[miniman82]

If I were in your shoes (I am actually, fellow 21CT55 owner), I'd always run my sets on a variac and monitor input AC voltage to make sure it's receiving the rated 117 VAC stated in the schematic. Higher voltages tend to cook irreplaceable parts, and I don't fancy trying to locate a flyback for any of my sets. I'm a big stickler on horizontal/HV circuit adjustments too, and it's served me well in collecting TV's.

I tried to find a resistor/diode substitution that worked well on my CTC-4, and in the end wound up with one of those adjustable high wattage resistors so I could home in on the perfect value without spending too much cash. Something in the 100-ohm range that is adjustable usually works, that way you can slide it around from 0-100 to see what the set likes. Just remember: if you do this while running the AC input at 117 VAC, you must always use a variac or B+ will still be too high if you forget. Most simply plug the set directly into the wall, then set the series resistance to whatever it needs to be for proper B+ readings. The tube filaments won't care about a couple extra AC volts on the line, but the effect is dramatic when looking at horizontal output cathode currect. A few input volts ends up spiking it higher than you'd expect, so monitor things and zero in on the best set of variables for it.