Dimly lit, with concert posters, gumball machines and a jukebox lining the open-faced brick walls, Cafe Nine is a cozy mixture of underground and vintage.

The only bar in New Haven featuring live music every night of the week, Cafe Nine has been a staple of the New Haven music scene for nearly two decades. While Rudy’s features live music on Saturdays and Toad’s is known for more mainstream concerts and infamous Saturday Night Dance Parties, Cafe Nine has always been dedicated to making live music available to the beer-drinking public whenever they want it.

“There’s always something going on here,” said Edward Zaretskiy, who has played at Cafe Nine with his band Mr. Ed and the Horses in addition to frequenting the bar as a customer. “It’s the only place around that’s real anymore.”

Cafe Nine devotees like Zaretskiy say owner Paul Mayer — who bought Cafe Nine in 2003 — has invigorated the bar and its nightly lineup, drawing on rock and roll, indie and “insurgent country” talents and boasting guests like Junior Boys and Wolf Parade.

Mayer said he has remained focused on the bar’s original mission: giving live music a home in New Haven.

“This is a real networking place for the local art and music community,” Mayer said. “We like to feature new bands because we want to be a place where people can come and try out their stuff on a wider audience.”

Mayer took over Cafe Nine from previous owner Michael Reichbart almost by accident. For seven years, Mayer played bass in his own band, the Swaggerts, in addition to operating a rehearsal and recording studio in Fair Haven. Mayer said he visited Cafe Nine to put up posters for an upcoming Swaggerts gig and met Reichbart, who informed him that the bar was for sale. Three months later, Mayer owned the place.

While the bar’s musical lineup under Reichbart consisted almost exclusively of jazz, rhythm and blues, Mayer said he is indebted to his predecessor for establishing Cafe Nine as a New Haven institution, in spite of their differing musical visions for the venue.

“He was very devoted to keeping live music going in New Haven,” Mayer said. “He put his heart and his soul and a lot of good karma into Cafe Nine.”

Guitarist Cary Pollick has been featured frequently at Cafe Nine with his band The Danglers since Mayer took over the bar. He said the current musical lineup draws a very mixed crowd from places like West Haven, Trumbull and North Branford and fills an important niche in the New Haven music scene.

“Paul’s really got a lot more rockabilly-surfer-roots-Americana type music,” Pollick said. “You’re not going to hear that at Toad’s.”

While the area around Cafe Nine has experienced some revitalization in the past few years — including the opening of Firehouse 12 on Crown Street and Foster’s Restaurant on Orange Street — Mayer says the bar has yet to make a mark on Yale’s campus.

“We’ve gotten more Yalies in the past few years, but it’s been a little bit difficult,” he said. “Maybe it’s a little outside the perimeter for most students, but I think that’s changing.”

To that end, Mayer is introducing a new Happy Hour series set to launch within the next two weeks with the goal of attracting more Yale clientele. From 6 to 9 p.m. on weeknights, the bar will feature half-price drinks and the opportunity for customers to bring in music on their iPods and laptops, link up to the bar’s sound system and play DJ for a 20-minute segment. The bar also features free wireless Internet.

Upcoming shows at Cafe Nine for this week feature Texan singer-songwriter Brennen Leigh on Sept. 19, fusion artist Uncle Moon on the 20th, and country-rock group Sarah Borges and the Broken Singles on the 21st. Saturday will feature an afternoon jazz jam from 4:30 to 7:30 p.m., followed by a dance party at 10 p.m.