BW5

The manufacturer datasheet indicates:

"This tube can be delivered either with a standard 4 pins base with a normal arrangement and two connection placed laterally on the base for feeding the heating filament, the two normal filament pins being short-circuited and joined to the cathode, or with a base 6 pins bas, the two filament supply pins have a larger section.

The first base allows the use of the "B.W.5" tube on sets already fitted without modifying the connections. »

This seems not correct, as all BW5 tubes we know of to date have either a 5 pins Bigrille base with 2 side connections, or a 7 pins Bigrille base with five thin and 2 thicker pins.