See also the Penzel-Mueller Albert System pages.
The Penzel-Mueller clarinet was certainly a pinnacle in clarinet production in the USA. Gary Kern has started a web site specially for this brand: http://www.penzelmuellerfanclub.com/
Penzel-Mueller fans, owners and collectors, please sign up!
The circa-1949 catalog PDF attached below shows the following models:
Super Brilliante, listing at $300
Bel Canto: $179.50
The Penzel Pacemaker might have been made by Penzel-Mueller or might have been after the company closed. Because Mueller is not listed, I have given it a separate page.
There were some clarinets made in cooperation between Penzel-Mueller and Pruefer. See one here.
These pictures show a P-M with special keys for forked fingerings, articulated C#/G# and the left Ab/Eb pinkie key.