the WC-122 does not have a top screen and is meant to be used on a receiver with the metal cover, WC-22 can be used with or without metal cover. one of the techs i use recommends that the metal cover be left on when in the wood case as it helps block some of the RF waves from cell phones and other electronics, taking it off doesnt improve the over all cooling that much. one of my receivers kept making clicking sounds everytime i flipped a record on the turntable next to it and i thought it was a grounding issue i finally figured out it was the cell phone in my pocket.