Hi Bruce (Bifwynne),
I've looked at the references you provided, and read your post, and I think that everything you've said is essentially correct.
Basically, your VS-115 has a lower output impedance than many or most other tube amps, on a given tap. The significant amount of negative feedback it uses is presumably a major reason for that. And it can be presumed that the output impedance of its 4 ohm tap is approximately half of the output impedance of its 8 ohm tap.
The lower the output impedance of a tube amp, the more closely the effects of the interaction of that output impedance with the impedance vs. frequency characteristics of the speaker will approach those of a solid state amplifier (which will have near zero output impedance, in most cases).
The one slight qualification I would make to your post (which you probably already realize) is to emphasize that JA's reference to obtaining a flatter frequency response with the 4 ohm tap than with the 8 ohm tap applies to his "standard simulated loudspeaker load," which has impedance characteristics that are quite different than those of your (and many other) speakers. As you probably already realize, for that and other reasons a generalization should not be drawn that 4 ohm taps will inevitably provide flatter frequency response than 8 ohm taps. It depends on the speaker.
In this particular case, though, given that your speakers were voiced for solid state amps, it can be expected that lower output impedance will result in a flatter response, everything else being equal.
Best regards,
-- Al
I've looked at the references you provided, and read your post, and I think that everything you've said is essentially correct.
Basically, your VS-115 has a lower output impedance than many or most other tube amps, on a given tap. The significant amount of negative feedback it uses is presumably a major reason for that. And it can be presumed that the output impedance of its 4 ohm tap is approximately half of the output impedance of its 8 ohm tap.
The lower the output impedance of a tube amp, the more closely the effects of the interaction of that output impedance with the impedance vs. frequency characteristics of the speaker will approach those of a solid state amplifier (which will have near zero output impedance, in most cases).
The one slight qualification I would make to your post (which you probably already realize) is to emphasize that JA's reference to obtaining a flatter frequency response with the 4 ohm tap than with the 8 ohm tap applies to his "standard simulated loudspeaker load," which has impedance characteristics that are quite different than those of your (and many other) speakers. As you probably already realize, for that and other reasons a generalization should not be drawn that 4 ohm taps will inevitably provide flatter frequency response than 8 ohm taps. It depends on the speaker.
In this particular case, though, given that your speakers were voiced for solid state amps, it can be expected that lower output impedance will result in a flatter response, everything else being equal.
Best regards,
-- Al