The 6AT6 amplifier triode with double diodes sharing the same cathode connection was designed for use in superhet receivers. The EBC90 has detailed photographs. The EBC90 is another example of the Mullard production of this valve. EBC90 would be the Philips/Mullard designation for this type.
The two diodes are the outer structures while the triode is housed in the central dark anode.
In this broken 6AT6 the construction is easy to see. The central dark cylinder is the triode. The outer bright plates are the diode anodes.
The common cathode tube has two separate sprayed coatings. On the right can be seen the emissive surface for the double diodes. The lower anode is bent by the attachment of the getter holder.
The filament passes four times through the cathode tube. The insulation is missing at each of the hairpin bends in the tungsten wire.
A close view of the triode grid.
A closer image of the diode construction.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 50 mm tall.
References: Datasheet, 3002 & 1040. Type 6AT6 was first introduced in 1946.