i answered this question about 2 hrs or so ago in DIYaudio.com........
if i had known this was for a piece of medical equipment i wouldn't have answered by telling him how to build one. MEDICAL EQUIPMENT FOLLOWS VERY STRICT SAFETY AND RELIABILITY STANDARDS, SO DON'T MESS AROUND WITH REPLACING PARTS WITH DIY AND SECOND SOURCE PRODUCTS!!!!!!! sorry, that one need shouting. don't mess around with a piece of equipment on which somebody's life may depend.......
when this question was cross-posted at DIYaudio, the little tidbit about it being for a piece of medical equipment wasn't included.....