CRT Emissions vs Cutoff

[Electronic M]

Sometimes a tube will still work perfectly with no cutoff. Cutoff is basically a measure of how well the grid can cutoff emissions flow from the gun. On sets with grid injected video it can matter more, but on sets with cathode injected video it tends to not matter much.

I had a good 10BP4 with no cutoff that looked great in a working chassis.

On some testers such as my B&K 466 you're supposed to adjust G2 for cutoff such that the meter reading increases by 2 divisions (4%)....No increase typically isn't an issue if there's good emissions, but neon bulb action (you get no increase then suddenly runaway uncontrollable increase with no ability to adjust to achieve something in-between) indicates a gassy CRT. I doubt yours is gassy.