Just rolled in a set of Electro-Harmonix KT-88s this weekend and the difference IMO was an overall improvement. The most noticeable difference was in increased headroom and a tighter more controlled bass. There was also a nice seperation of instruments in the highs and mids, a welcomed plus, because I love the sweet tone of the EL-34s but the KT-88s were right there as well. In general, I thought the EL-34 could muddy the bass a little when volume levels were cranked, where the KT-88 really held things together at high volumes. You know you've found a good thing when new things jump at you (in a good way) on familiar tunes that you couldn't zone in on before. Always brings a smile to my face. I was running the TAD-60 in tri-mode with the EL34s because I liked the warmth in the mid-range over the UL setting. However, I did like the extra power and dynamics UL provided, but I was constantly adjusting feedback to find that elusive level of warmth. With the KT-88s I have the TAD-60 set to UL mode now, with the feedback knob set at 2:30 and haven't felt the need to touch it once; its a perfect blend of warmth & dynamics that I couldn't achieve with the EL-34's. Tubes were purchased from the Tubedepot, they arrived in 2 days and were very helpful on the phone. However, 2 of them were running a little hot (715-720 range), so I freaked and called Paul, who was very good about walking me thru the setup, tubology 101, and assuring me that they would run fine. As you can probably tell, I'm new at this stuff, so it's nice to have a real pro to call when you need help.