Tape Baking - Fixing Squealing Tapes
Squealing tapes are not only an annoyance, but continuing to play a squealing tape can permanently damage the recording and sometimes the player too.
In mild cases, a squealing noise can be heard from the tape as it passes the metal rollers and heads of the playback machine. This squealing is also transmitted through the electronics of the playback head and so can also be heard mixed in with the audio. Distortion of the audio is often heard.
In severe cases, the tape will be so sticky that it will jam in the mechanism. Attempts to force the tape to play can result in oxide shedding from the tape, permanently damaging the tape and in some cases damaging the player.
Cause of Squealing Tapes
The most likely cause of squealing audio cassette and open-reel tapes is that over a long period of time, the binder that holds the magnetic particles to the backing of the tape absorbs moisture from the atmosphere causing it to become "sticky".
Which tapes are most susceptible to squealing?
We have fixed hundreds of squeaking tapes.
The vast majority of the tapes that have needed fixing are brands manufactured in the United States of America during the 1970s, 1980s and 1990s. And the majority of those tapes are Ampex brand. Scotch brand from the same era has also given us a lot of trouble.
It is unusual if a European brand of tape such as BASF or Agfa squeals, but it does happen occasionally.
In all this time, we have never needed to bake a tape manufactured in Japan (from brands such as Maxell, TDK and Sony), and we have never needed to bake any polyester-backed tape of any brand manufactured before 1968. EMI tapes manufactured in the United Kingdom in the 1950s and 1960s have always played as if they were new.
It's not only audio tapes that have this problem. We have also needed to bake Ampex brand VHS and Umatic tapes from the 1980s.
What to do if you have a squealing tape
If your tape is squealing, you should stop playing it immediately. Continuing to play a squealing tape can cause permanent damage to the tape, and in some cases may also damage the tape player.
Making a squealing tape playable
Because the problem of squealing is caused by moisture being absorbed into the tape, the solution to the problem is to bake the tape at very low temperatures (below 60 degrees Celsius)
Never attempt to bake your own tapes in a gas oven. You will end up with a pile of molten plastic.
Never attempt to bake your own tapes in an electric oven unless you can be absolutely sure that it will not exceed 70 degrees Celsius. If you're going to try it yourself, use an industrial-grade thermometer to monitor the temperature.
For tape on plastic reels, we bake as is. But for tape on metal reels we always unscrew one of the flanges to better expose the tape to the dry heat.
How long to bake
The length of time of baking varies depending on the thickness of the tape and the severity of the squealing.
Mild cases of squealing can be fixed in as few as 4 to 6 hours.
Moderate or severe cases may need to be baked for 12, 16 or even 24 hours.
The good news is that you can't over-bake a tape.
Also, you can take the tape out after a short period of time, test it, and if it isn't fixed then return it to the oven.
After the tape has been baked, allow the tape to fully cool down to room temperature.
Ideally, the tape should be gently fully wound in both directions (off the playback heads) before you play it.
If you play it for a minute and it doesn't squeal, stop playing the tape anyway and clean the heads with a cotton bud and isopropyl alcohol. After cleaning, if there is a large amount of oxide on the cotton bud then the chances are that the tape needs more baking. If the cotton bud is mostly clean then there's a good chance that the tape is ready to play.
This is just a guide, and tapes don't always follow the rules. You should always use your own ears and eyes when testing a tape.
Successfully baking a tape makes the tape playable for at least a few weeks, sometimes a few months. But once the tape has been baked it's best to have it transferred to another medium as soon as possible because the tape is likely to revert to it's squealing state.
Finally, baking fixes tapes only if they have a polyester backing. This accounts for the vast majority of tapes in the world. However, if your tape is the older sort that has an acetate backing then baking will not fix the squealing problem. Baking won't harm an acetate-backed tape. It just won't fix it.