I am sure it's a tube issue, but thought I'd check in here. I was playing my Rockerverb 50 when the volume started going in and out and gradually faded to zero (15 seconds or so). Turned it off and fired it up and nothing. I am going to check the tubes and fuses once it cools down. Any thoughts? If it was a fuse, I would think it would cut out instantaneously? So I am guessing and hoping its only a tube issue.