That clip is from a series called "The American Folk Blues Festival" -- a European tour that ran for a few years in the mid sixties featuring the cream of the crop of the blues. Some of these shows were televised and the clips were released on DVD a few years ago. Solid gold. The Howlin Wolf footage is worth the cost of admission all by itself. I believe that Sam is playing through a Marshall stack in that clip. As far as I know that's the only footage of him playing.