If you can only afford $300, get the Adcom repaired. Getting a Rotel is a sideways move.
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Very nice for the money (and this one is at a good price). disclaimer: I know not this seller.
Another one would be a B&K ST1400II if you can find one used.
As recommended, repairing the Adcom may be a good option. Also, if you like the Adcom, maybe stay with Adcom and move up the line? You could sell yours as is for repair, buy a used model and probably come out for less than repairing your 535.