Re: DECtape madness

[Paul Koning via cctalk]

> On Jan 16, 2018, at 1:04 PM, Doug Ingraham via cctalk  
> wrote:
> 
> On Sat, Jan 13, 2018 at 7:34 AM, David Bridgham via cctalk <
> cctalk@classiccmp.org> wrote:
> 
>> I've wondered if you might not make DECtape tape from 3/4" video tape.
>> I know that DECtape has mylar on both sides but what if you somehow
>> glued two strips of video tape together with the mylar backing on the
>> outside.  Probably want to build a jig of some sort and I'm not sure
>> what glue to use.
>> 
> 
> I have read on several occasions about the mylar on both faces of the
> tape.  I have over 300 reels of DECTape in my collection.  Most of these
> are 3M Scotch branded but around 30 of them are DEC branded in the blue
> plastic boxes.  I have never seen one with mylar on both sides.  This may
> have been something that existed early on but certainly wasn't the norm.

Well, the spec is clear about a protective layer on top.  And I've always been 
told that it's mylar.  And the fact that DECtape is far more wear resistant 
than regular magtape makes it clear it isn't constructed the same way.

It is correct that it doesn't have a glossy top layer matching the glossy 
substrate.  But that doesn't mean there isn't a top layer present.

paul

Re: DECtape madness

[Doug Ingraham via cctalk]

On Sat, Jan 13, 2018 at 7:34 AM, David Bridgham via cctalk <
cctalk@classiccmp.org> wrote:

> I've wondered if you might not make DECtape tape from 3/4" video tape.
> I know that DECtape has mylar on both sides but what if you somehow
> glued two strips of video tape together with the mylar backing on the
> outside.  Probably want to build a jig of some sort and I'm not sure
> what glue to use.
>

I have read on several occasions about the mylar on both faces of the
tape.  I have over 300 reels of DECTape in my collection.  Most of these
are 3M Scotch branded but around 30 of them are DEC branded in the blue
plastic boxes.  I have never seen one with mylar on both sides.  This may
have been something that existed early on but certainly wasn't the norm.



-- 
Doug Ingraham
PDP-8 SN 1175

Re: DECtape madness

[Jon Elson via cctalk]

On 01/13/2018 11:28 AM, Al Kossow via cctalk wrote:


On 1/13/18 9:04 AM, Jon Elson via cctalk wrote:


I don't know what you are talking about with Mylar on both sides. They were 
conventional magnetic tape, a clear mylar
film with oxide applied to one side.

the actual spec is here:

http://bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf


Ah, looks like a 40 MICRO-Inch protective coating.  
Certainly not a couple mils of Mylar on both sides of the Oxide.


Jon

Re: DECtape madness

[jim stephens via cctalk]

On 1/13/2018 6:20 AM, Noel Chiappa via cctalk wrote:

So why are reels of DECtape selling for unbelievable prices on eBait?
The ones in the post are from Bill Donzelli.  I'd imagine he's happy.  I 
looked at acquiring another one, but they went way high as you pointed 
out.  My friend with some of the TU-55 and TU-56's has several boxes and 
said not to bother, but I figured what the heck.


Bill didn't sell the 4 piece one.  I bought a single item last year for 
$5 bucks or so plus shipping.  I'm not sure why these have gone so high.


We are talking to a local fellow here in Los Angeles who is in the 
business of renting out a studio with ancient tape drives for production 
as needed and he has contact with a couple of guys who may be able to 
fab up heads.  We are interested in exploring that if it is feasible to 
have replacements made.  They currently make heads for the audio units 
there and could possibly make heads to any spec that is available.


I'm mainly asking around because it seems there are a lot of options for 
moving tape now days.  Media is scarce, but not unavailable. And unless 
you have NOS replacement heads that is one stopper for using original 
media with system.  I probably won't pursue it, but will at least know 
how hard the head problem is.


Thanks
Jim

Re: DECtape madness

[Mark J. Blair via cctalk]

> On Jan 13, 2018, at 08:52, Bill Gunshannon via cctalk  
> wrote:
> 
> So, where were all these people when I was trying to clean out
> my old house a couple years ago?  I threw out piles of tapes of
> various formats because I couldn't find anyone to take them for
> postage.

I'm sorry that I missed that event, Bill! I'd be happy to add a DECtape drive 
and a handful of usable DECtapes to my PDP-8/M project, but I don't want that 
dearly enough to pay the going eBay prices for that kind of gear at this time. 
Not that I can really complain, as I'm fortunate to have lots of other cool 
stuff running the range from free gifts to expensive purchases; I just haven't 
been at the right node of place + time + checking account balance to have 
acquired DECtape family gear yet, and I was born just a bit too late to have 
experienced it in college or the workplace.

