Tim is correct. "blooming" is common on CT-100's when large bright/white images appear on the screen. This due to the design of the HV regulation circuits. Keeping the brightness/contrast at their minimums while maintaining a viewable picture helps. The focus on my CT-100 does tend to jump in & out but is unrelated to the HV design. I believe I have a bad focus pot. Current back problems prevent me from pulling the chassis to confirm.
-Steve D.