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.
8877's continue to be one of the more difficult tubes to produce. Although
the move back to the San Carlos plant made them much better they still are
less reliable than other tube types.
I explain why at:
http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm
This is similar to the 572B Svetlana fiasco Ameritron (who I no longer do
any consulting for) went through, and seems to parallel the present 3-500Z
problem.
As difficult as it is for some to believe, transmitting power tubes are very
troublesome components. They are very much material sensitive, and
manufacturing process sensitive. It is almost like a black art, as anyone
who has been around tube manufacturing would know. Even small receiving
tubes operating in low-voltage systems were the most likely components to
fail in old tube equipment.
We seem to have forgotten all the lessons we have learned, and expect
solid-state reliability from vacuum tubes.
73 Tom
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