[Amps] THANKS re the 8877 failures and GE Medical

[W0UN--John Brosnahan]

At 07:05 PM 3/2/2003 -0500, you wrote:
>Rich made an incorrect statement that ETO was to blame for 8877 failures.
>
>The 8877 failures with GE medical were well known to be a manufacturing
>problem with the tubes. Eimac fought that problem for a long time before
>they had any useful tubes. For a long period of time virtually every tube
>was defective, none of the manufacturers using 8877 tubes could get a tube
>that lasted.

Tom--

Thanks for the clarification.  I was not at ETO during the 8877 fiasco--but
I was experiencing the same issues with the 3CPX1500A7s used in our
50 MHz wind profilers.  Totally an EIMAC issue  --  certainly not ETO's fault.

Just a few years ago there was a problem with some 3CX800A7s.  I kept
hearing from Eimac that we (while I was at Alpha/Power) were the only ones
having problems.  Couldn't find any reason why ~30% of the new tubes
would fail within about 100 hours of use.  They just got OLD very fast with low
emission and high grid current.  Fortunately (or unfortunately--depending on
your perspective) K1FO at Lunar Link was having the same problem and we
started comparing notes.  Steve did some excellent "CSI" detective work
and discovered that the tubes that would fail early would also put out full 
output
at a more reduced heater voltage than the long-lived ones.  In effect the 
heater
was enough different that the tube would act as if the heater was run
at excessively high voltage.  Eimac subsequently solved the problem
(to the best of my knowledge--I dropped out of the debate to have
open-heart surgery!) and I believe that the current 3CX800A7s are
much better.  But this issue persisted for more than a year--resulting
in Alpha amps working fine during their 48+ hour burn-in, but failing in the
field within weeks of being delivered.

But the issue added a lot of GRAY hair--although I cannot make a claim
that the heart condition was Eimac's fault!   ;-)

73--John  W0UN