Not so sound naive or anything, BUT:
I know how solid state and tube amps work, but what makes Rectifier/treadplate amps different from the first two? How do they actually work?
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single is 2 channel, 50W, silicon diode rectifier
dual is 3 channel, 100W, SS or tube rectifier, (2) rectifier tubes
triple is 3 channel, 150W, SS or tube rectifier, (3) rectifier tubes

the dual and triple also have a couple added features, but the older ones were also 2 channel.
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basically all amps have a "rectifier" nowadays. the name "rectifier" is basically a gimmick. the mesa boogie amps do offer the option of tube or silicon diode rectification, as mentioned above, but its not strictly reserved to the rectifier series of amps, if thats what your asking.
all amps have rectifiers. a rectifier converts AC power to DC power. dual and tripel recifiers just ahve 2 or 3 of them. and have the option to use tuebs to rectify power so when u turn it up you get this very nice sag to to the sdound