Atma-Sphere in CO?

@atmasphere Also, if I'm reading your post correctly, that means that my RCA 6SN7GT VT-231s won't actually work in the amp.  Right?  I don't think I actually have any GTA or Bs, unfortunately.

The GTs will work in all but the front position. Just use the Chinese 6SN7 in that location and you'll be fine.

The fundamental difference I suspect you'll hear is that the Franks have a more lush sound while the M-60 is more neutral. The difference is that the distortion signature of the Franks is based on the 2nd harmonic while the M-60's product (like all fully differential amps) is based on the 3rd. The ear treats both the same, but amps with a 3rd harmonic have overall a lot less of *any* harmonic, starting with the 3rd which is about 1/10th or less of what you see in an SET. So while it is still smooth and relaxed like an SET, its just got less of its own 'tonality'.

I'd be interested to hear what you think.

@cal3713 ,  I looked at the Music Room ad and remember that they indicated the amps were MK 3 and were 8 years old.  @atmasphere  can probably deconvolute the history of your new amps when you have the serial numbers.  Ralph nailed it on the difference between the Franks and the M-60s.  Your preference is going to be a matter of personal taste.   I love both amps, and really enjoy having both.  The M-60s are upstairs and the Franks are downstairs.  Even if I didn't have 2 systems, I would probably keep both amps.  BTW, I am using the shortest possible run, about 2.5 ft, of the Duelund WE replica (12 G) from the M-60s to my Coincident super victory IIs.   Ralph advised keeping the speaker cables as short as possible.   I've been very satisfied with the Duelund in my set up.