18 Jan
2016
18 Jan
'16
2:39 a.m.
I know that tapes have different coatings, so some are ferrous and other chrome based, but
what about the backing and "glue" that holds the two together?
Dave
G4UGM
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Chuck
Guzis
Sent: 17 January 2016 23:41
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: Re: Non-baking cure for sticky shed?
On 01/17/2016 02:00 PM, ben wrote:
Why not just grab a few 8 tracks from the truck out back.
...Or fill those old QIC cartridges with some old acetate-base 1/4"
open-reel audio tape? After all, it's all the same...
--Chuck 
18 Jan
18 Jan
8:33 a.m.
On 01/18/2016 04:39 AM, Dave G4UGM wrote:
I know that tapes have different coatings, so some are
ferrous and other chrome based, but what about the backing and "glue" that holds
the two together?
There was a tape sold by a few manufacturers (I think 3M's
was called Black Watch) that had a coarse black matte finish
on the back side. A problem with some drives which had fast
rewind speeds was that air was trapped in the tape wind, and
then once a bunch more layers of tape was wound on the reel,
the tape wrap would cinch and fold over a piece of tape.
This matte finish was supposed to cure that, and I think it
did. But, that finish was not as durable as the magnetic
coating, and would start to shed all over the drive, leaving
stuff on the data surface. I think about 5 years after the
stuff came out, most data centers searched out and trashed
all these tapes.
Jon
8:56 a.m.
On 1/18/2016 11:33 AM, Jon Elson wrote:
There was a tape sold by a few
manufacturers (I think 3M's was called
Black Watch) that had a coarse black
matte finish on the back side. A
problem with some drives which had
fast rewind speeds was that air was
trapped in the tape wind, and then
once a bunch more layers of tape was
wound on the reel, the tape wrap would
cinch and fold over a piece of tape.
This matte finish was supposed to cure
that, and I think it did. But, that
finish was not as durable as the
magnetic coating, and would start to
shed all over the drive, leaving stuff
on the data surface. I think about 5
years after the stuff came out, most
data centers searched out and trashed
all these tapes.
Jon
Interesting. I just happen to have a 3M
Black Watch tape right here next to me
that I'm using to test a Mark 300 tape
cleaning machine. The tape so far is
fine, not shedding anything front or back.
- J.
9:39 a.m.
On 01/18/2016 10:56 AM, js at cimmeri.com wrote:
On 1/18/2016 11:33 AM, Jon Elson wrote:
There was a tape sold by a few manufacturers (I
think
3M's was called Black Watch) that had a coarse black
matte finish on the back side. A problem with some
drives which had fast rewind speeds was that air was
trapped in the tape wind, and then once a bunch more
layers of tape was wound on the reel, the tape wrap would
cinch and fold over a piece of tape. This matte finish
was supposed to cure that, and I think it did. But, that
finish was not as durable as the magnetic coating, and
would start to shed all over the drive, leaving stuff on
the data surface. I think about 5 years after the stuff
came out, most data centers searched out and trashed all
these tapes.
Jon
Interesting. I just happen to have a 3M Black Watch tape
right here next to me that I'm using to test a Mark 300
tape cleaning machine. The tape so far is fine, not
shedding anything front or back.
- J.
9:46 a.m.
On 01/18/2016 10:56 AM, js at cimmeri.com wrote:
Interesting. I just happen to have a 3M Black Watch tape
right here next to me that I'm using to test a Mark 300
tape cleaning machine. The tape so far is fine, not
shedding anything front or back.
Sorry about previous reply, hit wrong button.
Well, I don't know if it was the Black Watch that was the
problem, or somebody else's version.
We started with spring-arm drives, which could not keep
constant tension on the tape. You'd hear this HORRIBLE
scrunch noise at various times when the tape was being
processed, which was the layers of tape sliding over each
other. Usually didn't cause problems, but on occasion it
could be so bad that the drive would lose tension and shut
down in the middle of the reel.
Vacuum column drives didn't seem to have much of this
problem. I think it was the jerk of tension when the drive
reversed to reread a bad block that started the slipping on
the spring arm drives.
Longevity of tapes was very spotty. Some expensive,
name-brand tapes just disintegrated after a few years.
Others have held up amazingly well. Last year I read in
some 1993 backups of my MicroVAX system with no trouble at
all. I did have to clean the tape head after every tape,
but that wasn't greatly different from when the tapes were new.
