On Nov 22, 11:36*am, "N_Cook" wrote:
What would cause the failure of one half of a 4 year old 12AX7 ? A very
careful owner.
One half tests out fine but for half using pins 1,2,3 cannot get any zeroing
on the tester even setting current down to 0.5 mA or less and for any grid
voltage setting. Can't see any obvious internal weld failure.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list onhttp://home.graffiti.net/diverse-

Hmmm... you did not differentiate whether the tube is 4-years-in-use
NOS, or 4 years from manufacture. Nor did you specify country-of-
origin if New.

If this is a Chinese 12AX7 four years from manufacture - that is a
VERY long time for some of these tubes. The owner should count himself
lucky for even that much life.

Peter Wieck
Melrose Park, PA