With the limited knowledge I have of tube power amps, I know that you're supposed to have a speaker cabinet connected to them at all times when running, correct? Now, what I'm wondering... is this always true? Say for example, if there is no preamp or anything that could be sending a signal into the power amp, and you've got the gain and everything turned all the way down... can it still damage the amp? Could someone explain in detail exactly how not having a speaker load damages the amp? I'd like to understand how it happens so that maybe I could answer my own question. The reason I'm asking this is because I'm looking into buying a used Mesa Stereo 20/20 tube power amp to use for guitar (*gasp* ) but I've only got one cabinet to use with it, and I'm wondering if it's safe to just not run a signal into the other side of the power amp. If it's not safe, do you know of any alternative solutions for this problem other than buying another speaker cabinet?