Jon
9:53 a.m.
On 1/18/2016 12:46 PM, Jon Elson wrote:
Longevity of tapes was very spotty.
Some expensive, name-brand tapes just
disintegrated after a few years.
Others have held up amazingly well.
Yeah, I think even among the same brand
/ model. Like I've heard bad things
about Black Watch before too, but all of
*my* Black Watch seem fine. Maybe just
differences in amount of use and storage
environment and luck of the draw.
Last year I read in some 1993
backups of my MicroVAX system with no
trouble at all. I did have to clean
the tape head after every tape, but
that wasn't greatly different from
when the tapes were new.
What media were those backups on (eg.
TK70)?
- J.
11:48 a.m.
On 01/18/2016 11:53 AM, js at cimmeri.com wrote:
On 1/18/2016 12:46 PM, Jon Elson wrote:
9 track, 6250 BPI, recorded on CDC Keystone (92185)
streaming drives, and read back on the same type.
I built an interface so I could read the tapes in on a Linux
system, and then used some publicly available software to
unpack the BACKUP formatted images to native Linux files.
The Pertec formatted tape interface is quite simple. My
interface is pretty simple, though, and is controlled
through the parallel port, so the tapes are processed at 25
IPS start/stop mode.
If I were going to do it now, I'd use a Beagle Bone, and it
probably would stream at 75 IPS.
Jon
Last year I read in some 1993 backups of my
MicroVAX
system with no trouble at all. I did have to clean the
tape head after every tape, but that wasn't greatly
different from when the tapes were new.
What media were those backups on (eg. TK70)?
11:18 a.m.
On 01/18/2016 09:46 AM, Jon Elson wrote:>
Longevity of tapes was very spotty. Some expensive,
name-brand tapes
just disintegrated after a few years. Others have held up amazingly
well. Last year I read in some 1993 backups of my MicroVAX system
with no trouble at all. I did have to clean the tape head after
every tape, but that wasn't greatly different from when the tapes
were new.
I've not noticed that the 3M 700-series "Black Watch" tapes were any
better or worse than other tapes of the time--if anything, they seem to
stick less. AFAIK, the back-coating on the 700 series was mostly a
matter of texture, not an applied substance.
There were, however, some terrible tapes. Scotch brand 8104 tapes are
among the nastiest. The tape binder often bleeds through the oxide face
of the tape. You can't even get the things through a cleaning machine
without having it jam--even after several passes (the silicon carbide
blade is scary-sharp, and the damned tape will even stick to that.)
I've found that coating is the only way to get those tapes to make their
way through a tape drive without halting.
Memorex tapes from the 80s (MRX IV and V) can be pretty lousy on their
own and Memorex sold buckets of them cheaply. Baking is pretty much
mandatory.
Strangely, a crappy tape from a manufacturer doesn't mean that the same
outfit's floppy disks are just as bad. Wabash-branded tape is actually
pretty decent, while Wabash-branded floppy disks are the devil's own
spawn. Go figure.
--Chuck
11:35 a.m.
On 01/18/2016 02:39 AM, Dave G4UGM wrote:
I know that tapes have different coatings, so some are
ferrous and
other chrome based, but what about the backing and "glue" that holds
the two together?
The difference in coatings between digital and analog tapes is pretty
profound, as is the method of recording.
Digital tapes want the magnetization characteristics to be as "steep" as
possible, with the least middle ground (i.e. linear region).
Analog tapes want just the opposite--a wide linear (or nearly so)
magnetization region. Audio tapes employ the use of "bias" (either AC
or DC) to push the recording into the linear area as much as possible.
Backing for reel-to-reel magnetic tapes is almost always
mylar/polyester, while audio tapes have used everything from paper and
acetate to mylar. There's a good reason for that--acetate is
inexpensive and performs well short-term. The problem is that it
stretches rather than breaks under tension, which isn't acceptable in
start-stop applications such as computer tape drives.
That's probably a good thing. Acetate based tapes degrade in an ugly
manner--and enclosing the reel in an airtight case exacerbates the
problem. You can tell the difference easily at this point in time by
the pronounced "vinegar" smell of deteriorating cellulose acetate.
The binder and lubricants varied between manufacturers and were
generally considered to be "trade secrets".
--Chuck
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8 comments
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cclist＠sydex.com -
dave.g4ugm＠gmail.com -
elson＠pico-systems.com -
js＠cimmeri.com