The 1B29 is a triggered spark gap. Two or more are used in series and the reference 1B29 below gives details of the type of circuit these modulators are used in.
The evacuation pip at the side. The central electrode has broken away from the top connector.
The broken electrode is loose within the outer cylinder.
The thin glass tube envelope is 21 mm in diameter, and including the base is 83 mm tall.
Reference: Data-sheet. Type 1B29 was first introduced in 1946. See also 1946 adverts.
Updated April 13, 2019.