[Heathkit] RX-1 question

[TChesek at Epix.Net]

I recently made mechanical repairs to a RX-1 for my shack and am going to replace the power supply electrolytics since I am getting an undesirable hum level. Since I'm replacing all of the electrolytics my question is in reference to an electrolytic in the audio section. The schematic shows a 20 mfd 150 v capacitor connected to the cathode of the audio output 6AQ5. This cap shunts a 330 ohm and a 15k ohm series resistor network to ground. My radio has a 2 mfd 50 v cap shunting the 330 ohm resistor only. Is this a mod, an earlier revision, or an error?

73,
Tom K3TVC