> Tom says:
>
> >tubes are the weakest and most unreliable link in ANY gear.
>
> Over and above semiconductors? Fine for many parts, but there's been
> plenty of semiconductor batches where poor manufacturing factors such
> as step coverage in metal and bad injection molding, poor design
> factors with too high current densities leading to metal migration,
> and other QC problems lead to just as bad a reliability as 8877s can
> show...
I'm speaking from the standpoint of service history of components.
When you get a good semiconductor, which is nearly 100% of the
time, you can expect it to last dozens of years. You can turn it off
and on all you like, drop it, kick it, step on it, and operate it for
years without worry. Semiconductors just don't take overloads real
well, even very brief overloads.
On the other hand the left-coast nichrome salesman claims
momentary parasitics do all or most of the damage to tubes, when
tubes are MUCH better at momentary overloads!
Tubes have much shorter service life since they wear out from use,
don't like to have the filaments or close spaced hot parts like
cathodes cycled, have problems with even miniscule amount of gas
causing a severe arc, and can't stand much vibration or mechanical
shock.
I hate to tell you this Peter, but tubes have always been a bigger
life problem than semiconductors, and it is getting much worse
now. It's tough to find a good source of glass tubes any more, and
you'd better have a big dumpster to throw tubes in if you do
reliability testing on modern 572B's and 3-500Z's!
73, Tom W8JI
W8JI@contesting.com
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