@georgehifi
George, I understand what you are saying about the speaker’s impedance being challenging for a tube amp in parts of the bass region. But note that the OP has indicated that the addition of the second amp, with the two channels in each amp paralleled, has improved the bass (which is to be expected given that paralleling the channels in effect creates a 3 ohm tap), and he has not indicated that there are any problems in that region.
Note also that he has said that "fuzzy sound in some of the midrange on some material is what brought all this up." And as I indicated in my first post in this thread the speaker’s impedance in parts of the upper mid-range and lower treble is in the vicinity of 20 ohms or more! Resulting in more of a mismatch to the tap on the amp than when a single amp had been operated in stereo mode. Which leads me back to the first of the two hypotheses I proposed in that first post, with the second hypothesis also being a possibility especially given that the amp has an output impedance that is very low for a tube amp (0.6 ohms in stereo mode, as I mentioned earlier, which would mean 0.3 ohms in paralleled mono mode):
Best regards,
-- Al
George, I understand what you are saying about the speaker’s impedance being challenging for a tube amp in parts of the bass region. But note that the OP has indicated that the addition of the second amp, with the two channels in each amp paralleled, has improved the bass (which is to be expected given that paralleling the channels in effect creates a 3 ohm tap), and he has not indicated that there are any problems in that region.
Note also that he has said that "fuzzy sound in some of the midrange on some material is what brought all this up." And as I indicated in my first post in this thread the speaker’s impedance in parts of the upper mid-range and lower treble is in the vicinity of 20 ohms or more! Resulting in more of a mismatch to the tap on the amp than when a single amp had been operated in stereo mode. Which leads me back to the first of the two hypotheses I proposed in that first post, with the second hypothesis also being a possibility especially given that the amp has an output impedance that is very low for a tube amp (0.6 ohms in stereo mode, as I mentioned earlier, which would mean 0.3 ohms in paralleled mono mode):
With the amp presumably now optimized for a 3 ohm load perhaps it isn’t happy driving such high impedances in the mid-range and lower treble. Or perhaps the tubes or something else in the amp isn’t well matched between the two channels, and the two channels are trying to put out slightly different signals and are therefore fighting each other to some degree as a result of having their outputs connected together.
Best regards,
-- Al