I would agree with Cory on this.
I may add that the RA100 would be similar to the DR Roadster set to spongy with full Tube Rectification tracking. However it is not super spongy. It seems to fall in-between. It has that perfect amount of sag and yet retains well defined articulate note clarity (may be due to the different output transformer and transfer characteristics.) I have tried and could not replicate the character of the RA100 with either the Roadster or Mark V running EL34's.) The Mark V cannot give you this type of tone even if using the tube tracking at 45W on CH2 with the amp set to Variac power. Keep in mind that the Mark V in 45W mode operates in Class A. The RA100 is a true Class A/B which adds some warmth. I would add that the RA100 performs well with single coil guitars (Tele, Strat, or other ) and sounds just as good with humbuckers too. I would say after getting the RA100 and playing all of my guitars though it, the different tones of each guitar is more noticeable than with the other amps I have.
The clean channel will not give you a pristine acoustic like tone that is more common with an open back combo ( Mark IV or Mark V can easily be dialed in to do this, note if driving a sealed 412 or 212 that will be difficult to achieve). However, the Clean channel of the RA100 is where I get lost all of the time. :mrgreen: Very soulful singing voice and it gets better with the power soak and moderate gain setting. The clean channel alone can achieve sweet satisfaction of nice rich mellow tone to medium British crunch. If there was an amp to take you back in time this would be it. The Hi/Lo as Cory mention does not compress the signal as much as the Mark V in Mark IV mode. I would say it is similar to a RAW or VINTAGE setting on the DR with tube rectification tracking without the expense of mushy bass. I believe the RA100 is well rounded considering it is only a 2 channel amplifier (note that the RA100 is a true 2 channel amp. The gain stack of the Hi/Lo uses V1 and V2 only, the preamp section of the Clean channel uses V4 and V5 only. There is no cascading and mixing between the Hi/Lo and Clean channel like with other Mesa Boogies).
The effects loop is simple but does not have a means to turn it off or on. It is activated by plugging in the jacks on the back. Best to use effect that have a true bypass when turned off.
The reverb can be adjusted to be active or turned off for the higher gain channels. I prefer to keep it on. It is not bad but I feel the Roadster has the best reverb character. The RA100 can easily be swamped with too high of a reverb setting (tends to become compressed and signal attenuation may occur, at lower settings this does not happen).
The RA100 is a great amp, I always get lost when I use it, lost in a good way 8) Controls are easy and straight forward. This is one Mesa that does not need much time to find a great tone with. Also this is the only amp that I would highly recommend use with V30's. Not sure how the oversized cabinet will sound with the V30 ( I could not stand the standard oversized cab with them), I would consider getting the smaller traditional sized cabinet over the larger one. I am using a traditional sized 412 with the original V30's that I pulled from my standard slant front Rectifier cab. Also note: some speakers may not be the best choice with the RA100, I have tried it with EV which made is seem a bit dark and not very soulful. V30's (or speakers with a similar frequency response) will win you over with the RA100.