I am not sure how you get distortion with nothing plugged in. DO you mean noise? Distortion requires a signal to distort.
Blows fuses right now every time you turn it on? Or blows them fairly often while otherwise functioning? Does it make a sound as it blows the fuse? A loud sound? If you disconnect the speaker, does it still take out the fuse?
As with any amp that blows fuses, look to power supply and power amp. If the output devices are shorted, go from there. If not, look for shorted rectifiers, filters, or shorts to ground from power rails. The main supply in there is +92v - this is a single sided amp. REmove the wire to the power amp board so the power supply can just sit there. WIll it hold a fuse that way?
If power supply seems OK, check the drivers and predrivers. Is the large output cap shorted? Is the bias string open?