Not sure if this counts as pro gear, but it seemed the most appropriate forum. I've had this unit for some time now, as my second 8 channels in my setup. Over the last 18 months, I've had all the tubes go bad three times. I chalked the first two times to having removed it from the rack and traveled with it, but... This most recent set has lived in the rack, and just like before, all at once, all the tubes go bad - bad as in presenting high-frequency overtones/distortion on every channel, regardless of gain settings. Any ideas as to why this is (keeps) happening? The only guess I have to this point is that the unit/rack get pretty hot, but not sure that would be it? Thanks in advance!