I've had two over the years at share houses, both found on the side of the road. Worked generally OK, but sometimes burnt the toast. I'm wondering if they were

I've had two over the years at share houses, both found on the side of the road. Worked generally OK, but sometimes burnt the toast. I'm wondering if they were tuned to a specific type of bread, and didn't really handle sourdough. Still see them from time to time in second-hand shops.