DeKay,
Thanks for your detailed and thoughtful response. I have several vintage USA types (GE, RCA, Tung Sol).
The immediate purpose of these tubes would be in the phase splitter of a mono power amp, so perhaps not as critical position as say in a pre-amp.
I was thinking it might be interesting to try a Euro made version. Mullard is a respected brand of GB tubes, so when I saw the first add for them, NOS military, that seemed like a good option for a good price. I thought someone might have come across a box of them that typically does not sell tubes and was selling them at reasonable prices to move them. When I saw 7 similar adds of different sellers from all over the world ... well you know the rest of the story.
Plus some of the pictures that are not identical across all adds, the lettering on the tube seems to be chalky (typical of NOS tubes) and bright and solid on others.
I think I will try a Euro tube, not sure I will try the Mullard ones discussed in this thread or not.
Since I do have a tube test system that can fully test all tube parameters, I tend to shy away from "pro" dealers as I can do the matching and weeding out myself.
Thanks again for your thoughts.
Dave