Best tube mono blocks under $15,000?

The impedance curve of the V2 that is shown in "Chart 5" here indicates that its impedance is around 4 ohms in the mid-bass region, slightly higher in the deep bass and upper treble regions, and rises to around 10 ohms in the mid-range.

Which means that a tube amp having relatively high output impedance/low damping factor (such as the MA-1's, which are presently listed at the Atmasphere website as having an output impedance of 2.3 ohms) will produce a mid-range response that is more emphasized, and bass and treble responses that are less emphasized, than would result with a solid state amp having low output impedance/high damping factor (such as your MC501's).

The MC2301 has a damping factor of 15, corresponding to an output impedance of about 0.5 ohms. Relative to a solid state amp such as your MC501's (damping factor 100, output impedance 0.08 ohms), the MC2301's will emphasize the various parts of the spectrum in a similar direction as the Atmasphere's, but to a lesser degree.

I suspect that a pair of MC275's operated in parallel mono mode would have an output impedance close enough to that of a solid state amp that the resulting impedance interactions would be similar.

I have no idea which kind of response would be preferable to you, or with the speaker generally, but those are some factors to consider.

Regards,
-- Al

A slight correction to my earlier post: The reference to a 0.5 ohm output impedance of the MC2301 applies to the 8 ohm output tap of the amp. If the 4 ohm tap is used instead (and that tap stands a good chance of being sonically preferable with this speaker in terms of amplifier loading), the output impedance would be about 0.27 ohms, bringing the tonal effects of impedance interaction somewhat closer to those of a solid state amp.

Sam -- thank you kindly!

Best regards,
-- Al