I too expected only good things from my first use of a VAC amp, and lugged home a well-broken in VAC Avatar a few years ago. The long story is somewhere else posted. Suffice it to say that it's horrendously high output impedence wreaked havoc with my newly-aquired Parsifal Encores (which are VERY easy to drive, btw), with disturbances as much as
+/- 5dB across the spectrum, as finally carefully measured
against two reference amps. Horribly overripe mid-bass, a giant low treble peak and no upper treble "air" made all discs unlistenable. I faxed curves to VAC and was finally told that the inexpensive AVATAR's output tubes were famous for nonlinearity and unpredictable results with real speakers, and that if I wanted really fine performance I had to get their bigger amps. Sad to say the Audio Refinement Complete ($995) I had on hand absolutely trounced
the $3800 Avatar in both triode and pentode modes.
I then came to look as Stereophiles "predicted plot" of real performance with an 8 ohm load with glass amps once in awhile in JA's reviews, but NEVER saw one with swings of the amplitude I measured (and many of us heard) through that Avatar. And yes, both channels were the same, the tubes were ok, power output was correct, etc.
Glad their higher end stuff is more linear, and that they've recently completely redesigned the 'tar.