The 6SQ7GT is a double diode triode sharing a common cathode.
The triode is seen at the top with the carbonised anode, the double diodes are seen as the anodes between the triode and the pinch. The bright screen below the mica connects to the cathode. The diode anodes are the rods either side of the cathode tube within the screening box.
This valve was designed for superhet receiver use where the diodes would act as signal detector and AGC detector and the triode would be the first stage audio amplifier.
Side view of the box anode of the triode and the bright screen box below.
Unlike most versions of the 6SQ7 family this has the triode anode with one side anode flange only. Most are symetrical with side wings either side of the central triode active area.
The wide glass tube envelope is 29 mm in diameter and, excluding the IO base pins, is 66 mm tall.
References: Datasheet, 1040 & 1043. Type 6SQ7GT was first introduced in 1939.