Baking or de-magnetizing toobs?

[Refugee]

Heating a valve will not help a great deal.
If a valve has started to slowly go to air firing the getter again might help in the short term however the leak will not have been sealed and the valve will continue to slowly go to air.
You might be able to make valves change there performance by applying a powerful magnet to them. This would be due to the magnetic field deflecting the emitted electrons between the electrodes as is the case in a TV tube. Anyone with a valve tester and a magnet can try this.
The least productive thing I have seen done often is putting speaker cables on little pylons to keep them away from something in the floor only for them to now be closer to mobile phone and other RF signals. You can try this too. Just poke a phone into the cabinet of an amplifier and send a text.
As far as heating goes the getter material has to be heated until it glows and this is hot as the melting point of glass. The valve has to be placed in an air cored coil that is fed with a linear amplifier and signal generator tuned to a harmonic that matches the size of the getter holder in order to get it to fire without melting the glass.
If anyone gets too enthusiastic with firing the getter the heat can weaken the weld causing the getter holder to fall off and rattle around inside the valve. The valve would be scrapped for this at the time of manufacture but for us it would have to be mounted in a position that avoids the loose holder causing a short circuit.

[Diabolical Artificer]

So pseudo science BS it is.

Yep, know a little about cargo cults David, it's also been posited that future generation's might concur we worshipped the car; we do odd things like touch wood, are suspicious of black cats/birds and believe a fat man delivers presents.Valves/toobs do appear to have gained a cult following with attendant ritual's.

I've just tested some valves for grid current GJ, interesting stuff.

Andy.

[ColinTheAmpMan1]

Originally Posted by Radio Wrangler

Cambridge Cambridgeshire and Massachusetts

It may be worth pointing out that Cambridge, Massachusetts is where MIT (Massachusetts Institute of Technology) is located, so not to be sniffed at.

Colin.

[Radio Wrangler]

That was the reason for the choice


dAVID

I see, thanks for the correction, science is good, here (in this thread) we have seen what happens when it is ignored.

[Radio Wrangler]

I can understand the fixation with vacuum tubes in the UK. It's the power of advertising. For decades we were hit with saturation advertising every winter telling us that they have aphrodisiac properties. There would be images of someone with a cold, while the voiceover relentlessly told us that "Choobs help you breed more easily"

So it's all TV adverts' fault!

David

[G6Tanuki]

If baking or de-magnetizing tubes made any difference, I'm sure it would have been mentioned/documented by the major manufacturers when valves were still seriously-mainstream items.

The extra costs of such techniques would have happily been absorbed by the military/aerospace sectors if it helped cut intermodulation-distortion in linear-amps by a few dB.

As it is, I trust in the likes of Saint Eimac and his acolytes, as handed down to us in the sacred scriptures entitled "The care and feeding of power-grid tubes".

See https://www.cpii.com/library.cfm/9 and achieve enlightenment.

Can we have a subsection here in "Components and Circuits" called comedy and/or satire?

[stuarth]

How about superfuses, 13A fuses for each item in your hifi setup. Only £25 per fuse for increased clarity and speed of the sound. Increased speed Perhaps it’s a clue about what these people are on.

Stuart

How about superfuses

Fuses, pah, just replace the live pin of a 13A plug with a neutral pin from another plug and wire direct. All gold plated (solid is preferred) of course.

[G8HQP Dave]

Originally Posted by GrimJosef

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.

I have several time been accused of calling someone 'stupid' on an audio forum, when all I did was tell him that he was wrong i.e. what he was saying was not true. Some people don't like being contradicted.

[thermionic]

........Don’t forget about the practice of fitting a ring magnet around the PL81 line output valve in some 405 line TVs, to negate the Barkhausen effect....

If they get to know about this, then magnets around audio output valves could be the next money spinner. 😜

[Karen O]

I've often wondered if car boot sales will be regarded as a religion in the distant future. Large numbers of people congregating on the Christian Sabbath... I've even worked out some scripture: blessed are the organiser, the vendor and the mug. The vendor bringeth and the mug taketh away. Attic to attic, mug to mug.

[Andrew B]

car boot sales

Even the quality of tat on sale at the boot sales has gone way down, soley seem to consist of broken mobiles and junk plastic goods the kids got a few christmases ago.

[Karen O]

I recall in a hobby mag back in the 70s an April fool's joke (or at least, I hope it was an April fool's joke) which recommended replacing the electrons in your speaker cable by putting a battery across them. I did some calculations at the time, and concluded that it would take a geological era to completely replace all of the electrons, even assuming that none completed the circuit.

Yes, the quality of car boot sales is not what it used to be...

[Dave1000]

Hmm, baking or demagnetising...……

I hope that I have picked-up the jist of the thread while scan-reading, especially as I am a technical non-starter with valves...

Anyway, I worked in a lamp factory for quite a while and making valves is no different to making lamps - believe me - some factories have been back and forth between the two and it is no coincidence that the major valve manufacturers were making lamps long before valves.
Re-firing getters...………………… The whole idea is to deliver all the barium that a getter has to the jacket/bulb wall when first fired. That said, all of the getters were fired using induction heating when I worked in the lamp factory. How were they fired back in the 50's-60's?

Demagnetising? Nickel is magnetic - common enough in lamps, but in valves?

Cryo treatment was new to me a few months back, so I Googled and some interesting papers came up, about metallurgy applicable to valve, but cryo treatment is one serious long way from freezing.

[julie_m]

Plus, the valve is evacuated. There's no way for heat from outside to get conducted inside, except through the glass and the external pins. There is not much radiant heat; and the anode won't be able to absorb any more radiation than it could emit under fault conditions. I doubt that sticking a valve in an ordinary kitchen oven is going to have as much heating effect on the internals as just running it in-circuit!

Still, I suppose it keeps these people off the streets .....

[Dave1000]

If the effects of radiation and conduction were quite as extreme as you imply, lamp bulbs/jackets would not get hot.

On modern machinery the best vac' you'll get in a jacket is about 10^-2 Torr, the getter takes it down one decade. That is with silicone oil diff' pumps. On older systems, they will have used mercury diff' pumps where the lowest pressure is limited by mercury vapour pressure - I do not know what the getter takes that down to.
Anyway, there is still an astonishing amount of gas inside a vacuum jacket - it may be around one millionth of an atmosphere, but it is also roughly a millionth of Avogadro's number of molecules (per 22.4 litres at STP), and Avogadro's number is? Around 10^26 if memory serves.

I did not ask what it was, but when doing some lab bench tests I inadvertently discovered the enormous jump in the effectiveness of thermal insulation between 10^-2 and 10^-3 Torr. I was assured by someone with FAR better Physics knowledge than me, that there was a very good reason for this.

[julie_m]

Originally Posted by Dave1000

If the effects of radiation and conduction were quite as extreme as you imply, lamp bulbs/jackets would not get hot.

Well, they don't, really, on the big scale. Tungsten filament bulbs used to get unbearably hot to the touch, but the filament inside was white hot -- the sorts of temperatures where forgetting to add 273 isn't going to make your answer that wrong. So there is definitely poor thermal transfer (and in a light bulb, there are plenty of molecules of gas to carry KE around).

Still, a more rigorous treatment than will fit on the back of a "ten papers left" slip is always welcome .....

[Dave1000]

Tungsten lamps are also nitrogen-filled (to about 10 Torr absolute IIRC).
Plenty of valves get to dull orange/red in part - so around 700C (IIRC again).