The first thing you should check is the filter caps in the power supply. Electrolytics tend to go bad as they get old, and when they do, they like to become short circuits. It's also possible that the rectifier bridge diodes (either individual diodes or a bridge pack) may have one or more shorted diodes. If all of these seem to be good, there is something else in there, probably with the amplifier section. But you should check the bridge and the main filter caps in the supply as a start.
Depending on whether you want to go quick and cheap rebuild or audiophile, it may not be very expensive, as long as the transformer isn't bad.
That is one other thing to try, I just thought of, disconnect the secondary wires of the transformer from the PS circuit, making sure the wires don't short, and try replacing the fuse and turning on again. If the fuse doesn't blow, then the tranny is ok, since it has no load at all.
Peace,
Dave