On a recent Tuesday night at Slade’s Bar & Grill, Kaicee King was in her usual spot by the stage, microphone in hand. “Wow, every week,’’ she said, her deep voice filling the blue-walled room. “Every week. My heart just jumps right out.’’ The stylish 74-year-old with the cropped gray hair presides over open mic night at the Roxbury institution.

Every Tuesday, the bar draws scores of happy regulars and crazy-good musicians, all filling the place with warmth and joy. The crowd is mostly black, and mostly middle-aged, with a few Berklee kids and octogenarians rounding out the demographic.

There are few places like this left in Boston and the whole city is the poorer for it. Wally’s, on Mass. Ave, has a similar welcoming vibe and superb music. But at Slade’s you get more room, great wings, and band-leader Frank Wilkins’s Tuesday night Talent Showcase.

Performers have to see Kaicee first if they want to belt out a song or sit in with the band. She takes their names, calls them up with that honey-and-gravel voice, and dances around the room snapping pictures while they perform. And after they’re done — if they’re good enough — she presses a palm to her chest, her long earrings swinging as she shakes her head in wonder.

On this night, a young Berklee grad named Evan Cole blew the roof off the place with Chaka Khan’s “Sweet Thing.’’ Mellow Mel, in a loud Hawaiian shirt, played the comb and sang the Dead’s “Next Time You See Me.’’ Herbert Stephens, 82, said, “I’d like to take you back a little bit,’’ and then launched “Ain’t Misbehavin.’’’ A lot of the singers are very good. A few have the manager suddenly remembering urgent business in his office. “Some of them make me sound like I can sing,’’ Kaicee says. “And I know better.’’

Musicians — some regulars, some traveling through — took spots on the stage with Wilkins’s band. Salim, tall and blind, pounded his djembe drum with such force that he didn’t hear Wilkins cue somebody else’s solo. Regular band member Pat Loomis plays sax with such enthusiasm and skill that it can be hard to concentrate on anybody else. He puffs out his neck in a way that seems impossible, making you wonder if he could blow out a carotid artery. He plays all over, but Slade’s is his favorite.

“This is where I feel most relaxed,’’ says Loomis, who lives nearby. “At most clubs, people don’t bother to talk to the musicians.’’

Countless people drive past this place between JP and the South End and never give it a glance. Hardly anybody comes over from the other side of Mass. Ave, apart from the Berklee students who come to play. Breaking old tribal habits in this city is still way too hard.

“A lot of people don’t think this is a safe part of the city,’’ Loomis says with a shrug. How much greater Boston would be if they didn’t feel that way.

This past Tuesday, Loomis, who also sings, was halfway through James Brown’s “Sex Machine’’ when the door opened and the bar erupted.

James Brown impersonator James Carr — known to everybody as JC — had walked in. The dead-ringer looked at Loomis — a skinny, mortified white guy — with mock reproach. Finish it, Loomis begged him. JC took the mike and danced back and forth, sweating and Ow-ing just like the actual JB. The crowd was in heaven. Sitting inches from an MBTA bus driver channeling the Godfather of Soul, you just felt lucky to be in this too-little-known gem of a bar, and plain sorry for everybody who wasn’t.

It felt like your heart would just jump right out.