Foregoing warranty rights

[Jeff Liebermann]

On Mon, 4 Apr 2011 16:27:32 +0000 (UTC), Meat Plow
<mhywattt@yahoo.com> wrote:

On Sun, 03 Apr 2011 19:34:29 -0700, Jeff Liebermann wrote:

On Sun, 03 Apr 2011 20:09:10 -0700, David Nebenzahl
nobody@but.us.chickens> wrote:

So where does that purplish glow come from? I've seen it.

Impurities in the glass envelope or gas in the tube.

If gas, take an anti-acid tablet and you should be fine in a few
minutes.

http://www.vacuumtubes.net/How_Vacuum_Tubes_Work.htm> Scroll down to:
C. Blue Glow -- what causes it?
for more details.

So even after a getter flash there is still a certain amount of
impurities? I've never seen a 6L6 that didn't have some blue inside
when in operation. It looks as though the blue only occurs where the
electron beams hit the inside of the glass. At least in new tubes.

Yep. As I vaguely recall (which means I didn't Google for a
reference) glass has the irritating habit of collecting impurities and
volatiles during manufacture. Irving Langmuir figured this out in the
1920's working on light bulbs. He would draw the best vacuum possible
and in a few days, find the bulb full of water vapor and other gasses.
The hot filament would break down the water into hydrogen and oxygen.
The oxygen would then oxidize the electrodes, and blacken the inside
of the bulb.

So, he invented a method of baking the glass to remove the volatiles
prior to evacuation and an acid bath to remove some of the impurities.
It also works nicely for vacuum tubes, but like all such processes, is
far from perfect. There's always some impurities left behind.

When we talk about a "gassy" vacuum tube, it's not a leaky glass
envelope or seal. The getter does best with reactive gases and does
nothing for eliminating noble gases, which will not react with metals
(or most anything else). It's those noble gases that remain (helium,
neon, argon, krypton, xenon, and radon) that you're seeing glow. Most
likely helium and argon mix. The small helium molecule will also
diffuse through the glass from the outside air. See photos at:
<http://en.wikipedia.org/wiki/Noble_gas#Discharge_color>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[whit3rd]

On Sunday, April 3, 2011 4:15:48 PM UTC-7, David Nebenzahl wrote:

On 4/3/2011 5:29 AM Geoffrey S. Mendelson spake thus:

So--and this is completely out of left field, I know--what would happen
if a guy put a vacuum tube--say a biggish octal one, like a 5Y3 or a
6V6--into a microwave and nuked it?

You mean, 'nuked it AGAIN', don't you? The usual manufacturing
of vacuum tubes is finished off with pumpdown, sealing, and then
running an induction coil to heat the little loop-thing
that evaporates a bit of metal (like sodium). It's called 'flashing',
and the silvery deposit ('getter') on the inside of the tube is intended to
be an oxygen scavenger for the long lifetime of the device.

In the case of photomultipliers, it is also done to create the photocathode
layer, often of some alloy that cannot be usefully blended until there's
a vacuum.

 

[Meat Plow]

On Mon, 04 Apr 2011 13:36:49 -0700, whit3rd wrote:

On Sunday, April 3, 2011 4:15:48 PM UTC-7, David Nebenzahl wrote:
On 4/3/2011 5:29 AM Geoffrey S. Mendelson spake thus:

So--and this is completely out of left field, I know--what would happen
if a guy put a vacuum tube--say a biggish octal one, like a 5Y3 or a
6V6--into a microwave and nuked it?

You mean, 'nuked it AGAIN', don't you? The usual manufacturing of
vacuum tubes is finished off with pumpdown, sealing, and then running an
induction coil to heat the little loop-thing that evaporates a bit of
metal (like sodium). It's called 'flashing', and the silvery deposit
('getter') on the inside of the tube is intended to be an oxygen
scavenger for the long lifetime of the device.

In the case of photomultipliers, it is also done to create the
photocathode layer, often of some alloy that cannot be usefully blended
until there's a vacuum.

They use getters in metallurgy to absorb impurities. The getter is
actually the "little loop-thing" and not the deposit that is a byproduct
of the flashing. Some getters are made of a special material and don't
need flashing. Don't ask me for a tube number. Tubes with graphite plates
don't need a getter as the graphite absorbs impurities.



--
Live Fast Die Young, Leave A Pretty Corpse

 

[Phil Allison]

"Jeff Liebermann"

When we talk about a "gassy" vacuum tube, it's not a leaky glass
envelope or seal.

** The term covers that eventuality too.

Any tube that has even a tiny air leak will glow a pinkish purple inside
like a bastard.

The getter does best with reactive gases and does
nothing for eliminating noble gases, which will not react with metals
(or most anything else). It's those noble gases that remain (helium,
neon, argon, krypton, xenon, and radon) that you're seeing glow.

** Maybe - but how would any significant amount of Argon get inside the
tube UNLESS there was air leaking in ?

Remember, Argon makes up less than 1% of air and does not react with metal
parts.

The vacuum inside a tube is less than one millionth of atmospheric pressure.

BTW:

Nitrogen mixed with a little CO2 makes a nice, white glow under low
pressure - its called a "Moore Tube"

http://en.wikipedia.org/wiki/Daniel_McFarlan_Moore

His untimely death was a bit shocking.


..... Phil

 

[Jeff Liebermann]

On Tue, 5 Apr 2011 09:53:16 +1000, "Phil Allison" <phil_a@tpg.com.au>
wrote:

"Jeff Liebermann"

When we talk about a "gassy" vacuum tube, it's not a leaky glass
envelope or seal.

