The LK199 is a voltage regulator made for the Wehrmacht during the period 1936 - 1945 in Germany. We also have the commercial version 150/40Z in the museum.
The maker's logo plus other information. The date seems to be 1943. The BAL716 stamp shows that it was made to the German Luftwaffe standard and inspected at that particular office. The RLM Eigentum indicated that the valve was the property of the Air Ministry of the Reich (1933-1945). Also the Type starting with LK is also an indication of a Luftwaffe specification.
The locating key on the side of the base.
The three pin base.
The Ln28729 is an alternative Type designation.
The wide glass tube envelope is 34 mm in diameter and, excluding the S3B base pins, is 59 mm tall.
Reference: Observation. Type LK199 was first introduced in 1941.