I’ve purchased numerous octets of both the Sylvania and GE 6550’s, over the last few decades, from both Upscale and TC Tubes. Both brands gave me the dynamics, spaciousness and clarity desired. The GEs were slightly ballsier in the bottom octaves. Tried some Winged ’C’ from Svetlana, before the plant burned (years back), which were nice. If still available, I may have gone back to them. Since I’m now on a fixed income and they’ve gone up in price(if/when they can be found); I compared my last set of GEs (still meter testing half-way into, "GOOD") with a new quad of Russian, Gold Lion KT-88, re-pops. Four KT-88s in one Cary monoblock, four GEs in the other. The KT-88s were as nice in every aspect, but- slightly lacking on the bottom, far as punch. Listening; I use SS amplification, below 80 Hz (actively/steeply crossed), so- that’s not an issue. When testing/comparing tubes; I run the mains full range, of course. TC Tubes and Brent Jessee are currently my go-to-guys, for power tubes. http://tctubes.com/6550-KT88-KT90-KT120-tubes.aspx
