The Gretsch 6128 Duo Jet guitar is really one of the best kept secrets out there. In late 1957, Gretsch switched the pickups on the Duo Jet to Filltertron pickups (think mini-humbucker) and so the tone changed as a result. DeArmond pickups are fat single coils, think P-90s and a Tele mixed together. Great pickups and will give you that raunchy sound that just oozes early rock and roll.
The Filtertron Duo Jets are a different animal. They don't twang as well as a DeArmond Duo Jets, but they have some of the raunchiest, midrange laden, low output humbuckers ever slapped into a guitar. Ray Butts designed the Filtertron and it is the first humbucker. Gibson gets all of the glory for that but the fact is that Ray Butts designed the humbucker before Seth Lover. Notable players include Pete Townshend who plays a 1959 Duo Jet and David Gilmour who plays a '58 or '59 Duo Jet. For those who have the David Gilmour Royal Albert "Remember That Night" DVD, listen to track 14, "Where We Start." Definately an incredible jazzy rock tone with the perfect amount of high end zing, with fat but smooth mid range with no hint of mud. It has Filtertons.
I don't know what it is, but a Duo Jet can pretty much do it all and a good one is a must own!