Thanks everyone for the advice. I am trying to place a pair of 6NS7s in a space where there is only about 3-quarters of an inch to 1 inch from the top of the tube to the shelf above. (The rack is open on all 4 sides, though.) So I will give the Pearl coolers a try and see what happens, and try a fan later if I need to.
I am not sure how much heat 6NS7s generate, as I have not used them before. (I have some 12AU7s in a headphone amp that are pretty cool, so I was hoping the 6NS7s were cool also.)
