> HELP: Hopefully my last question regarding this amp.
> Given that this is a
> common occurrence for the Amperex 3-500Z tube, I do not
> plan on replacing it
> with another one. So my dilemma now is what flavor of
> 3-500ZG tube is the
> best fit for the AL-80B? I hear it is a toss up between
> the 3-500ZG-RFP and
> the 3-500ZG-TAY. Your input would be greatly appreciated.
Mike,
You are into a statistical thing. While some people like to
pretend some sinister single event causes problems like
this, the truth is tubes are very difficult to build. As a
consequence there is always a percentage that are no good or
that fail prematurely.
The particular problem Amperex had was the filament helices
were too close to the grid and mechanically too unstable, so
after a few filament temperature cycles or a few hundred
cycles the filament would move over a few thousands of an
inch and touch the grid in many of the tubes.
This primarily occurred with tubes that were code dated in
the very late 90's or early 2000. I'd have to check the date
to be sure. Amperex stocked and sold tubes that were about
two years old (by manufacturing date).
I'm not sure what production run Amperex is selling now and
how reliable that run is. You might ask someone who
actually USES tubes what the most reliable tube is. Asking a
tube salesman might not produce the most accurate response,
since there is some motivation to sell product in stock.
Whatever tube you buy be sure you look at production date
and make sure that date has few known problems. The date is
normally a four number code representing year and week. No
matter what you do you will take a chance. The days of
buying a 3-500Z with confidence it would be perfect and last
many years vanished when Eimac closed the Salt Lake City
manufacturing of 3-500Z's.
73 Tom
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