The Y63 is a second generation tuning indicator with a 6.3 Volt heater. This type of indicator was used in many radios. This exhibit carries identification information in a typical M-OV lozenge style but the paper label on the other side GEC Tuneray.
The data-sheet gives that the 6G5 is electrically identical to the Y63 but has a UX6 base cap.
The paper label brands this M-OV product to the professional GEC range.
The display bowl.
The green display. The stronger the signal the greater the bright green area. This image courtesy of Mullard Magic.
The classic envelope is 36 mm in diameter and, excluding the IO base pins, is 87 mm tall.
References: Data-sheet & 1040. Type Y63 was first introduced in 1937. See also1937 adverts.