Here is an interesting finding, I swapped out the three IF tubes with spare tubes. No real change for the first and second IF tubes but the third IF tube (6EJ7) did yield a much different response curve, see below. Note the tubes were tested with a B&K 747 tube tester where good starts at 65 on a 0 - 120 scale.
Sylvania 6EJ7 testing at 77, this is the tube I have been using
Alternate tube, Zenith 6EJ7 testing at 80, note I still need let this tube run for a good amount of time, but interesting how much the tube affects the response. Also note about 1 turn on the alignment transformer and I can get the curve about correct but not as good as the first tube.
