I'd replace the screen grid resistors on a Fender Twin Reverb (between pins 4 & 6 on the power tube sockets) with 1K/5 watt resistors and you can forget about them forever.
I'd be afraid to use 5 watt resistors in place of the factory 1 watters. If something shorted with the 5 watt instead of 1 watt resistors it could cause a lot more damage.