I recently got the Fender TB-600 Pro head and was in love from the moment I plugged in. I hadn't heard a whole lot in the past about Fender heads, except that the guy from Green Day played them for a while; but after recently going to see Janes Addiction with Eric Avery back on bass, I was sold. Avery is one of my favorite all time players and he was rocking the TB-1200 with 2 6x10 cabs and 2 15's and he, as always, sounded incredible. Granted, I was hearing it coming through the house mains, compressed and everything else, but the tone was excellent. He has always had excellent tone, so that seemed like a reliable endorsement to me.
I had been in the market for a new head since selling my SVT Classic a while back when my last band was dropped from Interscope. (I still kick myself for doing that but I didn't play it for a year and was on hiatus). We still have an artist deal with Fender and I was able to get the TB-600 Pro for like 65% off MSRP. These heads go for $1200 or so new, so needless to say I got a good deal. It was either that or shell out for another SVT, and though I love the SVT and think its about the best bass amp ever, I wanted something rackmountable, a little lighter, etc.
Now to the amp: Its the Fender Tube Pre (Two 12 AX7's I believe) married to a 600 watt solid state power amp which results in massive amounts of headroom and very warm, adjustable tone. Some argue that tubes in the pre stage doesn't make a whole lot of difference in the tone and that having them in the power stage is where it counts, but I'd have to disagree, or make an exception with this head because the thing is just WARM. You can engage the 'tube overdrive' section and dial in and blend myriad of tone, from subtle warm vintage Bassman style tone to full on gnarly overdrive. Its got a really comprehensive eq stage as well but I'm not going to continue on about. This amp definitely shapes and ads its characteristic sound to your tone, so if you are someone who wants a GK or a head that only gives 100% accurate rendition of your bass, then this head isn't for you.
Bottom line, I've played, recorded and toured for years with GK's, Ampegs, etc. and this is one of the best heads I have ever played through. I haven't had it for long, so time will tell, but so far so good.