I got a Darkvoice 336SE from a forum member a few weeks ago, and the previous owner was nice enough to include a brown-base Sylvania 6SN7 (JAN-CHS-6SN7WGT) and some type of 6AS7 with a metal base/straight bottle. Since then I've tried a variety of low-buck 6SN7s, and I have to admit that I keep going back to the Sylvania. Most were either really flat sounding (GE, Motorola), or actually had a strong hum in one or the other channel (Tung-Sol mouse ear, RCA).
Today I got in a pair of 6SN7s labeled Hytron and CBS, and I'm listening to the Hytron now. Quite a warm sound, a little muted in the upper registers, but very natural voices (I watch a lot of movies and prefer headphones in the evenings). Very pleased with this one, but I think the Sylvania is still clearer overall.
Still on the lookout for interesting tubes, and have a couple of TS Tall Boy styles on the way, plus a Svetlana power tube. I also ran across one I hadn't heard of; the Shuguang CV1988. Is this worth trying, or skip for something better like Brimar, Mullard, or...?