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 on
http://home.graffiti.net/diverse-

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...........

"N_Cook" wrote in message
...
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 on
http://home.graffiti.net/diverse-

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

Jeffrey D Angus wrote:
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
If we told you, We'd have to kill you. Ken

Meat Plow wrote:
On Sat, 22 Nov 2008 16:36:08 -0000, "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.

Maybe a break in the grid wire near its winding start? Does the
filament glow on that side? Is the cathode shorted to the filament?

It could be an indication of grid emission.

Meat Plow wrote in message
...
On Sat, 22 Nov 2008 16:36:08 -0000, "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.

Maybe a break in the grid wire near its winding start? Does the
filament glow on that side? Is the cathode shorted to the filament?


No C/H leakage either triode. Can only see heater glow with this make of
tube, badged GT if relevant, by viewing underside of envelope. Both heaters
equally bright.


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

Meat Plow wrote:

On Sat, 22 Nov 2008 16:36:08 -0000, "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.

Maybe a break in the grid wire near its winding start? Does the
filament glow on that side? Is the cathode shorted to the filament?

Many years ago ! I have seen O/c anodes on these. Look for a weld
fracture near or in the glass where the pin is welded to the anode
support.

--
Best Regards:
Baron.

Ken wrote:

Jeffrey D Angus wrote:
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
If we told you, We'd have to kill you. Ken


Likely, the other way around.


--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you're crazy.

I also have tubes that have no emission but no visible defects; I ran
across a 25AX4 like that the other day. I suspect one of the welds is
broken but the gap is too small to see.

The 12AX7 is a miniature tube. I have miniature tubes with pins that
have broken inside the glass base. Usually I notice it when the broken
piece falls out. If it didn't fall out, I would have a defective tube
with no visible problem. (This usually happens outside the seal area so
that air doesn't enter the tube.)

In any event, your tube doesn't work. You're going to have to replace
it no matter what happened to it. You probably didn't cause it. It's
just one of those things.


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 on
http://home.graffiti.net/diverse-



--
Jim Mueller

To get my real email address, replace wrongname with dadoheadman.
Then replace nospam with fastmail. Lastly, replace com with us.

I dunno. My cat had a fine litter of kittens, except the dead one.
Looked perfect, but ...

Stuff happens, do not get too depressed

Happy Ears!
Al

On Nov 22, 8:36*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-

You will almost never see the weld crack since it usually only shifts
a thou. or two. I tested a tube for failed cathode ribbon connection
by connecting a 'good' tube filament - cathode [cold] across an RF
inductor on a Q meter and tuning for resonance, then connecting the
'bad' tube in it's place. The capacitance, tiny as it normally is, was
much less as shown be a significantly higher resonant frequency.

Neil S.

"N_Cook" wrote in message
...
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.





12AX7's are a lot like human beings.


Everyone who's ever died...

amazingly was alive right before their demise.

Probably just a coincidence though G

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).

In article ,
TwoMuttHeads wrote:

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).

Poor assembly tolerances?

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

N_Cook wrote:

What would cause the failure of one half of a 4 year old 12AX7 ? A very
careful owner.

Life, the universe and everything. Was it a Chinese valve ?

I got a Fender Twin Reverb to fix once. It was initially a puzzler. All the
valves lit up brightly and you could trace signal to the grids of the output
valves but after that ? ZILCH. O/P transformer was fine too.

Turns out ALL four Z&I (Zaerix brand) Russian 6L6GCs had gone zero emission but
looked visually perfect.

I had to sub some EL34s temporarily to get it going for him for a gig. I never
held any 6L6s. Only time I needed any in fact.

Graham

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...........

Amen to that ! They were the 2N2222/2N3904 or BC108/BC184 of their day.

Graham

Jim Mueller wrote:

In any event, your tube doesn't work. You're going to have to replace
it no matter what happened to it. You probably didn't cause it. It's
just one of those things.

Chuck it in the bin and charge the customer for a new one plus mark-up and time of
course. That's how Valve repairs are done.

Graham

TwoMuttHeads wrote:

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).

Who cares ? It's broken. Replace it !

Graham

John Byrns wrote:

TwoMuttHeads wrote:

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).

Poor assembly tolerances?

I hereby second you to the tube manufacturer to check them out.

Graham

Ooops I said tube !

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
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"Eeyore" wrote in message
...
Life, the universe and everything.

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.

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

Graham

Brenda Ann wrote:

"Eeyore" 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

"Eeyore" wrote in message
...


Brenda Ann wrote:

"Eeyore" 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??

Brenda Ann wrote:

"Eeyore" wrote
Brenda Ann wrote:
"Eeyore" 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??

Not at all. :-)

Graham

On Sun, 23 Nov 2008 22:05:24 +0900, "Brenda Ann"
wrote:


"Eeyore" wrote in message
...


Brenda Ann wrote:

"Eeyore" 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??



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" wrote in message
...
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

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

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!

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_pest
http://www.indium.com/blogs/Dr-Lasky...try.php?id=310

Graham

On Nov 23, 3:43*pm, Eeyore
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_pes...try.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.

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
Summaryendrites 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
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_pes...try.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.

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
Summaryendrites 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

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.

Depending upon their use, they may go quickly or slowly.

Regards,
H.

On Nov 22, 8:36*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-

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!

On Nov 23, 10:44*pm, Eeyore
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.


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.

Randy AB9GO

"AB9GO" wrote in message
...
On Nov 23, 10:44 pm, Eeyore
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.


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?

AB9GO wrote:

Eeyore 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.

Farnell.

Graham

AB9GO wrote:

Eeyore 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.

Likewise.

Graham

AB9GO wrote:
On Nov 23, 10:44 pm, Eeyore
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.

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)

"Peter Wieck" wrote in message
...
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.

For some reason, whenever a thread starts with "12AX7", "EL84", or "6L6", I
feel like I'm viewing the famous "Three Stooges" skit, "Niagara Falls",
after I read all the replies!

Why is it so important to debunk a failing tube that gave four years of
satisfactory performance?

Dude, just $#!^can the offending tube, and move on!

Omer