I sure wish that I would have anticipated that I'd become interested in 
retrocomputing in the 201x decade, so I wouldn't have gotten rid of a few 
specific items over the years that I now wish I still had, and I could have 
kept my eyes open for other items that I might have acquired cheap or free at 
the moment that interest in them was at a minimum.

Naturally, there's plenty of stuff in recent years that I have considered to be 
uninteresting junk to be discarded. I wonder if I'll regret having junked it in 
another decade or three, or if my sense of nostalgia will remain rooted to my 
younger years and earlier?

Re: DECtape madness

[Paul Koning via cctalk]

> On Jan 13, 2018, at 12:28 PM, Al Kossow via cctalk  
> wrote:
> 
> 
> 
> On 1/13/18 9:04 AM, Jon Elson via cctalk wrote:
> 
>> I don't know what you are talking about with Mylar on both sides. They were 
>> conventional magnetic tape, a clear mylar
>> film with oxide applied to one side.
> 
> the actual spec is here:
> 
> http://bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf

And that spec is quite clear, "protective overlay".  This is the reason for the 
legendary robustness of DECtape media.  It was possible to wear it out, but 
only if you used it -- as done at Lawrence University for example -- as 
permanently mounted public file storage so it was read/written many times per 
hour for months on end.  When used as private removable storage it was pretty 
much invulnerable.  Stories of DECtapes being laundered by accident and still 
working fine afterwards have been around for a long time.

paul

Re: DECtape madness

[Al Kossow via cctalk]

On 1/13/18 9:04 AM, Jon Elson via cctalk wrote:

> I don't know what you are talking about with Mylar on both sides. They were 
> conventional magnetic tape, a clear mylar
> film with oxide applied to one side.

the actual spec is here:

http://bitsavers.org/pdf/dec/dectape/3M_DECtape_Spec_Nov66.pdf

Re: DECtape madness

[Jon Elson via cctalk]

On 01/13/2018 08:34 AM, David Bridgham via cctalk wrote:

So why are reels of DECtape selling for unbelievable prices on eBait? See,
e.g. here:

I had those on my watch-list and just shake my head at the astonishing
prices for the things.

I've wondered if you might not make DECtape tape from 3/4" video tape.
I know that DECtape has mylar on both sides but what if you somehow
glued two strips of video tape together with the mylar backing on the
outside.  Probably want to build a jig of some sort and I'm not sure
what glue to use.


At Washington University, we bought 12" reels of 3/4" 
instrumentation tape and made DECtapes out of them.
The tapes were too thin, and if you left them sit too long, 
they would get print-through and start to have trouble.
As long as you used them every couple weeks, they would get 
rewound and you would not have a problem.


I don't know what you are talking about with Mylar on both 
sides. They were conventional magnetic tape, a clear mylar 
film with oxide applied to one side.  They were definitely 
made with a thicker Mylar layer than many magnetic tapes of 
the day, possibly to solve the print-through issue, but 
maybe also to prevent crimping of the tape on the pack.  I 
think the oxide formula had a more square-loop hysteresis 
curve than analog tapes, which contributed to our problem.


Jon

Re: DECtape madness

[Bill Gunshannon via cctalk]

So, where were all these people when I was trying to clean out
my old house a couple years ago?  I threw out piles of tapes of
various formats because I couldn't find anyone to take them for
postage.  I also threw out piles of other stuff (some of it old DEC
and Sun kit) after offering it on eBay and getting zero bids.  The
only thing I have successfully sold thru eBay was an antique
claw-foot bathtub.  I have stuff now that will likely go in the trash
because I really can't affords the space to be a storage locker
any more.

bill


From: cctalk <cctalk-boun...@classiccmp.org> on behalf of David Bridgham via 
cctalk <cctalk@classiccmp.org>
Sent: Saturday, January 13, 2018 9:34 AM
To: Noel Chiappa via cctalk
Subject: Re: DECtape madness


> So why are reels of DECtape selling for unbelievable prices on eBait? See,
> e.g. here:

I had those on my watch-list and just shake my head at the astonishing
prices for the things.

I've wondered if you might not make DECtape tape from 3/4" video tape.
I know that DECtape has mylar on both sides but what if you somehow
glued two strips of video tape together with the mylar backing on the
outside.  Probably want to build a jig of some sort and I'm not sure
what glue to use.

Re: DECtape madness

[David Bridgham via cctalk]

> So why are reels of DECtape selling for unbelievable prices on eBait? See,
> e.g. here:

I had those on my watch-list and just shake my head at the astonishing
prices for the things.

I've wondered if you might not make DECtape tape from 3/4" video tape. 
I know that DECtape has mylar on both sides but what if you somehow
glued two strips of video tape together with the mylar backing on the
outside.  Probably want to build a jig of some sort and I'm not sure
what glue to use.