The CV2747 (6U5G) is an American design of Magic Eye tuning indicator. The electrode assembly is mounted centrally in the envelope with the amplifier triode feeding the display. The display is viewed through the dome.
The 6U5G can be found with a UX6 base or the IO base as here. The attached data-sheet has base connections for both variants.
The 6U5G denotes the IO base cap whereas 6U5 would be the UX6 base version.
The voltage amplifier triode.
The wide glass tube envelope is 28 mm in diameter and, excluding the IO base pins, is 89 mm tall.
References: Data-sheet, 1043 & 1040. Type CV2747 was first introduced in 1952. See also1952 adverts.