Galien Krueger 800RB blows main fuses
 

On a Gallien Krueger 800rb bass amp, if the main fuses blow by just tunring on the power switch, what is the most likely cause?

Same thing it is in any amp that blows fuses. Shorted output devices or shorted power supply rectifiers. With the amp cold, check for E-C shorts in all output transistor strings. Check the main bridge for shorted legs. That should cover 95% of the time. beyond that, try the usual suspects - Shorted filter cap, some sort of short across the power rails, some sort of short across the output, shorts acrosss the primary. And of course loose hardware - any missing screws or nuts? A loose one under a pc board can short out most anything.

Gallien Krueger 800RB blows fuses
 

Thanks for your quick response. Found shorted rectifiers in the power supply section. The caps don't look too good either. That may be the real cause of the failure. I will change them too. Appreciate the help.