TU58 yet one more time.

Mattis Lind mattislind at gmail.com
Sun May 29 12:03:49 CDT 2016

I have been fiddling with a TU58-EX device, dual TU58 drives in a small box.

The capstans is replaced. I used silicone tubing which I glued on and then
sanded down a bit. PVC tubing in a  size that would fit seems to be
unavailable in Sweden.

The two capstans were a little bit different in diameter at first. Drive
one closer to 17 mm but drive zero around 16.5mm. Drive zero read 5 of 8
tapes (two more tapes had belt breakage). One tape gave "Invalid Directory"
in RT11 the two other gave "Error reading directory". On drive one just one
tape was readable.

So the decision was to get closer to the nominal 5/8" (which I read was the
OD in a post by Tony Duell). With both drives at 16mm drive zero still read
the same amount of tapes and drive one read the same tapes plus one more
which was not readable on drive zero.

Highly annoying. So I decided to read more on the TU58. The spec says that
the bit time is 41.2 us. When I measure I get reading of between 42 and 44
us. (Yes I should have measured before trimming the capstans). So now the
tape is too slow. Although the OD is slightly above the nominal.

Is silicone tubing too soft?

Having been working on a project to recover a tape from a Zilog S8000
machine together with AJ (http://mightyframe.blogspot.se/) I just thought
that it might be possible to read the TU58 and HP DC100 tapes with some
other hardware doing post processing in a regular Linux box.

Would it be possible to use a Floppy Tape (QIC-117) tape drive to read
them? It appears that the tapes are not identical in size. A DC1000 is 0.25
" while the DC100 is 0.15". The capstan position would also differ. Are
there other physical differences that I am not aware off?

Since the TU58 drive is not able to format a tape it could be useful to
also write a new tape with TU58 format. But I guess that there are
difference in coercivity between different tapes.

I have read that Rik Bos successfully converted HP85 drives to take DC1000
tapes by modifying the capstan and changing the write current.

Before I go ahead buying some old Colorado T1000 drive dirt cheap I just
like to ask if this project is doomed because of whatever reason.


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