The Dual Rectifier is loosely based on the SLO100. The earlier models were most closest to the Slo and are tighter, reminiscent of the Mark Series
The first Batch of Dual Rectifiers started in 1992
They were with Serial number R0001 to 500.
They included Beter Transformeres and a special different PCB (semi handwired). It was a true "solo head"
The tone in these first 500 , tighter than those that came after. The first 500 come in Revision C and D (A and B were prototypes. Which differ slightly in presence pot. During this time the "chrome-blackface" panals were introduce and made up until the first 1100 or so dual rectos.
After the first 500, Mesa started making the Dual Recto more Scooped, and less of a "solo head" but more of a rythm amp, as was the demand in the late 90s.
In 2001, mesa boogie made the 3 channal which is even more scooped and boomy bass.
So the first 500 have different OT, and a handwired outlet plug. the OT is not made anymore and is what gives these first rectos its tighter, more focused tone