Did you rebias them. If you move tubes around you must rebias. I had 2 of these at one time, I took tubes out and put them beck in I still checked bias even if they went back in the same spot. The D90 sounds great but is very fussy. I biased mine every month or so. I also did a hail mary when I turned them on. Very touchy equipment. I agree with Newbe also you could just have a bad tube, Move them around but again bias very time you move them. Do not swap 12ax7 with 12au7 as this can mess thing up alot. only use the tube recommended for that location, ARC's from that era again are very touchy.
