1949 Admiral 20A1 chassis question

[Tony F]

I have 2 identical 25 Hz chassis, one has this modification the other does not. It looks as if it is a factory addition. This is in the later serial number set. There are 2 ceramic caps (both 120 pf) tied in series for a total of 60 pf which is wired in parallel across R89 the 7500 ohm 25 watt power resistor that connects the cathode to the plate of the 6W4 half wave damper tube V18. The caps look like brown, red, brown, white color code. Could someone explain why this mod was done ? I don't see anything under production changes.
Page 4 of the pdf has the schematic
https://www.earlytelevision.org/pdf/...a1_sams_77.pdf

Thanks
Tony