Budda’s right, 5150’s can get unpleasantly bright with bright settings. If you had all jj’s in the preamp section it would make sense to blame the tubes because they’re dark, but you don’t. There’s a lot of ways to get it brighter without throwing money at it. Start with the 666 setting on the eq, resonance on like 3.5 presence on 7.5, you said you’re using the lead channel so gain on 3. Hopefully you’re using something as a boost, turn that tone knob up a bit more. Try that and just tweak from there. I’m not familiar with that cab or speakers but I’d imagine you’re going to end up adding a little bass because the resonance is set low and raising the treble to compensate if you raise the bass. If those speakers don’t have a lot of mids you have to crank the mids on the amp. It’s important to consider what your cab is doing to your sound. For example g12m’s I’ve got the mids dialed back a bit and resonance/presence up, g12t’s I crank the mids and pull back the resonance/presence knobs.