I don't have a blues jr. but I do have a Chandler blue tube into a Peavey Classic 60 tube power amp into a Marshall JCM900 4x12. I also have a single 12 closed back cab. Right now, I'm simply mic'ing it with a 57 a little off axis (45) from one of the lower speakers. Maybe the 4x12 has too much bottom?
This rig with a Les Paul sounds great when I push the pre.