[ChrisW6ATV]

Thank you all for the helpful information and comments.

Nick, I may put a piece of phenolic on the top surface of the HV box if/when I get this set going OK again; does "fish paper" accomplish the same thing, if I find some of that instead?

Username1, Tom, and Old Coot, I will go ahead and put a current meter on the H output cathode when I am ready to fire this set up again; also, I will run the Variac low to start, and observe the results of adjustments I make. The adjustment procedure for a CTC-4 does not specifically address the cathode current, but I will do so anyway.

Eric, my thought was to use some corona dope on any suspicious windings in the arc area once I have the wax carefully removed (and before I coat it with the silicone). Do you think it is a viable alternative to epoxy paint?

Bob, this set has a CTC-4B chassis, and seems to match the "late production" schematic diagram in the RCA 1955-1966 Field Service Guide. I thought I saw an RCA note that said all Gainsboroughs were "late production" models and were built with the changes in place; there is a list of them in the Guide that I will look at and compare with my set. There is no hang tag or any other service information in the cabinet or chassis. This is a maple-cabinet set, I think; it is a much lighter color than any walnut wood I have seen. Indeed, I would love to put a 21AXP22 back into it one day. The broken CRT was a 21AXP22A with the date code 6048, and from various tube date codes, this set was likely in regular use to perhaps 1966 or so.