I found this one used a couple of weeks ago. I like it. Supposedly the tapes were mis-labled as a concert in Mexico in '74, but they are actually rehearsal tapes. By and large the music is intereseting, but there is the occasional tuning, talking and stopping mid-song, but there are several instances where the tunes will go on for 7-10 mins at a time. Not essential but worth it for a decent price. I think there are 4 or 5 2cd volumes in the series as of now.