I have a 20+ year old Fender Bassman 135 Head that has stopped working. I am not getting a signal out to the speaker. Before taking it a someone and paying a bench fee, I am trying make sure I am not missing something simple. Hear are a little more details: I was playing through it and it was working fine and one day later - no output. It powers up, the fuse is fine and has not blown. I tried replacing the tubes since they've been in it for years and it still does not work. I swapped out speaker cabinets and cables, etc. I am the original owner and am familiar the knobs and functions - standby switch, etc. I tried the normal and low inputs. Any thoughts/suggestions?