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

Trelja:
in my experience, it is the openess and truth of tonality
that sets the midrange of the EL34 apart from anything else,
tube or solid state. The most concise way I can put it is
that when used in a sympathetic system, it sounds simply
"right". The EL34's midrange can, in the best of
circumstances, make me think that nothing else sounds as
real.
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Agreed. Couldn't have been said better!

I had McIntosh 2301 mono's with KT88 and now I have old Manley 240REf mono's with el34 aand like them better in my setup, more spark and musicality to my ears.

for many it boils down to bass, more bass, less bass, etc. bass, bass, bass. the 6550 and KT*** tubes offer a darker, more mellow sound; more bass. The 6550, kt120 and kt150 tubes do give off a lot of heat. very hot. the el34 tubes are more lush, and musical. the midrange is great. but- the Tungsol EL34B tubes give a punch to the bass. also Gold Lion gold pin 12at7 tubes help with bass, and Tungsol gold pin 12ax7 tubes add a bit to the upper frequencies. Get an amp without tubes. Buy your own. I sell Black Ice Audio gear (Jolida Audio). I have used different tubes. There is nearly as many opinions about tubes as there are different tubes. The tubes I mention represent excellent value, and reliability. In the Fusion 3502S amp I prefer the EL34 tubes to the 6550 tubes. (like the JD302CRC amp)

Another neck snapping time jump...I have to mention (really...it's a required thing) that after using various tubes (including all the ones mentioned by bob) in 2 recent power amps including a wonderful Jolida 502P, and currently a Dennis Had SEP HO (that's right...a HO...says it right there), I discovered Gold Lion KT77s and they're now my favorites by a wide margin. Highly recommended. This took me a while to discover as I'd bought a pair of JJ KT77s and they're not so good and they put me off 77s altogether, but the GLs are different and sound so much better it's kind of amazing.

+1 on Primaluna.  It can use both tubes, plus many others including KT120, KT150, and others.