>
>> 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!
// Out of the last five 8877s I autopsied, only one indicated parasite
damage (loose gold) -- which came from an out-of-warranty AL-1500
amplifier.
>
>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!
// One of the two tubes in my SB-220 was manufactured by Amperex in
France in 1967. It still delivers the goods. My SB-220 does not use
stock VHF suppressors.
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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