I replaced my GT 12ax7a that I think comes standard in the SM400 with a Ruby Tube 7025 STS. It's really interesting how different pre amp tubes can change your tone. This tube really warmed up the tone and mellowed out the top end I always thought the SWR highs were a little brittle sounding. This Ruby tube has alot more gain also. I'm guessing that's the reason my amp seems a bit louder than it used to. Anybody else have any experience with these Ruby tubes? It's not a 12ax7a so I'm wondering if it might mess something up by using it in place of a 12ax7a.