Go here:
https://antiqueradio.org/BK1077BTelevisionAnalyst.htm
Scroll down halfway down the page and click to enlarge.
I really didn't know there was a "b" model for the 1077.
I knew there was a "B" model for the 1076 which has a jack for external audio in.
Also it has a different phototube which gives it a slightly sharper picture.
Be careful around that phototube or you'll be rigging one of these in there.