Where's The Doorknob Capacitor?

[Tom9589]

I had always thought that a 500 mmf doorknob capacitor was required to filter the high voltage when using a metal CRT. The inner and outer aquadag coatings with the glass envelope in between serves as a filter capacitor for all-glass CRTs.

I noticed that the doorknob capacitor is not used on color sets with 21AXP22 (metal) CRTs like the RCA CTC-5.

How come?