The B suffix on this 12AX7 denotes a different construction from the 1940s original design. This exhibit is in 2015 an example of current manufacture, in this case Chinese, for the valve audio market.
The bright structure on the left is part of the electrostatic screen between the triodes.
The anodes are boxes that are wider than the original design. This increased spacing will change the anode AC resistance.
The thin glass tube envelope is 22 mm in diameter, and excluding the B9A base pins is 50 mm tall.
