I'm trying to find info on the differences between the different B-15 circuits. So far I'm having trouble finding an exact answer, but I'm sure this must have been discussed here at some point. If anyone can point me in the right direction, much obliged. I've been able to find some info about the difference between B-15NC and B-15NF. But I'm more interested in the difference between 60s and 70s models. I understand the cabs got a little bigger in the 70s, which makes for a bit more room for low notes. But what about the circuit itself? I do know the 70s versions are 30 watts as opposed to the 25 watts for the 60s. Did that alter the sound much? Or is the sound generally the same across decades?