Moose: What is the difference in sound between the 77A and the 77B, B1, C,
C1, D and DX and other ribbons?

I have a 77d and a 77dx. The main difference seems to be the transformer
strappings. When strapped the same (I think mine are set up at 150 ohms), my
humble ears cannot distinguish which is which. To be a bit more clear: the
choices are indeed different on the two, but at least one, maybe two, are the
same. If you really want to know the choices, let me know.