[morzh]

Well, fuses do save things though their primary function is to prevent fires and the rest be d**ed.

As for diodes: are they axial cylindrical ones?
What is your max wattage per channel and the load in ohms?
Take your max wattage, (say, 25W) divide it by your speaker's Ohms (say 4), extract square root (app. 2.4A) and multiply by two (2channels), you get 4.8A max load.
Now because your diodes conduct 1/2 time, 4A is a good rating that in the datasheet will be marked as "Average Forward Current".

Your reverse blocking voltage should be also 2 times the output voltage so if you have 25 V, 50 to 60V is good.