Accessing a TK50 or TK70 from RT

Jerome H. Fine jhfinedp3k at
Sun Jun 12 07:54:11 CDT 2016

 >Adrian Graham wrote:

>>On 12/06/2016 12:15, "Rod Smallwood" <rodsmallwood52 at> wrote:
>>>>Nearly there I think. I have loads of TK50 tapes to format.
>>>I'm pretty sure the TK70 can only read TK50 tapes and not write to them...
>>Thanks Graham
>>     Now that sounds highly likely. Does the TK70 controller support the
>>TK50 drive perchance?
>>I have a TK 50 controller I can aways put that back in.
>The TQK70 controller supports the TK50 drive, yes. If you're needing to bulk
>erase it might be easier/quicker to get hold of a degausser then just init
>before writing as necessary.
I seem to remember that Adrian is correct and that the TK70
controller does support the TK50 drive.  However, my question
would be "WHY?" use the TK50 drive if you have a TK70 drive?

One answer would be if you had tapes already formatted as TK50
and you were only going to write small files.

Since the TK70 drive (with a TK70 controller) is so much better,
the better answer is to use the TK70 drive. However, as Adrian
pointed out, once a tape is formatted as a TK50 tape, the TK70
will NOT be able to write to that tape UNLESS you first bulk
erase the tape.  Over a decade ago when I used the TK70 for
a few years as my primary backup drive, I did a bulk erase of
dozens of TK50 tapes and NEVER had a problem.  Be VERY
careful with a bulk eraser which is under powered - they tend
to break very quickly if used for more than a few minutes.

Instead, I fortunately found an old voice coil from a speaker
that was powerful enough (about the size of my fist) and was
able to bulk erase TK50 tapes by repeatedly moving the voice
coil in a circular motion in contact with the plastic container of
the TK50 / TK70 tapes first on one side, then the other for
about 30 seconds.  At that point, the tape could be INIT by
the TK70 and then both TK70 read and write operations were

What is VERY helpful is that it is possible to COMPARE
a BACKUP image file using BUP.SAV in RT-11 on a
PDP-11/83 in about the same time as writing the image
file - or about 7 minutes if I remember correctly for a full
32 MB image file of an RT-11 32 MB partition.

A word of caution.  KEEP the head cleaner solution handy.
I used wooden Qtips and rarely kept the metal cover on
any more since the tapes shed so much that cleaning is
needed after less than an hour of TK70 usage.  The actual
head cleaning is fast, only a minute or two.

If you have any more questions, please ask.  Let us know
if you are successful.

How is the RX02 drive coming?

Are you still using the RD53 drive?  I haven't heard of anyone
else being successful these days with an RD53 drive that has
not had a lobotomy (sticky bumper pad removed from the
head assembly).

Jerome Fine

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