i get .75mm is .44 square mm. and there are a million square microns in a
square mm( 1000 squared).
So the cross sectional area would be 440,000 square microns. And with 14
amps I get
3.16e-5 amps per square micron. I don't think current density is a problem.
73
Bill wa4lav
At 08:56 AM 10/14/02 -0400, wl fuqua wrote:
>Filaments generally loose emission long before they thin out and burn out.
>Also, in comparison to light bulbs they run a good deal cooler.
>Semiconductors, to function, require a crystal lattice structure. So it
>would not take much
>shifting of atoms in the lattice to make them nonfunctional. Also, your
>dimensions seem
>to be incorrect.Current density (amps per square units)??
>
>73
>Bill wa4lav
>
>At 08:31 AM 10/14/02 +0100, Peter Chadwick wrote:
>>I believe the problem is metal migration - a well known phenomena in
>>semiconductors. There, in order to maintain life at 150 deg C chip
>>temperature,
>>the maximum current density is about 2 to 4mA per square micron, depending on
>>the exact metal process. A 3-500Z filament is, from memory, around 0.75mm in
>>diameter, so the current density is way above 2mA per micron!
>>
>>Using AC prevents metal migration. As someone else said, the military aren't
>>generally looking for extended life in tubes - maybe in big TWTs in
>>radars, but
>>they'll be run on AC. Howver, an automatic polarity reversal circuit with a
>>latching relay isn't hard to do....
>>
>>
>>73
>>
>>Peter G3RZP
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>
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