* On Tap At a time when it seems like every old band in the world is getting back together, how about a reunion of a band that never was? Spinal Tap, the British hard-rock group depicted in the 1984 ''documentary'' This Is Spinal Tap, will play at a concert in London this summer.
* Oh, Brother Four of the original members of the Allman Brothers Band, including Gregg Allman and Dickey Betts, have reunited and are working on a new album. The working title of the summer release is Seven Turns.
* A 10-Foot Boxed Set To honor the 200th anniversary of Mozart's death, Philips Classics will release recordings of nearly everything the composer wrote. The first of about 180 compact discs will be out this August, the last by the end of 1991. Much of the material comes from previous Philips albums, but many works will be newly recorded, including, Philips says, about 1 1/2 hours of music that has never been performed before.
* He Getz It On Alto saxophonist Stan Getz will have a new album, Apasionado, out next month, produced by Herb Alpert. The music will have a big-band feeling, thanks to a seven-man horn section.
* Ride 'Em, Cowboy Jon Jon Bon Jovi has sung about being a cowboy before. Now he's had a chance to play one for the movies. Bon Jovi wrote a song, ''Blaze of Glory,'' for the film Young Guns II, and went to New Mexico to hang out on the set. While he was there, moviemakers dressed him as a cowboy for a scene in which he gets shot. Whether Bon Jovi's appearance or the scene itself will survive the final cut is anybody's guess; the film is due in July.
* Platinum Blonde Among the songs on Lita Ford's new album, now being recorded, is the Alice Cooper hit ''Only Women'' (as in ''only women bleed''). Producing the May release is Mike Chapman, who did the same for the singer's last album, Lita. No word yet on a title for the new effort, but how about: Ford.
* Newest Edition As a group, New Edition hasn't released an album since 1988's Heart Break. As individuals, however, Ricky Bell, Michael Bivins, Ronnie DeVoe, Johnny Gill, and Ralph Tresvant have been busy. The first three recently released the chart-climbing Poison under the name of Bell Biv DeVoe. Gill just put out a self-titled solo debut. And Tresvant is said to be planning his own album for the near future. All of this activity doesn't mean, however, that New Edition is history. A spokeswoman for the group's label, MCA, says the band will continue in one form or another.
* Forever Young A new Paul Young album will be out this summer, his first since late 1986. Other Voices features such guest stars as Steve Winwood, Stevie Wonder, Dave Gilmour, and Chaka Khan. Young, below, wrote three of the 10 songs on the album, which also includes two cover versions of 1972 hits by other artists: the Chi-Lites' ''Oh Girl'' and the English Congregation's ''Softly Whispering I Love You.''
