<My first question: I've worked with at least 3 TK50Z (SCSI) in the
<lunchbox size case, and they are all very dependable.  Are the 
<uVax type TK50's more commonly bad, or am I just unlucky? (I 
<seem to remember Brian Chase saying he had several of them,
<and they were all bad.

Tk50s were not that reliable due to heat.  Also the TK50Z is the same drive
with an added scsi adaptor.  Yes the 50Z drive can be taken from the case 
and used with the Qbus board.

<Third question: Could the problem be the Vax itself, maybe not sending
<enough power to the drive or something?  I haven't tested these drives
<in other machines.

Assuming the uVAX PS is good that shoulld not be a problem... but checking 
the PS to see that it is working is a good thing.  Note: the BA123 has TWO
power supplies and I've seen one go bad.

<Lastly, can these tapes be rewound by hand?  There's only about 3 inches 
<of tape sticking out the door, and this was a good tape before today.

Yes, you need three hands one to unlock the tape, hold the door and rewind 
the tape.

Allison