In the 30s listeners could turn for variety to "all-girl" jazz orchestras--full-fledged big bands that usually camouflaged some pretty fair musicianship under the banner of "novelty act." These days, of course, no one would countenance the use of "all-girl" as a descriptive; Diva, a jazz orchestra comprising women only, get around the problem by punningly characterizing themselves as "no man's band." That's not entirely true; much of a big band's musical personality derives from its arrangements, and most of the arrangements Diva played on its debut album were written and produced by Michael Abene and John LaBarbera (both excellent scorers). But the 15 women who play those arrangements do them plenty of justice. The ensemble playing has the admirable mix of ease and tension that has characterized some of the best big bands, drummer and leader Sherry Maricle drives with authority, and the soloists shine--particularly the young trumpeter Ingrid Jensen, the journeywoman Chicago trombonist Audrey Morrison, and saxists Virginia Mayhew (tenor) and Claire Daly (baritone). If you weren't told, I doubt you'd characterize Diva as a band utterly lacking in Y chromosomes, and like it or not that remains the ultimate compliment. They don't "play like girls," to borrow the favorite put-down of jazz sexists throughout the century. But they don't play exactly like the guys either, and that subtle difference in particular makes Diva's progress worth watching. Their appearance marks the scheduled closing of the Jazz Showcase at its location in the Blackstone Hotel--ironic, since the band brings more women to the Showcase stage in one week than usually appear there in a year. (The hotel's new management has not only shuttered the classy main entrance on Balbo and removed all alcoholic drinks from the Showcase bar but pushed proprietor Joe Segal to a new locale, where he'll open in a few months. So Thanksgiving weekend should bring a few choruses of "Auld Lang Syne" for the old joint as well.) Friday through Sunday, Joe Segal's Jazz Showcase, Blackstone Hotel, 636 S. Michigan; 427-4846.