I was thinking you should probably be aware of this too.
The Dual Recs have two rectifier tubes. Thus the name, I guess. I've never seen inside one of those but I'm guessing there's a seperate rec tube for each output tube pair (There's two pairs).
The Triple Rec has a whole nother output tube pair and boasts another 50 watts. So, three output tube pairs... three rec tubes. "Triple Rectifier"
This may not seem like abig deal but look at the Lone Star. It also has switchable rectifier types. It has two output tube pairs, just like the Dual Rec but only one Rectifier tube.
The really confusing thing is the Single Rec. It has one output tube pair but only a Solid State rectifier. One would think that they would continue with the theme and give it a switchable rec tube too. Oh, well.
Anyway, Silicon Diode rectifier vs. Tube is an age old debate. Niether is better. They're just different.