Bryan, I just read all of the posts. About the mica caps. With the arrow pointing to the right, if the upper left dot is black then it is mica. If it is silver, then it is paper.
Any chance that when you tried to kill the HO tube that you did hurt it? If you managed to get it just a bit gassy could the grid start to conduct once the drive gets near it's peak and clip the waveform?
I'm not sure what your horizontal oscillator stage looks like. If it's a cathode coupled multivibrator, then perhaps that tube is just weak. I must be showing my ignorance here.
Chelsea, my cat, just looked at the computer screen, snorted, and left.
Enough of my weird theories. I think your set's looking pretty good!
John