Originally Posted by
petrat
IME, valve amp performance is 90%+ about the circuit & transformer design, and only a few % about the particular valves utilised. For instance, Radford and EAR both have (very different) designs that use EL34s, both giving results superior to the majority of 'bog-standard' KT88 amps. Similarly, the MacIntosh 275 uses a different circuit design to raise it's performance above the norm. for KT88 push-pull amps.
My Leben power amp has the facility to re-bias across a wide range of power valves (KT120, KT88, KT66, EL34, KT77, 6L6GC, 5881, 350B, etc), and although I haven't tried them all, there is a lot less difference than most people would imagine with the ones I have tried, the overall performance being overwhelmingly determined by the circuit topology and the o/p transformers. In fact, I suspect a blindfold test would show it'd be quite difficult to reliably, repeatedly, identify which valves were being used.