The dx has a slightly higher output than the d.
The a is a different animal altogether.
It's huge and sounds pretty good for a mic that's very old.
I recovered one once from the rafters of a church where it was the
sole pickup mic for the service
The c, i think that's the one with the pattern ring around the bottom
of the mic and really barely exists any more.
If you check the Vintage Microphones site, it commands a high price if
one ever shows up
My brother has one in his collection.
RCA recalled most of them and replaced them with the c1.
The dx was the last mic in the series and sounds best in my opinion
in bi directional but it usually was used in cardiod in radio control
rooms.
The bk 5 is probably the best sounding unidiirectional but the best
sounding bi directional to me is the 44bx and the BK 11 as the more
modern version.
I love RCA ribbons.
Stephen Sank probably can give you a better review of the entire
series as could Clarence Kane or Wes Dooley.
Stephen hangs around this forum but I've never seen Clarence or Wes
post here.
These guys are the last living authorities on RCA ribbons with
Clarence being the senior expert and all do re-ribboning and
refurbishing of top calibre.

On 20 Jun 2004 16:00:33 GMT, (Jim Kollens) wrote:

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.

Mike Cleaver Broadcast Services
Voice-overs, Newscaster, Engineering and Consulting
Vancouver, BC, Canada