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Old 14th Feb 2019, 7:27 am   #1
Diabolical Artificer
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Default Baking or de-magnetizing toobs?

Came across this statement on an audio forum - " I used to bake them once a year. (There's a special heating procedure to activate the getter to eliminate gas.) Now I use demagnetization instead of baking, I suspect it works better than baking. (Demagnetize the tubes with a tape demagnetizer when the amp is on.) "

Pseudo science BS or sound practice? AFAIK the getter is activated by a big inductive current when manufactured, surely a tape de-gausser will do nowt.

Andy.
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Old 14th Feb 2019, 8:29 am   #2
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Default Re: Baking or de-magnetizing toobs?

It gives them something to do. The guy is probably frustrated that he can't get hold of liquid nitrogen and do the full cryo thing as well.

The getter was originally activated by heating the active metal to the vaporisation point to sputter it onto the inside of the glass. It isn't going to notice his domestic oven or him waving a demagger near it.

During manufacture inductive heaters took the whole of the interval metal structure up to red heat during pumping to accelerate outgassing of adsorbed/absorbed gasses so the pump could whisk them away and leave less for the getters to mop up after the bulb is sealed and the getters are fired. Again, the temperatures he'll be using are trivial.

Future anthropologists, on discovering evidence of these practices will just mark it up as a religious ritual. Compared to the biggies in the religious ritual field ( Human sacrifice and whether milk or tea should go first into a cup), this one will be left to moulder in an obscure paper in some peer-reviewed journal. Look up 'Cargo Cult' for something similar.

Besides, the guy hasn't yet discovered the importance of positioning his valves with respect to the Earth's magnetic field and ley-lines while demagnetising them. He's got years of fun ahead.

Maybe we ought to have a god of pseudoscience. Name suggestions?

David
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Old 14th Feb 2019, 9:02 am   #3
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Default Re: Baking or de-magnetizing toobs?

Well as we already have pseudo-Dionysius, perhaps Pseudo-Osram, the Saint of messing with valves.
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Old 14th Feb 2019, 9:54 am   #4
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Default Re: Baking or de-magnetizing toobs?

I'm not aware that magnetism has anything whatsoever to do with gettering. It will have no effect.

But temperature is a factor in getter effectiveness. The details vary with getter composition, temperature and the particular gases being pumped. But as a general principle getters will work to some extent at room temperature, will work better as the temperature rises up to some optimum value and then, in some cases at least, will start to re-release the absorbed gases if the temperature is raised too high.

If you've monitored the grid current in a valve (particularly an output valve) which is powered up for the first time after a long period of disuse you might well have seen, as I have, the current rise quickly as electron emission and impact ionisation starts, it continue to rise, perhaps over minutes, as the valve electrodes heat up and release absorbed gas, and then it slowly fall, over tens of minutes or even hours, as the getter comes up to the envelope temperature and starts to pump away the evolved gas.

So it's not impossible that some sort of baking might help. The trouble with baking is that you really need to get the getter hot without overheating, say, the valve's Bakelite base. That's usually easier to do just by powering the valve up.

Cheers,

GJ
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Old 14th Feb 2019, 10:00 am   #5
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Default Re: Baking or de-magnetizing toobs?

Good grief, I've heard it all now! I even stumpbled across a site which recommended de-gaussing CDs and DVDs! I thought the information layer was aluminium and the rest was plastic? I wonder if a certain Audiophool salesman flogs (expensive) devices for this purpose?
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Old 14th Feb 2019, 10:07 am   #6
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Default Re: Baking or de-magnetizing toobs?

Just had a wicked thought. David, with your overall brilliant explanations and author skills you would make a great "plant" in one of those audio forums. Using fake theories and suggestions the wind up possibilites would be endless!
Rob
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Old 14th Feb 2019, 10:41 am   #7
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Default Re: Baking or de-magnetizing toobs?

How do we know they're not all plants, each unaware of the others and all trying to rev each other up?

It could explain things.

"There's this guy in Cambridge working on laser cooling to create and stabilise a stylus and cantilever from metallic hydrogen. There's enough leak of cold to keep the moving coil assembly superconducting. All he needs to do now is get the cables and step-up transformer cold and superconducting. It ought to sound AWESOME" nicely ambiguous between Cambridge Cambridgeshire and Massachusetts

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Old 14th Feb 2019, 10:46 am   #8
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Default Re: Baking or de-magnetizing toobs?

Quote:
Originally Posted by G4YVM David View Post
Well as we already have pseudo-Dionysius, perhaps Pseudo-Osram, the Saint of messing with valves.
I like it. But to be glumly serious for a moment (it's a super-power of mine) these are old gods and already have names; greed, vanity, pride...

I learnt something today about the sociology of religion, having looked up Cargo Cults - thanks David. Audiophoolery seems to me to have something to do with Gnosticism - salvation through hidden knowledge only available to those having undergone induction into the cult, and layers and layers of such waiting to be scaled when you do get in and find you're merely a bottom-rank neophyte. Again, that's a very old idea!
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Old 14th Feb 2019, 10:53 am   #9
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Default Re: Baking or de-magnetizing toobs?

