That would be 5U4G. Based on the info at the deHavilland site, it appears that the 5U4G, 5U4GA, and 5U4GB would be suitable. The 5AW4 is also suitable for at least some versions of the Ultraverve.
According to my older GE and RCA tube manuals, the coke bottle-shaped 5U4G reaches its maximum diameter of 2-1/16" at a point 3-3/16" above the bottom of the base/top of the pins. The RCA manual indicates a tolerance of +/- 3/16" on the height of the tube, and presumably some of that tolerance would apply to the 3-3/16" figure. Hopefully that will be enough information for you to determine if that tube will fit. If not, if you can indicate how far below the panel the upper surface of the socket is, and the diameter of the opening, I can measure the diameter of a 5U4G I have at the corresponding height.
Regards,
-- Al
According to my older GE and RCA tube manuals, the coke bottle-shaped 5U4G reaches its maximum diameter of 2-1/16" at a point 3-3/16" above the bottom of the base/top of the pins. The RCA manual indicates a tolerance of +/- 3/16" on the height of the tube, and presumably some of that tolerance would apply to the 3-3/16" figure. Hopefully that will be enough information for you to determine if that tube will fit. If not, if you can indicate how far below the panel the upper surface of the socket is, and the diameter of the opening, I can measure the diameter of a 5U4G I have at the corresponding height.
Regards,
-- Al