Quote:
Originally Posted by miniman82
Not to sound alarmist or anything, but it's rare for even a new CRT to tip the scale all the way to 100%. Try this: read for emission while slowly advancing the cutoff knob from full CCW to CW. If you are able to modulate the emission with the cutoff knob in a linear fashion you're good, but if at some point in advancing the cutoff knob it suddenly shoots up to 100% from nothing you have a gassy tube on your hands. I only mention this because at one time I had to understand why a 21AXP22 I had was testing new but glowed purple in the neck when powered by an actual chassis- it has to do with the fact that any gas inside the tube turns it into a gas regulator instead of an electron emitter. As you advance the cutoff control, at a certain point the gas inside will ionize. Once that tipping point is reached and the gas ionizes, it will read 100%.
Only sure way to know is put HV on it. If you can put 20kv on the ultor rim and not see a blue/purple glow, I'd call it a winner.
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I just tried it. I was indeed able to get a linear response on emissions starting with the cutoff fully CCW.
Right when it reaches 100% is right when it starts showing up on the low-tracking/cutoff display, and it just a small tweak there to get it into cutoff.
The last few sets I've worked on (a couple 70s vintage sets) did have 100% emissions on this tester as well with proper cutoff.
I'm just hoping this is right and the tube isn't gassy. As soon as I can I'll try applying HV to it.