[Mondial]

That looks like a 20 ohm resistor to me (red, black, black). It appears that you have the second type chassis, with the cathode of the 6A7 grounded through the 20 ohm instead of directly. This resistor was removed in late production, and the cathode was then grounded to the chassis. See the last page of the nostalgia air info on the 610. It mentions the change removing the resistor.

I would use that second type schematic for reference, as it shows the resistor already removed. It should not change other aspects of the schematic wiring or connections to the osc coil