Hello All, I changed the 3rd mixer back to a 6C4, checked the mechanical alignment and am now warming up the URM-25 and R-390A. For the RF alignment the manual refers to using an electrical dummy load, a DA-121/U. This is not part of the URM-25 pack. Is this necessary or should I just use a 50ohm load? If it is necessary, does anyone have the values used in the dummy load? Jim