@atmasphere -- thanks for the info; they're being sold by someone in Santa Ana, CA, who apparently inherited several (that had never been used) from his uncle. I listened to them, and they sounded good, but would have to be paired with other speakers to cover the low mids and lows, so I passed. If anyone is interested, they should check craigslist in the greater LA area.
Does anyone have experience with Bohlender Grabener RD 75 ribbon transducers?
If so, could you compare them to Magnepan 1.7i, 3.7i or other ribbon panel speaker?