Another RCA CT-100 discovery B8001599

[dtvmcdonald]

This thread about brightness got me off my duff (combined, I might add, with a
fake bomb scare that kept me away from the office) to check if something
in my set's setup had changed to make for dimmer pictures. And since checking
requires a scope, I checked the DC restoration, at least on the red.

It turns out that my occasional tweeks of the gray scale had got my marks
for the brightness control a bit off, but every other adjustment
was spot on. Fixing the "normal" settings gives a picture that is 100% watchable
on a day like today ... overcast but with the window shades open.

And yes, the DC restoration is in the 85 to 90% range. That's measuring how much the sync tip level
at the red grid changes divided by difference in grid voltage between full white screen and
deepest black blanking.

When my set was first working it did bloom, but now it never ever does. I
don't know why. It could be the parts replacements in the HV section, including
regulating the focus voltage with a string of Zeners. Or it could have been
the setting of the range of the brightness control. I'll never know.