I purchased my DSL40CR in Sept 2020. Its never left my bedroom, never been played particularly loud and (unfortunately) I have not had a lot of time to use it.  The presence and resonance originally worked when I received the amp but now turning either of these two knobs has no effect.

Also there has always been an occasional, infrequent, weak 'crackle' noise.  Is this a tube problem or is this normal for this amp?

Is there an 'easy' fix, like swapping tubes?  Is that something I can do myself?

Please let me know what my options are.

Thanks,

Dean