Net booting would definitely be the slickest way to do it, but not all
VAXen have net boards (although of course they should!).

I've been thinking of ways to solve the same problem, and it seems to
me that if you need to write a bootable TK50 for your MicroVAX, the one
machine you have that you can be sure is able to write TK50s, is your
MicroVAX.  Since all VAXen have some form of serial console ROM, it
shouldn't be too hard to write a program that runs on a PC (or whatever)
and keys tape (or disk) blocks into VAX memory a block at a time and
then deposits commands in the controller registers to write them out
(or maybe deposits a small program to do it, I don't know if [T]MSCP
controllers can use polled I/O).

I used this technique to build ITS boot tapes on a DEC-20 a couple of
years ago.  Sure I was up all night, but the next morning I was logged
into a running ITS system.  That system had MASSbus tapes though, which
are a lot easier to program than the [T]MSCP devices that are more common
on VAXen, writing the mini-DSRs would be a pain.

Writing RX50s on a PC is no problem at all (you need to change the drive
parameters table but that's easy), so that's an option.

John Wilson