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Digest Number 81
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According to telescope making volume 3, the filament materials in
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order of merit are tungsten, tantalum, molybdenum and columbium. Nichrome may also work as Nickel is a possible material. Nichrome may be more easily available if you work in an industry that uses furnaces as it is used for furnace elements . Electrical pass throughs can also be constructed by drilling a hole and then making sure that contact does not touch the sides and use a neoprene or similar insulating material to insulate. Also from telescope making vol3. Geoff ------------------------ Yahoo! Groups Sponsor |
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Hans Summers
Nichrome is also used in every day household toasters! The average household
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toaster holds two slices of bread. From my reading, it contains about 5m of nichrome wire and the power consumption is about 1 KW (UK mains 240V ac). Note that these ratings are applicable in air. I do not know how this is likely to change in a vaccuum. I suspect the problem with Tungsten might be oxidation. H P Friedrichs has used tungsten light bulb filaments in homemade triodes etc. See his book Instruments of Amplification . He found the lifetime was only of the order of 15 minutes, when he removed the tungsten wire from a light bulb and reused it in his valves. This was extended to a matter of hours when he retained the entire lightbulb assembly i.e. did not handle the tungsten wire. Personally I would like to have a go at making some valves (lack of time at the moment) and am wondering if nichrome would be suitable rather than tungsten, and be much more convenient and easy to obtain. Hans -----Original Message-----
From: gjnelson@... [mailto:gjnelson@...] Sent: 08 December 2003 14:39 To: VacuumX@... Cc: dominic-Luc Webb Subject: Re: [VacuumX] Digest Number 81 According to telescope making volume 3, the filament materials in order of merit are tungsten, tantalum, molybdenum and columbium. Nichrome may also work as Nickel is a possible material. Nichrome may be more easily available if you work in an industry that uses furnaces as it is used for furnace elements . Electrical pass throughs can also be constructed by drilling a hole and then making sure that contact does not touch the sides and use a neoprene or similar insulating material to insulate. Also from telescope making vol3. Geoff ------------------------ Yahoo! Groups Sponsor To unsubscribe from this group, send an email to: VacuumX-unsubscribe@... Your use of Yahoo! Groups is subject to |
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arcstarter
--- In VacuumX@..., Hans Summers <Hans.Summers@t...>
I would think that once proper vacuum has been reached there won't be enough o2 left to cause any appreciable wear. Seems that for aluminum the classic format is that of the heavy gauge spiral tungsten filament. Aluminum in particular will alloy with the tungsten prior to evaporation. Choice of wire size is somewhat important as if your gauge is too fine the AL will dissolve through the filament and casue it to break. The site www.lesker.com contains TONS of useful vacuum information, including suggested filament materials to be used with target evaporants. The chart at: irements_Boats7.cfm? CFID=218535&CFTOKEN=45377807§ion=tspttboats&init=skip describes the voltage, amperage, power, max temperature relations for their thermal evaporation sources. The old evap I'm resurrecting uses a tungsten 'boat', specifically the EV31A010W model, at: oat_EVS29000_35000.cfm? CFID=218535&CFTOKEN=45377807§ion=tsboats&init=skip You can't beat the price - each boat is $5 or such. Peak temperature is listed at 1800 C. Friedrichs hashis book Instruments of AmplificationOhho sounds like I'll have to buy this book! -Bill |
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Hans Summers
I would think that once proper vacuum has been reached thereTrue enough; I think it's quite likely that the degree of vacuum attained by H P Friedrichs wasn't too high. Friedrichs has used tungsten light bulb filaments in homemade triodes Ohho sounds like I'll have to buy this book!I can confirm it's a great read! Hans |
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