This from Chazz Avery's beatlesource.com: As with the previous Hamburg visit in 1960, specific date information apparently does not exist. Sometime during this visit, Paul's Rosetti "bass" was allegedly smashed. As a result, he played piano and/or simply sang during performances. It has been reported that he would play Stu's Hofner bass upside-down but no photos seem to exist.
As a result, it was during this trip when Paul pruchased his first now-famous Hofner "violin' bass at a local Hamburg Steinway music shop. It became the second Beatles' guitar pruchased in Hamburg that would become a world-famous Beatles' icon.
It was during this Hamburg visit that The Beatles (without Stuart) made their initial recordings with Tony Sheridan on 22-24 June.
Although he was only "sitting in" with the band, these were Stuart's final days as a Beatle. A letter written 31 April 1961 by Stuart, to his mother, announcing his leaving the band can be seen - here. This might narrow the dates of these photos to March through maybe early May 1961.http://beatlesource.com/savage/1961/61.03.27%2007.02%20top%20ten/1961topten.html