I'm occasionally asked if I prefer globe shaped tubes over their shoulder type counterpart. Indeed I like the globes better, not only for their aesthetically more pleasing shape but in some cases also because of their sound. Please take this sound judgement with the usual precautions since they are valid only for my listening taste and in my amps.
The photo above shows a selection of globe tubes. Back row, from left to right: RCA 46, Taylor VT25, Cunningham CX345 (UX245), Taylor VT51, RCA UX210. Front row: RCA UX201A, Cuningham CY327, Cunningham 56.
The next photo shows their counterparts in the more modern ST (shoulde type) glass:
I have not compared all of these tube types directly in amps or preamps. My experience is mostly with 45/UX245, 10/UX210.
Let's have a closer look at the differences between the glass versions, starting with the 45:
There is a big difference in the size of them, which is not always the case between globe and ST tubes. The ST tube uses the narrowed top of the glass for some extra mechanical support of the electrode structures. This is accomplished by the insertion of a mica disc which clamps into the top and holds the tube structure. The structure of the globe tube however is basically 'floating' in the glass. It has been speculated that the absence of the mica in the globe tubes might contribute to their sound. Any additional stuff in the enclosure can release gasses during the life time of the tube.The next phot shows a close up comparison:
Nothing but metal and glass in the globe tube. A big mica disc in the ST. I am also a proponent of the hypothesis that this is the main reason for the sound difference.
This is even more apparent with the 10: