Dual Rectifier refers to the fact that the amp has a switch that selects between two options: tube rectification and solid state (silicone diode) rectification. The former has a saggier and the latter a bolder tone/feel/output.
Do Triple Rectifiers have a third option to that switch? Or is the name Triple just a marketing thing possibly related to the fact that, AFAIK, the first Dual Rectifiers only had two channels and Triples added the third channel?
Edit: Looking at the Triple Rec manual, there is definitely no third option on the rectifier selection switch. But it still remains a little unclear what the name refers to. From what I’m gathering, it could be that there are a total of three rectifier tubes, as opposed to Dual Rec’s two tubes. But if anyone knows for certain, I’d appreciate the knowledge!