[Mondial]

The wattage rating of a substitute resistor may be calculated from either the current drain or the voltage drop across the original field coil.

The service data says that the current rating of the power transformer is about 70 mA, or .07A.

Power = I x I x R or .07 x.07 x 1140 = 5.6 W


Or another way is to take the voltage drop across the original field of about 75 volts and calculate power from it. P = V x V / R or 75 x 75 / 1140 = 5 W

Although the actual dissipation is only about 5 Watts, you want a safety margin, so a 10 to 20 Watt resistor would be recommended.