Ed, sometimes the bakelite slider inside will break (usually partially but recently I ran across one that broke completely) and that will make things pretty horsey. One, the switch won't work well any longer. Two, you can't get the knob out occasionally. If you go back several posts, you'll see a tutorial I made showing how to disassemble these and repair/rebuilt them. I was hoping that might become a sticky or a tech note, but guess not. Once you do that, they usually work just like new. Good luck.
