The Y63 'magic eye' tuning indicator is housed in a classic shaped envelope with the electrodes held in a glass pinch. The leads from the pinch are connected to pins in the International Octal base. The triode section is clearly visible in the main picture and requires a grid voltage change of 22 volts for maximum visual change. The display is green.
The 6G5 = 6U5 is electrically identical but fitted with a UX6 base.
This is a second generation indicator with a 6.3 volt heater. This type of indicator was used in many radios. This particular exhibit has been masked at the top to enhance visual contrast.
The Marconi brand label. The M-OV etched identification can be seen in the main image.
Typical construction has the amplifier triode below the display bowl with the anode taken up into the bowl to control the display.
The cathode tube is coated for both the triode and the display.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 91 mm tall.
References: Data-sheet, 3002, 1043 & 1040. Type Y63 was first introduced in 1937. See also1937 adverts.