I don't care what anyone says and they'll aways say a watt is a watt but, valve amps are loud! Transistor amps are only half as loud as valve amps and class D amps are only half as loud as transistor amps. I do use a class D amp myself but only because I'm getting old and valve and transistor amps are getting heavier. But I accept the limitations and 600w class D is loud enough for me. Back in the day though, a 100w valve head and a pair of 4 x 12s would have been more than enough for any venue without P.A. support. In fact, there was no P.A. support!