Depending on the popularity of the piece, when a manufacturer changes models the market can become flooded with demo units and units from people upgrading to the latest and greatest. This can depress prices for a while then prices may rise again when fewer pieces are available, then may flatline. In the case of really old stuff from the the late 50's and 60's like Marantz, McIntosh and even Dynaco, prices increase above original cost due to inflation. The cost of a Stereo 70 in the early 60's was about $63.
