Quote:
Originally Posted by Electronic M
One possible point of contribution to the grayscale issues is difference in phosphor efficiency of a 15G and a 21FB CRT. Phosphor efficiency changed substantially between the two.Circuits that were meant to balance colors on a 15G where colors were inefficient across the board, and the phosphor efficiency varried radically between the weak red and IIRC the strong blue probably are a ways off of optimum for later phosphors.
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Your restorer should not be messing with the gray-scale and color balance issues at ALL at the moment. He's liable to go about fixing a non-issue, thus making the situation worse. The entire point of the then all-new sulfide phosphors in the 21FBP22 was to get more equal beam currents between the three guns. The 15GP22 and 21AXP22 ran with a ratio of red gun current to blue gun current of ~4 or 5. The ratio of red gun current to blue gun current in a 21CYP22 is ~3. The ratio of red gun current to blue gun current in a 21FBP22 is only ~1.5. Of course this will vary a bit from sample to sample, but the point remains the same. Even a cursory glance at the datasheets for the two tubes in question would have revealed the difference.
In fact, conversion instructions for converting 21AXP22 based sets to the 21CYP22 or 21FBP22, and instructions for converting the handful of 21CYP22 sets over to the new 21FBP22, very often included simple changes in the matrix circuitry for this very reason. Without them, proper setup is an exercise in futility. Redag the 15GP22 and put it in the set already.