I try to create the bulb, not so difficult but need to prepare project curve for top and bottom spiral.
For the middle just use helical sweep.
After create half spiral, than copy and rotate. Done
First step, create helical sweep with trajectory (see the picture), pitch 4, and sketch diameter 17 cyrcle.
Step two, create projected curve from view and side view
Step three, create sweep with the projected curve for trajectory and use diameter spiral to make sketch
Step four, similar with step three but for the top side
Step five, After got half spiral. DO copy and paste special with rotate 180 degrees
any video related to model