well the nagra is a portable recorder, it's main use is to record shit in the field...it's extremely good at that, very solid construction and the batteries last forever. it's amazing and unbreakable
what i did is to simply run a synths output into it, overdrive and keep it running while playing and messing with the knobs...playback at different speeds and stop the tape by hand here and there.
literally just playing around, but the results are stunning. i wouldn't hesitate to get one of them if i had the cash
i had the mono version, but theres some stereo ones floating around as well - i wouldn't use it to saturate entire mixes but more as a recorder and sound design tool