[Info-vax] DLT Tape degaussing services

[Rich Jordan]

On Mar 16, 11:09 am, billg... at cs.uofs.edu (Bill Gunshannon) wrote:
> In article <89e275f6-842f-4502-aef1-4adc8db44... at d19g2000yqb.googlegroups.com>,
>         Rich Jordan <jor... at ccs4vms.com> writes:
>
>
>
> > On Mar 13, 5:34 pm, John Santos <j... at egh.com> wrote:
> >> In article <gpeblu$cj... at naig.caltech.edu>, g... at ugcs.caltech.edu
> >> says...>
>
> >> > Richard B. Gilbert <rgilber... at comcast.net> wrote:
>
> >> > > Simply degaussing DLT tapes is not a good idea.  They have some sort of
> >> > > "formatting" or a "clock track" that is necessary for proper operation.
> >> > > Once degaussed, they may never work again.
>
> >> > As I understand it, that isn't true for DLT.  
> >> > (Or at least not the current versions of DLT.)
>
> >> > It is for Ultrium (LTO) and some others, though, so one
> >> > should be careful before degaussing a new tape system.
>
> >> > Also, in some cases degaussing is required.  DLT1 uses the
> >> > same tapes as a DLT IV, but the magnetic signal is different.
> >> > A signal left from the older drive will not get fully erased,
> >> > and will interfere with the new data signal.  
>
> >> > According to wikipedia, the DLT formats that do use a
> >> > servo track use an optical track on the back of the tape.
>
> >> > -- glen
>
> >> Many years ago, I got a degausser at Radio Shack for less
> >> then $20 IIRC.  It is *not* a static magnetic field; it uses
> >> A/C current to generate a 60Hz (probably 50Hz would work
> >> just as well) varying magnetic field, and you had to move
> >> it slowly around the tape, not just hold it in one place.
>
> >> It worked great for 9-track open reel tapes, and for TK50s
> >> and TK70s (DLT versions -1 and 0, I think, based on the
> >> current numbering scheme.)  People used to occasionally
> >> try to write to a TK50 in a TK70 drive, which would muck
> >> them up, or write to a TK70 in a TK50 drive, which would
> >> work fine, but render the cartridge unwritable in a TK70
> >> drive.  (Bad because you couldn't tell by looking at it
> >> this had been done and TK70's cost about 2-3 times as
> >> much as TK50's at the time.)  Degaussing usually fixed
> >> both these conditions.
>
> >> No idea if it would work with a DLT IV tape or not,
> >> but it sounds like a cheap enough experiment to try.
>
> >> --
> >> John Santos
> >> Evans Griffiths & Hart, Inc.
> > John,
> >      unfortunately Radio Shack tells me they no longer carry those.  I
> > haven't seen one on ebay this past week either (there are a couple of
> > others though).  Without knowing the 'oersted rating' there's no way
> > to know if one of those would be powerful enough; the manual warns
> > that hand held tape degaussers may not be strong enough to do the job.
>
> I use one of those Radio Shack degausers on all my TK50/TK70 Tapes
> and it works OK.  I also have huge bar magnet that was used to bias
> the tablet on a Tektronix Graphics Terminal that works real good, too. :-)
> (They ship them inside a large metal pipe.  I have stuck them to
> girders in my basement and they are very hard to get back off!)
>
> bill
>
> --
> Bill Gunshannon          |  de-moc-ra-cy (di mok' ra see) n.  Three wolves
> billg... at cs.scranton.edu |  and a sheep voting on what's for dinner.
> University of Scranton   |
> Scranton, Pennsylvania   |         #include <std.disclaimer.h>  

I don't have anything that big; just magnets from the older large size
winchester drives, which are inadequate to the task.

I may have tracked down a Radio Shack unit locally; if I can borrow it
I'll give it a try and report back, but I'm not hopeful.

Rich