The Allman Brothers Band’s "Mountain Jam" — a live version that originally covered sides three and four of the 1972 double album Eat a Peach — is one of those tracks that captures a certain essence of its era. Not that it was one of their greatest songs or performances: the song is barely there, and side four is mostly a bass solo. But the free-flowing instrumental catches the feel of time and place: late night, the Fillmore East in 1971, the tail end of a marathon show, both band and audience off in the zone.

Saturday’s Tweeter show ended with another "Mountain Jam," one of the surprise oldies that the Allmans have dug up since founding guitarist Dicky Betts got kicked out of the band and took much of their repertoire with him. And this jam was a more emotional one — it was dedicated to Widespread Panic guitarist Michael Houser, who’d passed away from cancer over the weekend. Incorporating bits of "Will the Circle Be Unbroken," it started sprightly and ended somber, like a New Orleans funeral in reverse. This was where the new line-up found its footing, with Derek Trucks and Warren Haynes curling guitar lines around each other, and where the band found their way back to the zone.

The news about Houser might explain why Saturday’s show was otherwise so spotty and low-key, with no real barnstormers and few big solos from Haynes. Or maybe it’s just that they haven’t yet recovered from the loss of Betts, who was booted two years ago over personality differences. Newest member Derek Trucks (nephew of drummer Butch Trucks, and husband of Susan Tedeschi) has inherited most of the lead-guitar work, and so far he’s too obviously a disciple of the late Duane Allman (looks a little like him too) — even his original solos sounded as if they’d been learned from old Allmans recordings.

The best thing about the sacking of Betts is that it has forced Gregg Allman to sing more, and his voice has gotten more weathered and world-weary with each passing year. Aside from "Mountain Jam," the show’s most vintage number was the venerable "Whippin’ Post," which sounded less like a classic-rock chestnut than a deeply felt blues howl. No wonder it’s second only to "Freebird" as the song of choice for wise-asses to yell for at everybody else’s concerts.

The opening band, the New Orleans–based Galactic, are one of the few young jam bands with a genuine grasp of funk, and with the smarts to have hired an old-school soul singer (Theryl "Houseman" DeClouet) as their frontman. That doesn’t keep them from the occasional noodling, but they sounded tough and mean last weekend. Maybe they noticed the number of bikers in the Allmans’ audience and didn’t want to risk getting beat up.