transformer with no center tap
 

Any way to hold +/- rails steady when no center tap to ground (single secondary)? Tranformer puts out 40 volts rectified, but when hooked up to a chip amp drifts to like -28 an +12 (or visa versa, can't recall). Also curious if a solution exists, if can apply to a transformer where there is like 30 vct and 60 vct using 4 secondaries if one could use 3 out of 4 to get 45 volts.