You test a tube on your tester and it's 100%+ and you drop the filament
voltage one step wait half a minute and with little needle deflection if
any - a good sign of lots of life left BUT I've just been told that
inspection of the flashing can really give you a better idea of the
tubes usage - So I have several same make / year 12AX7 that are supposed
to be nos and of the group there is one that has about 65% the amount of
flashing inside the top as the others do -

Is this a sign of many hours usage or production variations?

Ozzy 2005 said:

You test a tube on your tester and it's 100%+ and you drop the filament
voltage one step wait half a minute and with little needle deflection if
any - a good sign of lots of life left BUT I've just been told that
inspection of the flashing can really give you a better idea of the
tubes usage - So I have several same make / year 12AX7 that are supposed
to be nos and of the group there is one that has about 65% the amount of
flashing inside the top as the others do -

Is this a sign of many hours usage or production variations?


None of the above.
It's just that the heaters in certain tubes are covered with some kind
of coating.
Some brands have the coating extended all the way to the ends of the
heater, others do not.
What you see is the heater lighting up due to the lower resistance
when cold, and where the coating isn't applied.
Any tube with this heater construction will show this "flashing",
whether old and worn out or brand new out of the box.
Nothing to worry about, actually.

Philips and associated brands (Mullard, Valvo, Mazda etc.) in
particular are well known for their "flashing" .
Telefunkens as a rule do not show this effect.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

You test a tube on your tester and it's 100%+ and you drop the filament
voltage one step wait half a minute and with little needle deflection if
any - a good sign of lots of life left BUT I've just been told that
inspection of the flashing can really give you a better idea of the
tubes usage - So I have several same make / year 12AX7 that are supposed
to be nos and of the group there is one that has about 65% the amount of
flashing inside the top as the others do -

Is this a sign of many hours usage or production variations?


None of the above.
It's just that the heaters in certain tubes are covered with some kind
of coating.
Some brands have the coating extended all the way to the ends of the
heater, others do not.
What you see is the heater lighting up due to the lower resistance
when cold, and where the coating isn't applied.
Any tube with this heater construction will show this "flashing",
whether old and worn out or brand new out of the box.
Nothing to worry about, actually.

Philips and associated brands (Mullard, Valvo, Mazda etc.) in
particular are well known for their "flashing" .
Telefunkens as a rule do not show this effect.

--
Sander de Waal

Sander has confused the "flash" of light when powering up a tube (common on
Mullard tubes) with the size of the silver getter "flashing" (the silver
colored area created when the tube is new), which is what the original
poster was asking about.

The size of the silver colored getter FLASHING is an indicator of how much
internal gas has been absorbed since the tube was made. This can be an
indicator of use and wear of the tube, or it can be an indicator of slight
vacuum leakage in the glass envelope. In either case, I could not consider
a tube to be NOS, if it has lost a significant amount of it's original
flashing. In the case of most 12AX7, this silver area normally extended
down to first mica when the tube was manufactured.

cheers!

cowboy

"cowboy" cacheoverflow@yahooDOTcom said:


Sander has confused the "flash" of light when powering up a tube (common on
Mullard tubes) with the size of the silver getter "flashing" (the silver
colored area created when the tube is new), which is what the original
poster was asking about.


OOOPS!!!! Thanks Cowboy, you're right of course.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

Sander deWaal wrote:
"cowboy" cacheoverflow@yahooDOTcom said:



Sander has confused the "flash" of light when powering up a tube (common on
Mullard tubes) with the size of the silver getter "flashing" (the silver
colored area created when the tube is new), which is what the original
poster was asking about.



OOOPS!!!! Thanks Cowboy, you're right of course.

Thanks guys ! I can't stand these people say NOS unused and now I know
they are full of it by the photos of these tubes with almost no getter
flashing left. Saved me lots of trouble.

On Mon, 14 Mar 2005 12:39:02 +0000, Ozzy 2005 wrote:

BUT I've just been told that
inspection of the flashing can really give you a better idea of the tubes
usage -

Like, who? Is there some problem with telling us who said that?

Frankly, I'd like to help, but I'd like to know who
the mysterious fount of this BS is, so I can go attack it
at its source. I'm not into shadow-boxing.

--
Ned Carlson Triode Electronics Chicago,IL USA
www.triodeelectronics.com

On Mon, 14 Mar 2005 12:39:02 +0000, Ozzy 2005 wrote:

BUT I've just been told that
inspection of the flashing can really give you a better idea of the tubes
usage -

Like, who? Is there some problem with telling us who said that?

Frankly, I'd like to help, but I'd like to know who
the mysterious fount of this BS is, so I can go attack it
at its source. I'm not into shadow-boxing.

--
Ned Carlson Triode Electronics Chicago,IL USA
www.triodeelectronics.com


I think saying the tube's "current condition" would be more accurate than
saying "usage".

The flashing on a tube can degrade for a lot of reasons, and not all of them
involve any usage. I have unpacked 50 year old NOS tubes that were in
sealed boxes (the kind you have to rip open to get the tube out) and the
flashing was degraded. Some tubes are notoriously "leaky". A good example
is the GE made VT-4C broadcast triode. These should have a huge flashing
that is 4 inches in diameter at least, and I have seen NOS ones rot on the
shelf, such that the flashing was about as big as a quarter. Needless to
say, these gassy tubes burn up in the first 5 minutes that 1250V is applied
to the plate.

So what I am saying is, a reduced flashing does not necessarily indicate any
malice on the part of the seller, but it DOES indicate a tube that is no
longer going to function as new. I would further say that the flashing is
the most reliable visual indicator of a tube's current condition, but it
should still be tested for shorts & transconductance, as well as being
tested in a real world application, such as an amplifier.

for folks who want to learn more about extending tube life and assessing the
condition of a tube, I can highly recommend Bob Tomer's classic 1960 bible
on the subject, now out of print, information can be found he

http://www.amazon.com/exec/obidos/tg...l/-/188258029X


cheers!

cowboy
cacheoverflow AT yahoo DOT com
(and I am a big fan of Uncle Ned's expertise, something I cannot say about
most "experts" in the tube audio world)

Thanks guys ! I can't stand these people say NOS unused and now I know
they are full of it by the photos of these tubes with almost no getter
flashing left. Saved me lots of trouble.

There was likely wide variation of the amount of getter material
applied to the getter ring or D holder, and how much get flashed
onto the inside of the glass envelope. But if you see some
white then there's been some gas in there. All white means that
the vacuum all leaked out.... Other than that I don't think you
can really tell how used a tube is by looking at the getter.