I started my lift with my uVax II with no TK50, and now I have two, 
but apparently neither of them works.  The first came to me with 
a tape still in it, which was already a bad sign.  I inserted
it into the bay, and connected it to the dangling cable of my
TQK50 card, (and the power of course) turned the machine on, and I got:

no green light, flashing red light.

I read some miscellaneous postings from this newsgroup, dejanews,
and the nice little page at www.vaxarchive.org/hw/tk50ctrl.htm,
and decided, yes I was brave.  So I opened up the tape drive, and saw
that in fact the tape was wound up on the takeup reel pretty far, and
apparently the drive didn't want to rewind it.  

So, I got another today.  This one had no tape in it, but when 
I powered it up and inserted a tape, a never got to see the green
light (another bad sign).  It pressed the load switch to the 
unload position, and then again I got flashing red, no green.  
Then I saw a brief green light, and the tape seemed to make that 
familiar rewinding noise.  This time, I could lift the door, and 
remove the tape, but there was still tape sticking in the drive.

I removed the cage from this drive, and managed to get the tape 
completely out, but not rewound.

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.

Second question: I've heard that the tape drive itself inside the 
TK50Z is actually the same, but there is a SCSI card interfacing
to the drive, to make it look like SCSI to the outside world.  
If this is true, could I remove the drive from one of these 
boxes, and use it in the uVax?

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.

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.

Doug