• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Anyone got any opinions on this?

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Well electrons in motion are deflected by magnetic fields that cross their path. I won't go into details but check some school physics books. So electrons traveling from cathode to anode will have their path altered by any magnetized parts within the tube or by magnetic fields comming from outside. This will have the same effect as changing the tube geometry and hence the tube characteristics. So demagnetising the tube will put everything right again. Now if the effects of magnetized tube parts is audible I don't know.

I vaguely remember doing an experiment in school that involved winding a coil around a tube and passing a current through it thus causing a magnetic field in the tube. If the coil current is turned up enough the tube would cut off. I don't remember the magnetude of that field though.

Just now I held a powerfull magnet up to a 5687 in my amp and I could feel the attraction to the tube. So magnetization is surely possible. Did not here any effect on the sound though.

Damn, now I have to demagnetize my tubes.
 
diyAudio Senior Member
Joined 2002
Hi,

Tubes contain ferrous materials so , yes, they can become magnetized....
Whether that affects their performance is a different matter.

However, by using the force of a magnetic field it's not unthinkable that some parts inside a tube can be dislodged.
IOW, I'd be careful with a strong magnetic field in proximity of electron tubes, you may just as well cause some permanent damage IMO.

If you're convinced demagnetizing makes an audible difference, there are more "gentle" means around to do just that.

Cheers, ;)
 
Especially for AC, read music, currents inside a tube or conductor travel with an electric field. An alternating electric field goes together with an alternating magnetic field.
This is what we learned at school, some long time ago.:rolleyes:

And just like Heater mentioned, in every CRT electrons in motion are deflected by magnetic fields that cross their path.

I just happen to have a worn out 6DJ8 and a 12AX7.
Broke the glass and removed it.
Got a magnet and hold it close to the internal parts.
I was surprised, the Anode, Getter, and all the supporting metal are all attracted by the magnet on both tubes.
This I didn't expect.

We have to demagnetize our tubes !
Now, is there somebody who can clearly here the difference when a tube has been treated ?
 
BTDT = there was a big huge thread started here (on the Else forum?) a while ago, from the same thread, AAMOF. Consensus was an uneasy "it might do something but for the most part, no". Akin to resistors, capacitors and wire, but plausible this time. (Hey, you're modifying the dynamics of the active device. Now you can actually change things. For the better? Probably not.)

FWIW, nickel, like mild and silicon steels, doesn't retain a significant magnetic field. It's not a magnetically hard material.

Tim
 
"Magnetic force is a tiny, tiny horse."

It would be a nice project for an enterprising physics student to:

1. Measure the remanent magnetism on a variety of tubes and tube structures to see how much is ever there.

2. Taking the biggest number and doing some simplifications estimates on geometry, calculate the order-of-magnitude magnetic force on the electrons.

3. Calculate the order-of-magnitude force on the electrons from the applied electric field.

4. Compare 2 to 3.

While you're worrying, think about the effect of that magnetism on the population of the "up" and "down" spin states.
 
We have to demagnetize our tubes !


I think so, there was a definate change for the better i belive.
What we need is a few more (voodoo sceptics) to try it and give their impressions. (common Frank give it a go, does`nt cost anything, we know the Belgiums are tight with their money, so this should be right up your alley, you should hear something on your high res system) wish someone could measure what`s going on.

Cheers George
 
BTW I'll reflash your tubes for 'ya. They sound clear and brighter. The sound stage really...glows... searing hot highs... :D

http://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat1.html

(It's not shown but I've heated the rather large chunk of getter and support structures on top of a 6BM8 to approx. 1500øF. With a better coil and more power I can do sides.)

Since this is inductive (strong AC magnetic field), it also demagnetizes things...so it's on topic mmmmm'k. ;)

Tim

P.S. FWIW, I didn't notice any change in the getter on the glass after doing this.
 
diyAudio Senior Member
Joined 2002
Hi,

(common Frank give it a go, does`nt cost anything, we know the Belgiums are tight with their money, so this should be right up your alley, you should hear something on your high res system)

It seems to me you're confusing us lot with our neighbours up North but never mind...

Still, I already tested that quite some time ago and occasionally demag my entire system with a Densen CD.
That certainly works for me.
With tubes costing an arm and a leg, some of them almost irreplaceable, I'm rather cautious. I'm sure you understand.

DENSEN DEMAG

Cheers,;)
 
The reason behind this is that small magnets in the signalpath are, with time, orientated in one direction. This produces a detrimental effect on the signal. The DeMagic signal actually relocates the magnets, and thereby breaks the magnetic field and it's negative effect on the sound.

aahhhHAAAAHAHAAAAHHH!! I'm sorry Frank but that just goes in the joke bin! Seriously man!

Tim
 
FWIW, nickel, like mild and silicon steels, doesn't retain a significant magnetic field. It's not a magnetically hard material.

Exactly. It occurs to me that that only a magnetized grid would have any effect on the action of the electrons (a shift in the space charge?), but the grid is usually molybdenum wire so any magnetic field (if any) would be extremely weak. I don't see how a magnetic field of any magnitude would affect noise in a tube.

John
 
Here`s one to think about, have you ever got hold of a great used tube that`s in good condition, that has`nt be fired up for years and thought wow this is a great tube, only to find that after a few months that it has lost it`s wow factor, just maybe the tube has become magnetised, and lost it`s wow factor. I know it`s happened to me more than once. Maybe because it has`nt been fired up for years it demagnetised itself, just a theory.
Cheers George
 
diyAudio Senior Member
Joined 2002
WOW AND FLUTTER IN THE GUTTER...

Hi,

Seriously Frank if you have an old Tandy demagnetiser (nearly everyone had one back in the good old cassette days) give it a go on some of you old tubes.

Now I'm sure you guys are going to tell us all what it was that needed demagnetizing and how that worked too?

I'm not here to give courses in electronics but maybe some could do with a refreshment course?
Especially those of you toying with words such as space charges and such??:rolleyes:

Why bother with demagnetisation if you clearly don't have a clue what it's about in the first place....Tssskkkk....

I see it coming already but no, I won't explain how a demagnetizer works.:whazzat:

Cheers,:rolleyes:
 
I used to use a massive revox unit to wipe 1/4 tape. I think the way it was explained to me was that it set all the fingers on the surface of the tape straight up and down. Don't think it would be good for "refreshing" tubes though, I remember picking up barbells with it.:D
 
georgehifi said:
Here`s one to think about, have you ever got hold of a great used tube that`s in good condition, that has`nt be fired up for years and thought wow this is a great tube, only to find that after a few months that it has lost it`s wow factor

Yeah, it's called "novelty". You get used to having this "Great, new thing, wow!" and all the flaws dawn on you. Same thing happens even to me after building an amp. I usually maintain my objectivity though. Also applies to any other reasonably complicated device, cars for instance. Just human nature.

Tim
 
Why bother with demagnetisation if you clearly don't have a clue what it's about in the first place....Tssskkkk....
Comming from the man who thinks white noise on a cd is the holly grail.

Because Frank, that`s the only thing i did to create a sound change in the system, and it was because of the demagnetiser that the change happened, please unless you`ve tried it, do`nt comment, unless you can come up with a plausable believable answer, have an open mind until someone can close it with proven fact.
Mate i was a non believer just like you, (voodoo), until i tried it.
Something happens

Cheers george
 
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