Here's some of the Thingmaker heating unit variations.

This is the original Thingmaker oven. Silver in color, with the standard Thingmaker logo on the front.

This is an early version of the oven. What makes it unique, is the power cord. It's covered with black & white striped cloth. It was included in Creepy Crawlers Thingmakers.

This is the oven that came with Jillions of Jewels sets. Very colorful sticker on front.

This one came with the Super Cartoon Maker sets. One of my favorite ovens. Nice bright logo sticker on front.

This is a Canadian version. Everything's pretty much the same as the original Thingmaker, but on the front sticker, says Mattel Canada LTD.

This is another great one. Like the Canadian version above, but on this one, the silver metal is totally replaced by red metal. Very cool looking. The plug is red also.