My Unison S6 is a parallel, single ended, Class A integrated amp that was Stereophile "Class A" and received multiple 5* reviews online. It sounded good with the Tung Sol EL-34B power tubes (3 per side) that came with it, but was not a match for my modified Pathos TT RR. With the new Sophia Electric blue EL-34-ST tubes the S6 is a revelation, matching the TT RR's timbral accuracy and surpassing it in articulation, bass heft, and three-dimensional imaging. If I were to put a % on it I would estimate that the S6 is 60%-70% better/more musical with the Sophia tubes versus the Tung Sols.
Note that I am using Mullard, Amperex, or Sylvania (black) long plate 12AX7's in both amps.
Jeff Day reviewed these new Sophia tubes for Positive Feedback, and also on his "Jeff's Place" blog.
Note that I am using Mullard, Amperex, or Sylvania (black) long plate 12AX7's in both amps.
Jeff Day reviewed these new Sophia tubes for Positive Feedback, and also on his "Jeff's Place" blog.