does it help reduce EMI if the EI cores are in a separate chassis? pardon my ignorance but i'd like to understand more. also what does it mean to be "screened"? thanks!
yes, but it does not mean you can not put the psu and the amp in the same chassis.
i made my el84 set amp and there is no hum whatsoever!
i made many high powered solid state amps with big traffos and there is no noise at all!
everthing depends on layout and grounding techniques! which in turn comes from experience!
"screen": means to shield something from something! in case of traffos, the primary turns are screened by using copper or aluminum foils to shield the primary winding from the secondary winding! a single copper layer can also be used. noise from the mains can be drained to ground in this way.