Archiving 9-track magnetic tapes

In the process of asking everyone on the planet if they had copies of old MIT CADR source code, I ended up with some 20 year old 9-track mag tapes.

I knew this would eventually happen and had been settup up the VAX with a TS11 drive to read them.

I had hear about "stick shed syndrome" but didn't really understand what it ment. Fortunately some other more experienced archivists cautioned me about how to treat the tapes before reading.

If you google for "baking magnetic tapes" you'll find a lot of information on this subject. Here are some common links:

To be safe a "special oven" needs ot be used. It should be a convection oven with controlled temperature and low humidity. It should have internal air flow and slow temperature ramps. A normal kitchen oven will not work.

I have boiled down the proceedure into these steps:

As an experiment I attempted to contruct a simple convection oven out of a plastic Thermos cooler.

plastic Thermos cooler

I did some testing with the Thermos cooler. It provided a small convenient "chamber" which would hold heat. I used a 75 watt light bulb connected to an X10 dimmer. I placed a digital humidistat inside and a computer readable thermocouple.

Inside the cooler I made an "H shaped" partition out of cardboard to keep the direct radiation from the light bulb off the tapes and installed a small fan to circulate the air. I made the partition H shaped to try and cause a top-to-bottom circulation of air, like a convection oven.

I also placed some "dessicant rocks" inside to absorb moisture.

plastic Thermos cooler

I did some testing and found the temps to be pretty even from top to bottom once the fan and partition where installed (without them there were hot spot. I also scaled back from a 100 watt bulb to a 60 watt and then back up to a 75 watt.

I turn the bulb on 100% and then wait for the temp to reach about 128F. At this point I scale back the brightness a bit and shoot for 130F. Once at temperature I let the tapes "soak" for 8 hours. After 8 hours I turn off the bulb and let the chamber come back to room temperature on it's own.

I run the chamber during the day and let the tapes cool over night. The I read them the next morning.

DEC TS11 tape drive (outside) DEC TS11 tape drive (open)