dynatech
chambo, a Dynatech serial number starting with an SB prefix would mean 'special build'.
The hand made bikes produced at Ilkeston between 1974 and 1987 had the SB prefix of course, and many believe that it's use was exclusive to Ilkeston.
However, when production of competition bikes moved to the Special Products Division, the SB designation was still used for certain bikes. It was also used on a few prototype frames produced at SPD.
SB 9598 would be one of the last bikes in the 'special build' sequence.
I would think it was built for a pro rider - SA as suggested by Midlife. Not absolutely sure of this but the 5 could indicate it was the 5th bike built for that rider in 1992.
Ordinary Dynatech numbers started with A in 1990, then B in '91. C in '92 etc.
Hopefully should be able to get my Dynatech 500 out on the North Derbyshire roads soon !