I have a JCM900 4100 head and a JCM 900 4102 2x12 combo. I think they're great amps. There were a couple of different veins of JCM 900, the Dual Reverbs and the SLX models. They sound different. One important thing to remember is that when they were first released they came with EL34's and latter switched to 5881 and briefly had another kind of power tubes, but I forget which ones. If memory is correct, in the 90's Marshall was having difficulty getting EL34 power tubes from their suppliers. The JCM 900 was released in response to people modding their JCM 800's. Marshall designed the 900's to be a modded version of the 800's. For some reason I've seen the 900's get a lot of slack over the years. I've never understood why. I think they're great for Rock, Punk and High Gain situations and I personally like their clean sound. I don't play blues or bluesy rock, but I know people that have used them for that sound. I prefer the ones from the early 90's and final run of them in the mid late 90's when they used EL34's. I'm not really a fan of 5881's. The ones with 5881's can be converted to EL34. Marshall would even do that as part of a warranty repair when they started using EL34's again at the end of their run. The reissues available now use 5881's I believe.