At the risk of overpopulating, since I just put this up on Gearheads ...
My band played a gig at Harpers Ferry in Boston last Friday; we walked on stage at 10 pm, nice big crowd (350 or so), picked up my guitar and my Twin head was dead in the water, lights on, tubes glowing, but no output.
First, I panicked, then I ran out to the car where I keep a Crate PowerBlock, a little $99 solid stage portable head, 150 watts bridged, the thing is teeny. I plugged it in (luckily, I keep a Holy Grail reverb on my pedal board), and connected it to my cabinet with the two JBLs. I had never tried it before.
I was thinking, this is going to sound thin and terrible, but to my surprise, it sounded pretty good, although I found out later that the cabinet ohms were too low for the head, so it cut out on me when I pushed it hard. After a couple of songs, I went back to the Twin and miraculously got it working, and it stayed for the rest of the night. It's being repaired now.
The morale of the story, to me, was that I was so uptight about not having the expensive, modified "magic Jerry" Twin head for the gig, yet when I heard the board recording, I was surprised to find that while the sound was very clean with no tube warmth, it actually sounded fine. So, a lot of the tone seems to be in the combo of the DiMarzios and the JBL E-120s, as well as your fingers. Maybe I need to carry less gear ... LOL.
Anyway, here's video of the first tune with the Crate head, you can see it cut out on me on the second guitar solo (watch the blue jewel light behind me), with me fumbling with the guitar knobs, and also during the power chords right before the end of the song.
In comparison, here's a Cumberland from later in the set, with the Twin, although I played the Tiger in bridge/humbucker mode, so not the best A/B comparison.