“Sing Out” sends out a musical happy birthday salute to Chris Strachwitz. Today is his 78th birthday, which goes well with his personalized license plate: “78S”). Strachwitz is not only one of the great collectors of music, but also has run Arhoolie Records for 49 years, and “Sing Out” features some of the highlights, from Mance Lipscomb to Clifton Chenier, Savoy-Doucet Cajun Band and many more. Tonight’s program also takes a look at the San Francisco Symphony’s summer programming.