[morzh]

I am not sure how valid this is, but if you look at the XXFM tube, it requires -1V bias of the Grid to GND (K).
This bias develops on the 10 Ohm resistor. Which would make it 100 mA current. Which is total return current of the radio, so it is not that improbable.

So, 0.1A square is 0.01 and times 10 is 0.1W. For convenience, 1W will do.
Now, the same current travels through the 140 Ohms, and this sould make it 14 times more power, which would be 1.4W. For this, I would use 5W resistor.