The 6AT6 amplifier triode with double diodes sharing the same cathode connection was designed for use in superhet receivers as detector, AGC rectifier and first audio amplifier.
The shape is distinctive and Dario do not depart from the standard.
The diode anodes cascading down around the central triode.
Turned slightly the separation between the diode anodes can be seen.
The thin glass tube envelope is 17 mm in diameter and, excluding the B7G base pins, is 47 mm tall.
References: Data-sheet, 3002 & 1040. Type 6AT6 was first introduced in 1946. See also1946 adverts.