I have a friend who wants to change the tubes in his jcm 900 with 5881's to el34's. It should be as simple as switching out the tubes and rebiasing right? Anybody have any good info on doing just that with this type amp? There really aren't any amp techs without having to drive 2 1/2 to 3 hrs and I am hoping I can help him do the switch. Any info or thoughts/tips would be greatly appreciatted.