CRT Emissions vs Cutoff

[MuzzcoVW]

Been a long time guys. I have a GE 21FDP4 out of an old Philco here. It tests with great emissions but tests pretty much no cutoff. As far as I know it was never rejuvenated. Refresh my memory, what causes no cutoff but really good emissions? I do have a replacement CRT for the set when restoration is completed and am curious what i might see if I try using this one first. Thanks, Craig.

[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.

[MuzzcoVW]

Originally Posted by 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.

Thanks. Considering what this CRT is, even moderately usable would be awesome. It's currently in a Predicta Full Dress, 9L60 chassis. Can't wait to finish the chassis so I can check it out.