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Old 3rd October 2005, 01:16 AM   #1
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Default Demagnetizing tape heads

I know it requires a demagnetizer, but there are 2 different types. AC ones and 1.5vDC cassette. Which one I choose?

Should I DIY or buy one?

Then, how do you demagnetize a tape head?
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Old 3rd October 2005, 03:12 PM   #2
AuroraB is offline AuroraB  Norway
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You need AC to demagnetize anything....
The DC thingies for casssettes I have never used....they must contain some inverter to generate an AC field, but I don't think they have enough energy to demag a proper head.

You can make one.... LOTs of thin wire turns of a soft iron core,- something liike a 5 inch nail or similar.... enough windings to be fed by any 9-12 V AC adapter without blowing fuses, - should do the trick.....

You operate it by moving it as close to the heads as possible, without scratching the head, - then remove it slowly....repeat a couple of times...

There might be DIY descriptions out there, and several makes were sold some years ago..... do some googling.....
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Old 3rd October 2005, 04:19 PM   #3
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Han-D-Mag

http://blevinsaudioexchange.com/handmag.html

is supposed to be a good one but at that price, I will not even think of buying one.

Quote:
You can make one.... LOTs of thin wire turns of a soft iron core,- something liike a 5 inch nail or similar.... enough windings to be fed by any 9-12 V AC adapter without blowing fuses, - should do the trick.....
Isn't a 5 inch nail a bit oversized for this task?

What AWG do I take to build one?


Surprisingly, I haven't found any DIY demagnetizer. The only resources I can find are "how to demagnetize tape heads". There's no guide on what you should use or anything.
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Old 3rd October 2005, 05:38 PM   #4
AuroraB is offline AuroraB  Norway
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Had a look at the link.... this is exactly what I had in mind....price isn't really bad either, but for one-time or sporadic use, maybe a little bit high...

A suitable coil could be some hundred turns of AWG 38-40-42, or in that range... yo need a coil to produce a strong AC field without drawing too much current from the transfo.........some 40-50 mA should be enough...which makes coil impedance of 2-300 ohms at 50 ( or 60) Hz.

Come to think of it...if you can find an old 12V relay, possibly of the larger kinds, with round or oblong coil square section, - they used to be about 2 " long,... should be an OK coil for the purpose....then make a core ( or wand if you like ) out of some soft iron, -- you see the shape in the link...put some shrink tube over the tip to protect the heads.... should do the job....
The core should be soft grade iron, -- not any stainless or high grade alloy....

REMEMBER -- DO NOT DEGAUSS WITH POWER ON THE RECORDER!!

EDIT : After some thinking-- you probably need a lot more field strength than the DIYthing I just described.....
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Old 3rd October 2005, 05:52 PM   #5
AuroraB is offline AuroraB  Norway
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Found these ::

http://www.datalinksales.com/degaussers/wd1.htm
http://www.athana.com/ddequip/wd1.html

HERE .. look at the middle of the page:
tape head demagnetizer 120V/60 HZ

http://www.electronicplus.com/conten...=ac&subcat=acl

If you are serious about this, - go buy the tool.......
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Old 3rd October 2005, 08:34 PM   #6
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I have a couple of old answering machine solenoid coils. I lost the ferrite stick going in the middle.

Maybe 50mA would be enough, I see some 6W commercial ones on ebay.

I just need to fold a nail and wind a couple of turns of wire on it and put some tape on it?
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Old 3rd October 2005, 09:31 PM   #7
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http://my.execpc.com/~rhoadley/magelect.htm

I just found this site. An electromagnet running off 2 D batteries can hold 500lbs!
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Old 3rd October 2005, 10:36 PM   #8
AuroraB is offline AuroraB  Norway
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A magnet running on DC is a MAGNETIZER, not a demagnetizer. You do need AC.
Check the last link I gave you--- 20$ for a demagnetizer is acceptable, - and not least working as intended...
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Old 3rd October 2005, 10:52 PM   #9
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Quote:
A magnet running on DC is a MAGNETIZER, not a demagnetizer.
I just need to build an electroMAGNET and put AC in it finally.

Winding some wire around a ferrite "donut" large enough for the head to fit in the middle.

Quote:
20$ for a demagnetizer is acceptable
But not for me!

I can build one for 0$
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Old 6th October 2005, 09:04 AM   #10
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The cassette demagnetiser is handy for things like car cassette players, where you can’t easily get at the heads and tape path. They work pretty well – the original was designed by TDK, who are one of the major tape manufacturers. There was also a very good cassette version designed by Discwasher, which had an exceptionally strong permanent magnet in it, and used some trickery to decay the magnetic field – I think they used some kind of magnetic shield. The hi-fi magazines tested it back in the early 1980’s, using equipment to measure the magnetic field left after use, and it actually did a very good job. However, the cassette versions only demagnetize the tape head, not other metal sections in the tape path, so it is best to use one of the AC versions. Quoting from my TEAC Information Supplement, Stereo Cassette Tape Deck:

1. Turn the deck power off.
2. Turn on the demagnetizer and bring the tip of it close to the heads. Move the tip up and down across all the heads and other parts in the tape path.
3. Slowly withdraw the demagnetizer about 12 inches (30 cm) away from the head area.
4. Turn off the demagnetizer.

Be sure to keep all recorded tapes away from the demagnetizer during the demagnetizing of the heads. (End of quote.)
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