Probably five years ago I ordered one of those Kramers from MusicYo.com just to mess around with. It wasn't too bad, considering it was made out of particle board.
Anyway, it came with a licensed Floyd Rose and a D-Tuna. The D-Tuna works by utilizing the fine-tuning mechanism on the Floyd.
As you probably know, on the Floyd, when you fine tune "up," clockwise rotation of the tuning knob forces a lever underneath <i>down</i>, tightening the string tension. Turning it clockwise allows it to raise, thereby relieving tension on the string.
The D-Tuna is basically a replacement for that little lever that is a bit longer and has a rotating casing. That casing, when in the correct position, pops underneath the tuning knob and is just the right thickness to raise the pitch two semitones. when turned 180 degrees, it allows the lever to snap back to it's normal position. That way, you tune the guitar to drop-D, and when you want it in standard tuning you engage the little D-Tuna to pull the string tension on your low string up to E.
That is probably extremely over-worded, as I have little luck with concision. Anyway, I hope it helps. If not, some links are below.
And, to answer your "operation question", it takes a lot of adjustment and calibration to get it just right (just like the rest of a Floyd Rose), but once it is in you can just snap back between E and D by turning that little knob. Pretty cool...
Here is the main website. The FAQ has some OK info:
http://www.dtuna.com/
Here is the MusicYo D-Tuna page:
http://www.musicyo.com/planet/evh_dtuna.asp
The best site ever...the US Patent Office website-this thing was actually patented by a guy named Robert Benson. Here's the patent:
http://patft.uspto.gov/netacgi/nph-...5,359,144.PN.&OS=PN/5,359,144&RS=PN/5,359,144
If you click on "images" and have Quicktime you can view the drawings, too.
Cheers!
