Played 6 shows this week, 3 of which, I ended up using the rig for sound (instead of just an onstage monitor). -- [SM 900 / Goliath Sr ]. I own several pre Fender SWR's, but this hasn't come up before- after about 10 mins of play (with the gain and master both around 3/4) the volume just drops out to about half power. A few mins later, the full power comes back (normally after I've ran the master up ) and then blasts my poor drummer! I'm assuming this is the tube needing replacing, but seems like in my 400s and Redhead, the tube made a crackling sound before I replaced those. Wanted to get some opinions before relying on a new tube, cause I won't have a chance to test it out at that vol before we play next weekend. Not using any effects. Stingray 5 / L2000 - Both with new batts.