Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
A shorted component, possibly one near the output stage of the amplifier, is undoubtedly shorted. A hum being produced, hints that the shorted component might be a capacitor, possibly a large one if the hum is low-toned.
Check all capacitors, esp. the largest ones, for signs of either leakage, overheating, or a bulging top... all signs of capacitor failure.
And look for other components that might have been overheating... since you have blown more than one fuse, they have had some chance to do so. A usual sign of overheating is a brown patch on the circuit board under a component.
How old is the Wurlitzer Omni amplifier in question?
If you are restoring an organ from the 60s, you have quite a job - and quite an interesting challenge - ahead of you.
The advice I already gave applies, except that if your model is a whole organ rather than a modular audio amplifier, then concentrate on the audio amplifier portion, if it is an electronic or electrical organ rather than one of the odd 'tone generator' type organs.
And some online research, and posting at OrganForum, wouldn't hurt, anytime a specific detail (that I cannot advise you on) is a puzzle or a problem. OrganForum is at