As of 4/92 there were 3 revisions to the circuit. They are RF-1A,1B and 1C. By 5/93 Mesa was up to revision RF-1F. In typical Mesa fashion, they prototyped the product on the consumer. The first 500 had used different OT's and PT's. For someone to say there is no difference, I disagree unless you own one of those 500. They have attack like a pack of wolves. The Modern channel is ferocious and the Vintage channel is very sweet to modern high gain depending on the EQ settings. The Vintage channel has a sweet spot where the gain compresses to the most musical vowel like voice, yet could shred with a bit more Treble.
I have a Chrome Chassis 4/92 PCB 1992 RF-1C # 023X with a final Mike B. tech in 6/92. I have chosen to keep this over any other two channel and three channel. IMHO, my new Road King is still a bit different in how it sounds compared to the DR 023X. I guess you would have to be there and do a side by side, but only 500 people in the world can do this. This amp actually hangs with the SLO 100. Schematic wise, these amps are almost identical with a few exceptions, yet sound different. In a side by side with my 1993 SLO 100 it falls a bit short only in the overall clarity. I beleive this is due to the Bass response being higher in the DR.
The SLO has to have the Master above 4-5 to really come alive, but when it does it is in a class by itself.
Not all of the first 500 had the chrome chassis. By the end of the 400's I have seen 2 with the normal black chassis and chrome diamond plate.
The transformers were both made by Schumacher.
The Racktifiers sound no different and were wired the same way the heads were. They are identical in every way except the size of the chassis and the position of the on/off and standby switch. DR's do not suffer from and other anomolies like RF interference, so what difference would a 1/4 inch less in wiring make?
With the George Lynch mystique about the first 500 and how he looks for a secret marking and the Racktifer mystique abuzz in the Rectifier world, I tend to think that hearing and seeing is believing.
The schematic on the Tubefreak site does not fully apply to the first 250.
I had to have Mesa get me one, and it was hand drawn and applied only to the input to the V1A and how it switched from clean to vintage and the different vaule of resitors and capacitors in the circuit.