[Amps] SB-220 question

[Catherine James]

I've just bought a Heathkit SB-200.  Superficial inspections looks good; no sign of burned contacts, corrosion, etc.  Transformers appear fine.

There do not appear to be any Harbach board modifications made.  I will need to install the softkey before I can use the amp, and I am planning to put in the soft-start at the same time.

There is one connection that I cannot reconcile with the manual, but I am no expert on this amp.  See the photo below:

https://s3.amazonaws.com/files.qrz.com/r/n5wvr/SB_200_plate_wiring.jpg

The plate connections of the two tubes run through a capacitor/inductor circuit to a green RF choke.  There is a short uninsulated wire that runs from this choke to a lug, and it appears that it once connected to a screw terminal on the capacitor bank wall.  However, it is hanging loose.

There is also a capacitor of about 5800 pf running from the end of the green RF choke to a grounded lug on the sheet metal panel above the capacitor bank.  I am not seeing this in the manual at all.

Is there a known SB-220 mod where this direct connection is replaced by a capacitor?  What purpose does it serve?

73,
Cathy
N5WVR