According to Edith Reiter's 2014 book, this instrument was completed on 17 September 1906 and sold to a customer in Germany.
Howe & Hurd (2004) describe heckelphone #23 as a model 36b. As of 2020, it is part of the collection of musical instruments at Münchner Stadtmuseum in Munich, Germany, where it is catalogued as item no. MUS-89-8.
Before becoming part of the collection at the museum, heckelphone #23 belonged to the Bayrische Staatsoper München (the Munich opera), where it was used for the first performance of Salome in Munich, on 25 November 1906. It is therefore likely that the Munich opera acquired heckelphone #23 directly from the Heckel factory.