I run KT120s in my Atlas and it's a dream. In order to make it fit I had to use "socket savers" to extend the tube socket. They are available online. I think Rogue started making the holes bigger to fit at some point. The biggest issue according to Mark was the extra heat and the capacitors that are close by. That's why I like the socket savers because the give extra clearance. I bias hot, at 55, but that's because my speakers, Quad ESL57s sound much better that way. Rogue suggest biasing at 35 but said that 45 is good too. I've had mine for close to 2 years with no issues and I must have 1000 hours on the tubes.