Hi all! My first post!
I have a Princeton 65' guitar amp which I have always treated with care. The other day however when I turned it on the signal (playing through the clean channel) was distorted and lacking of any treble response. The distortion sounds a bit like the effect from a dist. pedal however when the notes decays they all end in a fart-like crackling sound.
I have no idea how I came to harm the amp. Does any of these symptoms sounds familiar to anyone?/Any suggestions? I'm planning to change the fuse and unscrew the speaker to check if it is torn in any way. I have found the schematic, but cant make a lot of sense out of it.

any response is highly appreciated!  <3)