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Originally Posted by robinshack View Post
Just had a wicked thought. David, with your overall brilliant explanations and author skills you would make a great "plant" in one of those audio forums. Using fake theories and suggestions the wind up possibilites would be endless!
Rob
A different version of that exercise, where the competent are set against the incompetent, has been going on for decades Rob, first in the paper press (see Hi-Fi News, for example, after about 1976) and then online. When non-specialist readers are faced with two competing explanations then how are they to know who's right and who's wrong ? I've been a member of audio fora for years and so have a lot of other competent electronics people. There can be genuine and lively (and sometimes very angry) debate there. But complete consensus tends to be reached only when the membership has narrowed itself down to a smaller group of the like-minded. People call this the 'echo chamber' effect where I only join groups in which everyone thinks the same way that I do. We then all reinforce one another's opinions and life is calm.

That's not to say that rubbish can't be refuted. But it does take a good deal of care and clarity and, sometimes, quite detailed work. The most important thing is not to start out by telling anyone that he's stupid or gullible. We might think he is. Indeed he really might be ! But telling him he is will guarantee that we fall at the first fence.

Cheers,

GJ
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Old 14th Feb 2019, 11:14 am   #10
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Default Re: Baking or de-magnetizing toobs?

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Originally Posted by G4YVM David View Post
Well as we already have pseudo-Dionysius, perhaps Pseudo-Osram, the Saint of messing with valves.
I will not enter the debate on heating or de-magnetising vales... what next.

But the patron Saint of valves is St. Alexander (or St. Getterix for the Roman speaking types).

Alan
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Old 14th Feb 2019, 11:23 am   #11
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Default Re: Baking or de-magnetizing toobs?

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Originally Posted by robinshack View Post
Just had a wicked thought. David, with your overall brilliant explanations and author skills you would make a great "plant" in one of those audio forums. Using fake theories and suggestions the wind up possibilites would be endless!
Rob
Sadly, as a frequenter of one of those audio forums I can tell you that no amount of technical explanation overcomes belief in this type of foo and as for the wind up possibilities it is so easy as to be pointless.

Mains cable lifters anyone?
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Old 14th Feb 2019, 11:50 am   #12
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Default Re: Baking or de-magnetizing toobs?

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Sadly, as a frequenter of one of those audio forums I can tell you that no amount of technical explanation overcomes belief in this type of foo ...

Mains cable lifters anyone?
I see your 'mains cable lifters' and I raise you 'aligning your fitted carpet's gripper rods, since these can clearly affect the EM field in the room'. Sadly that one really did come up.

Cheers,

GJ
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Old 14th Feb 2019, 12:19 pm   #13
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Default Re: Baking or de-magnetizing toobs?

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Originally Posted by GrimJosef View Post

I see your 'mains cable lifters' and I raise you 'aligning your fitted carpet's gripper rods, since these can clearly affect the EM field in the room'. Sadly that one really did come up.

Cheers,

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Old 14th Feb 2019, 12:21 pm   #14
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Default Re: Baking or de-magnetizing toobs?

Demagnetising valves? Well, if they are magnetised, yes it will, affect electron flow. After all, colour CRT's look seriously wrong when this happens.

I'm wondering if he has got as far yet as demagnetising the valve in his microwave oven. Somehow I can't see it improving performance...
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Old 14th Feb 2019, 12:29 pm   #15
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Default Re: Baking or de-magnetizing toobs?

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I like it. But to be glumly serious for a moment
Just for a moment perhaps, then onwards and upwards!
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Old 14th Feb 2019, 12:36 pm   #16
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Default Re: Baking or de-magnetizing toobs?

Operate your EF86 heaters from 8.2 volts, this releases more electrons and gives a richer sound with a more authoritative bass and clearer sound-stage.
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Old 14th Feb 2019, 12:47 pm   #17
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Default Re: Baking or de-magnetizing toobs?

This is good!

Yup, restoring old radios and pre-war tellies is a relatively sane interest.

Just a matter of having a suitable comparison standard. I'm no longer thinking of having a stone circle installed in the field outside our village to shift the ley lines so I don't have to change the layout of the cables in my living room.

To take a step beyond Peret Walker's sign, Scientific method rules here.

David
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Old 14th Feb 2019, 12:57 pm   #18
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Default Re: Baking or de-magnetizing toobs?

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Originally Posted by GrimJosef View Post
But temperature is a factor in getter effectiveness. The details vary with getter composition, temperature and the particular gases being pumped. But as a general principle getters will work to some extent at room temperature, will work better as the temperature rises up to some optimum value and then, in some cases at least, will start to re-release the absorbed gases if the temperature is raised too high.
So it's not impossible that some sort of baking might help. The trouble with baking is that you really need to get the getter hot without overheating, say, the valve's Bakelite base. That's usually easier to do just by powering the valve up.
I thought that the getter was largely barium, if not completely so. The fact that it gets spread around on the inside of the glass envelope increases the surface area. I suppose that it is possible that some gases might be simply adsorbed, but I suspect that oxygen (certainly) and nitrogen, which form the majority of air, are chemically combined with the barium. You can see that the getter has turned into a white powder (barium oxide) when the vacuum in a valve has failed drastically for some reason. No amount of heating will "liberate" the oxygen.

I know this from an exercise I did years ago to make barium nitrate from barium oxide - you need fuming nitric acid and patience.

Colin.
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Old 14th Feb 2019, 3:01 pm   #19
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To take a step beyond Peter Walker's sign, Scientific method rules here.
I thought it was "Ohms Law Rules Here", more authority (pun intended).
 
Old 14th Feb 2019, 3:22 pm   #20
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Default Re: Baking or de-magnetizing toobs?

Hence the "a step beyond" phrasing. I didn't want to leave out Kirchoff, Lenz, Newton, Dirac, Heaviside, Rayleigh, Kelvin, Maxwell, Boyle,..............

David
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