The only difference in capacitance I see is Cgp, 0.24 pF for the 6146A
vs. 0.22 pF for the 6146 and the 6146B. Doesn't sound like any
difference at all, unless maybe the average values are quite a bit
different for the 6146B vs. the other two (but what would cause that?).
I don't question those who say there's a problem with some rigs, but
on paper all three tubes do seem to be the same (at the lower screen
voltage the 6146 is designed for). Apparently RCA thought the same
thing.

No conclusions, just ruminations...

73,
Mike, KK6GM