They arrive early, sometimes as much as an hour before the first note is played.

Residents of Morningside House, a Leesburg assisted-living facility, come to the dining room and position their wheelchairs or claim seats in rows of chairs — just as they have nearly every Tuesday evening for 19 years. The folding doors at the front of the room are opened to reveal the activity room, which has been transformed into a stage. One by one, the musicians take their places.

Promptly at 7 p.m., guitarist Bob Brown opens the show with a joke and then introduces the first song, and the musicians launch into an up-tempo rendition of a classic Lefty Frizzell song. The longest-running weekly jam session in Loudoun County is underway.

For the next 90 minutes, nine musicians entertain the audience with a selection of bluegrass, country and gospel standards, punctuated occasionally with one of Brown’s jokes. The audience sits quietly during the songs, some with their heads bowed. But many sing along quietly — to the gospel hymns, in particular — and applaud enthusiastically after each song.

The show ends with a rousing version of the defiant “Mama Don’t Allow No Music Playin’ Around Here.” Many of the instrumentalists take turns at the microphones to show off their skills, to the delight of the audience.

Former Loudoun Chamber of Commerce president Randy Collins “is to blame for the whole thing,” Brown joked afterward.

Collins, who now has a similar position in Mount Airy, N.C., traced the genesis of the sessions to a chamber mixer at Morningside House early in 1997. He told the facility’s director that if they would provide the space for free, he could recruit a group of musicians to entertain the residents. The jam sessions started shortly thereafter, and have continued ever since, he said.

“It became almost like a ministry,” Collins said in a telephone interview. “People who are musicians, in any kind of genre, just love to play. And especially bluegrass musicians — they just like to sit around and pick.”

The musicians come and go from week to week and year to year, Brown said. As many as 20 musicians have crowded onto the stage at one time, although the number is usually much smaller, he said.

“The jam sessions provide a place for the more seasoned players to hone their craft,” Collins said. “But we always get a lot of novices that come in. So they can sit in the back and just play along.”

Nikki Allen, marketing director of Morningside House, said the residents look forward to the Tuesday night sessions. “It gives them the excitement of having live music right in front of them,” she said.

“The seniors are just an awesome audience,” Collins said. He recalled an elderly woman who approached him at one of the sessions and told him she had outlived two husbands, her children and all of her friends.

“She said, ‘I didn’t have a lot to live for. Now I live for Tuesday nights,’ ” Collins said.

Several performers in a jam session last week said they enjoy the camaraderie among the musicians.

“It’s my Tuesday night card game, if you will, to get together with these guys,” said Brown, the owner of a Leesburg real estate firm.

Guitarist Bill Wiley, who lives outside Leesburg, said he needed something to do after he retired and his wife died.

“My wife gave me a guitar around 1960, and I had never learned to play it,” he said. “After she passed away, I got some lessons and started going around to nursing homes to play. . . . It makes me feel good.”

The jam sessions are free and open to the public. In good weather, they all move outside, where the music sometimes attracts passersby, Allen said.

“We encourage the public to come,” Brown said. “The bigger the crowd, the better we play. I think that’s true of all musicians.”

Collins looks back fondly on his involvement with the jam sessions.

“It was a lot of fun, and I’m thrilled to death that it continues,” he said.