All Atma-Sphere MA-1s have had 14 output tubes for quite a few years. I have 14 tube MA-1 Mk II.3s that I use and demo, as well as a pair of a pair of 12 tube MA-1 Mk Is. The differences are substantial, much more than the power rating difference. It would be interesting to compare the ART 2 against the just introduced MP-1 Mk III driving the MA-1s. I imagine we'll see and hear the MP-1 Mk III at the Rocky Mountain Audio Fest.
Brian
Brian