A search might turn up some more discussion of this unit. Supposed to be a really nice receiver, when Marantz was still U.S. made.
It has the 20b tuner in it, one of the very best that Marantz ever made. I think I read somewhere that they are kind of a bear to work on, but that is rumor only. Depending on what amp you are trading, the condition of the Marantz 19, and of course what you are looking for, it could be a good move..
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EDIT: Scroll down a bit and read the thread on the similar Model 18, there is a fair amount of info on both units there.