Eleven actors helped Orson Welles stage his legendary "War of the Worlds" radio drama on Oct. 30, 1938. Just one of them is alive today: 89-year-old William Herz Jr.

Mr. Herz considers himself unworthy of acclaim. After all, he was a bit player in that broadcast; he portrayed a ham-radio operator and had just one line of dialogue. But this weekend, he'll be honored at the Friends of Old-Time Radio Convention in Newark, N.J. As he sees it, convention organizers turned to him because they can't "bring up corpses." He agreed to attend as a favor to fans.

"I'm the only thing left," he says, "so I'll be Exhibit A."

Festivals and conventions celebrating early- and mid-20th-century entertainment -- vaudeville, silent movies, radio, swing bands -- are popular across America. Fans come to relive memories, find treasures at memorabilia booths and shake hands with heroes. The problem is that it's getting harder to find performers from those eras to show up and be applauded.

When Stephen Salmons, co-founder of the San Francisco Silent Film Festival, talks about the good old days, he's not referring to just the 1920s. He's also longing for the 1990s, when there were still top-name actors alive who had appeared in silent films. Douglas Fairbanks Jr. and Fay Wray attended festivals well into their old age. (He died in 2000 at age 90; she died in 2004 at 96.) Now, with only about a half-dozen silent actors alive who had any kind of billing, event organizers are inviting the offspring of dead stars or hiring young impersonators.

At the Old-Time Radio Convention, which expects 600 attendees this weekend, leaders have begun inviting television stars -- over the objections of purists who argue that only radio performers should be welcome. "If it becomes 'Friends of Old-Time Television,' I'm out of there," says Arthur Anderson, 83, a member of the convention's organizing committee. Mr. Anderson began his long radio career as a child actor in 1935, on the children's show "Let's Pretend."

There are tense discussions at planning meetings, admits the convention's spokesman, Sean Dougherty. "But there are people of goodwill on both sides," he says.

The purists say diluting the guest list with TV stars deflects attention from the uniqueness of radio's golden age. Americans set the standard for artistry and sound effects in radio drama, says Anthony Tollin, a radio historian who directs recreations of old shows at the convention. "We perfected the theater of the mind, and then we turned our backs on it."

Noel Neill played Lois Lane on TV's "The Adventures of Superman" in the 1950s, and has no radio credits. Still, she's a special guest at this year's radio convention. The board agreed to invite her because Lois Lane was on radio before TV. "It'll be a stretch for me," says Ms. Neill, 85. "I don't know how they'll react to me because I wasn't on radio." She'll bring memories as a listener, however. "We had a radio. Yes, we did." (Like the 40 other invited guests, she's being paid only for expenses.)

When the radio convention started 30 years ago, staged recreations of old scripts would usually feature about 70 percent of a show's original actors. Now, only about 5 percent of the actors are originals, and some aren't too healthy. Raymond E. Johnson was the ghoulish host of the radio show "Inner Sanctum" in the 1940s. At several conventions in the late 1990s, Mr. Johnson, weakened by multiple sclerosis, performed from a wheeled-in hospital bed. He died at age 90 in 2001.

Other nostalgia circuits face similar predicaments. There are 15 to 20 big-name "ghost bands" on tour, playing the music of swing-era stars such as Tommy Dorsey and Glenn Miller. The bands are mostly young players fronted by old bandleaders who knew or played with the namesakes.

Silent-film groups have resorted to showcasing children and grandchildren of legendary performers. The San Francisco festival, which drew 9,000 film buffs to its three-day event in July, has hosted Charlie Chaplin's 79-year-old son, Sydney. It's a coup when festivals can find someone who actually made a silent film. Lately, many have turned to Diana Serra Cary. In the 1920s, as a child actress dubbed "Baby Peggy," she made more than 125 silent films and $4 million.

Ms. Cary, 86, was honored last week at a film festival in Italy, where she told her story. Cast aside by Hollywood as she got older, with all her money spent by her parents and others, she watched her films' plot lines get recycled into Shirley Temple talkies. She blames radio for leading audiences to demand movies with sound. "People had this itching ear and they wanted to hear," she says.

Another American art form that petered out around the same time is vaudeville, traveling variety shows with songs, comedy and dancing. While some have revived vaudeville in recent years, it's tough to track down living old-time vaudevillians.

One famed vaudeville dancer and comic, Rudy Horn, is now a frail 96. This week, in his Chicago apartment, his eyes barely open, he offered memories of working as a performer at Al Capone's club, twice dancing at Franklin Roosevelt's White House, and learning rubber-legged dancing from his pal, Ray Bolger, the scarecrow in "The Wizard of Oz." Until a stroke three years ago, he made public-speaking appearances once a month.

Estelle Rooney, 89, still speaks occasionally about growing up in her father's traveling vaudeville show. Her late husband was Pat Rooney III, whose family vaudeville dynasty dates back to 1867. Ms. Rooney has appeared before groups to talk about her father's blackface routines, and the act she staged with trained dogs and doves. She also explains when she realized that vaudeville was dying: In the 1930s, "we couldn't start our show until after Amos and Andy were finished on the radio," she says.

Many vaudevillians, unable to make the jump to radio and film, eventually moved to Las Vegas, becoming small-time performers, makeup artists or dance instructors. Frank Cullen, founder of the Boston-based American Vaudeville Museum, suspects some of them, now in their 90s, still live there. "But a lot of folks don't want to hobble out for their last bow," he says. "They want to be remembered as they were. Or they're realistic enough to know they've been forgotten."

At the old-time radio convention, one committee member who supports opening up the guest list to more-recent performers is Brian Gari, whose late grandfather, Eddie Cantor, was one of the biggest names in radio. Mr. Gari, 53, believes familiar TV veterans bring in younger attendees, who then learn about radio's heyday.

"Do you want people to show up or not?" Mr. Gari asks. "In 2015, maybe we should have Howard Stern. By then he'll be an old-time radio guy."

Fred Foy, 83, was the announcer on radio's "The Lone Ranger" from 1948 to 1954. He'll be at this weekend's convention, signing autographs with the words "Hi-Yo Silver!" He assumes that when he's gone, people like him will be replaced at the convention by TV sitcom stars. He accepts that. "The convention has to evolve," he says.

Until that time, however, he plans to come back each year to treat convention attendees to his trademark dramatic voice. As the "William Tell Overture" plays in the background, he'll deliver what is considered the most recognized opening from radio's golden age: "Return with us now to the thrilling days of yesteryear ..."