Destructive Imaging of DECTAPE II Media

Mark J. Blair nf6x at
Tue Jan 27 13:22:08 CST 2015

> On Jan 27, 2015, at 09:46 , Al Kossow <aek at> wrote:
> On 1/27/15 9:22 AM, Alexandre Souza wrote:
>> why not using a 15x slower mech and using a slower (and cheaper) ADC?
> Because the amplitude from the read head is a function of tape speed.

Right. I don't necessarily need to run the tape at 30 ips like a real TU58, but I probably will need to run it somewhere in that ballpark.

>>    Or use a band from a known good cartridge, at least to recover the data.
> I was going to suggest that. Any DC-100 sized cart can be used as a donor, and you
> only need a couple of them.

True. This would take less effort to implement since I could use a TU58-XA mechanism instead of fabricating my own transport, and the effort of designing motor control stuff would be similar in either case. But there would also be some advantages to abandoning that danged belt drive tape mechanism and using some type of reel-to-reel mechanism that doesn't involve rubbing a belt against the oxide surface, too.

> There was a post about saving HP tapes by doing something to them (heating them?)
> but now I can't find the post.

I thought that I had read something like that, but I also don't recall when/where. A baking cycle might be beneficial just like it is for other old magnetic media, but I don't recall whether baking was also helpful in releasing stuck drive belt from the oxide.

> Chuck was trying to find something to keep the hole
> in the oxide from interfering with the EOT/BOT sensing, but I don't know if he found
> something that worked reliably. You need something that is opaque to IR.

I wish that DEC had included unpopulated provisions for optical end of tape sensing in the TU58-XA rather than entirely cost-cutting that sensor out of the design. I see that the cartridges still include the BOT/EOT holes and the right-angle mirror; presumably, the drives that they used to preformat the tapes in the factory used those for BOT/EOT sensing prior to writing the magnetic BOT/EOT symbols.

> I also thought someone already imaged the 730 carts, but I can't find those either.
> Maybe they were for the 750.

I have found some 730 cart images online, and at the moment I expect that my only way of booting my 730 will involve using those with tu58em. I'd still like to image the carts that came with my machine, though, which may be different versions.

> I have 100+ TU58s that I need to get to this year and already replaced the rollers with
> new ones made from norprene tubing.

I've already replaced the drive roller rubber in a few of my drives with black latex rubber tubing. The stuff I used is essentially the same as the yellow tubing used for wrist rockets and water weenies, except it's black, and of a suitable diameter to fit the aluminum roller hub and have about the right outside diameter when installed. To cut it, I stuck a short length on a piece of plastic rod, chucked the rod in a Harbor Freight mini lathe, and cut pieces with a surgical scalpel while the chuck was spinning. I simply cut many more than I needed and selected the ones that turned out the best, as there was a lot of variation in width from my eyeball-cutting, and variation in squareness of the edges depending on how I held the scalpel. I probably threw away five pieces for every one that I selected, but the end results look very neat.

Mark J. Blair, NF6X <nf6x at>

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