Possibly NOT Hotpoint.
One of the early black-and-white runs was filmed at Boston Gas, and I would doubt if it would be Hotpoint. Could be, though.
However, I do know for a fact, that the later B & W shows were filmed with Frigidaire appliances. Says so in "The French Chef Cookbook."--in the acknowledgements, though. Julia NEVER, EVER did a commercial for a product, unlike Jim Beard or Craig Claiborne. Alton Brown seems to be following in her non-endorsement footsteps. In the preface to "The French Chef Cookbook," she tells a story of how the cooktop was not properly grounded, and she got a shock from the lavalier microphone she was wearing.
In "From Julia Child's Kitchen," she first mentions the Cuisinart, though never using the brand name, She came up with a very funny description, something like "Super-blender-shredder-food processor."
She also mentions in "From...." how she dried her newspaper in the microwave and caught the thing on fire.
We won't see her like again. Rest easily, Julia.
Bon Appetit!
Lawrence/Maytagbear