A "very" foolish thing to do! as if the "proper" rating fuse is installed and it blows on loud music then it indicates that the loading on the output stage is incorrect, this possibly because the speakers being used are not the original and are of a lower impedance (resistance) type, or that additional speakers have been added in parallel which will have the same effect.
Shorting out a fuse such as you have effectively done will cause overheating of the output stages and at some point they will blow, and because of the age of the unit replacement parts are liable to be very difficult to obtain.