Product review (5 stars): Inexpensive repair
For just ~$22 I was able to repair a very old Jenn Air "Convertible cooktop" model 3300 series No. 8853.  The burner control knob broke leaving a loose feel as I turned it (no click as it passed through the off position). It only took about 5 minutes to replace the part.  I plan to remodel my kitchen at some point in the future and did not want to buy a new cooktop or (heaven forbid) live without 4 burners and the griddle. I have a picture of the original Jenn Air brochure that was left behind when I bought the house 20 years ago.  I'm guessing the Jenn Air was installed around 1975.