When Essra Mohawk plays the Tin Angel on Sunday, it will be a triple celebration.

It will be a homecoming for the husky-voiced Philadelphia singer/songwriter, who moved to Nashville in 1993.

Once here, she'll celebrate her 62d birthday (which is Friday) - and it will be the 40th anniversary of her critically acclaimed second album, Primordial Lovers - which, with two other early albums, was digitally remastered and rereleased this year.

"Good songs don't get old," Mohawk says by phone from Nashville while packing for her trip to Philly. "Time gives them more credibility."

"It's wonderful to see record companies finding historical value in her past," says George Manney, the drummer-turned-filmmaker who played in her band during the '80s.

And what a past it's been. Mohawk, whose work has drawn comparisons to Joni Mitchell, Carole King, and Laura Nyro, has written for the Shangri-Las and Vanilla Fudge (both before turning 20), Tina Turner, and Cyndi Lauper. She was one of Frank Zappa's Mothers of Invention, performed in the Schoolhouse Rock television series, and sang in the Jerry Garcia Band.

"The enduring success of 'Change of Heart' " - a Mohawk song covered by Lauper - "is testimony enough," says Michael Tearson, an on-air personality at WMGK-FM.

Tearson was on WMMR-FM during Mohawk's first go-round through the record business of the '60s and '70s. Her music, combining complex melodies with mystical, poetic lyrics, was a heady mix of folk, rock, and jazz that had a hard time finding an audience when her early albums - including her 1969 debut Sandy's Album Is Here at Last! and third album, 1974's Essra Mohawk - were released on major labels such as Reprise and Asylum.

"Had the songs been heard wider, Essra would have had wider respect," Tearson says.

Though her music has elements of what's known today as "freak folk," Mohawk's influences seem to range from jazz (Anita O'Day) to English folk (Sandy Denny). When asked, Mohawk says she's not very well-educated musically, copping only to being inspired by Billie Holiday and Ronnie Spector.

And what of her lyrical inspiration?

"My writing comes directly from within - that is to say, the One Source - and is totally uninfluenced, as is my music for the most part," Mohawk says. "It's about whatever it wishes to be about. I simply let it come through me."

It's that self-motivated muse that has guided Mohawk since she was a teenager. Born Sandra Elayne Hurvitz in Northeast Philadelphia, the graduate of George Washington High School released her first single, "The Boy With the Way," on Liberty Records in 1964, under the name "Jamie Carter." (The name Mohawk came later, from her then-husband and producer on Primordial Lovers, Frazier Mohawk.)

"A friend of my mother's told a neighbor about me, and the music business came knocking," Mohawk says.

By the time she was 17 she was offered a job as staff writer with a publishing company in the famed Brill Building, where such hitmaking songwriters as Carole King and Neil Sedaka plied their trade. Mohawk didn't feel comfortable with that deal, or with another "unreasonable" contract offered by United Artists.

Instead she hooked up with producer Shadow Morton, and wrote songs for the Shangri-Las ("I'll Never Learn") and Vanilla Fudge ("The Spell That Comes After"), then returned to Philly to regroup.

"The circle was small in those days," says Manney, who knew Mohawk from Northeast Philly. "In the late '60s my band, Stone Dawn, had a female vocalist-guitarist, too. I couldn't wait to see what Essra would come up with."

What Mohawk came up with was due to a chance meeting with Frank Zappa in 1967 in Greenwich Village. "Frank asked me to try out a new electric piano he'd just purchased, as the Mothers of Invention's keyboard player was ill. When Frank heard me play and sing my songs, he hired me on the spot."

Mohawk became a Mother, performing as Uncle Meat. "One day at rehearsal, Ray Collins, the Mothers' lead singer, said to Frank, 'How about 'Uncle Meat' for the name of a rock star?' Frank spun around, pointing at me, and announced, 'You're Uncle Meat!' "

Zappa started to produce her first album, Sandy's Album Is Here at Last!, but she walked out of the studio when he "said something that humiliated me." Zappa left the producer's chair. "We remained friends long after the fact," she says, "but never discussed what happened that ended up changing the course of my first album."

The project was released sounding more like a demo than a completed album. Then, in 1969, Mohawk was scheduled to play the three-day Woodstock musicfest in August, but her driver made a wrong turn and she missed the helicopter that was to take her to the staging area.

Mohawk contends that it was her description of that missed opportunity that led Joni Mitchell to write the classic song "Woodstock." (Mitchell's then-boyfriend, Graham Nash, was also said to have inspired it.)

"I'd been telling her about our people being together and how incredible that was and what it might mean for the future - I read her a poem I wrote about it," Mohawk says. "She came back the next day to play me the song."

Primordial Lovers showed up in record stores in 1970 to critical acclaim for her rich voice and free-form songs. But it got lost in the marketing shuffle, and fans like Tearson had to intercede. "It was the time of Joni and Laura Nyro, and I thought Essra's glorious voice deserved to be on the shelves with them," the DJ says. The former WMMR DJ says he called the local reps for her label, Reprise, and pestered them until Primordial Lovers was on every record-store shelf in Philly. "That album deserved a wider audience," Tearson recalls.

Mohawk continued recording on smaller labels, producing albums such as 1985's New Wave-ish E-Turn and 2003's roots-rock You're Not Alone. "I continue to accumulate experience, increasing my musical palette," says Mohawk, who struck gold in 1986 when Lauper's version of "Change of Heart," on True Colors, hit No. 3 on Billboard's Hot 100 chart.

At work on a new album due out by the end of this year, Mohawk knows that each of her past albums has been radically different from the last, and likes it that way.

"Life is a creative endeavor, an exciting work in progress," Mohawk says. "It's a lifelong symphony."

Essra Mohawk

Sunday at 7:30 p.m. at the Tin Angel, 20 S. Second St. Tickets: $16. Information: www.tinangel.com, 215-928-0770.