Audio Restoration Page 6

Restoration - Tape

All tape consists of three primary components: iron oxide (the magnetic medium that you record to), the "binder" or glue (that sticks the oxide to the tape) and a plastic carrier. Until the 60's, tapes used acetate as the carrier. You can tell if you have an acetate tape because it is translucent when held up to light. It won't stretch but can be brittle. After the 60's mylar replaced acetate. If you have an acetate tape and it smells slightly like vinegar - breakdown is already underway. Do not bake acetate tapes. It will only make the problem worse and possibly damage the tape.

In the 1970's, tape companies changed to a new binder (or glue). The problem is this binder attracts moisture and when enough moister is gathered, the tape gets sticky. Tapes with bad binder will squeal, jerk and/or stutter and sometimes come to a complete stop when being played or rewound. The reason is the "glue" sticks to the heads and other parts of the playback machine. There is a way to fix this. Baking that tape at a low temperature (130 to 135 degrees F) will reactivate the binder by driving out the moisture and that tape will play like it was new. For awhile. You can expect things to get gummy again in a month or so, but you have enough time to get that audio off the tape onto something more stable.

Cooking times depend on the width of the tape. As a general guideline:

Three to four hours (minimum) for quarter-inch tapes
Five hours for half-inch
Six hours for one-inch
Eight hours for two-inch tapes.

3-M tapes from the '80's will require only around half that time. Don't be concerned about over-baking the tape, a couple of hours extra won't hurt it. Use an accurate oven thermometer. Most oven thermostats are not very accurate. A too cold oven will do nothing to fix the binder and a too hot oven could cause print-through and melt or warp plastic hubs and reels. One word of warning - this is very tricky to do in the average home oven. First, it's difficult to find a setting that will raise the oven to 130 degrees. Most ovens don't seem to want to look at anything under 200 degrees or so. Then keeping it there can be an exercise in frustration. Most oven thermostats are designed to do two things: full on or full off. If the temperature drops below what the thermostat is set for it will turn the oven full on and keep it going until this inaccurate thermostat overshoots your set temperature and turns off. We've seen ovens at that point reach 170 degrees. You're better off putting sending the tapes to us or someone else.

Temperature, tape condition and number of reels will also affect the length of baking. Flip those tapes once every hour and when you're done, put the tape back in its box and allow it to cool off for the same amount of time it was baked. We do not recommend gas ovens for this. They produce water vapor - and that's what you're trying to get out of those tapes. For those with a gas over - try this: replace the inside 25 watt appliance lamp with a standard 100 watt light bulb. Find a muffin fan, similar to one in a PC power supply to circulate the air. This should give you a nice stable 130 degrees once you experiment with the fan speed and placement. Without the fan, you probably won't get beyond about 110 degrees.

When baked, the tape will expand and become loose around the hub. For this reason, use flanges to protect the tape from coming apart. If the tapes is wound on plastic reels with small hubs - rewind it onto a large reel with NAB hubs. Be careful to how you thread the tape around the hub. If there's any "folds" you could end up with mechanical distortions that will transfer to other layers causing dropouts.

Tapes can rarely exhibit a failure known as lubricant breakdown. You can tell this by a white residue that's left on the heads and guides. Binder breakdown will leave a dark, gummy residue. (see picture at right) Baking will not cure lubricant breakdown - it'll only make it worse. Make sure which problem you're dealing with before you shove that tape in the oven.

Storing tapes "tail-out" after having been played minimizes the effects of "print-through" and improves the chances of long-term survival. "Print-through" is a form of mechanically induced tape echo. Tail-out storage will hide print-through as "post echo."

If you discover that the tape is unplayable while in fast winding, come to a slow stop. Fast winding the tape may cause further damage because oxide may adhere to the back of the previous layer. In addition, old splices may come apart.

Tape, like albums, is also very susceptible to mildew contamination, and once that happens, it is very difficult to clean. Mold will destroy the oxide on a tape and that's the portion of the tape where the sound data is stored. The tape can be run through a special machine or cleaned by hand but it's slow, laborious and that means: expensive. What you usually end up with is a clean tape with lots of gaps in the audio. But sometimes what is on that tape is important and that's what you have to do.

It's very important to read the "fine print" here.

As is all things in life - your mileage may vary and results are not guaranteed.

Check the tapes in the oven frequently. If thing's don't look right, pull them out.

Always use a good stand-alone thermometer inside the oven to make sure the temperature stays within the 130 - 135 degree range.

Don't use a gas oven.
Don't bake an acetate tape.