On the subject of potted vs. open-fame BC-610 modulation transformers: I don't have a BC-610, but I do have a modulation transformer for a BC-610-D I purchased from Fair Radio many years ago, and it is open-frame. It presently resides in the Old Buzzard Rig (see http://ne1s.rfburn.org/Old_Buzzard.html) 73, -Larry/NE1S