baked onpossibly some kind of bonding agent needs to be used . by passing a current through it the exact solution is unknown to me . you should try to make some sort of tube resembling a diode whit a very exact plate distance to figure out wich mixture gives the best emission .

i know for a fact you can buy strontium and barium carbonate in small quantities for very low cost . i just dont know the purity or the mix it comes in

ive seen pictures of the fullmusic plant and believe they use some kind of electroplating to get the emission layer on the cathode . possibly in a bath whit positive charged liquid whit a negative wire hanging the solution . attracting particles in the process

HEATER WIRE
the emission layer for barium cathodes should have an optimum temp .
i believe that was somewhere in the region of 900 -1300 degrees Celsius
I
heaters for DHT can be either . nickel ribbon EG flattened nickel wire sprayed whit emission coating . for a bigger working surface . most old tubes used this including 2a3 AD1 ect

OR you can go fancy like emission labs does . and use "hard metal fillaments " in other words using tungsten wire . instead of hard to use nickel . this needs some saying .

"TUNGSTEN can sag and will glow hotter than nickel be course of its higher melting point . its harder . but can still sag into your grid ,
so some kind of spring will need to be used ,
tungsten does have a much longer lifespan than nickel . (shouldnt wear out at 1300 degrees ) and has high tensile strength

prolly gona continue tomorrow
 
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grids
grids . can be made from very simple to very complicated . from just a spiral wire to hard metal frames wound whit super thin wire for ultra high gain .
a spiral wire . can be used . or you could make your own tools to make grids . i could give you some ideas . but it would require you to be able to make hight tolerance parts .

mica can be cut pretty easily . if you have smal drills you can produce a lot of mica's in one go . then split the pack of mica . into induvidiual sheets
mica can be bought almost everywhere its in toasters suspending the heating element . you can buy 10 packs of 10x20 mica . on ebay for a few bucks . easy to cut make a few holes for mounting grids and heaters whit a dremel . and cut the mica whit a knife .

most vacuum tube mica was specially threated whit aluminium oxide and a binder to avoid flash overs . thin ceramic could also be a option . harder to work but looks cool .


getters i suggest you read this . Getter Materials

good options for gettering are
* magnesium low temp . can only absorb oxygen
* barium getters
* plates coated whit zirconium powder . wich is sinistered on . 6s19s uses this for active gettering


bases some ebay sellers sel UX4 8 pin octal european side contacts or P you can use silicone to glue the base to the bulb . ive also dug up a mix for the original glue . if you need it . found it on a website discussing the posibility of asbestos in tube bases or the glue that binds the base to the tube . but i think silicone is your best bet for the sake of simplicity .
 
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Rotary type AC compressors will pull a better vacuum then reciprocating piston type compressors. I would try to find cheap or free not so worn out 1hp-2hp rotary compressor. Diffusion pumps can be made, or bought for a few hundred dollars. I would tap the bottom of the compressor and take the oil for the diffusion pump right from the compressor, put an oil separator on the exhaust of the compressor and run a capillary tube from the oil separator to the intake of the compressor. You can make an oil separator from a copper pipe and brass or stainless wool, or just buy one for $50 or so.

A 2 stage HVAC or lab type vacuum pump might be fine, most go under 20 micron, many close to 1 especially lab pumps. These can be expensive, and be prepared to change the oil very often to ensure the units longevity.

You might also want build an induction heater to keep all the insides glowing dull red during pump down and to flash the getter. I have no idea how to get barium inside.

Also, you cathode must be oxide coated or thoriated. See wikipedia. http://en.wikipedia.org/wiki/Hot_cathode
 
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