Magnet too close to tubes?

[rockon1]

Just fitting this speaker in my amp. Its big magnet sits directly under the tubes. They are in its magnetic field but barely (I think). Ive heard of cases where a tube can be messed up if its too close. Amp works fine and I dont see anything funky happening. Im assuming its fine ...so how close is too close? Bob

http://i42.tinypic.com/o73ihz.jpg

[edgewound]

...so how close is too close? Bob



Probably if you broke a tube.

I wouldn't worry about it. Looks fine.

[Jade]

Holy Crap! With the size of that speaker magnet, I'd guess most everything in the same zip code is in it's magnetic field!! LOL

Just kidding, I'm with Edgewound, I wouldnt worry about it.

Jade

[GearHeadFred]

You think that's bad? I have an EVM12L in my Blues Junior! Maybe the electrons get curved a little.... but it sounds good!

[rockon1]

Thanks guys. I didnt think it was too close but I have heard of cases where they can be figured I'd check. The 6V6 directly above the magnet is 3/4 inch away. Kind of cool having a speaker made in Leeds in the amp. Its a neutral, punchy speaker. Bob

[donnyjaguar]

Without question the magnetic field will impact the flow of electrons from cathode to anode. Guessing in this case it'll pull them toward one part of the plate. Whether this will impact performance is something you can test for. Run the amplifier into a non-inductive load and measure gain whilst moving the speaker in and out of the cabinet.

[VacuumVoodoo]

If you put a steel/iron tube in a magnetic filed, what will the magnetic field inside the tube be? Right, zero or very close to zero. The plate IS a shield around the cathode and grids.That's also why electron tubes don't fail when exposed to EMP from nuclear explosion. Neither will your speaker magnet affect the amp.
On a side note, old TV CRT picture tubes were not magnetically shielded and therefore placing speakers close to them often resulted in weird distortions of the picture.

[Swarty]

I wish I had that much clearance in my '51 Deluxe. I have about a 64th of an inch, they butt right up to the back of the magnet of an old G12H 75hz (I had to take the plastic cover off or there was no way!).

[donnyjaguar]

If you put a steel/iron tube in a magnetic filed, what will the magnetic field inside the tube be? Right, zero or very close to zero. The plate IS a shield around the cathode and grids.That's also why electron tubes don't fail when exposed to EMP from nuclear explosion. Neither will your speaker magnet affect the amp.
On a side note, old TV CRT picture tubes were not magnetically shielded and therefore placing speakers close to them often resulted in weird distortions of the picture.

No disrespect intended here but...

No, there will certainly be a magnetic field present inside the tube. Plonk a compass on a steel plate and introduce a magnet to the underside and you'll see.

The EMP issue is more to do with the fragile ESD sensitive PN junctions of semiconductors. In a tube the distances are far greater.

A picture tube is no more magnetically shielded than a 6L6GC.

As for the amp in questions, my advice is to test it and see if there is any negative effect such as hot spots on the anode or decreased (or increased) gain.

[alexandergj]

Re: valves too close to speaker magnet

see http://www.chambonino.com/work/miscguitar/misc6.html

This guy knows his stuff.

[VacuumVoodoo]

No disrespect intended here but...

No, there will certainly be a magnetic field present inside the tube. Plonk a compass on a steel plate and introduce a magnet to the underside and you'll see.

The EMP issue is more to do with the fragile ESD sensitive PN junctions of semiconductors. In a tube the distances are far greater.

A picture tube is no more magnetically shielded than a 6L6GC.

As for the amp in questions, my advice is to test it and see if there is any negative effect such as hot spots on the anode or decreased (or increased) gain.

Uhmm...I think I need to do some experiments and verify. Chamboninos encounter with the Laney is very interesting.

[JerryP]

I've had issues with tubes too close to the speaker in a Mesa MK1.
Jerry

[rockon1]

In my case the edge of the magnet is directly below the tube. Im thinking its less likey to be an issue than if it was along side the magnet? Bob

[donnyjaguar]

Thanks for the link. I should really do something similar for all the unusual conditions I've come across. Most of them from my own builds. :)