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, http://pages.prodigy.net/jimmcshane/tubes.htm .
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 JSPHT8338@aol.com. 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'?