It's possible that the caps are pulling too high a surge current for the rectifier tube....
Try pulling all the tubes except the rectifier tube. Be sure the caps are fully discharged, then watch what happens when you take it out of standby. If you get the tube flash, then I would suspect that the caps are the issue.
To repeat, discharge the caps again (through a high wattage resistor) before retesting.
However, I wouldn't expect the caps to cause the fuses to blow after all had settled down and while you were playing the guitar. That suggests that something else could be wrong. (also?)