I hate my obsession

[Dr. Vegetable]

If it's not a bad tube, a crackling sound is often caused by a cold solder joint or broken wire. If you are comfortable safely working on the internals of an amp, you could inspect everything for any visible problems and heat up any cloudy-looking solder joints with an iron. Also look for any components that may have been damaged by too much heat and replace them.

I've diagnosed a lot of gear problems by doing a purely visual inspection. Even so, most electrical problems are invisible and you may need to bring it to a pro.

Good luck, and be safe!