Why would an amplifier keep blowing fuses?

Maybe there is to much juice going through the amp, or there is a short in the amp that you need to fix

Look at the fuse if it is black or the fuse element is obliterated then you have a dead short to ground check all wires for short to ground if fuse has a small break check and make sure you are using the right size and type of fuse after that it will be internal to the system also check that a speaker is not shorted

One possibility is that thee is a short circuit in the loud speakers or the speaker wiring. Disconnect the loud speakers, replace the fuse, and see if the new fuse blows.
A minor possibility is that the amp has a dual supply voltage selector (e.g., 125V or 240V) and the selector has been set to the wrong voltage.
If the supply voltage is correct and the speakers are OK, then you have a fault inside the amp.
This could be a protection device such as a varistor, which is a device that protects the amp if it receives an excessive power supply voltage (such as a voltage spike caused during a thunder storm or a power cut). The varistor goes short circuit. This prevents the excess voltage getting into the rest of the amp, so nothing else gets blown up, but you have to replace the varistor to get the amp working again.
Check the resistance <cross the power input. If it is zero and you have a varistor on the power input, try disconnecting it. If the amp starts working, then you need to replace the varistor, otherwise the amp is not protected and another voltage spike could seriously damage it.
Another possibility is that the power supply transformer has burned out. Try disconnecting the output of this transformer and replaceing the fuse. If the fuse still blows, the transformer is probably burned out.
Finally, you could have short-circuited transistors in the output stage of the amp. You may be able to check this by measuring the emitter to collector resistance of the output transistors. You will need a multimerter that can measure low resistances. Most transistor amplifiers have resistors of the order of 0.5 to 5 ohms in series with the emitters oif the power transistors, and you need to detect the difference between a short-circuit transistor and two of these resistors in series, so you have to be able to see the difference between zero resistance and 1 to 10 ohms.