Best tubes for Sonic Frontiers 80

I have tried many different brands and the most pleasant combination for me was Siemens CCa as 6922's and Svetlana 6550 winged C.
My second 6922's favorate are the Amperex 'orange globe' and my second choice as power tube is El 34 Telefunken, less power but still top performance, at least for me.
Mullard is always a fantastic expensive tube option and Ei 6dj8 a very good inexpensive top choice.

By far my favorite tube in the SFS-80 was the Ei KT-90 Type 3 tubes. - Make certain to give them 400 hours (not an hour less) to open up and gain the liquid midrange.

Coupled with some nice NOS Bugle Boy input tubes or Tele Diamond base, etc. this amp will sing!

Good luck on your search.

I utilize the KT90s on the SFS80 amplifier and it sounds fantastic. The bass is strong, the highs are good and the mids are almost perfect. My system consists of almost all tube based SF components. I use the SFS80 amp, SFL1 preamp, SFD1 DAC and finally the SFT1 transport. The Canton 807DC speakers I'm using are bi-wired and not the most efficient at 88SPL but still sound quite nice at mid volume listening levels. I have a spare set of 6550 and they're not bad but not as good as the 90s. Only problem, the KT90s are becoming more difficult to find and the price continues to climb.