Are EL34 based amps more musical than KT series based ? Or it's purely a matter of design?

I think it’s hard to make an EL34 not sound sweet. You have to really mess it up. The larger KT tubes will (by comparison) give you brute force, dynamics, impact - but it’s hard to keep all that while getting them to sound as "sweet" at the same time, as the smaller tubes which seem to do it so naturally (EL34, EL84, 6L6’s etc). I think VAC’s recent high-end lines do a GREAT job at that (plus next-level articulation and refinement), but takes some doing and ain’t cheap.

Vintage tubes amps are a lot of fun and a nice break from the "hifi" sounding amps because they’re so inherently musical. Part of that, I think, is the use of those tube types. But there are those limitations - power, and usually bass impact / dynamics.

Matching and preference will play a role which one you like.

mulveling, "ain't cheap" is an understatement, VAC's top and near top of the line separates are extremely expensive, but you say they are worth it.

I have no complaints regarding the dynamics and bass of the VAC Avatar SE EL34 based integrated. I suppose, it also depends a lot on particular signal tubes that you use. These 60 watt/ch in ultralinear mode sound quite powerful.

So, there is something inherently very musical in EL34/EL84/6L6 tubes.

I love the sound of EL 34 tubes, reminds me most of tube amps from the past.  A ripe romantic type sound but without any bass slam. 

@yogiboy On my Quicksilver amps I can use both types. I prefer the sound of the KT88 compared to the EL34. It all depends on the speaker that you are using. I find that the KT88 sounds bigger and brighter than the EL34!

+1 yogiboy. 100%, so true. Was just sharing this on another thread about this, its a fact. Matching to your preferred sound is key, all speaker dependent for sure.