Best tubes for Sonic Frontiers 80

My amp is a Sonic Frontiers 80 (in stereo) and I am wondering what would be the best power tubes for this piece of equiptment. Currently on this site there is two pair of Ei- KT90 for a fair price.As of now I am running EH KT-90 which sound fine but as we are aware of we must search for the holy grail. Excluding Gold Lion for
price,(KT-88) what would be my best power tubes for my amp? This amp can take, EL-34.KT-88, KT-90 & 99.
Thanks for all the help.
Tube types will depend on what tonal qualities you're are looking for and will depend on your ancillary equipment as well as the speakers you are driving. I've used 99A's, KT88's, 6550c's and EL34's. They all sound different. I ultimately chose SED 6550's and EI 6dj8 Elites which seemed more balanced and neutral in tone. YMMV.
Surf, the Ei KT90 type 3 is a VERY-good-sounding 6550/88-type tube and was voted the best-sounding new-production 6550/88-type tube in the most-recent 'Vacuum Tube Valley' test. I've used them in c-j Premier Elevens, NewGen 94s (2 pairs each amp), and Quicksilver V4s. Mike Sanders of QS recommends them but recommends against the EH KT90, as does Jim McShane, .

In spite of the several recent (say, this year) comments I've read about plate-structure misalignment and subsequent glowing-red plates, NONE of my 18 glow anywhere but the filaments. I've recently bought 4 new matched quads from an eBay seller whose e-mail address is His eBay BIN prices were $104, and his non-eBay price is $100 per matched quad. You might try him--great service, too.

EL34s are known for their harmonic richness and sweetness in the midrange, but usually they're soft in the trebles and less controlled in the bass--at least in an amp that can use 6550/88s.

Newbee, what is a '99A'?
Jefferybehr, The KT99a is a KT90 in disguise. This is the original tube Sonic Frontiers used in the SFS80 and the SFM 160's. It was made by Yugo and relabled by Gold Aero. I found its tone powerful but a bit on the cool side of neutral, even after changing out the small tubes which I believe were relabled Siemans. FWIW I agree with your comments re EL34's and that is about how they sounded in the SFS80 (except for Tesla E34L's which were also relabled and sold by Gold Aero. These were, for lack of a better discription, sort of 'technicolor' and did not lack high frequency energy. Since I'm talking about my observations of 'tone' with the SFS80 (and a couple of other amps) I've just never been a fan of the KT88. The upper mids and highs are excellent but I have not experienced a similar smoothness and balance in the lower mids and bass. But then I've only used a couple of current production brands including SED's.
I'm using the Ei KT-90 Type 3 in my SFM-160s. I completely agree with Jeffreybehr. I also purchased mine from JSPHT8338 and have been completely satisfied.
Thanks all for your help. By the way the drivers are original Tesla 6922s, I was thinking of switching them with new EH 6922s and save he Teslas for my preamp (Audible Illusions 3) So I will give further thought to buying a quad of EiKT-88.

Everybody on this Board is great
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.