Yesterday took some time to compare three sub-miniatures, Raytheon 6832, Melz 6N16B-VR and Sylvania 7963. First, I should say that all these tubes are exceptional. Moreover, they are more similar than different. And the differences that exist are very subtle. So while I try to accentuate these differences below, in reality, they are quite small.
As before, I found the 6832 to be the least 3-D of the bunch. The stage is relatively flat. Imaging and layering is less precise, and there is a little less clarity. In complex passages, it was a little harder to separate each strand. That said, the tone is right, vocals have good body and warmth, it is a very nice tube, all in all.
At times, the 6N16B-VR can be breathtaking. Exquisite clarity and an almost magical 3-D space. There is a sense of immersion, being surrounded by the music, rather than the stage being somewhere in front of you. But... the vocals are a bit thin, and on some recordings, even a bit reedy. On most recordings, this is a supremely enjoyable tube, but once in awhile, I found the vocals to be a little grating. (I should say this is with Senns 700 and an LD 1+ with MUSES02 opamp.)
The best of the four sub-miniatures in my possession (including the Sylvania 6021) is the 7963. It has all the 3-D magic of the 6N16B-VR plus that warm, silky-smooth Sylvania mid-range. As cheap as these sub-miniatures are, I recommend all three. But if the choice is one, and only one, then the Sylvania 7963 is the way to go.