Quote:
Originally Posted by Electronic M
When a CRT is weak or old it can have a long warmup time to it's stable operating point. I'd guess that if you put that CRT on a tester and watched it's emission/cutoff readings it would probably change over that same 5 minute interval.
I've got a color set with a weak CRT with poor life. All guns will start dim and the weakest one will take the longest to warmup and stabilize (which makes the colors look weird for a bit).
Generally speaking the CRT gun voltages listed in the schematic are the correct settings for a new CRT (because that is what they would have had when recording that data). The optimum CRT grid and cathode voltages are the ones that correspond to the contrast and brightness settings that look best. Those settings will drift as the CRT ages from use.
Keep in mind that you want to NOT* adjust the picture for the brightest possible image with good contrast (doing that drives the CRT hard and given it seems to be a tired CRT that will kill it faster than normal). You want to adjust for the dimmest picture (with good contrast) you deem comfortably watchable (at least if your concerned about CRT life).
*Unless you plan to ride the CRT hard till it dies, and then replace it...Some people do that when they have a replacement on hand.
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Interesting and got it. This CRT is clearly high hours since it is the original and was pretty dead when I got it. I zapped it with the rejuv on the CR-70 and it brought it back to life with good emissions and cut off, but yes the life test was poor. I consider it borrowed time and I don't plan to make this a daily use set. It sounds like this can explain some of the remaining warming up issues though.
FK
(attaching bonus pic of original Ratheon diode)