Hi Rick, have a great time in Berlin, it's a great city.
By coincidence I asked the same question as you last summer - there's some advice from Eva on this thread!
http://www.jbonamassa.com/forum/viewtopic.php?id=6723
Edited to add the quote:
eva wrote:I read in the internet that the Roadhouse Club (adress is: Genter Str. 65) has Blues Jam sessions every Tuesday starting at 8 pm and the BeBop Bar (Berlin Kreuzberg, Willibald Alexis-Str.40) has a Jam session every Sunday staring at 9 pm - I can´t tell you if the clubs are good or not, because I´ve never been there, but that´s what I found ....
But you can also just wander around in Berlin and you´ll find a good place - Berlin is a cool city for sure !
Also be sure to check out Tacheles, it's not a blues club, although I did hear a dub remix of Muddy Waters when there, but it is a really cool place: http://www.tacheles.de
"The recently formed Edinburgh Blues Club has identified an appetite for the personal communication between musicians and audience that the blues long ago perfected." The Herald Newspaper (Scotland)
http://www.edinburgh-blues.uk