[old_tv_nut]

There's another little story about the change to brighter red and yellower green phosphors. If a tube in an old set was replaced with one with more efficient red, the luminance drive to the red cathode had to be reduced so that the correct white color would be maintained, and RCA published a service bulletin showing how to do it.

But wait, you say, the R-Y drive goes to the grid, so doesn't it have to be reduced also?
Well, no. The new CRT with more efficient red also had the yellower green phosphor. Now, turning on yellowish green was like adding a little red at the same time, so you would want to turn off red to a greater extent than before, as the color moved from red to orange to yellow to green. This meant the R-Y gain should increase compared to the Y (luminance) drive, or in this case, R-Y drive (grid) should stay the same when red Y (cathode) drive was decreased. The increased R-Y gain compared to Y had the unfortunate side effect of making pure reds overly bright, but this was preferable to having the wrong hues in between red and green, which included flesh tones.