Re:
Much later than you think, actually. That logo was used in the late 90s, IIRC. Given the cantilever brakes, I would guess at 1997: yours was probably one of the last with those brakes. The 80s and very early 90s Ridgebacks had a different logo, top tube close to horizontal, and various other differences - quite different bikes altogether, really.
Give yours a good clean and service and you should have a dependable bike.