Looking for a flyback for a RCA CTC 15

[ARC Tech-109]

You would get a higher voltage output going to a solid state doide, not much but the regulation would be tighter given the lower resistance. 1N4007's, are good for 1Kv each and the focus is about 3 to 5Kv, add another for good measure.
You could do the anode side as well with a long string of 4007's, the only issue is the 1N4000 series of diodes are not exactly fast, the 15.734Khz horizontal might be too high for them and a failure is almost guaranteed to burn up your flyback. Personally I'd stick with the original tubes, my Magnavox T940 runs a 3CN3 for the HV, 480ma heater which comes out to be just over 1.5 watts at 3 volts. It put up with 3 of us kids and never had a flyback issue, its still running with the same HV tube today.