TwoMuttHeads wrote in message
...

What would cause the failure of one half of a 4 year old 12AX7 ? A
very
careful owner.
Which raises another question- why would one side of a 12AX7 (or any
other similar twin triode) test markedly different from the other
side? I've seen big mismatches in 12AX7 tubes. I can see where used
tubes that have different "roles" in the circuit could "wear" unevenly
depending on how their used (driver, phase splitter, etc).


As its likely to be a stock fault the full number is GT Groove GT12AX7M red
paint, no other identifying marks. Probably post 2002 manufacture.
The anode extension plate is just spot welded to the wire interconnect,
reverse side impression of spot weld present, so not obviously mechanically
poor weld. The grid extender is tube so crimped and welded. Looking at
another, unknown, make of 12AX7, the anode extensions are tube also, so
crimp+weld , so presumably more reliable to resist (normal?)
thermal/dimensional stresses in use.
Unfortunately 3 more of probably this same valve batch in this amp.


--
Diverse Devices, Southampton, England
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