Tweeks on tubes - bring out the demagnetiserss - diyAudio
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Old 31st July 2004, 08:19 AM   #1
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Default Tweeks on tubes - bring out the demagnetiserss

There is a thread on the Tube Asylum about this tweek. It is to do with demagnetising tubes. Many guys are skeptical about this.
So the only way to find out is to try it out. So all you need is an old speaker . You can break it and take out the magnet , unless you have a demagnetiser.

I used a ferrite magnet from a 6 inch speaker. Be careful because my 6922 tube almost crashed into the magnet when I took it close to it. I passed the tube through the middle of the magnet a few times and then slowly drew it away till it was about two feet from it.

The tube is used in a unity gain buffer stage .
When introduced between my DVD-A player and the amp it robs the music of 'air and hf cleanliness'. Simply put, it sounded duller than a direct connection between DVD-A and amp.

After the tweek it sounded far better. No other changes were made. It is still not as good as a direct connection but it no longer sounds dull. I am floored. I never expected this. Try it out and let us know what you find. I don't know how well this works with tubes that are run in for a long time.
I would really like to know what you find.
Cheers.
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Old 31st July 2004, 04:35 PM   #2
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I've got some weird effects from magnets, putting blue glow spots on the glass in places even the sun doesn't shine and cutting off the tube by bending the electron flow around a bit too much (good way to burn up the screen grid in a beam pentode, I'm sure).

Nickel, the common metal used for plates and such, though magnetic, has an insignificant residual field. That's why it's used in many transformers and not permanent magnets (Alnico alloys aside, but those contain another ferromagnetic element or two). Any magnetic field will only be deleterious to the operation of a tube anyway. And lastly, you know what makes a magnetron work? Magnets!

Tim
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Old 31st July 2004, 05:10 PM   #3
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Tim, your point is a good one- if we want real, demonstrable effects, we ought to be talking about the use of magnets to modify electron flow in tubes. Now, THAT is a tweak.
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Old 31st July 2004, 08:53 PM   #4
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I passed the tube through the middle of the magnet a few times and then slowly drew it away till it was about two feet from it.
I could be wrong, but would this not *magnetize* the tube instead? I always thought you required an AC field for demagnetization. How can the unchanging, polarised flux of a permanent magnet cause demagnetization?

Take care,
Doug
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Old 31st July 2004, 10:16 PM   #5
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Default demagnitiserssssssssssss

Yep, that too. I figured it was a typo...
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Old 1st August 2004, 12:07 AM   #6
jlsem is offline jlsem  United States
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I could be wrong, but would this not *magnetize* the tube instead? I always thought you required an AC field for demagnetization. How can the unchanging, polarised flux of a permanent magnet cause demagnetization?

A magnet has two ends; the north pole has positive magnet force and the south pole has negative magnet force. You can demagnetize a tube by waving the south pole end over it with a counterclockwise motion. To remagnetize it, just wave the north pole end over it with a clockwise motion. Vice versa for Australians and New Zealanders.

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Old 1st August 2004, 12:42 AM   #7
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Quote:
Originally posted by jlsem
A magnet has two ends; the north pole has positive magnet force and the south pole has negative magnet force. You can demagnetize a tube by waving the south pole end over it with a counterclockwise motion. To remagnetize it, just wave the north pole end over it with a clockwise motion. Vice versa for Australians and New Zealanders.
Sorry, but that won't work. When you try to demagnetise something by reducing the forcing flux to zero, you are always left with the remanent magnetism. Because this is a fixed proportion of the forcing field, the only way that you can demagnetise something is to take it through successively smaller cycles of demagnetisation until the remanence is effectively zero. That's why demagnetisers run off AC and why you gradually pull them away from the thing to be demagnetised (perhaps a tape head).
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Old 1st August 2004, 01:02 AM   #8
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jlsem, would you please give EC8010 his leg back? It came off accidently when you pulled it.

Doug, you're making a logical error and assuming logic.
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Old 1st August 2004, 01:21 AM   #9
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Sorry, but that won't work.
I have never actually been to Australia or New Zealand.

John
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Old 1st August 2004, 06:18 AM   #10
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Default Doug is right.

Actually one will need an ac generated magnetic field that slowly decays to zero.
In my case it was a dc field but I did oscillate it out of the magnet where it would see a varying field and drew it away reasonably far from it. Not as good as an ac field but better than a static dc field.
It however made a difference !
Cheers.
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