I'm just trying to clean up the sound of this old Bassman 135. I've only used it about 3 years out of the last 30. I've never replaced any of the tubes, and now I'd like to see if I can get rid of some of the fuzzy, farty sound. I'm not at all smart about tubes; I don't know which of the tubes might be trashing the sound or which ones would be worth replacing. A local amp shop said they could improve the sound "dramatically" for about $300. I don't think the amp is worth that much of an investment. I've searched this forum for some help on this but I couldn't find what I was looking for. Anyone know of any threads or tutorials on performance improvement of old tube amps?