I just bought an old Oahu 8" amp. Some of the tubes sound microphonic, and if I'm going to replace them, perhaps I should consider a different complement altogether. Currently it has: one 6N7 a pair of C9s one 80 Can anyone tell me what sort of sound that arrangement is designed to deliver, AND what you'd recommend in order to maximize gritty, early breakup? I play blues rock. Many thanks!