Which 6SN7's for Rogue 99 Pre

Pretty hard to beat either your Sylvania VT231's or the Kenrad's mentioned by sugarbrie. If you feel like experimenting a bit, you might want to try some 5692 tubes, which are in the 6SN7 family tree. I have used them with very good results, I personally believe that they produce a more cohesive overall musical experience than the VT231.

Sugarbrie mentioned the Sylvania 6SN7Ws: The two tall versions sound identical and are absolutely astounding in their musicality, sound stage and imaging. The shorter ones might singe your ear-hairs with their highs(unless your system is laid back in the upper registers). the TungSol 6SN7GT round plates(not with the mouse ears though)have very much the same attributes as the tall Sylvanias and work excellently together. I'm using one each in my Cary SLM-100's. If you switch out your Sylvania(bottom getter from the 40's) VT-231s for either of these: Your biggest improvement will be in depth of sound stage. I suppose you already know to shop for the lowest noise tubes possible, though finding either of these at all is getting harder by the minute. I've tried the Ken-Rad bottom getters and the VT-231s were a bit more natural, though not by much. I've not tried the CBS 5692 Red Base as it's scored consistantly low on every 6SN7 family tube shootout that I've read.

You only need 2 quality 6SN7's for the 99 Mag.
The 2 other tube positions have no effect on the sonics.
I cant remember which 2 positions to use quality tubes in. Ask Mark before you lay down big bucks for 4 tubes.

I think the right set of 6SN7s is the more important set. I spent quite a while trying to find the best combo a year or two ago, and to my recollection the pairing of left and right sets definitely made a difference. My efforts resulted in a pair of RCAs on the right and Tung Sols on the left (specs on the tubes are buried under the cover).

Good luck

Sylvania BAD BOYS are good

TUNG SOLS MOUSE EARS are good

RCA Grey COATED GLASS are great

Mullards ECC33 = CV2821 are fantastic

Will be trying TUNG SOLS Black coated glass & round plates, KEN RAD VT231 and SYLVANIA 6SN7W black base soon.

Don't forget, tubes may not sound the same on differ amps, so, its always personal experience.

Good luck.