I'm trying to find a way to get my DEC
Rainbow's monochrome output onto a
newer monitor than my aging VR201 (especially since I zapped something in
it and my diagnostic efforts to date haven't fixed it).
I can't remember the video output on the Rainbow, but I wanted to do
something similar to have one setup for the S-100 machines. After
looking on eBay (before I banned them from my use), I found a device
that basically had RCA audio/video inputs with a VGA output. It also had
the advantage of having an analog TV tuner built in so I could also use
things like the old video games that had the Channel 3/4 output.
The device is buried somewhere so I can't tell you the brand.