The 13D9 is a mystery valve in that no reference to it can be found in the available literature or on the internet. However, it is widely reported to be a special quality ECC81 or M8162.
The getter ring support is in the form of a bright U-channel "strut" that extends right across both micas and a fair way above the upper one. Quite different to the Brimar 13D9 in construction.
The anodes are small boxes with extended side flanges.
Thanks to R J Sutherland for the excellent images and information.
The thin glass tube envelope is 21 mm in diameter and excluding the B9A base pins, is 47 mm long.
