Man, I'm sitting here listening to my IHA-1 and it is such a wonderful amp.... Thanks Dennis Had! I finally settled on my tubes- a 1952 Brimar U52 and a pair of 1945 TungSol 6SN7GT VT231 Black Glass Round Plates. Absolutely, positively no more tube rolling for me. Tube rolling can be a counter-productive disease. In my view, I think you find a tube combo that works for YOU and then just stick with it. With the tube combo settled I can now free my mind of all of my equipment OCD tendencies and redirect my focus to enjoying my music collection.