I've been blessed!

[old_tv_nut]

I sat down with the service info and reread the grayscale tracking procedure, partly in case it might be needed when the B+ is restored normal, but mainly to try to understand how it works.

The strange thing is that the CRT grid DC bias points in the chroma section are adjusted to correct highlight color, even though the controls are labeled "background" and really do affect the background more strongly than the highlights.

The instructions say to set the "background" controls to counter any tint in the highlights and then adjust the G2 controls to counter the resulting tint in the shadows.

After reading this carefully and looking at the electrical characteristics of the CRT, I realized that the CRT gun is actually a variable-mu (variable gain) tetrode, and when the G2 controls are adjusted after adjusting the grid bias, the CRT is operating at a different mu (gain), effectively changing highlight white balance.

I also note that the CTC-5 called for a 8200 Kelvin color temperature, not as blue as the 10,000 Kelvin that was spec'd for later chassis. In any case, I don't believe accurate color temperature was ever achieved by eyeball, as the eye adapts too readily to color temperature changes. No TV repairman had a colorimeter in that era.