The 6D6 is a variable μ pentode for AGC controlled amplifiers at RF and IF in superhet radio receivers. This exhibit also carries the American service designation of VT-69.
Electrically the 6D6 (UX6 base) is identical to the Type 58 (UX6 base) and the 6U7G (IO base).
The base carries the RCA logo and country of origin - USA.
Not a lot of detail available at the top but the control grid wound on copper supports connects to the top cap and the other two grid supports can be seen above the top mica.
The classic envelope is 39 mm in diameter, and excluding the UX6 base pins is 109 mm tall.
References: Data-sheet, 1040 & 1043. Type 6D6 was first introduced in 1936. See also1936 adverts.
