In most cases, a blowing fuse signifies an error in the circuitry. Such an error can arise due to a major power surge, failed or shorted power tubes, or damaged rectifier tubes in the amplifier.
Simply replacing a fuse is not a sufficient solution to this problem, and the replaced fuses may not only blow but also permanently damage other parts of the amplifier. A fuse blows up and stops the continued functioning of the amplifier so that the damage doesn’t get to the internal parts of the amplifier.
Checking the power and rectifier tubes is the best way to remedy blowing fuses. In most cases, the problem lies with a single tube, and it’s very rare when sets of tubes get damaged simultaneously.
The power wire of the amp grounding out is also a major cause of fuse blows. This grounding may harm the internals of the amp, and the fuse is designed to blow before it happens. Ensure that all the contact points of your wiring are secure and the wire is undamaged.
Installing wrong fuses in the amplifier can also cause them to blow. Lower rated fuses continually blow whenever the power is switched on because the amp reaches their threshold almost immediately. However, having higher rated fuses is also risky because it is similar to not having a fuse at all. This may lead to actual damage to the amplifier.