(Reuters) - An amplifier used by George Harrison during recording sessions for Beatles albums Revolver and Sgt. Pepper's Lonely Hearts Club Band is expected to fetch 50-70,000 pounds ($80-110,000) at auction next month.

The rare Vox UL730 amp and cabinet will be offered at Bonhams' London entertainment memorabilia sale on December 15.

According to the auctioneer, the amp's connection with the Fab Four was only recently discovered when an engineer who had been asked to fix it noticed the name George Harrison scratched on the chassis.

Subsequent research showed the amp to have belonged to Harrison, guitarist for the Beatles, who died in 2001.

Very few amps used by the Beatles have come to auction before, and to find one that was used on two such significant albums is truly rare and exciting, said Stephen Maycock, a consultant to Bonhams.

Revolver (1966) and Sgt. Pepper (1967) came at the height of the Beatles' creative powers, and are considered among the most important recordings in pop music.

Bonhams said about six 7-series amps went to the band in 1966. John Lennon and Paul McCartney moved to more powerful models in the series later in the year, but George continued using the 730.

Another highlight of the auction is expected to be the original cover artwork for the 1969 Rolling Stones album Let It Bleed, estimated to be worth 30-40,000 pounds.