Slight Drop in Brightness
 

I fired up the Avante yesterday and noticed that the brightness had changed a bit. The level I had set weeks ago where the blacks were set to the point just below washing out. For an example, in scenes I watched earlier, facial details were lit properly and detail in dark hair were there. Yesterday the faces were much darker with less detail and their hair was jet black with less detail as well. I had to bump up the brightness control just to restore the image. I wasn't a big adjustment to get it back. The contrast was fine. I retested the tube and it was good and I have a large range on the brightness and contrast controls.

So why would the brightness level change?

Can you post the schematic of the video section? What model year is this set?
Did you watch the same exact source material both times?

I've seen CRTs get sleeping sickness from sitting a few weeks. Some sets are more prone to it than others.