Well, I went back out with my B&K 466 tester and
. The tube went into the Green right away (about 56 on the "5" scale) just above the Red+Green scale. After about 10 minutes, it came up to the start of the "G" (about 60 on the "5" scale). I will let it run a little longer when i get a chance. I just had to know that the tube was ok. Also, it is actually a 12LP4A, not just a 12LP4, FWIW. The tube is also a Marconi (painted on the underneath of the Bakelite). I hadn't seen that before.
Tony