I acquired a new keyboard yesterday from a thrift shop. It's an old IBM rubber dome keyboard from what what I can tell. It is large and built like a model M but doesn't have the click in they keys. On the back of the keyboard is a 3 way toggle switch which changes the volume on the built in speaker. The model number is 6247440. I tried using it on all my computers but had no luck. It would not register, just make a loud humming sound. Does anybody out there have any info on this keyboard? Thanks.