12AX7 failure

TwoMuttHeads <menwagoh@msn.com> wrote in message
news:d9efcc43-7959-4314-bf00-99208d1b7a78@w22g2000yqd.googlegroups.com...
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).
Click to expand...

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
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
 
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:49292F9B.DEF6D033@hotmail.com...
Life, the universe and everything.
Click to expand...
42?
 
N_Cook wrote:

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.
Click to expand...
Why do you fret over nothing ? Valves 'GO'. It's their nature.

Graham
 
Brenda Ann wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message

Life, the universe and everything.

42?
Click to expand...
Passed that ages back sadly. Mind you I still get taken for being in my
40's.

Graham
 
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:49294BC0.93D9C691@hotmail.com...
Brenda Ann wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message

Life, the universe and everything.

42?

Passed that ages back sadly. Mind you I still get taken for being in my
40's.

Graham
Click to expand...
I take it that went over your head?? :)
 
Brenda Ann wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote
Brenda Ann wrote:
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote

Life, the universe and everything.

42?

Passed that ages back sadly. Mind you I still get taken for being in my
40's.

I take it that went over your head?? :)
Click to expand...
Not at all. :)

Graham
 
On Sun, 23 Nov 2008 22:05:24 +0900, "Brenda Ann"
<brendad@shinbiro.com> wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:49294BC0.93D9C691@hotmail.com...


Brenda Ann wrote:

"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message

Life, the universe and everything.

42?

Passed that ages back sadly. Mind you I still get taken for being in my
40's.

Graham



I take it that went over your head?? :)
Click to expand...

Lost his towel??
 
The 12AX7 owner said he was a careful owner, but maybe not careful enough.
Maybe if he had ordered the Snake-Oil brand tube cozies......and vibration
smugglers and wrapped his 12AX7's in those that tube would be alive and
transfering the emotion of true music today..........


"Jeffrey D Angus" <jangus@socal.rr.com> wrote in message
news:gg9i2l0194i@news1.newsguy.com...
Peter Elem wrote:
12AX7's have become "fools gold" in this inflated acoustic psycho-babble
golden ear but tin brain market...........

And this answers the question how?

Jeff
Click to expand...
 
On Nov 22, 11:36 am, "N_Cook" <dive...@tcp.co.uk> 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-
Click to expand...
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
 
On Nov 23, 9:53 am, Peter Wieck <p...@aol.com> wrote:
On Nov 22, 11:36 am, "N_Cook" <dive...@tcp.co.uk> 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
Click to expand...
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!
 
Peter Elem wrote:

AS with $5 vacuum tubes, $150 audio vacuum tubes sometimes fail at an early
age.........One culls them out and often very old tubes just keep on going
fine. 12AX7's have become "fools gold" in this inflated acoustic
psycho-babble golden ear but tin brain market...........
Click to expand...
Do their brains suffer from tin pest ?
http://en.wikipedia.org/wiki/Tin_pest
http://www.indium.com/blogs/Dr-Lasky-Blog/entry.php?id=310

Graham
 
On Nov 23, 3:43 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
Peter Elem wrote:
AS with $5 vacuum tubes, $150 audio vacuum tubes sometimes fail at an early
age.........One culls them out and often very old tubes just keep on going
fine. 12AX7's have become "fools gold" in this inflated acoustic
psycho-babble golden ear but tin brain market...........

Do their brains suffer from tin pest ?http://en.wikipedia.org/wiki/Tin_pesthttp://www.indium.com/blogs/Dr-Lasky-Blog/entry.php?id=310

Graham
Click to expand...
That's funny! I buy all of the old 60/40 solder I can find because if
the tin dendrite issue that will be comming in the future. Tin
dendrites have been known to grown to over 10mm in length. That is
why NASA and critical biomed devices (pacemakers and ICD's etc) will
continue to use lead in their solder, and so will I for as long as I
have a supply.

Randy AB9GO

Current carrying capacity of dendrites
Bjorndahl, W.D.; Lau, J.C.
Aerospace Applications Conference, 1994. Proceedings., 1994 IEEE
Volume , Issue , 5-12 Feb 1994 Page(s):399 - 405
Digital Object Identifier 10.1109/AERO.1994.291179
Summary:Dendrites are sometimes found on electronic hardware during
failure analysis or trouble shooting activities. Problems due to
dendrite formation can vary from catastrophic failure to occasional
electronic glitches. If a dendrite is thought of as a fuse in a
circuit, then it is apparent that it can have, depending on size, a
wide range of current carrying capability. Mathematical modeling and
experimental analyses were conducted to determine the reasons for the
wide range of observed behavior. Mathematical modeling indicates that
the resistivity of the dendrite and the thermophysical characteristics
of the substrate on which it is grown determine its current carrying
capacity. More specifically, the modeling indicates that maximum
dendrite size and time to failure are determined by the power loss
within the dendrite and the rate at which heat can be transferred away
from the dendrite. Small dendrites are stable and can grow until they
reach a size at which internal heat generation cannot be accommodated
by the heat loss due to conduction through the substrate. Dendrites in
low voltage applications on substrates with high thermal diffusivity
are more likely to lead to failures with high power loss, whereas
dendrites in high voltage applications on low thermal diffusivity
substrates (e.g. tin on glass/epoxy circuit board material) are more
likely to lead to high resistance shorts. Experimental results and
failure analysis observations agree qualitatively and semi-
quantitatively with the results of the idealized dendrite model
 
AB9GO wrote:

On Nov 23, 3:43 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:
Peter Elem wrote:
AS with $5 vacuum tubes, $150 audio vacuum tubes sometimes fail at an early
age.........One culls them out and often very old tubes just keep on going
fine. 12AX7's have become "fools gold" in this inflated acoustic
psycho-babble golden ear but tin brain market...........

