Look like the original is probably a 2 Watt wirewound?
Under normal operation, the pot dissipates only 0.16 Watt, but at turn on its quite a bit more. Before all the tubes heat up, there is almost 500 V across the voltage divider, and the pot is subject to about 100 V. Calculating the power (100 x 100 / 10000 ), it is 1 Watt under those conditions, so to be conservative I would go with a 2 Watt replacement
That 's great. I have already ordered 5W, but was not sure. The original is wire wound. The new one will fit nicely.
Thanks.