Cary Audio CAD-280SA V12R

Yes. It’s actually "I" to "R" upgrade. I owned a stock V12R for a while and sold it a year ago to try other-brand Monoblocks to test different amps with my custom designed speakers. The lucky new owner loves it and has compared it to other high $ amps. With further upgrades to the V12R, it truly holds its own.

The V12"I" to V12"R" conversion involved upgrading the main output transformer to the "Big Blue Wire" transformer, among other things - and was a notable difference for those who went from I too R.

The stock Ruby EL34 tubes are actually Shuguang EL34-BSTR tubes and they sound fantastic after removing the stock Audio1 caps and replacing with much better coupling capacitors and added Hexfred diodes. Yes, the stock V12R can be upgraded again to bring it to any entirely different level compared to the stock version of itself.

I rarely ran my V12R in 100wpc Ultralinear mode. It always sounded more engaging in the 50wpc strapped Triode mode, particularly after the 2nd round of extended upgrades were completed. It was a fun and unique path in the tube amp journey.

I rarely ran mine in 100wpc ultralinear mode also . The nice part is you could switch between UL mode and triode mode on the fly , even with music playing . Running only two tubes per channel ( about 17 wpc ) was very sweet if your speakers were efficient enough for the low power . Mine was a stock V12R in that beautiful red paint . I made a meter to plug into the back to adjust the bias but found out the red indicator lights next to each tube was accurate enough . I really miss that amp but now have Bottle Head 300b monoblocks , First Watt F6 , Conrad Johnson Classic 60 and a pair of Nelson Pass 6 wpc monoblocks that I built myself . I only need about 8 wpc to drive my Tekton Enzo 2.7's . Let us know what you do but that Cary kicks butt .   

BTW.... mine sounded better in single ended . My Cary SLP-05 pre amp / Ayon 2s player combo sounds better single ended also , go figure .  

Had the I version and now have the R version. Really nice amp, and as the other  posters noted, quite a few upgrades.

should be also noted that the first input tube has regulation on plate voltages, so you can pop out 12AZ7 and replace with 12AT7 or similar without rebiasing the socket. I have found that driver tube EL84 type and brand makes a huge difference on the tonal quality of the amp.

and the amp will run 6L6GCs up to KT88s. my favorite tube for this amp is the shuguang Western electric Plus 6CA7 fat bottles. A magical sounding tube.

there was also a monoblock version of the V-12 for over 200 watts per side, but they do not come up for sale very often.

I have one and am extremely happy with it. It's got Ruby EL34's and Generex Gold Lions for the front end.  That's the place where tube rolling gets interesting.
I'm an older guitar player and changing input tubes was the way to find how to get an amp to talk.
On the other hand, I just want to hear everything as I imagine the recording attempted to be.
I like the amp enough, I've looked at buying a spare.