Hendrix used to jam with other famous musicians, such as Jim Morrison and Johnney Winter, at Steve Paul's club "The Scene" AKA "Steve Paul's Scene" in New York City.

I once read that his barbituate use there caused him to have to be carried out on some nights.

http://www.towerrecords.com/product.aspx?pfid=1465562
"These are late-night jam sessions recorded at Steve Paul's Scene Club (a notorious musicians' hangout) in New York City in 1968. Hendrix was a frequent guest; here he's backed by bluesman Johnny Winter and members of his band, as well as drummer Buddy Miles and (occasionally) an extremely messed-up Jim Morrison on harmonica and vocals. The sound is variable but listenable throughout, and the performances are surprisingly together given the probable level of substance abuse by the principals."