| Strictly speaking the bias should be changed if fitting a 12AU7 rather than AX7 but since the object is to change the sound, most don't bother and as long as the resistors don't mind possible increased dissipation (most don't) then just swap away. The point of the AX is the higher gain and (usually) better balance of the circuit but you want different harmonics and characteristics so the change will provide it.
Matt S |