When I looked at the Hi-Tone site, I thought they mentioned output tube options - as in you could have EL34 or KT88. It's easy enough for them to do, the pinouts are the same, just a matter of biasing. Personally, I'd recommend the KT88s, but if you really want it to sound/behave exactly like an original, it's gotta be the EL34s. I am considering switching my single pair of EL34 (technically 6CA7) head over to KT88s, next time the tubes go (single pair; I end up pushing them pretty hard, and I've been going through my stock of pre-loved EL34s to boot vs buying new so they will go pretty soon).