A fifty won`t get more time, just more distance. A 50mm Rodenstock Yaserex or Yaseron or something was a cheaper alturnative when new. It requires a different auto focus cam. 11x will be top magnification.
If your times are that short, you have the wrong bulb or the electrics are screwed up somewhere. I would worry about overheating. 13139 Phillips I think is correct. It should be a 75watt and maybe 25 volts. Can`t remember the volts.
Set the input voltage selector to 220 or 240 and that will cut down brightness. It is on the rear side of column base.
30cc of each YMC each will reduce the light one stop. 60cc each 2 stops.
Check out the Electrics before you damage something.