Thanks for the replies everyone I didn't think a bad tube could be so dramatic. I tap tested the tubes and it seems that 1st Power tube and the V4 preamp are the culprits as they're the ones crackling.
Recently my dsl40c has been acting up in the triode setting by producing a low hum that doesn't change in volume and isn't present in the pentode mode. It worked fine but the humost was annoying. Today I turned it on and experienced the most God awful noise I've ever heard from an amp .
It...