Well I went and bought a NOS rebuilt 7JP4 off ebay a couple weeks ago.
"Untested" and cheap, and we all know what that usually means!
Sure enough, it was NOS but sure enough it was defective.
I had to pull the base cap off to fix a short caused by a wire out of place.
Putting the base cap back on a tube with 12 active pins is a special kind of hell that no one should have to endure
After several tries with various types of extensions soldered to the pins I finally did it, the base isn't absolutly snug against the tube but close enough for me.
It works!