[Fender_man]

These are all good questions. While others may disagree with me, I think that swapping the Celestion 75s for the Vintage 30s might actually backfire on you. Granted, the Vintage 30s will, in all likelihood, break up earlier than the 75s, but I think you could actually lose some of the bottom end that you’ve got presently with the 75 watters.

I think the 6CA7 is a good replacement for EL34, but I think of it as having a cleaner sound than the EL34, with less output distortion, which you may miss. In any event, I don’t think the 6CA7 will contribute any significant bottom end your sound. The fact that your amp has an open-back design is probably one of the biggest factors contributing to the absence of pronounced bottom end. I suggestion that you get closed-back cabinet -- either 2x12 or 4x12 -- and run it as an extension speaker to help enhance the low end. Check your amp’s impedance setting; if it’s set for eight ohms, leave it there when you employ the extension cab; if it’s set to four ohm, leave it at that setting when you run the extension cab.