Flashback to 1969: Jefferson Airplane’s vocalist, Grace Slick, is recovering from throat node surgery. Two of her bandmates, guitarist Jorma Kaukonen and bassist Jack Cassady — who grew up playing together in Washington — have extra time on their hands. So they form a side-project group more focused on country and blues genres, eventually opening shows for Airplane. That group, Hot Tuna, started playing acoustic sets in the early ’70s. Apart from a heavy rock period later that decade, the band is best known as an acoustic act. While members have come and gone, the core duo of Kaukonen, an inventive finger-picking guitarist, and hard-driving bassist Cassady, are the official Hot Tuna. They allow audience members to tape their live shows just like the Grateful Dead, too. With 2015 marking the 50th anniversary of Jefferson Airplane, these old hippies bring their accumulated wisdom to the National on Tuesday, Dec. 1. Tickets are $20-$25. Doors at 7:30 p.m. thenationalva.com.