I have a single rectifier that I bought used a year ago and recently the clean channel was getting some distortion. I had to turn the gain up to get any sort of volume out of it, but at that point there was no difference between the clean and crunch settings. I changed the tubes hoping that it would fix it, which it did, but now I am getting almost no volume out of my clean channel. I switched from EL-34 to 6L6 power tubes, but other than that everything is the same. Is this a bias issue I need to have checked out or is it still a problem with the tubes?
Could be something as simple as a dirty volume pot... open it up and have a look. Might just need cleaning, could need changing.