So this is my first tube amp, and it was working great so far.
However, Yesterday during band practise, after it had been on and working perfectly for two hours, the volume suddenly dropped. When I checked the amp to see what was going on, I noticed that one of the tubes (the one on the left) was way hotter than the others. when I turned down the volume, where was a small lightning inside the tube, and then no sound. From what I've gathered from the internet, the tubes weren't paired or biased properly. When the amp is on, the other tubes light up normally.
Anyway, when I bought the amp, the people at the store had only two tubes installed (the two in the center), to cut the output down and make it playable in the store.
I wanted to know if there is any specific manipulation to do in order to do that. (I have a gig in 4 days and I probably won't have neither time nor money enough to have the tubes changed and the amp biased before then).