According to Edith Reiter's 2014 book, this instrument was completed on 27 October 1911 and sold to a customer at an unknown location.
Howe & Hurd (2004) describe heckelphone #51 as a model 36b, with a one-hole bell and a central peg.
As of 2004, this instrument was reported to belong to the the Residentie Orkest in The Hague, Netherlands, to whom it had been given as a gift by Richard Strauss for a performance of the Alpine Symphony. It is likely (although unverified) that Strauss ordered heckelphone #51 directly from the Heckel factory.