Better to find a HV probe than blindly change parts on a set that new IMHO. If you are runing 18KV of HV the set will wear out it's CRT that much faster (lower HV= more cathode current to achieve a fixed brightness level=shorter cathode life), and if you are running over 30KV the CRT could arc internally and be damaged.
This is the cheapest decent looking one I could find on the bay:
https://www.ebay.com/itm/Vintage-Dyn...AAAOSw4ZNcm-y1
If you check any remaining local TV repair shops, haunt Ham radio and antique radio swapmeets your bound to come upon a cheaper HV meter (I think I paid less than $15 for the last 3 I've had).
You may even find a TV repair shop that will test the HV for you...I'd even loan you a meter if you're close by.