From: utzoo!decvax!duke!harpo!eagle!mhtsa!alice!rabbit!wildman
Newsgroups: net.audio
Title: Re: Pinch rollers and biasing
Article-I.D.: rabbit.159
Posted: Wed Jan  5 12:06:07 1983
Received: Thu Jan  6 06:32:14 1983
References: rocheste.364

	WE've already been over this once, but here goes again:

	THE PRIMARY CAUSE OF HEAD MAGNITIZATION IN TAPE RECORDERS
IN THE MODERN ERA IS THE TURN ON/TURN OFF TRANSIENTS THAT ARE CIRCULATED
THROUGH THE HEAD.  THESE CURRENTS ARISE WHILE THE POWER SUPPLY VOLTAGES
ARE CHANGING WHEN THE DECK IS IN FLUX BETWEEN ON AND OFF (OR THE OTHER
WAY AROUND)
	The tape itself is a very minor cause of magnitization.
If you have played a tape once on a magnitized deck, it doesn't
matter any  more, regardless of the inccorrect statements that
have appeared here regarding coercivity of magnetic recording tapes.
	For those of you who are knowlegable in circuit theory,
the cause of magnitization is the pulse that most head amplifiers
send through the head on turn on, and turn off.  The second most
significant cause is the current leakage through either the coupling
capacitors or the input stage of a directly coupled head amp.
	I repeat:
	If you have played a tape on a magnitized deck, and then
demagnitize the deck, it doesn't matter any more.
	If you want to know a lot more about this subject that you
ever cared to, read the last two years worth of the Journal of the
Audiom Engineering Society in your favorite technical library.
Use the master index at the end of each year to find the right
issues.
	Please, people, if you don't know what you are talking about,
don't talk.  If you have to, at least admit that you are speculating.
(Some people do that.  These people are usually right, which just points
out human nature.)
	I quit!

	Oh yes, lacquer thinner often has heavier hydrocarbons
that will act just like oil when you get done.  I wouldn't use it.
I use freon for general cleaning and isopropyl  when someone has
let things get out of hand to the point that I need a firehose.