How to identify mu metal?

[RoadrunnerOZ]

It is highly magnetic and does not unroll easily. The edges are sharp.

Sounds like MU metal

 

[Murdock]

Unfortunately, my Varian 360 MS at home keeps blowing my 16A room fuse, so this test is not possible.

okay, I will test that. (I have done it, known Mu metal as well as other possible materials are very magnetic, I can not see any saturation)

Here are a few examples of materials that I would like to test:

Shielding material for a input and mains transformer

View attachment 141381View attachment 141382

or this very soft sheet metal. You can find it in old tube R2R recorder, where it is wrapped around the V1 tube (usually an EF86). This metal feels a bit like lead sheets which is used to seal roofs.

View attachment 141383

I would also say the roll is mumetal. It looks similar to the roll in Neumann KM5* which is Mumetal.
I’m not so sure about the thick shield. It looks more like steel.

 

[rock soderstrom]

I would also say the roll is mumetal. It looks similar to the roll in Neumann KM5* which is Mumetal.
I’m not so sure about the thick shield. It looks more like steel.

That's how I see it too. The roll comes (I think) from a high-quality R2R tube recorder (Telefunken M24?) the thick material from a microphone pre-amplifier that was used more in PA systems. Both devices were built in Germany at the end of the 50s, but the micpre amp comes from the GDR. Mu metal has never been cheap and requires special ingredients and manufacturing processes...I can well imagine that it was not so easy to get back then.

Just a theory...

 

[RoadrunnerOZ]

Does it rust:
Y - steel or transformer iron
N - MU metal or stainless or aluminium alloy or pewter
Is it very magnetic (and doesn’t rust)
Y - MU metal
N - slightly magnetic- stainless
N - non magnetic - alloy or pewter

 

[CJ]

Regular steel works for shielding too. (doh on me)The big UTC cans for the LS series knock down most of the gremlins with the internal shields working on what's left.

 

[RoadrunnerOZ]

A lot of transformers use steel as a shield anyway as part of the construction.

 

[Ike Zimbel]

Regular steel works for shielding too. (doh on me)The big UTC cans for the LS series knock down most of the gremlins with the internal shields working on what's left.

+1. I keep various pieces of steel around my bench that I can use to see if adding a steel piece will lower the noise floor of whatever I'm working on. Does not need to be grounded to work, just insert between sections of a device and see/hear what happens. Usually this is between the PT and one channel's electronics. Just last month I was able to drop the NF on the 2nd channel of a tube Eq 3-5dB to match the first channel by installing one of these steel L-brackets behind the front electronics board.

 

[CJ]

Nickel lams are great for getting g a lot of inductance with few turns but unfortunately this means that they are also great at attracting stray fields, so you seldom see mu metal shielding around steel lams.

And himself nickel lams are usually used in the most noise sensitive spots like mic/,line inputs. Peerless and Triad have the best shielding then UTC.

 

[Markku01]

Put it in the Varian 360 MS and look for a wave length if 10.87 Angstroms.

Or use a magnet, if mu metal the magnet will pull on it hard then loose strength as the mu metal rapidly saturates.

Or cut a razor blade sized slice and put it in your shaver, if it is mu metal you will have a close shave and a severed jugular vein if it contains 4% Cobalt.


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If you are lucky enough to find some old style heavy duty telecom switching power supplies, their transformer cores are pretty good quality. The transformers themselves are huge. And the filter chokes are wound using heavy copper ribbon approximately 1.5 inches wide.

 

[scott2000]

keep various pieces of steel around my bench that I can use to see if adding a steel piece will lower the noise floor of whatever I'm working on. Does not need to be grounded to work, just insert between sections of a device and see/hear what happens

+1.lot of excitement waiting to happen while playing that game of operation in some cases...

 

[Ike Zimbel]

+1.lot of excitement waiting to happen while playing that game of operation in some cases...

Well, yah...you want to be careful moving a piece of steel around inside a chassis, especially on tube gear.