Seeking to head off a strike by musicians of the Philadelphia Orchestra set for Thursday, the city’s mayor called players and management into his office Wednesday and got both sides to agree to a ten-day extension of talks. “Orchestra management says it is facing a $4.2 million deficit, and had asked the musicians to agree to a reduction in the size of the orchestra or a pay cut or a combination of both. It also wanted to change the pension system in a way the musicians say would reduce benefits. The musicians countered that cuts in personnel or pay would undermine the quality of one of the world’s great orchestras.”