The 6U4GT is a television efficiency diode for use within the line timebase circuit. The diode allows energy from the collapsing magnetic field in the line coils to be fed back to the HT rail. The maximum peak inverse voltage for this stressed component is 3,850 Volts.
The octagon border around the Type designation etched into the glass looks very much like an RCA product. It is possible that this was a re-badged.
The anode has a small front-to-back dimension of about 5 mm.
The wide face of the anode exists to maximise the radiating surface and thus cool the valve. The Brimar name is printed on the base cap.
In this closer view the heater can be seen to be wound around a ceramic central tube.
The wide glass envelope is 28 mm in diameter and, excluding the IO base pins, is 72 mm tall.
References: Data-sheet & 1040. Type 6U4GT was first introduced in 1952. See also1952 adverts.
