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I'd use the CRT tester before proceeding. 21AXP22s aren't easy to find and are expensive. 21FBP22s are comparably easier to find, but take a non-trivial amount of parts and work to adapt to a CTC-5.
Once you know the CRT is okay here are a few other things worth having for a repair:
HV meter capable of measuring 30KV.
Test pattern generator or DVD capable of putting out a crosshatch pattern, and color bars.
B&K 1077 analyst (if there's sweep or signal chain issues using one to do signal injection troubleshooting can save you hours of fumbeling around trying to troubleshoot something tricky...Most analysts need a recap too so it's a good warm up project).
Two things I highly recommend doing on a CTC-5: installing CTC-7 HV control pot circuit and installing CTC-7 contrast/brightness circuit.
If you compare the CTC-5 and CTC-7 Sam's schematics (earlytelevision.org has both under color TV -> technical information) the only difference between the CTC-5 and CTC-7 HV reg circuit is the 7 replaces a fixed resistor from the 5 with a potentiometer and a smaller fixed resistor. Having an HV adjustment makes life better.
I haven't tried the contrast/brightness mod yet (wanted to see the original circuit work for a while first), but RCA recommended it as a cure for various complaints and a performance upgrade. Supposedly it uses the same control pots as factory and just changed the wiring and possibly some fixed value parts.
If you have owned and watched other roundy chassis before, but NOT a CTC-5 reduced expectations are also a good thing to have....The CTC-5 was the Muntz(it was so Muntz like that Muntz actually bought CTC-5 Chassis from RCA to rebadge as their first color set)/Portacolor (both had a lack of DC restorationin the video going on) of RCAs roundy fleet. RCA cost reduced and simplified that chassis so far that they were the worst performing RCA roundy color. This coming from a guy that has owned and restored every RCA color roundy except the CTC-7,11 and 12 (well my 15s are clones/rebadged, but reasonable representation none the less). Even the CTC-20 which was a rectangular CTC-19 back engineered to use up the old stocks of roundy CRTs and cabinet hardware and was a 6GH8 eating machine was a better working set, when working, than the CTC-5.
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