You can't "mod" one of these and "change" it to a normal tube amp - you'll need to punch it for two actual preamp tube sockets AND install the sockets, replace the power transformer with one that can handle the additional filament current load (and whatever else), modify the power supply filtering to handle the additional tubes, replace the entire PCB with a circuit board usable for a full tube guitar amp, work out all the required lead dress and ground schemes...by the time all that is done you might as well buy a REAL tube amp for less than your total investment in one of these things. These are not normal tube amps that you can "mod" or adapt to other circuits. They are digital amps with a tube power section *only*. That is not something you can "mod in the ways being discussed. And based on the failure rates, do you *really* want to use ANY of the existing parts? Why stick up for printed circuit boards you can't use for anything else? What a waste of money IMO.