diytube.com

As far as electromagnetic shielding and such, I've no clue. :?
When working at radio frequencies (RF), you definately can get strange results. I did some tests a month ago where an anodized chassis acted much different than a nickel plated one (both aluminum) in the same test setup. Since the anodized surfaces weren't conductive, the RF energy radiated from the enclosure very differently.
So grounding issues are the less 'magical' problems I understand. An oxidized ground lug, for instance, could give you hum fits on an old chassis. That's one neat thing about the blue board, as the ground plane is all on the PCB.
The more pragmatic reasons of steel vs aluminum are well stated in another thread here. I think Ed has won me over, though, and I'll start using a steel chassis more often, if only to support the 60W OPT of the Eiclone. I just hope my Unibits hold up! :) Cutting oil suggestions anyone?

Shannon

Steel will have better magnetic shielding, where aluminum has virtually none. With the trannies on top and the curcuiry beneath the chassis, any stray magnetic fields from the transformers will be blocked or attenuated
by the steel.

Also, don't forget, orient the output transformers 90 degrees from the power transformer so any AC hum doesn't get coupled across.

Thin guage (.040 to .060) steel isn't too bad to work, and is a lot better
IMHO for amp construction. Aluminum will offer e-field shielding, Steel gives both E and H, all in one. If you get a pre-painted chassis, there is one less required step. If you don't like gray or black, it is easy to paint over, rather than dealing with bare aluminum (zinc chromate primer, then paint, etc).

/ed B in NH