Where to scavenge mu-metal?

Nope, only in higher-end legacy lab equipment. With legacy I mean >>25 years old.

Wrapped around old oscilloscope tubes. I don't think old TVs ever merited its use.

Old oscilloscopes or the like would be your best bet for this

Barry

snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote in news:461d3fec$0$759$ snipped-for-privacy@news.aaisp.net.uk:

TV's used electroMAGNETIC deflection,which overwhelms Earth's field. Those big,short TV CRTs just are not as sensitive as a long,narrow electrostatic deflection scope CRT.

Also trying to probe my memory here. After bending it might require annealing again. AFAIR that is done in a hydrogen atmosphere, not for the faint of heart. Sounds rather dangerous, IOW don't do this at home.

All the mu-metal shields I have dealt with came pre-formed and ready to mount. This was a long time ago and considering the cost it is usually best to design a unit so it doesn't need mu-metal. If it does, then IIRC one of the large vendors was VAC in Germany (Vacuumschmelze).

Not sure how fancy the furnace needs to be, but I believe the part about requiring annealing after any rework is accurate.

--- sam | Sci.Electronics.Repair FAQ:

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I have vague memories of hearing that if you bend it (or straighten it) then it loses its special properties and needs to be re-annealed in some fancy vacuum furnace thing or something like that. If you found a weird-shaped piece of this stuff inside an old oscilloscope then I I'm not sure that you could use it unless you needed it in exactly the shape that you found it in.

There is a German place that sells little mu-metal boxes (cylindrical cans actually):

Actually I suppose the existence of the mu-metal foil product brings into question whether it really matters whether you bend the mu-metal. Perhaps someone else knows for certain.

Chris

Look at old oscilloscopes.

Bill K7NOM

The laws of magnetics have not been repealed in the last 25 years.

ALL good quality scopes using CRTs have mu-metal shields.

Even ones made today.

........ Phil

On flat screen displays? What for? Sorry, but that would be like applying sun screen under the swimsuit.

Note that he wrote he needs a square foot. I've only seen that much in really old scopes. Newer CRT versions have a skinny shield right around the CRT and that ain't going to be enough to harvest a complete sqft from.

Back in the days of 90 degree delta-gun shadowmask tubes, an external magnetic shield most certainly was used around the bowl. The degaussing coils were usually fixed to it, and it mounted using the same four corner bolts as fixed the tube to the cabinet front. Many were my sliced fingers, from the razor-sharp edges of these shields, when I was an apprentice engaged in replacing these tubes ...

Arfa

Try learning to read sometime !!!

More expensive Asian scopes ( ie 60 MHz and up) usually have a mu-metal shield on the CRT.

Examine almost any European, US or Australian made scope and you will find it has a full size mu-metal shield -excepting scopes employing PDA (Post Deflection Acceleration) where the mag shielding is not needed near the tube face.

....... Phil

I was looking for some mu metal one day, and someone suggested CoNetic:

Hope This Helps! Rich

Hmm. Its on topic and probably useful. Even addresses the annealing question. Are you new to SED?

foot

No, he just can't figure out which of 20 names to use.

Why?

John

There is good reason for this. Bending, especially repeated bending could harden pure iron by introducing dislocations. The dislocations pin the magnetic domains. This is the background to the distinction between literally hard and soft magnets. Proper annealing would anneal out the dislocations.

Bill

-- Fermez le Bush--about two years to go.