<Where could I find details on this protocol? I always found the TU58 very
<unreliable. I tried to build standalone backup many times, and every time
<it said the tapes were created successfully, and every time it would not

One problem is TU58 can and does over run the input buffer if the target 
system can read it fast enough.  I've found over 15 years of using TU58
as a small storage that it's is extremely reliable and if there are problems 
to first check the drive puck (they melt and die from age) or check the 
target system.  Usually if its a slow target slowing down the serial rate 
does it.

<Somewhere I have a cabinet with two TU58's in it and a serial port on the
<back. The thing might even work, I don't know. I think Ragge made TU58
<images for NetBSD once, maybe an emulator could feed these images to the
<11/750. That would be a nice way to get a completely empty 750 to work
<again!

If the drive pucks are ok likely it will work.

If you get desperate and it's still not working I have the C program
of Dan Tsu's from off the net.  I can locate it and send the zip file to 
someone that can put it up in an FTP.

Allison