recently i just upgraded my marshall 2x12 combo to an older used rack mounted mesa mark iv and older half-back 4x12 mesa cabinet. i get amazing sounds out of the amp but the guy i bought it from said he hadn't changed the tubes in a few years. should i just take it to a shop and pay them to change the tubes or change them myself. i dont kno much and dont want to mess this amp up. if someone wants to see the pics i need a host. oh, right now the power tubes appear to be mesa 6L6 tubes the outter two are a bit bigger though