Loving my new DSL40CR, but I find that the Classic channel on green is too quiet compared to on red. I can balance the volume of the Classic and Ultra with the knobs, so no problem there. And on Ultra, there isn't much difference in volume between green and red, so that's no problem either. So, I need to either make Classic green louder or Classic red quieter. Can I do either of those with a safe tube swap? Thanks for any thoughts!