"Some" of the thin metal shielding around video monitors and television sets is
made of a mu type metal. I like to salvage that metal for use as shielding on
projects. One such application is the reduction of magnetic fields and hum
reduction on new projects.
cheers,
skipp
ps: The microwave power transformer article is available free in the files
section of the: http://groups.yahoo.com/group/rfamplifiers group.
[paste]
Dear Boris,
This may not be entirely scientific, but I had a similar problem
using old television receiver transformers that made noise.
What I did was to put a 1/8" sheet of aluminum (or copper
if I could find some), just a bit larger than the transformer
footprint, under the transformer. I used machine nuts
both on top of and underneath the aluminum plate,
with flat washers and lockwashers in all sixteen positions.
My friends used to call this humming "Yarf" for some reason that
I can't remember, but it was a hurdle all of us who used to scarf
surplus xfmrs on Radio Row in NYC had to jump when building
HB gear.
Hal
W4HBM
> Borislav Trifonov <bdt at shaw.ca>
> I had a 1.5 kW microwave oven transformer (MOT) that I took apart,
> removed the magnetic shunts, and when putting it back together, I
> interleaved the laminations (originally, all the Es were together as
> one E; likewise the Is). The transformer hums quietly on its own, but
> when I put it in my project chassis, which is steel, I found out
> that it had huge leakage as it made the chassis hum very loudly.
> Knowing that MOTs are made with the bare minimum of materials, I
> figured that the core was saturating and added 15% more turns to
> the primary (about as much as I could fit).
> That helped a bit, but it was still pretty bad. I also
> added a copper tape around the windings, outside the core, as
> the 'flux band' sometimes seen in transformers (especially in
> audio equipment).
> That made a small difference. The chassis still hums too loudly.
> I've put in too much work in the current project chassis to replace
> it with a non-steel one. So I'm wondering about magnetic shielding.
> Mu-metal has very high permeability but saturates easily and is
> only useful for weak fields. Often I've seen tube audio amp
> transformers either completely encased in, or at least wrapped
> around the edges of the EI, with silicon steel or soft iron,
> which reduces leakage flux. However, I actually was
> not able to find any appropriate material. Any suggestions?
> _______________________________________________
_______________________________________________
___________________________________________________________________
Get Juno Platinum for as low as $6.95/month!
Unlimited Internet Access with 250MB of Email Storage.
Visit http://www.juno.com/bestoffer to sign up today!
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|