Off the shelftransformer cans?

[bluebird]

The UTC A series didn't have copper between primary and secondary windings.  But they had tape/fishpaper between every layer. Jensen/Cinemag often use foil between pri/sec and the foil is carried out on a wire that should be grounded. Its suppose to break up the pri/sec capacitance and help out your high end. Just keep in mind everything you do to break up capacitance to extend high end will take away inductance and hurt your low end.  I spent a good year winding and experimenting until I got something I liked and felt was worth the trouble. I settled on putting tape between every layer like a UTC. Pain in the butt. But in all my experiments the copper tape never made much of a difference, layer winding or not.

Regarding shielding, I tried 0.06" steel - copper - steel - nested and it wasn't good enough for a mic input transformer done on an EI core thats not humbucking.  You really need mu metal for mic input.  A couple of bent pieces the size of a ruler, inside a steel case finally did it for me.

 

[mkiijam]

Thank you.

 

[abbey road d enfer]

Is the HF shielding really needed?

In a heavily RFI/EMI charged environment, yes.  Prevents capacitive coupling bet windings.

[/quote] Does the copper cause some loss? If it is allowed to make a closed loop, yes. That's why the ends must be isolated (which single-side metallization provides). If you use copper foil, you must insert an insulator where the ends meet.
[/quote]