The San Francisco Symphony occasioned a very special guest for its latest performance — one that has been around for decades but only rarely comes out to play: the enormous, magnificent Ruffatti Concert Organ. Commissioned specifically for Davies Symphony Hall from the Padua firm Fratelli Ruffatti, the instrument, with more than 8,000 pipes, was the largest concert organ in North America when it was installed in 1984. Denève Conducts Saint-Saëns’ “Organ” Symphony: San Francisco Symphony.