the flyback fails internally and sends the hv to unknown levels, I have not seen it blow the end of a tube off but i have heard reports from others that it does this.
I have seen a few fail to the point of excessive hv and the noise is quite disturbing, lucky I had no tube damage on these occasions
looks like its been like that for some time, replace that connector and resolder the chassis header and clean the header pins- you get a bad connection on horizontal header and this does happen