I am with Tom C. Discharge the CRT & pull off the anode lead.
Pull the 3CU3 socket & clean it with 91% isopropyl alcohol.
Clean all the wires to it & the "cup" also. Put back together with
the new 3CU3 & try it.
BTW dischage the CRT AGAIN before reassembly !
BTW #2 most HV rect tubes DO NOT have a filament glow !
73 Zeno
LFOD !