Lenox — Violinist and conductor Pinchas Zukerman‘s relationship with the Boston Symphony Orchestra began in 1969 at Tanglewood with a performance of Tchaikovsky’s Concerto for Violin in D Major. On Saturday, Aug. 3, he will make his 23rd Tanglewood appearance, joined by his wife, cellist Amanda Forsyth, performing, for starters, Beethoven’s Romance No. 1 in G for violin and orchestra. But the weightiest event of Saturday’s concert is the American premiere of Avner Dorman‘s Double Concerto for violin, cello and orchestra.