The Excursion switch is a speaker dampening switch. L = Loose, M = Medium, T = Tight. Lower volumes are for the L setting and as you increase volume use M or T. New/Old is a Pentode Triode switch. Thats not a rumor. The Class A B changes the bias on the power tubes. Class B is set with the bias pot, class A max's out the bias. Mine measures 89ma in class A. I always ran mine in Class A. It is in fact a desirable option on these amps even though tubes dont last as long.