Antonio, the "pure iron" perhaps is difficult to find today.All is steel with different carbon grade.
I don´t know why, but the stainless steel dont work well as magnetic shield.
A curiosity: the espensive mu-metal, permalloy, ultraperm, etc.... are nikel-alloys based (more 80% Ni), similar as they usually stainless steel cousin.
Mystery.
For shielding 60 Hz mains transformers used in video terminals we used to use lamination stock (grain oriented silicon steel) as a flux band around the core. It was the same material used for making M6 laminations and for tape winding large mains toroid cores.
Not the same permeability as mu metal but not as costly either. You might be able to find some but getting that stuff in North America is probably more difficult now than back in the early 80s (when I worked in that industry) since most transformers and transformer materials suppliers are off shore.
Not the same permeability as mu metal but not as costly either. You might be able to find some but getting that stuff in North America is probably more difficult now than back in the early 80s (when I worked in that industry) since most transformers and transformer materials suppliers are off shore.
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The copper band cancels out the leaking magnetic flux, so it doesn't change the effect even if it's floating or grounded, so it's usually floating like TonyTecson says. However, if there are picking up hum through capacitive coupling from transformer windings, grounding may help.
In order to cancel the magnetic flux, this copper needs a certain thickness, and almost no effect can be expected from the copper foil tape.
It's too late for a post from 7 years ago, but...
Looking at the first posted photo, there is each rotary switches on the front that switches between R and C, which seems to be for switching the load of the cart. If so, the wiring loop at the input may be causing a significant flux pick-up from the transformer.
In order to cancel the magnetic flux, this copper needs a certain thickness, and almost no effect can be expected from the copper foil tape.
It's too late for a post from 7 years ago, but...
Looking at the first posted photo, there is each rotary switches on the front that switches between R and C, which seems to be for switching the load of the cart. If so, the wiring loop at the input may be causing a significant flux pick-up from the transformer.