[RFI] Are nuvistors sturdier than transistors?
ingraham.ma.ultranet at rcn.com
Thu Aug 30 19:20:58 EDT 2007
> Rephrased: I was taught that germanium transistors
> 'aged', and that old tubes could develop base leaks -
> both happening even when on the shelf - plus traditional
> glass tubes suffer damage from overheating thus also
Transistors age because the impurities migrate, and the doped areas and
junctions eventually blur, due to entropy. Migration is much more
pronounced in Ge than Si, so you can see aging happening years faster with
Ge devices than Si. But even Si transistors (and therefore ICs) do
eventually go bad, if you wait long enough.
As for tubes, I'm sure others can tell the real story, but I thought the
main aging process was loss of cathode emission efficiency, happening as a
result of heat and/or current. But this effect wouldn't happen on the
shelf. Slow gas leaks are supposed to be minimized by the "getter" added
inside most tubes. I wonder if nuvistors have (or benefit from) a getter.
The getter causes a chemical reaction by combining with air, thus
maintaining the vacuum. But a side effect is deposits coating the inside of
the tube, so it doesn't leave the tube "good as new" and eventually the
deposits effect the internal elements too.
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