Topic: "Baking" old open-reel tapes

[DSatz]

Hi. I've posted about the fact that I'm going through all the dozens of cartons of old tapes that I have in storage, and transferring them to digital so that I can (as the case may be) donate the originals or, for the most part, discard them. Many of the tapes are open-reel recordings that I made in the 1970s and early 80s on Ampex 406 and 407 tape. Those types of tape are at the epicenter of the "sticky shed syndrome"--the tapes are permanently ruined if you try to play them, unless they're gently baked in a convection oven at a controlled, low temperature first. See attached photo for some tragic results from this afternoon--remnants of the oxide layer of part of a tape; it separated from the backing when I pressed "stop" while winding the tape.

Since I have so many of these tapes, I decided to get my own oven, rather than to bring tapes by the dozens to a transfer engineer who does this baking as a side service. I'll only need it for maybe six months, but it takes me over an hour each way to get to and from his shop, so it makes relative sense for me. I plan to practice on a tape that's already badly damaged; then once I get the hang of it, I'll bake all Ampex tapes pre-emptively before trying to transfer them. My current understanding is that the temperature should be around 130 degrees Fahrenheit and the baking time should be maybe 4 to 6 or 8 hours. I sure hope this works ...

--best regards

[GLouie]

DSatz, you missed my overview of tape baking at the August AES Tea Time Topics! PM me for the outline notes.

There is a wealth of info on the web, but some of it is old, some wrong, etc. and there is a lot to sift through. I suggest starting with the Ampex patent for tape baking, which suggests 52-54C (122-129F). Then the short answer to time of baking is that it depends. Many people recommend longer times now, it seems, such as 24 hours, where you used to hear 6-12 hours. This may be that the decomposition is now worse, or some people have 2 inch tape vs. 1/4 inch, or something else. Extra time does not seem to be harmful.

[anodyne33]

If I remembered any of the tricks of the engineers I worked with years ago I'd spew them out, but I'm familiar with oxide flying off a 2" tape like Pigpen just walked through the room. If the Ampex technique isn't working for some reason I'll ping a couple of those guys for you. Good luck.

[GLouie]

Yes, I've experienced one example of the oxide separating from the backing out of thousands of baked reels, so it does happen. I haven't seen any tips on preventing or predicting this.

[seethreepo]

I've also heard using a food dehydrator can in some cases provide good results as the temperature can in some cases be more consistent and precisely controlled. 

[jerryfreak]

I've also heard using a food dehydrator can in some cases provide good results as the temperature can in some cases be more consistent and precisely controlled.

by definition they are low temp and high air circulation

an Excalibur is just a big box you could do a dozen or more at a time

and its a handy kitchen tool, esp if you garden and have an onslaught of seasonal fruits and veggies

[GLouie]

I've not used a food dehydrator, as we have an old surplus germ oven like this (but older):

https://www.sonicraft.com/tape-baking/

As long as the temperature can hold at 130F, with little overshoot, I think you are good to go. A home cooking oven seems to fluctuate way too much. To low a temp is also bad; you won't get much change in the tape even with a long bake time.

[daspyknows]

Double check temperatures using another thermometer.  Oven thermometers are often not exact and missing by a few degrees may cause problems.

[DSatz]

I ordered a thermometer and a food dehydrator; the thermometer arrived today. There isn't a lot I can do with just that, but it's a start.

GLouie, hi! Nice to see you here (as well as the other place). Unfortunately this forum doesn't allow files to be attached to private messages, but I'll send you my private email address--unless you'd like to post your notes as an attachment to a message here; it's up to you.

--best regards

[daspyknows]

I ordered a thermometer and a food dehydrator; the thermometer arrived today. There isn't a lot I can do with just that, but it's a start.

GLouie, hi! Nice to see you here (as well as the other place). Unfortunately this forum doesn't allow files to be attached to private messages, but I'll send you my private email address--unless you'd like to post your notes as an attachment to a message here; it's up to you.

--best regards

Upload to WeTransfer and use the link.  It's a 2 step process which is a workaround.   

[DSatz]

OK, my dehydrator has arrived and been tested, and tomorrow I'll try baking my first tape. (I may have to order a chef's hat from a costume store.)

But I have a question: The advice from various sources that I've seen seems to agree that tapes should be wound smoothly (e.g. "library wind") before baking them. I can certainly do that--but if possible I'd like to understand why it's important, and how important it actually is (or isn't).

--best regards

[EmRR]

But I have a question: The advice from various sources that I've seen seems to agree that tapes should be wound smoothly (e.g. "library wind") before baking them. I can certainly do that--but if possible I'd like to understand why it's important, and how important it actually is (or isn't).

--best regards

I think it's to avoid any chance of base deformation, as with long term storage. 

[GLouie]

You would need a transport with no fixed guides if you need to library wind a sticky tape before baking - somewhat rare. Sometimes you may not have much choice, but I think there are some physical changes going on and a smooth wind is better for the bake. For sure, the tape pack shrinks after baking and can be very loose - don't put it on a machine that is not gentle.

[DSatz]

GLouie, the Nagra IV-S has no fixed guides in the path when a tape is being rewound, and the QGB large-reel adapter (which also has only rollers) gives further control over the tape tension.

But since my Nagra gear is in storage, for my first experiment I used a Revox A 77 with the tape going directly from one 7" reel to another, not passing through any guides or over any heads (which is beginning to sound like "over the river and through the woods"). If you hold down the play button, about 2/3 of the reel will shuttle from the feed side to the take-up side at a stately pace. The last 1/3 I drew across by turning the take-up reel manually. The tape pack is decently even--not perfect, but better than you'd get from a fast wind.

The cookie is in the oven now, set for 8 hours. Do you think with a 1/4" tape on a plastic reel, there's any point in flipping it at the 4-hour mark?

[EmRR]

I know I've seen warnings about plastic reels warping, I don't know offhand what the recommendations are.