Whelp, since it's the cathode bias circuit for the power tubes and each is individually biased, and bypassed with a 100uf cap, its your power tube bias resistor and i'd hazard a guess the "line" is a 1 for 1 watt.

You would never need a 10 watt for a single EL84 tube, so i'd say 1 watt.

You might want to put in a 2 or 3 watt to be safe.

Look at the power supply resistors and see if they put lines or numbers inside the resistors, that would be the "key" to help deciphering(if they did that) There's bound to be a 1,2,or 3 watt resistor in the power supply somewhere.