A lovely Bartels double from April 1929 and listed at G&H. Many thanks to Mr. Beach for his efforts in acquiring the pics. Note the "K" after the steel type. There aren't that many families with the last name "K" post WWI. Bartel's didn't make 344xx examples and I'd looks to Suhl for a maker having that serial number range in the late 1920s.

A DR by Ludwig Schiwy of Berlin with Böhler steel tubes with number 15xxx as found in DGJ Vol. 13, Issue page 74 has a very similar "K" on the lower rib. Schiwy didn't make 13k examples and with a April 1938 date at the Suhl proofhouse, I'd looks toward one of the Merkel craftsman as being the source for it.

Kind Regards,

Raimey
rse