** The term covers that eventuality too.

Ok. My bad grammar. I meant that if the tube is deemed "gassy", it's
probably not an air leak in the envelope or seal. It's more likely
gaseous diffusion of helium or neon through the envelope.

Any tube that has even a tiny air leak will glow a pinkish purple inside
like a bastard.

Yep. I've seen the pink glow. The only way I could tell the
difference between the nitrogen glow of an air leak:
<http://en.wikipedia.org/wiki/Ionized_air_glow>
and that of a helium diffusion through the glass leak:
<http://en.wikipedia.org/wiki/Noble_gas#Discharge_color>
was that the nitrogen glow would not last very long as the filament
would burn out due to oxidation.

The getter does best with reactive gases and does
nothing for eliminating noble gases, which will not react with metals
(or most anything else). It's those noble gases that remain (helium,
neon, argon, krypton, xenon, and radon) that you're seeing glow.

** Maybe - but how would any significant amount of Argon get inside the
tube UNLESS there was air leaking in ?

Remember, Argon makes up less than 1% of air and does not react with metal
parts.

Oops. Y'er correct. Only helium and neon will diffuse through glass.
Argon and larger gas molecules won't diffuse through glass.

The vacuum inside a tube is less than one millionth of atmospheric pressure.

Yeah, but the pressure differential is 14.7 lbs/sq-in. Over the
surface of the 6L6, that's about (assuming a cylinder):
Surface Area = 2 Pi r^2 + 2 pi r h
= (2 * 3.14 * 0.7^2) + (2 * 3.14 * 0.7 * 3.0)
= 16 sq-in
Surface pressure = 16 * 14.7 lbs/sq-in = 235 lbs.
(Yes, I'm guessing at the dimension for a 6L6 as I don't have one
handy). That's quite a bit of pressure pushing the helium and neon
atoms through the glass. Still, for helium, the diffusion rate is
slow (helium through pyrex at STP):
<http://teaching.matdl.org/teachingarchives/browser/trunk/matml/transport/problems/hepyrex-solution.pdf?format=raw>
8.0 x 10^-8 m^3/hr

Nitrogen mixed with a little CO2 makes a nice, white glow under low
pressure - its called a "Moore Tube"
http://en.wikipedia.org/wiki/Daniel_McFarlan_Moore
His untimely death was a bit shocking.

I guess his murderer didn't do a proper patent search before starting
work on his invention. We're more civilized these daze. Instead of
murder, we have litigation. It's much like murder in slow motion.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

 

[Phil Allison]

"Jeff Liebermann"
"Phil Allison"

When we talk about a "gassy" vacuum tube, it's not a leaky glass
envelope or seal.

** The term covers that eventuality too.

Ok. My bad grammar. I meant that if the tube is deemed "gassy", it's
probably not an air leak in the envelope or seal. It's more likely
gaseous diffusion of helium or neon through the envelope.

** Unfortunately, that idea is at odds with observations of tubes that show
internal glowing.

Egs: It happens to tubes that are used or not and are old or not PLUS most
even very old tubes show no sign of gas.

The only correlations I have seen are:

1. Certain batches all have the issue.

2. Tubes that have suffered long term overheating.

3. Tubes with visible corrosion on the pins and / or cracks in the glass
near the pins.



...... Phil

 

[William Sommerwerck]

Only helium and neon will diffuse through glass.

This is way OT, but Chicago Miniature Lamp claimed that helium diffusion
shortened the life of incandescent lamps.

 

[Cydrome Leader]

Phil Allison <phil_a@tpg.com.au> wrote:

"Jeff Liebermann"
" Jeff Urban"

If they need it and you fix it, and they pay you - WHAT
is disreputable about that ?

The lack of a certificate from the manufacturer attesting to my
competence.

** ROTFL - I doubt there is even one importer or manufacturer in Australia
capable of making that determination with any accuracy. After all, how
would any of them know ?? They are NOT operating repair businesses, have
no understanding of them and generally take no interest in the topic.

Anecdote:

One time, back in the 80s, I worked for a repair business that had
"authorised" service arrangements for several brands of guitar amp -
including Marshall, Acoustic and ELFA.

The Greek lunatic who imported Acoustic into Australia decided that he could
" micro-manage " the servicing of his brand by making up " kits " of spare
parts that all service techs would have to buy to repair various classes of
fault. All one needed to do was tell HIM the fault scenario and he would
nominate the kit that you needed to purchase. Ordering individual parts as
required was simply no longer an option.

He claimed to me on the phone that all the auto importers and makers were
doing the same thing and it was more " efficient ". Soooo, I told him about
the fault in the unit I had on the bench - that it suffered from loud,
very intermittent crackling noises. After a long pause, he said to ship the
unit down to him, in Melbourne, 500 miles away.

The boss and I did no such stupid thing, of course.

Anecdote 2.

A Melbourne based maker of guitar amps ( ELFA) had issues with their latest
models:

1. The quad op-amps ( all RC4136s) in the pre-amp section were from a faulty
batch ( rejects?) with about a 50% failure rate in the first 3 months. The
maker had earmarked all their remaining stock for manufacture and REFUSED to
supply any spares to us for warranty repairs.

2. Some nut case, probably as an after thought, had fitted stereo headphone
sockets to the amps with no series limiting resistors. The left and right
earphone connections were simply linked to the internal amplifier module and
the speaker connected itself when there was no plug in place.

Soooo, soon as anyone plugged a mono jack into the headphone socket - bang
went the Sanken 60 watt amp module inside. Then, soon as the mono plug was
removed, a 40 volt DC rail was linked to the 12 inch speaker and burnt it
out.

This is great, I laughed out loud over this one!