Not sure how to ask this, but is it not possible that a circuit is designed for a particular version/brand of a tube - in my case the JJ EL34L, and that the sound of the amp takes that tube into account ("voiced"?). In other words, I'm questioning whether a tube really has an inherent sound independently of the ciruit in which it is used, they seem to be two parts of the equation leading to the sound of a paricular tube in a particular amplifier. I've heard many amps using the same basic tube type with very different sound attributes (the type of differences you ascribe to the sound of Siemens versus Telefunken versus Mullard); I have to imagine the circuit is just as an imporant factor as the tube type/brand. Of course, this is no reason not to try tube rolling (I have done a lot of tube rolling on my CAT JL2 with Amperex, RCA, GE, Syvania, etc), but the maker of my Ars Sonum told me to tread lightly.