In a message dated 2/9/2012 5:11:40 P.M. Eastern Standard Time, smulder3 at cox.net writes: http://www.tubecollector.org/927.htm The 927 is a photo cell. It was used, among other things, as a sound on film pickup tube on old 16MM Bell and Howell sound projectors and probably others as well. 73, John, W4AWM