Ok, so I picked up this Marshall head in a trade for a guitar and some work on the owners 6505. Date code on the transformers pegs it at 1996. There is a sticker on the chassis that says "this amp is fitted with 5881 tubes.....bla bla bla" But it has a newish looking set of TAD EL34's, and I looked at the board, all the mods to convert the original el34 circuts over to 6l6 seem to be in place. So, my options would seem to be either put a pair of 6l6's in, adjust the bias as needed and flip it from there, or go to the trouble of undoing all the factory mods, and set the bias correctly for el34's. As far as I know and can find info on, the least desirable option seems to be to leave the 6l6 mods in and run el34's anyway, which may be why the guy I got it from was so disappointed in the thing in the first place. So, question is, does anybody have an opinion on which is preferable in a 4500, 6l6 or el34?