No, the strippenkart was not valid for NS train rides within Amsterdam. The strippenkart was a paper-based ticket system that was used for public transportation in the Netherlands, including buses, trams, and metro lines. It consisted of a card with pre-printed strips, and passengers had to physically punch or "strip" the appropriate number of strips for their journey.
NS trains required separate tickets or travel cards specific to the train system, such as the OV-chipkaart or paper train tickets purchased from the NS ticket machines or counters.
Since then, the strippenkart system has been phased out and replaced by the OV-chipkaart, which is a contactless smart card used for payment on various modes of public transportation in the Netherlands, including trains, buses, trams, and metros.