in my amp:
--Kenrad (vt231) black glass = BIG, lush sound (but still open, unveiled), bass bloom, music full of weight, the BEST in my amp (but NOT in my preamp!)
--sylvania vt231 = sparkling (like TWL said... "twinkly") up top, crystal clear, extended
--sylvania 6SN7W (NOT the metal base) = also transparent, a little thin, tight bass
--tungsol, blackglass round plate = neutral, balanced, SMOOOTH (perfect in my preamp)
RCA grey glass vt231 = lush, but also veiled/dark
national union black glass vt231 = very similar to kenrad, but a little more veiled (still very good)
GE 6SN7 GTA = good all-around neutral tube, much better than stock/chinese tubes, nothing totally outstanding about it