|
I pulled this quote from an old CTC-5 thread of Dave May in 2013. The quote is from Old TV Nut.----
" If the drives required for the red and blue guns were equal to make white, then the pattern would need to be elliptical, with the B-Y gain = 2.03/1.14 = 1.78 times the R-Y gain. (These are the ratios dividing the B-Y and R-Y axes before the chroma is modulated.) However, the red phosphor in the early tubes is weaker by about the same ratio, so equal (approximately) is correct (that is, the pattern is circular).
By a fluke of changing both the green and red phosphors in later tubes, the red gun requires less drive to make white; so there was a fix to reduce the red luminance drive; and at the same time, the yellower green sulfide phosphor means that the extra R-Y drive is still needed, to approximately compensate by making the difference between reddish and greenish colors greater. So, the matrix adjustment does not have to change, and can stay with a circular pattern when a new CRT (e.g., 21FBP22) is substituted. "
I was wondering if anyone has a schematic or an idea of which components were altered for the reduction in the red drive? I already found the contrast/ brightness fix schematic for the 12BY7a video cathode modification.
Thanks,
Ed
|