I have a Dayton 5amp Speed Control that the Rectifier shorted between the cathode & anode. The part # is: 66497 RCA Date code C-7613. I've called & searched everywhere & no one has any info. I've tried to replace it with: "S8040R-ND" & "S4010LS2-ND" but on variable speed the motor just hums. Any help would be appreciate! Here are some pictures.