My CT-100 lost HV (from losing one B+ line).

[benman94]

Going gassy is a process, not a single event. It's possible to have a tube that's going gassy with no blue neck, no focus problems, etc. Just periodic arcing as the first symptom. Remember, every gassy 15G out there (and there are a lot of them) was good at some point.

I slowly lost a 16AP4 to a leak. The first symptom was (probably, looking back on it) arcing. It became more frequent, then it got very dim and lost the ability to focus. Now that said, it's been a SLOW process. A few years minimum...