In this exhibit the B309 is labeled as MWT (Marconi's Wireless Telegraphy) and was sold for professional communications systems and additionally and more prominently it is marked as the ECC81.
This double triode was designed for RF use and is of the low impedance type.
The triode sections end on. Front to back each triode is only 2 mm thick.
The overall width of the triode is 10 mm. The anode is one piece folded with a square end and stitched through. The second triode can be seen on the right.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
Reference: Data-sheet & 1040. Type B309 was first introduced in 1953. See also1953 adverts.
