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georgehifi 5th March 2005 01:22 AM

Proof that demagnetizing tubes works
I've started a new thread on this, as this new visual proof that demagnetizing tubes has a significant effect in reducing the noise floor of the tube, thanks to John Swenson from Audio Asylum for the effort he's put in to get conclusive proof that demagnetizing tubes works.

Cheers George

Sch3mat1c 5th March 2005 02:09 AM

Now remagnetize it and complete the proof. Also, make note of the values of noise and distortion reduction, and run controls.


georgehifi 5th March 2005 02:36 AM

What blows me away is up to 36db of noise difference around the 3k and 10k mark. For those of you who did'nt realize the db scale is over on the right, (use the horizontal slider).
I demaged my tubes using the simple Radio Shack tape head demagnetizer, they can be found on ebay second hand for around $5.00, take the tube out stand it upright on a table and circle it half a dozen times slowly spirling upwards till your 6 or so inches away from the top of the tube, keep it about half an inch away from the side of the tube as your doing it as i think that touching it maybe too close.

Cheers George

DigitalJunkie 5th March 2005 03:34 AM

Hmm... Curious..

audiousername 5th March 2005 05:45 AM

This data has been discussed here previously. I'll try to dig up the thread then post a link.

audiousername 5th March 2005 06:03 AM

After digging through 20 pages of SY's posts, here 'ya go.

georgehifi 5th March 2005 06:05 AM

Yes it has Jason, but not the link to the at the startof this thread , if i posted it in the other thread it would have been buried at the end of 44 posts.

This is a very enlightening graph(study) that John Swenson has measured, and i belive that it deserves a re-discussion, as too many doubters poo bared it without any proof of the contrary in the old post that i started about it.
This new one has had 95 reads in 2 hours, that's got to be proof of being popular for some to read. Even the doubters.

Cheers George

audiousername 5th March 2005 06:11 AM

Yes, it does seem to be popular.

You must note that the 6AR8 is a beam deflection tube, and is far from the average audio valve. It would not surprise me if that this particular valve is sensitive to magnetic fields deflecting the electron beams within it.

Even if it is proven that it is measurably beneficial for the 6AR8 to be demagnetised, the result cannot be generalised to all valves.

georgehifi 5th March 2005 06:28 AM

From what i've read of his posts on this tube(6AR8), it's used in his BDT Preamp which is comparable to the very nice but expensive Melos preamps, and his test on demagnitization are using audio frequency from 20hz to 20khz.
So it looks as though this tube can be used in audio.

Cheers George

audiousername 5th March 2005 06:31 AM

I do not doubt this valve this can be used for audio. Heck, you can whip up a volume control with a hexode if you felt like it.

My point was that the internal construction is atypical of common audio types, and the results from any investigation into the demagnetisation of 6AR8s cannot be generalised to all valves without further investigation.

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