It depends. Most of those old Jennings were adjustable over 15 pounds. If the limbs are bottomed out at 50 pounds, you should be able to getdown to 35 pounds. If they are not bottomed out, then you need to find out what the maximum peak draw weight is and go from there. Also, if it has the old tri-draw wheels, where the draw length is adjusted by moving the cable from one slot to the next in the wheels, then the draw weight is less in the short draw slots than it is in the long draw slots.
You might want to check the bow manual at Bear/Jennings.
http://www.fredbearoutdoors.com/tech-info/pdfs/compound-manual.pdf