Do their brains suffer from tin pest ?http://en.wikipedia.org/wiki/Tin_pesthttp://www.indium.com/blogs/Dr-Lasky-Blog/entry.php?id=310

Graham

That's funny! I buy all of the old 60/40 solder I can find because if
the tin dendrite issue that will be comming in the future. Tin
dendrites have been known to grown to over 10mm in length. That is
why NASA and critical biomed devices (pacemakers and ICD's etc) will
continue to use lead in their solder, and so will I for as long as I
have a supply.
Click to expand...
Likewise.

You can still get it legally even in the EU for repair of pre PB-free equipment.


Randy AB9GO

Current carrying capacity of dendrites
Bjorndahl, W.D.; Lau, J.C.
Aerospace Applications Conference, 1994. Proceedings., 1994 IEEE
Volume , Issue , 5-12 Feb 1994 Page(s):399 - 405
Digital Object Identifier 10.1109/AERO.1994.291179
Summary:Dendrites are sometimes found on electronic hardware during
failure analysis or trouble shooting activities. Problems due to
dendrite formation can vary from catastrophic failure to occasional
electronic glitches. If a dendrite is thought of as a fuse in a
circuit, then it is apparent that it can have, depending on size, a
wide range of current carrying capability. Mathematical modeling and
experimental analyses were conducted to determine the reasons for the
wide range of observed behavior. Mathematical modeling indicates that
the resistivity of the dendrite and the thermophysical characteristics
of the substrate on which it is grown determine its current carrying
capacity. More specifically, the modeling indicates that maximum
dendrite size and time to failure are determined by the power loss
within the dendrite and the rate at which heat can be transferred away
from the dendrite. Small dendrites are stable and can grow until they
reach a size at which internal heat generation cannot be accommodated
by the heat loss due to conduction through the substrate. Dendrites in
low voltage applications on substrates with high thermal diffusivity
are more likely to lead to failures with high power loss, whereas
dendrites in high voltage applications on low thermal diffusivity
substrates (e.g. tin on glass/epoxy circuit board material) are more
likely to lead to high resistance shorts. Experimental results and
failure analysis observations agree qualitatively and semi-
quantitatively with the results of the idealized dendrite model
Click to expand...
Do you have a link for that ? I heard somewhere a typical tin whisker can support 30mA.

Graham
 
Eeyore wrote:

Why do you fret over nothing ? Valves 'GO'. It's their nature.
Click to expand...
Depending upon their use, they may go quickly or slowly.

Regards,
H.
 
On Nov 22, 8:36 am, "N_Cook" <dive...@tcp.co.uk> 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-
Click to expand...
Hi,

Given that it is dead, if you really wish to find out you could always
crack & remove the glass and then check the internal connections.
Nothing to lose!
 
"AB9GO" <randallr@healthall.com> wrote in message
news:f12c5eb6-ec20-48e5-bdb0-9634faae282f@y1g2000pra.googlegroups.com...
On Nov 23, 10:44 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
Likewise.

You can still get it legally even in the EU for repair of pre PB-free
equipment.
Click to expand...
Yes, but the price is getting higher and it is no longer commonly
stocked.


I have at least 4 or 5 rolls of 63/37 or close to that.. enough to last me
personally for the rest of my life. Maybe I could send some out in 30'
chunks for those that need it?
 
On Nov 23, 10:44 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
Likewise.

You can still get it legally even in the EU for repair of pre PB-free equipment.
Click to expand...
Yes, but the price is getting higher and it is no longer commonly
stocked.

Do you have a link for that ? I heard somewhere a typical tin whisker can support 30mA.

Graham-
Click to expand...
ieeexplore.ieee.org/iel2/1110/7210/00291179.pdf

Is where I got the abstract. I am not a member so I cannot access the
entire document. Sorry.

Randy AB9GO
 
AB9GO wrote:

Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:

Likewise.

You can still get it legally even in the EU for repair of pre PB-free equipment.

Yes, but the price is getting higher and it is no longer commonly
stocked.
Click to expand...
Farnell.

Graham
 
AB9GO wrote:

Eeyore <rabbitsfriendsandrelati...@hotmail.com> wrote:

Do you have a link for that ? I heard somewhere a typical tin whisker can support 30mA.

Graham-

ieeexplore.ieee.org/iel2/1110/7210/00291179.pdf

Is where I got the abstract. I am not a member so I cannot access the
entire document. Sorry.
Click to expand...
Likewise.

Graham
 
AB9GO wrote:
On Nov 23, 10:44 pm, Eeyore <rabbitsfriendsandrelati...@hotmail.com
wrote:
Likewise.

You can still get it legally even in the EU for repair of pre PB-free equipment.


Yes, but the price is getting higher and it is no longer commonly
stocked.
Click to expand...
au contraire

Many if not most wholesale suppliers have leaded solder in their
specials sheets every month. The price is actually a lot lower than it
was a few years ago.

Ron(UK)
 
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