arf (10/25/82)
I have a tape deck that has recorded and played for many, many hours. Every now and then I think that I should demagnitize the heads, but then I recall a piece of wisdom from somewhere in my past that says demagnitization doesn't make any difference in the performance of a tape deck. Should the heads be demagnitized? If so, how often? can you recommend a particular demagnitizer? Can demagnitization do any harm?
wmartin (10/25/82)
DO, DO, DO demagnetize! It is far better to demagnetize too much than never or too seldom! If you don't, the residual magnetism build-up will reach a point where it will wipe off the high frequencies from your tapes during each playing. The generally-accepted "best" demagnetizer is made by the leaders in the field of magnetization metering and equipment, the R. B. Annis Co. I think you will find an ad in the classified pages of Audio from them, if not, I can look up and post their address. Unfortunately, their demagnetizer is a professional piece of gear, and costs quite a bit. Luckily, most home tape units don't require the capability of this device; it is needed for 32-track mastering recorders and similar wide-tape transports. One thing they do sell which was reasonably priced (when I bought mine) is a pocket magnetometer. There is no other way to tell if a deck needs demagnetizing (note: not just the heads -- ALL the metal around the tape path can get magnetized [ferrous metal, that is]). I get by with an old Radio Shack demagnetizer. There are ones being made by Nortronics, Teac, and other tape-oriented manufacturers, too. Other electronics chains should have them (does Olson Electronics still exist? all their local stores are long-since closed). They are essentially electromagnets, with extended pole piece(s). If you can, try plugging one in at the store before buying it and leave it on for some minutes to see how hot it gets; some heat up very fast and have to cool for ten minutes between uses. If the pole piece that comes in contact with the head is bare metal, either be VERY careful you don't bang your heads with it, or cover it with plastic (I use the insulating boot from an alligator clip). When you use it, plug it in (usually they have no switch) while it is several feet away from the deck. Move it in slowly to the head area, and run the tip over all the heads, the capstan(s), tape guides, lifter arms, And any other hardware that comes close to or in contact with the tape. Then remove it slowly from the vicinity of the deck, and unplug it when it is again some feet away. Otherwise the forming and collapsing magnetic fields can induce MORE magnetism in the stuff you want to DEmagnetize! People on this net may have a good chance to borrow a professional piece of this equipment (magnetometer and demagnetizer) if you have a good relationship with your computer center. A place with mag tape drives may have such gear on hand; otherwise, they may rely on contract PM and the CE will have the gear. If you can't borrow it, maybe you can lug in your tape decks and check them out and demagnetize them there at the center, or when the CE is running the weekly PM, or the like. Especially if the deck has never been demagnetized, it would be good to check it out with pro gear the first time. Then you can buy a cheaper model and demagnetize each time you clean heads. A good hifi service shop can do it, but I assume you want to avoid paying for it... I think most modern recorders are much less likely to become dangerously magnetized than the old ones were, with different materials used and better design. I haven't had any detectable magnetization on my TEAC or Tandberg reel decks, and my cassette machines haven't been used long enough to acquire much magnetization anyway. I probably have become complacent about it, and this will now remind me to check them all out and run through a demagnetization session as PM. One last point I should have mentioned above: a demagnetizer is a tape eraser. Keep all tapes far away from it when it is in use. It might retain some permanent magnetism when turned off, so don't store it with tapes, or in a drawer under a wood tape shelf or the like. Regards and happy listening! Will Martin