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How the magnetic affect the sound of tube amplifier

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Today we receive a lot of thulium magnetic for a researching project (they are super strong magnetic!). The EL-34 PP amp came into my eyes when we were discussing about the project. A strange idea came into my brain suddenly: the magentic can affect the moving path of electron, and the tube is working based on electron emitting and moving, so how will the magnetic affect the tube amplifiers?

I decided to give a try. I have 3 tube amplifiers in the office: a EL34 PP amp, a 12ax7+6N1 tube headphone amp and a 6F3 3W small SE amp. After power on them for a few minutes, I put a magnetic close to the tubes and wave it. There's nothing happen when wave near EL34. But when put the magnetic close to the preamp tube 6N2 of EL34 PP, clear "pop" sound can be heard in the speaker. Then I tried with headphone amp and 6F3, both have clear "pop" sound when wave the magnatic near the preamp tube. But no clear sound can be heard at the power side.

I don't have time to listen how it affect the sound quality. And I don't have golden ears to distinguish the differences. But I think it's a interesting test, gurus with golden ears can try to listen to the sound quality affected by the magnetic, maybe there'll be some amazing result:p
 

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Joined 2010
While I think about it,

put one by a magic eye tube and thats it as well the electron flow will be stuffed..unless you can demagnetise it.. the display will be distorted..

Its good fun though if you don't mind wrecking an EM80 etc..watch the display twist as the electrons are pulled and pushed about..


Regards
M. Gregg
 
Well, if the magnetic can distortion the cateye, it must have some effect on the performance of other tubes. I know the electron beam is enclosed in a small metal enclosure, but there will be effects, more or less. I think some one can find the differences, becuase some declare they can find the difference between 2 power supply cables...
 
A static magnetic field will bend a beam of electrons - that is how a TV CRT works. It won't make much difference to a triode, because all the electrons end up at the anode eventually.

I can just see the next 'audiofool' trend! Take a 5 dollar magnet, put it in a 2 dollar ceramic case, and charge people 95 dollars for a "static field audio enhancer".
 
Disabled Account
Joined 2010
A static magnetic field will bend a beam of electrons - that is how a TV CRT works. It won't make much difference to a triode, because all the electrons end up at the anode eventually.

I can just see the next 'audiofool' trend! Take a 5 dollar magnet, put it in a 2 dollar ceramic case, and charge people 95 dollars for a "static field audio enhancer".

Ohhh can I have one..LMAO

:D :D

Scan coil degauss chassis unit 10$ a pop return every 6 weeks works even better on non ferrous chassis...LOL

Regards
M. Gregg
 
A really, really interesting issue here !

This caused some serious head scratching here. SY's experiments are interesting, but that can't be the full story.

A Tube can be approximated by Child-Langmuirs-Law:
2d1678e4f273bc05ba470ab9b278da7a.png

There is not any simple way of putting the B-Field (or its vector potential) directly into that. It gets really ugly really fast here.

But if you put a magnetic field through the tube, from top to bottom or the other way round, the electrons are deflected and move in circles:
An externally hosted image should be here but it was not working when we last tested it.

Now, as the field gets stronger, more and more electrons will just orbit around the cathode (they can loose energy because of scattering).
Sadly, this depends on the velocity which the electrons come out of the cathode whichthis is distributed by some famous function (Gaussian, Maxwell Boltzmann or something)

So a (static )magnetic field MUST have some influence. A Magnetron in your microwave works exactly in that way (Radar Basics - Magnetron)

Maybe I can find some additional information.

I can just see the next 'audiofool' trend! Take a 5 dollar magnet, put it in a 2 dollar ceramic case, and charge people 95 dollars for a "static field audio enhancer".
:D:D:D
Yes, that would be the easiest way of making some $$$ without ever having to look at a formula
 
The pathlength of the electrons is on the order of millimeters. Spacing between the electron stream and the magnet is on the order of a centimeter. The potential between cathode and anode is on the order of 200V. So you can readily calculate the velocity of the electrons, the strength of the field, and consequently the deflection of the electrons.

Or you can stick a magnet near a tube and see that it doesn't really do anything.
 
Magnet on tubes is a BAD idea. Learned that the hard way: Guitar combo amp with an output tube right next to the speaker, prone to rattling the tubes. I installed spring loaded retainers on the tubes to see if that help. Then I'm wondering why the tubes (thin bottle el34s) keep shorting and burning up.

Played around with tapping the tube and at some point figured out adding/removing the retainer made the difference. The retainers (steel) had became magnetized themselves, due to contact with the speaker magnet, and were attracting one of the grids, or supporting parts, and shorting it to another element. Back to the stock 'bear trap' retainers, and all was well.
 
There was some talk about demagnetising valves in Electronic Engineering, July 1948, which generated some interest (see Dec 1948). It was observed by more than one person that magnetising an EL37 could increase heater hum, which could be cured again by demagnetising it. Most interestingly, the reports suggested that the effect was very consistent in triode mode, but apparently random for pentode mode.
I don't know if anyone got to the bottom of it though.
 
SY, yes, the effect negligible when using usual audio tubes.

I found the original article of Albert W. Hull, the "inventor" of the magnetron.
I can't attach it here because the filesize is too big. (PM me your Mail adress if you need it)
In that article is a nice diagramm of a tube in an adjustable magnetic field.
The results are some nice triodish curvers:

An externally hosted image should be here but it was not working when we last tested it.


So this is some kind of current controlled tube.
 
I could never hear any difference, but I noticed long ago that a magnet could move the blue glowing spots around on poor quality tubes (glowing because of a little gas, poor vacuum). I suspect that a very slight difference might be measurable if not heard near clipping in beam pentodes since the changed path would be a little different due to the beam plates and ribs inside the anode. After reading that scientists had found ways to control right-hand versus left hand spin of electronics, I thought about writing an April Fools Day article about getting stereo amplification out of individual tubes using opposing spins. Magnets would fit in there somewhere! I wonder if any have tried magnets on sheet beam demodulator tubes. They're what Zenith used to get around the RCA color tv patents, like pentodes but having two plates, and deflector electrodes that could switch the flow back and forth between plates. HP also used to make a counter tube where a pulse would made current jump from one anode to the next. Magnets might mess with that.
 
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