wow, can't believe i missed this topic for so long lol!
I owned a jsx 212 combo for 8 months. I found the clean channel was dead ( i know its supposed to be good for pedals, but it just lacked any sparkle ). The crunch and lead channel were good and i found the amp with the el34's to be really articulate. Tried a set of groove-tube 6l6's but just couldn't get rid of the amp-fart with the bass above 4.
Reliability was a huge issue in this amp. The pots are cheap plastic underneath the knobs, one broke off in the first week. The amps have poor quality soldering and mine would suffer from gig-ending volume drops. First time was about 2 songs from the end of the night, thought it was the soundman. Took it to the shop, they said it was a bad tube and they tested in for about 8 hours (with a cd player????). Second time it went was start of 3rd set, plus the reverb stopped functioning. Took them 10 weeks to 'fix' it, which i don't know or care if they did because i got a pro-rated refund and bought the mesa, couldn't be happier, even with the $1000 in the price difference. I think the amp had cold solder joints and the fx loop was shorting out causing the volume drops because it never blew a fuse or had a bad tube.
If you get this amp, your paying too much for joe's name, the quality and reliability isn't there. The combo is heavy and only has a top handle. Not an overly loud amp either. Would I recommend it? Not even if my name were Joe Satriani.