[Info-vax] DLT Tape degaussing services

[Bill Gunshannon]

In article <89e275f6-842f-4502-aef1-4adc8db44b8d at d19g2000yqb.googlegroups.com>,
	Rich Jordan <jordan 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
billg999 at cs.scranton.edu |  and a sheep voting on what's for dinner.
University of Scranton   |
Scranton, Pennsylvania   |         #include <std.disclaimer.h>