I'm amazed Magnavox didn't put a fuse in the power supply, to protect the transformer against shorted electrolytics or even a short in the rectifier tube. However, I have to wonder why the house fuse or circuit breaker didn't trip open as soon as the filter cap shorted; after all, these caps are in a position to short the AC line directly to ground when they fail. Another thing: Didn't the set's owner notice that the sound had a 60-Hz hum when the filter cap started to go bad, long before it shorted?
As much as these Magnavox phonographs cost when they were new, I don't think it would have added that much to the price to include a line fuse. Magnavox was a top-of-the-line manufacturer in the 1950s, not one to cut corners, which makes it difficult for me to understand why they would leave the transformer unprotected. The only other thing I can come up with is that there may well have been a line fuse in the set, but the owner foolishly bypassed it. Again, I wonder why the owner didn't get the hint when the sound became distorted from 60-Hz AC hum when the filter cap was just starting to fail. Why the person would just leave the thing on when the cap eventually shorted, leading of course to the transformer burning up, is far beyond me.