This Vox AC30tbx had a serious case of the "I ate my power tubes" in the middle of an outdoor concert. That part's not unusual. AC30s are known to be hard on their tubes. What's weird was how. The legs of both bias resistors were sheared off at the PCB.  Because apparently that is a thing that the laws of nature and physics allows. Metal can decide to just opt out now. Some new resistors and a fresh quad of EL84s were the solution. We also changed the cut control to function as a master volume.  It's an easy mod that is just as easy to reverse. It's a good experiment for those that want the classic AC30 sound, but don't want to sacrifice their hearing.