CTC-4 Director 21

[benman94]

The fact that you aren't seeing red doesn't automatically point to the red gun of the CRT. You could (and almost assuredly do) have a matrix or demod issue. My CT-100 had problems in the red adder that completely killed any red on the screen; the 15GP22s strongest gun was actually the red gun however.
If the tube was going gassy, I strongly suspect you'd have at least major focusing issues, etc.
Get the chassis working first, then worry about the CRT. Even if the CRT is garbage, I'd finish the restoration and wait for a clunker CTC-5 with a good 21AXP22 to surface. There's little point in having an operational CTC-4 without a good 21AXP22, and you'd be throwing good money after bad by putting another 21FBP22 or 21FJP22 in it.