On Nov 23, 9:53*am, Peter Wieck wrote:
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
I have some Groove Tubes here and they are all "Made in China". They
are marketed to the Guitar amp user. Many are sold through Sam Ashe,
Guitar Center and other music shops. Even the box they come in is
styled like a Fender amp. They have an odd distortion marking scheme
and biasing advice. The tubes are rated as to distortion: Early
Distortion 1-3, Normal Distortion 4-7, and Latest Distortion 8-10. "
The bias should always be adjusted when changing power tubes, UNLESS
YOU ARE REPLACING GROOVE TUBES OF THE SAME TYPE AND RAITING, THEN NO
ADJUSTMENT IS NEEDED. " Bad advice IMHO.
Find an old timer repair guy and they will tell you that getting only
4 years life on a tube is not unusual. Some go bad in minutes and
some run forever or so it seems.
Randy AB9GO
p.s. Here is an example of running forever:
http://www.centennialbulb.org
Age: 107 years and counting (as of 2008)
Installed: First installed at the fire department hose cart house on L
Street in 1901. Shortly after it moved to the main firehouse on
Second. In 1903 it was moved to the new Station 1 on First and McLeod,
and survived the renovation of the Firehouse in 1937, when it was off
for about a week.
Proof of Longevity: From local newspaper records; also GE engineers
researched it. Was donated to the Fire Department in 1901 by Dennis
Bernal who owned the Livermore Power and Light Co.
And there is another one in Texas:
Happy 100th B-Day Palace Bulb!!!
On September 21, 2008 the Palace Bulb of Fort Worth, Texas will be the
2nd bulb in history to have burned 100 years! Our best wishes for a
wonderful celebration to all the folks at the Stockyards Museum, and
for another 100 years!