That's actually what I did this morning when I had a few minutes to actually focus on it. It's working, so that's a relief. The closest GC is 2 hours away.Try this. DO NOT PLUG AN INSTRUMENT IN BUT MAX THE AMP MASTER, GAIN, TREBLE KNOB and put your ear near the tweeter. Now turn the tweeter attenuator up and down. You should hear the tweeter hissing to variable levels. PLEASE BE CAREFUL! AGAIN, DON'T HAVE ANY INSTRUMENT PLUGGED IN THAT COULD CAUSE ANY POPPING THROUGH THE TWEETER. I don't want you to hurt your ears. You may not have to get too close to hear the hiss if the treble, gain and master are maxed.