Strange. Go to swap tubes. Bias meter reads almost tweed levels. Put a 5ar4 in place of the 5u4gb and get readings like i should with the 5u4gb. I'm hoping the bias probe just went south on me but it seems to be functioning properly. Any thoughts on the cause? I've been using another amp a lot lately but used this old faithful twice recently, including Saturday night. It was fine but seemed a little stiff. That's why I thought I'd change tubes and speaker after that. To re voice the amp. It's been fine for a long time and nothing done except that it got weird a year ago and one of the caps under the doghouse thang was loose on one end. I re-soldered it. That fixed that. Nothing else done to it.