> I was able to borrow one of those Sun tape drives
> that reads the 150MB tapes ... made then the two NetBSD tapes ...
> went back to the 3/50.
> 
> >b st()
> Boot: st(0,0,0)
> st: Error:
>         sense key is 5  error is 0
> scsi: dma never completed
>         sense key is 6  error is 0
> scsi: dma never completed

Quite possibly your 3/50's boot ROM does not support the QIC-150
drive.  The older ones will only handle a 60MB drive.