EL 34 vs. KT 88 ---- What's the difference?

There is a very clear difference in the way these tubes sound. I have no idea whatsoever what the differences are in terms of construction etc. The EL 34 is known as the queen of the mid-range for good reason (I don't know the king) it clearly excels in producing a certain full and yet sweet sounding midrange it rolls off the top end a bit and tends to loose control of the bass but both end of the spectrum are reasonably pleasant. The KT-88 produces a more robust powerful sound especially at the extremes of the frequency spectrum. The mid range is there but it tends to be clinical sounding and less musical. The KT-88 is simply a bigger sounding tube and it will rock you, its just not going to be as polite sounding as the EL-34. I really like it for some types of music and it won't struggle producing tighter bass and sparkling treble. I hope that helps.

I gotta get me some and my amps back and running,  I have switched to an 845 SET for the moment