Jack Walrath, my former client, is a jazz trumpeter from Montana who went to Berklee and played with Mingus and lives in New York.

Applejack Walroth is a bluesman from Chicago who played with Boz Scaggs at the 2009 Hardly Strictly Bluegrass.

Jack Walrath also played with Willie Nelson in the 1990s which got my hopes up that he had snuck out to mean ol’ frisco for this hit.

he says he’s the bass player on Maxwell st circa 1966

and1: Bob Devine on Delmark blog:
A guy named “Apple-Jack” Walroth showed me how to pack the rare records so that they wouldn’t shatter in shipping. I later learned that he was a musician, played blues guitar and was picking up the blues harp from some of the players around Chicago — Little Walter, Shaky Walter Horton (also known as “Mumbles” Horton who had earned the “Shaky” nickname on the basis of his head movement when he played), Jr. Wells and others. Apple Jack made a point of telling me not to take any advice from Charlie Musslewhite, known as “Memphis Charlie”, another harp player who was deemed by Koester to be an excellent blues man, but one of the dimmest and least reliable workers at the store

here is video of Charles Mingus group doing “Sue’s Changes” at Montreux, 1975:

he is sometimes also known as Jack Zappa:
from TapeOps:
As a songwriter, home recordist, and musician who gigs frequently, sometimes on stage I encounter the ugly and dreaded situation where the AC power paths will be such that when I am holding my instrument [harp mic or electric guitar], and also touching the PA mic as I sing, I get zapped by the way-too-familiar 110 volt electric shock. Yes, after the fact, I flip the amp ground switch when there is one, or reverse AC plug on the amp otherwise. And yes, some amps have a grounded 3 prong plug and some just have 2 prongs. All amps are not created equal and all circuits are not always properly grounded, by any means. We are not at liberty to rewire every faulty circuit we encounter in the universe. Any musician who plays out frequently under many different scenarios is almost certain to be zapped once in a while. But I don’t want to get shocked in the first place, and don’t always have the luxury or desire of using a cordless mic to avoid the problem.