The 6D6 is a variable μ pentode for AGC controlled amplifiers at RF and IF in superhet radio receivers. Electrically the 6D6 (UX6 base) is identical to the Type 58 (UX6 base) and the 6U7G (IO base).
The Brimar identification is printed onto the Bakelite base cap.
The two part steel screen is held together with a spring clip. The words are Goat NY and Pat Pending. This was probably tin plated originally to give a shiny finish.
The classic envelope is 40 mm in diameter, and excluding the UX6 base pins is 107 mm tall.
References: Data-sheet, 1040 & 1043. Type 6D6 was first introduced in 1936. See also1936 adverts.
