I have looked at the horz blanking setup in the CTC 10/15/16/16XL/20 , and it very much looks like they use the same setup in all of them, with only slight variations.
Making a guess on how it works, using pulses from the FBT, (on the grid) it then passes the blanking pulses via a .22uf to the cathodes of the RGB-Y amps, tied to gnd with a power resistor at the end of the chain, wave can be anything from 10-15, depending on the set.
It also seems to pass blanking pluses to the cathode of the color bandpass amp (cathode follower setup), this is tied to gnd via 820pf / 390 ohm res, (all versions )
This I assume is to insert blanking to chroma, where the above is for luminance?
Only the CTC-10 shows what the wave is on the cathode, (10v ptp ), I will assume this is the same for all sets , or rather close, since they all have the same circuits.
https://imgur.com/yCoszDQ
At this point, I do not remember what the waveform was like at that point on my set, but as mentioned, I did not replace the 820pf / 390 ohm res off the cathode of my bandpass, as they were before I got it, but now I think I may try next time I have it apart & perhaps r188 (power resistor at end of -y amp chain) .
This also may get me nowhere, but I have replaced pretty much everything else in the blanking circuit.
Granted, I don't see the lines as much as a real problem right now, more of an annoyance.