The safest way to back them up is to record them straight to a recordable CD and then transfer that recording to a PC to clean them up and burn them back to CD. Luckily, with a tape deck you don’t need a pre-amp and so you can use the ‘out’ phone plugs to plug directly into the ‘in’ of a CD recorder or line of your PC’s sound card.
After a few years the iron oxide on the tapes breaks down and if you are unlucky you might only get the chance to play it once before it’s all displaced on to the tape head and that’s the end of the story. Also, inside the cassettes there usually a layer of ‘bubbled’ paper each side of the spools to cushion the spools and stop the friction of plastic on plastic occurring; again these usually get damp and puffed up and so in fact stop the spools running smoothly.
Assume that you’re only getting a once chance to get a decent recording:
1. Clean the tape heads thoroughly with some alcohol and let them dry thoroughly.
2. Fast forward and rewind the tape a couple of times to loosen the tape up and hopefully get it play without jamming up.
3. Set the recording levels to about 75% (put in a decent tape to calibrate the recording levels to just touching the ‘reds’) so that you should get a fairly decent level of recording.
4. If and when the sound / recording levels start to drop off, stop the tape at a point between tunes and clean the heads again. You don’t need to bother about the CD recorder / PC recording as one side of a C90 is obviously 45 minutes and CD-Rs are around 74 minutes.
5. Once you’ve finished recording one side of the tape ‘finalise’ the CD and ‘grab’ to your PC to clean up, amplify etc
6. Finally, ‘burn’ your recordings at a low speed to a good quality CD.
Alternatively, send them to me and I’ll do them for you!