Power Resistors in Guitar Amps

[Helmholtz]

So would you routinely change 100K 1 Watt carbon composition resistors in an input stage to metal film or metal oxide?

No, I don't routinely change components. Exception would be a known component problem in an amp series.

MeO can be better or worse than carbon film resistors, there's a large variation in noise data (more than a factor of 10) for both types. I would use MeO resistors only for wattages above 1W.
Preferred type for low wattage, high resistance is Me-film. But the noise values of CF are not much worse.

Prof. Zollner analyzed the total noise in a typical tube amp input stage. His conclusion is that the main noise contributors are the input grid stopper (only thermal noise) and the tube itself.
He states that the excess (flicker) noise of the resistors (including good quality CC types) is inaudible.

[Mick Bailey]

Quite some time ago I posted here about an amp build I did with regular 1/2W carbon film resistors. It worked out pretty well so I built another using 0.6W metal film. I couldn't tell any difference in noise with that particular build.