1971 Ampeg V4B.
It looked like hell and the caps were old and tired and saggy. The power tubes (7027s from god knows when) were all unmatched. It was dusty and crusty, just how I like 'em. Had the old metal switches that would shock you if you weren't wearing shoes. The saggy caps actually lead to the amp doing AWESOME things for heavier guitar tracks, especially through a run-o-the-mill Marshall 1960 cab.
We hardly ever used it in the studio, and I was favoring a blackface Bassman at the time. I had a need for something brighter and britishy, so I picked up a Vox AC15 and flipped my dear Ampeg. This kid came in to try it, and once he plugged into it and strummed a chord I thought "am I really going to do this?"
He bought it and took it straight to a tech to have it re-capped and re-tubed, so I'm sure it's not the same thing anymore. Even though I get way more use out of the Vox, I feel like an ass for letting that Ampeg go because it had an irreplaceable character. And "character" is my favorite word when mentioning ANY piece of gear.