Converting a 17GP4 to a glass tube in a 1951 rca

[Turle]

As the title suggests, I have a 1951 rca console. It’s an early rectangular set with the kcs 66 chassis. It uses a very specific rectangular metal tube which unfortunately is very weak . I only have a known good 17HP4 glass tube , everything seems like it would work, however upon powering it up, the set refuses to develop high voltage, I can’t seem to figure out why. It has no problem generating high voltage with the old metal CRT.

Has anyone had experience converting metal tubes to glass before? I’m
Completely stumped