Detlof: I think the difference in sound just comes from lifting the glass tube globe (the bottom of it on my signal tubes) and the plastic tube base (on my output tubes) up off of the tube socket. My tube sockets have slightly raised centers. This way vibration is only transmitted by the pins (instead of both the pins and the bottom of the tube. Rec makes a very good point that by raising the tubes you are then exposing the pins themselves. Again, although I practice this myself, I do not recommend it because of the risks involved. My tubes are also not enclosed and are easy to check and monitor. I cannot hear a difference when I raise the 5687 driver tube in my amp (but I do it anyway). The 6922 types though do sound better to me (more detail though at the same time a little smoother on top - kind of hard to describe) and the 300B's seem to focus better and play a bit louder while still maintaining clarity. My tube amp is enclosed in a closet off the living room (where the speakers are located) and receives very little air born vibration and this may be why this additional tweak is even audible to me at all as it is not a major change in sound, but a change (that I like) nonetheless.