I have a Bassman 135, and when I check to see how all the power tubes were lighting up I have noticed that two of them are not as bright as the other two. The owner before me put in two 6L6B, and two 6L6S Groove Tubes, and the dim ones are the B's. My question is....what is happening when an amp does this, and should I not play it until I retube it with all matching power tubes? I just bought a matched quad set of SED winged C 6L6GC's. Any info would be much help.