Sovtek 6L6WXT+ Quartett

Tested on a 100w fender amp with black face circuitry (also tested outdoors):
efficiency, gain increase over the whole range, deep bass, crystal clear highs, more audible (but not annoying) mids due to the general increase in gain.
Little or no distortion up to the maximum volume (very light saturation, not unpleasant).
Very "technical" pro tubes but on the other hand the weak side is the timbre, less creamy and slightly harder.

Great tubes, of course they were new, so they played louder than the old ones , but I think after a couple months, they are still louder than those original ENGL's.
When you bias them a bit more to the hot side of settings, They have a nice blue glow, which means that they are of good quality, as I heard from an amp tech. Difference that I've encountered when playing with bias, is that when you turn them hot, sound starts to SHRIEK alot (hi gain channel), it is crushing and perfect sound for black metal for example. But after all I bias them only a little bit hotter than the recommended setting and its perfect and very well ballanced sound in all channels. I will surely buy them again!