Yesterday I set out to the thrift stores hoping to find a foot pedal from just about anything that I could use with this machine, as the old carbon pile pedal had stopped doing anything except off and full steam. The lady at Salvation Army brought out two old machine that were "tore up". One was a Brother that contained almost as much metal as a library card, but had an electronic foot pedal. The other was a rather pretty Singer 201 with the geared motor. I bought both for $10.00!! Returning home, I wired the Brother pedal to the original outlet setup on the Semper (travesty, I know) and it worked brilliantly. It has superb range and control. I turned the thing over to my eldest, who, not wanting to go out to the shop in the cold, produced a spool of my grandmother's old thread, deteriorated so that we were barely able to thread the thing. She wound the bobbin, threaded up, and laid in a doubled over piece of what looked like light sack cloth. Even with that old thread, the thing sewed the nicest, prettiest straight stitch, and left my daughter positively beaming.
Thanks to all for all the help trying to identify this gem. If anyone has any further thoughts, I'd love to hear them!!