An ultra-rare guitar amp used by George Harrison during recording sessions for the Beatles' albums 'Revolver' and 'Sgt. Pepper's Lonely Hearts Club Band' is expected to fetch upwards of $100,000 when it goes under the hammer Dec. 15 during a Bonhams' London entertainment memorabilia auction.

The original owner of the vintage Vox UL730 amp and cabinet was only recently discovered when an engineer tasked with fixing it noticed the name "George Harrison" scratched into the chassis. Further research confirmed that the amp indeed was once owned by Harrison. He may have been known as the "Quiet Beatle," but he certainly wasn't quiet when playing though a cranked Vox amp!

"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," says Stephen Maycock, a consultant to Bonhams.

Other items of note up for sale include the original album cover artwork by Robert Brownjohn for the Rolling Stones album 'Let It Bleed,' which is expected to sell for more than $60,000, and a Martin acoustic guitar previously owned by Eric Clapton that is expected to fetch upwards of $45,000.

Check out the complete list of items in the auction, which also includes nearly 400 rare and one-of-a-kind memorabilia pieces from Queen, Bob Dylan, Pink Floyd and others.