Funny, I have a BK 3026 as well, which is in need of service.
Seems the manual does not exist, so... that's no help to either of us (if you're still looking)...
FWIW, I measure 9VAC on J106 and 41VCT on J103. I don't think my transformer is toast, I measure 1.0 and 1.0 ohms for both halves of J103, and 0.8 ohms for J106.
My problem: the output stage burned out. Also, since this thing had been sitting open on a shelf for some time... most of the knobs, nuts and a few screws have gone missing...
Tim