It's not all the time my band gets to do soundchecks but I am thankful for recently getting one to iron out a major electrical oddity.
Certain notes the bassist played made my Vibrolux crackle like mad. The soundman declared one of my speakers blown but I thought it was a tube and was tapping the tubes and driving myself crazy.
Someone suggested that I move my amp to a different circuit from the bass amp and sure enough if that didn't fix the problem. What the heck would cause that?
Sure would have ruined the show for me had I not caught that in a soundcheck.