Grebenshchikov, or simply BG to fans, will gather with the classic Akvarium lineup of the 1980s - including Alexander Lyapin on lead guitar, Seva Gakkel on cello, Andrei "Dyusha" Romanov on flute, Mikhail Vasilyev and PyotrTroshchenkov on percussion, Vladimir Kudryavtsev on bass and Yevgeny Guberman on drums - for a one-day concert June 25 at St. Petersburg's Yubileiny Sports Palace.

A similar one-day stadium concert will be held Saturday in Moscow, both of them marking the 25th anniversary of the band's founding. The line-up and repertoire of the concerts will roughly follow that of a series of eight sold-out concerts Akvarium played in 1986 at the Yubileiny – concerts that marked Akvarium's breakthrough soon after surfacing from the "underground" of acts frowned upon by Soviet authorities.

Despite his now-legendary status, Grebenshchikov has managed to avoid becoming a rock dinosaur and to remain creatively relevant - partly thanks to abrupt stylistic switches and unexpected career moves. The original Akvarium line-up disbanded in 1991. Grebenshchikov soon had gathered a new group, called simply the BG Band, and adopted a new style heavily influenced by Russian folk music. The band released the "Russian Album" in 1992 – a sharp departure from earlier works – and then, rather confusingly, renamed itself Akvarium.

Now the "new" Akvarium has been sent "on vacation" for at least six months, while Grebenshchikov puts in long, laborious rehearsals each day with the "classic" Akvarium – prompting the inevitable rumors that Grebenshchikov may be preparing to dump his current band.

Despite such rumors, Grebenshchikov insists that playing with his band remains "awfully interesting" He said he and the new Akvarium still have about two albums' worth of good material in them – although he admitted to having "a couple of ideas" he'd rather pursue on his own.

"[The new] Akvarium is a definite music universe, with its own laws and regulations. What can I do if I want to do something different?" he said in an interview with The St. Petersburg Times. "Almost all of the guys have their own solo ideas, so I'd like to move into open seas and to give a chance to the others to do the same. So when we gather after six months we can see where we are."

But while Grebenshchikov looks to the future, his fans, being fans, will welcome Wednesdays look at the past.

The classic Akvarium had a reputation for being "not a rock band, but a lifestyle," and Grebenshchikov liked to describe the group as "a family, in the Grateful Dead vein."

The new Akvarium, has continued with Grebenshchikov's eclecticism, succeeding in combining Russian folk music, Celtic tunes and 1960s psychedelic rock to perfection – as was clearly evident at a "friends-only" concert at the local club Vatrushka earlier this month.

So why take such a lengthy break now? For Grebenshchikov, who thrives on change, the move is logical: "It has become too comfortable for me. The second Akvarium has reached a state where everything is brilliant and great, so the question arises: What to do now? Continue playing? Should we? I don't think we should."

Such talk indeed suggests the band may break up. But while Grebenshchikov looks forward to playing with his old partners, a revived classic Akvarium seems likely to be a one-day wonder.

"It's simply interesting for me to play with [guitarist] Lyapin and [flutist] Dyusha – to see how the old chemistry works in 1997," he said. "It's also a funny experiment; the music is so incompatible with what is going on now, and so out of contrariness I feel like playing (the old songs] and seeing what happens."