[Info-vax] DLT Tape degaussing services

[John Santos]

In article <gpeblu$cjh$2 at naig.caltech.edu>, gah at ugcs.caltech.edu 
says...> 
> Richard B. Gilbert <rgilbert88 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.