Atmasphere: Yes, I did speculate above on just this factor, and how it might have been a confounding variable in my audition results. Thanks for confirming that. I'm wondering what your take is, in light of how that impedance issue may have affected my listening impressions in these trials, on my conclusion that higher power may in effect be its own virtue, and not just for louder listening levels.
Your point about differences in the tubes' output impedance relative to the way they're wired makes me wonder exactly how VTL (or any non-OTL amp maker employing a mode switch) has chosen to 'optimize' their output transformer in the presence of such a switch. To judge by the fact that VTL eschews various output impedance taps for the speaker load in favor of utilizing the entire secondary and optimizing it for a middle-of-the-road 5 ohm nominal load, it might be reasonable to assume they've likewise optimized the primary for a value midway between the source impedances presented by tetrode and triode modes. This approach would seem to be a practical compromise, but it does imply some theoretical room for improvement were the mode switch simply to be dispensed with (particularly for those customers who spend the big bucks for the Reference models with the intention of taking advantage of the very high power to run them exclusively in triode mode).
Of course, such concerns could be of merely academic interest to a manufacturer of OTL amps, but the manufacturer of non-OTL's might argue that even a slightly-less-then-ideally-optimized output transformer will still present a more consistent load (meaning possibly less colored) to the output tubes than will a speaker. As they say, every choice in audio represents some kind of tradeoff...
Your point about differences in the tubes' output impedance relative to the way they're wired makes me wonder exactly how VTL (or any non-OTL amp maker employing a mode switch) has chosen to 'optimize' their output transformer in the presence of such a switch. To judge by the fact that VTL eschews various output impedance taps for the speaker load in favor of utilizing the entire secondary and optimizing it for a middle-of-the-road 5 ohm nominal load, it might be reasonable to assume they've likewise optimized the primary for a value midway between the source impedances presented by tetrode and triode modes. This approach would seem to be a practical compromise, but it does imply some theoretical room for improvement were the mode switch simply to be dispensed with (particularly for those customers who spend the big bucks for the Reference models with the intention of taking advantage of the very high power to run them exclusively in triode mode).
Of course, such concerns could be of merely academic interest to a manufacturer of OTL amps, but the manufacturer of non-OTL's might argue that even a slightly-less-then-ideally-optimized output transformer will still present a more consistent load (meaning possibly less colored) to the output tubes than will a speaker. As they say, every choice in audio represents some kind of tradeoff...