Troubleshooting with a variac

[maxhifi]

The original owner discarded it because the knob's set screws were stripped and it would spin freely. It was from a school and I suspect students forced it. I removed the knob to use it and haven't bothered to find a new one or repair the old one yet. It would be a whole lot easier to use with a big knob, the variac needs some serious torque to control! Test equipment gets the least maintenance of any of my gear, and it should get the most!