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Agreeing with the earlier suggestions, eliminate external causes first. Disconnect everything from the TV and back off the AGC pot to get a blank white raster and see if the hum is still there. (I don't think a CTC-10 had a 3-position service switch, but if so, all the easier on the blank raster!!!)
Next wild guess is that I had a Magnavox roundie doing something like that (single-color hum bar, one at a time). I recall that it was a heater-to-cathode short in one of the 6GU7 tubes (might be the G-y amplifier tube in your case). Just a guess, so don't be disappointed if it's a bad guess... That type of problem can be a real head-scratcher to locate.
Charles
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