I would say so. What sort of improvements are you expecting? I would guess, not having heard the SF in years, the Mac would have a larger, more precise soundstage and better timing. Obviously the tubes will make a large difference but even with stock tubes the Mac should have better silence and a more effortless sound. I still don't know many folks who don't drool on themself when they listen through the 275.

If you want to drool, then plop 30k on a Lamm ML2.1 and be done with upgrades for as long as you live. I've yet to hear anything better tube wise. To me, it's a single ended tube amp done right.