I have a pair of these which are original equipment on a 70ish Raleigh Grand Tourer (Reynolds 531db f&f), but mine are labeled Weinmann rather than GB or Altenberger. I believe they are all the same brake though.. Mine came with a set of finned aluminum Matthauser brake pads on them. They work decent for me. And they are a bit unusual so they get comments when we're at a bike gathering..
Bruce Schrader San Francisco, CA
===== "Not all those that wander are lost." -J.R.R. Tolkien (1892-1973)