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Old 11th August 2007, 03:59 PM   #1
Calvin is offline Calvin  Germany
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Default Alloys for filaments

Hi,

does anyone know who could supply for filament alloys of the following types?

75% Ni
18% Co
5% Fe
2% Ti

or
79% Ni
18% Co
2% Fe
1% Si

or
54.50% Ni
44.50% Co
1% Fe



thanks
Calvin
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Old 11th August 2007, 05:35 PM   #2
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Alloys like Nichrome, Chromel, German Silver, are useful if you need to rewire your toaster. These are never used in VT practice. Even if the heaters run at red heat, these are made from tungsten wire.

Alloys of all types have a nasty tendency to accumulate large amounts of gas that will leak out and ruin the vacuum (such that it is).

If it's your intention to go to all the bother to make your own VTs, then it's worth a little bit of extra bother to get the right item for the heaters.
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Old 12th August 2007, 10:55 PM   #3
sds2000 is offline sds2000  United States
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In the US small quantities ( a foot or so ) of tungsten, thoriated tungsten etc wire can be obtained from companies that supply these wires to labs that do spectroscopy with these heated filiments. An example company is Scientific Instrument Services, Inc. at www.sisweb.com. You will find many types of filament wires sold in the section on "Mass Spectroscopy, Filament Wire". There may be such companys in you own country as well. If your planning on making you own tubes best of luck


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Old 12th August 2007, 11:03 PM   #4
Magura is offline Magura  Denmark
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I'd have a chat with a supplier of TIG welding equipment. The electrodes comes in quite a few different alloys, maybe some that are near your requirements.

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Old 13th August 2007, 06:39 PM   #5
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I use 2% thoriated tungsten tig electrodes. This would be great for making tubes, except their is no way you will be able to make a filament out of such a brittle material.
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Old 14th August 2007, 12:42 PM   #6
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check out this article :
http://www.r-type.org/static/ef80.htm

"The heater is a V shaped component that looks deceptively simple. In practice the Tungsten wire used to make the filament is 7 μm in diameter and fragile. When forming the heater, the wire is wound on a Molybdenum rod mandrell that is subsequently disolved away in acid. The heater helix is formed into the hairpin shape and dipped in an alumina insulating coating that is dried by passing current through the heater wire itself."

and : http://www.r-type.org/static/add045.htm

" The basic spiral of tungsten wire with plain wire at each end had then to be shaped and insulated as well as made impervious to damage. The heater shapes were either a single V, as for the EF80, or an M shape as the design needed. The shaped heater was insulated by holding many heaters in a jig and dipping them into an alumina based liquid coating. When the alumina was dry the jig provided connections to the ends of the heaters so that by passing a current through the heater the alumina could be baked into place."
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Old 16th August 2007, 12:41 PM   #7
Calvin is offline Calvin  Germany
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Hi,

thanks for Your replies so far.
Its not my intention to built VTs, but I was asked by a manufacturer for sources.
The alloy formulas are of them and since they manufacture the probabely best and finest audio tubes available today, they ought to know why they want these alloys and no others. Tungsten for example is not usable for their kind of heater/cathode construction.

jauu
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