I bought a used DSL40C and I frequently get kind of a dull/faded/hollow sound out of it. So I started thinking about changing the tubes to see if that helps. That just lead to a whole lot of confusion that I'm hoping for some help with. Originally I was planning on replacing all of the tubes, but when I went to my local Guitar Center the only tubes they had in stock were Groove Tubes 12AX7s so I bought 4 of them and replaced all 4 existing tubes with those. I think it sounds better but I'm really not sure. So I figured that the preamp tubes must be where most of the tone comes from (especially since I live in an apartment and can't crank the amp at all). That said, I put a volume pedal in the effects loop so I can crank the volume knobs almost all of the way and still lower the sound level to an acceptable level. So my questions are: 1 - Does the volume pedal in the effects loop really help give me the same (or similar) sound to what I would get if I could really crank the amp? I'm sure it's not the same, but am I at least helping achieve the same thing? (I may ask this question in a separate post). 2 - I just read about V1...V4 in the pre-amp tubes so now I'm totally confused. Should I consider different tubes for different positions among the 4 pre-amp tubes? Or was it fine replacing all 4 with Groove Tube 12AX7s? 3 - Is there any way to try different tubes (manufacturers/models) without spending several hundred dollars on several different sets? I'm guessing not since once you plug it in you own it. The possible combinations are practically endless. Just wondering how other people have gone about trying different combinations out. 4 - How much of a tone change could I expect replacing the power tubes (EL34 I think), especially given my apartment situation? Part of this goes back to question 1. And if I do replace them what manufacturers/models should I try? I'm going for a Slash/G&R tone here with my Epiphone Les Paul (hopefully soon to be replaced by a Gibson Les Paul). 5 - Am I really limited to 12AX7/EL34 for the preamp-power tubes or should I consider other models as well? Thanks in advance!