Being a professional musician often means an unpredictable paycheck. Even for an internationally famous one like Dr. Fink of Prince & the Revolution.

Fink, a Twin Cities keyboardist/producer/composer, is selling 54 lots at auction this week of his Purple memorabilia and instruments — including an unreleased Prince album, rare rehearsal tapes and a synthesizer used on the Purple Rain Tour.

Why? Because he doesn't want to have his two adult sons deal with this later and, frankly, he needs the money.

"Income is very inconsistent in this industry," Matt Fink said before he jets to London for the live-streamed auction on Nov. 15. "Prince did take care of us. There were difficult times between then and now."

When working for Prince from 1979 to '90, Fink set up a retirement plan but he had to tap into those funds while he is still working. Now 66, he hasn't started collecting Social Security yet. So, a friend suggested cashing in on the collectibles market.

Bob Pratt, an avid Minneapolis music collector, introduced childhood friend Fink to Propstore, a London-based auction house with a representative in the Twin Cities.

"Propstore will not put it on their site unless it's 150 percent authentic," said Pratt, adding that not all auction houses are as judicious in verifying provenances.

Fink mentioned his Propstore auction to fellow Revolution members Bobby Z, Lisa Coleman, Wendy Melvoin and Mark Brown but none of them wanted to offer items.

The keyboardist said he is neither guilty about selling nor sentimental about the items.

He made representatives of Primary Wave, which manages half of Prince's estate, aware that he was auctioning his collectibles.

Among the 54 lots are:

• An Oberheim OB-8 8-voice polyphonic analog synthesizer used in the recording studio and in concert in the 1980s.

Fink said there were four of these synthesizers in Prince's world, one of which is on display at Paisley Park. The one Fink is offering was his backup for the tours behind "Purple Rain" and "Parade."

And the synthesizer still works, he assured.

• A collection of 39 Prince archival cassette tapes, from 1979 to '90.

Fink recorded the tapes on boom boxes, Walkmen and concert consoles.

The prized recording is an unreleased studio album by the Rebels, a 1979 Prince side project. It was his first recording with his first band — Dez Dickerson, André Cymone, Gayle Chapman, Bobby Z and Dr. Fink — after Prince had made his first two albums as a one-man band. It was recorded that summer in Colorado.

"Prince did it on the sly," Fink said, "and then came to Warners after the fact and said, 'Look what I did. Can you do something with this?'"

Warner Bros. Records did not want to release a side project at the time, though Prince branched out two years later by writing and producing a record for the Time.

"That Rebels cassette has been out there as bootlegs," Fink pointed out. "I've never bootlegged anything."

He doesn't know if whoever buys it could legally release it. A copy of the unmixed Rebels record exists in Prince's vault.

Even though he's not possessive, Fink made digital copies of all the cassettes he is putting up for auction.

• Fink's paratrooper jumpsuit from the first Prince concert in 1979 at the Capri Theater in Minneapolis. Later, Dr. Fink switched to wearing scrubs. He has kept his old outfits in vacuum-sealed bags in storage.

• T-shirts from different Prince tours. "Eighty percent of them were never worn," he said.

Propstore's auction this week offers more than 1,800 music and movie items, including John Lennon's Vox amplifier and other mementos from the Beatles and Oasis.

Fink said his sons don't want his Purple stuff, though he is hanging on to some keepsakes, including his Grammy Awards for "Purple Rain." He still retains arguably his most valuable music possession — his song publishing and recording royalties, though he will consider selling those at some point.

After Prince died in 2016, some people in his orbit — including Prince's first ex-wife Mayte Garcia, first manager Owen Husney and former executive assistant Karen Krattinger — sold Purple collectibles.

Fink said Propstore predicts the auction could bring $150,000 to $350,000.

Fink, whose last full-time job at a streaming company ended in the pandemic after six years, still performs on occasion with the Revolution and with St. Paul & the Minneapolis Funk All-Stars. He's working on a music project with Utah tech entrepreneur Sabe Anderson.

While many Prince associates have attempted solo careers, the keyboardist said he preferred to stay true to the Prince legacy.

Despite what he's selling, the St. Louis Park native still has at least eight different Dr. Fink scrubs for wearing onstage.

"I've got white, teal, purple, blue, dark blue, black," he said. "I've got everything for every occasion. The new modern scrubs with special embroidery on there. I've got my own symbol now."

Like Prince.