Certainly, that's the way we accessed the condition of those tubes back then. Turn all screens down and advance each one. They should roughly be the same but be aware that due to the color spectrum, the green will be the brightest, the red close but not as bright, and the blue (even with a strong gun) won't look as bright and crisp and the green and red.

If your blue looks good, the red and green should look better. From your description, you have a soft tube. It might perk up if you run it a few hours continuously.



We don't know who worked on it and we don't know why he tried it or if he even knew what he tried was simply an isolation "brightener" (he may not have know the difference between a brightener, and isolator, or a combo device).

I worked on tons of those when they were daily drivers and while soft guns were common (I must have changed several hundred 21" roundies), heater to cathode shorts were not all that common in these tubes.

My guess is that they correctly diagnosed a weak picture tube and added the isolator thinking it was a heater boost brightener.

John

WOW, this BBS sure has been glitching out a lot lately! :yes::sigh:

I’m getting this message a lot!
“The server is too busy at the moment. Please try again later.”

jr

Me too

like this, it's borderline unusable :(

Back in the day we tried an isolator a couple of times. It smeared out fine detail in the pic due to parasitic capacitance-to-ground (since video goes in via the cathodes). Don't recall ever trying it on a rectangular tube, though it might do better due to the unit's smaller size.

What does an isolator do really?
Cause it seems that the CRT already has it's own winding off the main power transformer separate from everything, save for a pull up to 200-300v, is it not already isolated by that heater being powered that way?
Or is this isolator removing that path to the pull up and any ref to ground through it?

OK I didn't read your post well enough. Separate winding on power xfmr. Dumb senior moment! DOH. :screwy: Parasitic capacitance would still be a problem though.

The CRT filament usually shared its power transformer winding with the 6BK4 high voltage regulator tube. There was usually a .1 cap to ground from the semi- floating filament circuit. When needing an isolation transformer because of a heater to cathode short in one of the guns, removing that .1 did help with the smearing issue sometimes.