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Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!inuxc!pur-ee!uiucdcsb!jabusch
From: jabusch@uiucdcsb.Uiuc.ARPA
Newsgroups: net.audio
Subject: Re: ringing in my ears
Message-ID: <5700094@uiucdcsb>
Date: Mon, 16-Sep-85 13:01:00 EDT
Article-I.D.: uiucdcsb.5700094
Posted: Mon Sep 16 13:01:00 1985
Date-Received: Thu, 19-Sep-85 04:08:08 EDT
References: <481@ihlpm.UUCP>
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Nf-ID: #R:ihlpm.UUCP:-48100:uiucdcsb:5700094:000:1483
Nf-From: uiucdcsb.Uiuc.ARPA!jabusch    Sep 16 12:01:00 1985



	Yes, all TV's are this way...  the high voltage required to drive
the electron guns has to be DC.  The standard way to create this voltage 
is to generate a low-frequency signal that is above hearing range and then
amplify it.  The amplification is done through a transformer, usually re-
ferred to as the 'flyback' transformer.  It's basically just an AC stepup
device.   The next stage is a rectifier of some sort, which supplies the 
final DC needed for the CRT.
	The problem with these circuits usually starts when the original
oscillator goes off-frequency a little.  Since this oscillator runs around
20KHz, any variation can throw it into audible range.  The ringing sound
is usually caused by the windings of the transformer, the laminations of
the core, and occasionally nearby components vibrating slightly in the 
strong magnetic field.  Remember, the output of the flybak must be at least
1000VAC to operate most of the CRT's in use, and must be much higher, gen-
erally speaking, for color CRT's.  Some stereo amps use the same style of 
high-voltage generation, but this is rare today.  Dimmers are not always
potentiometers, but are occasionally made of oddball parts.  I have seen 
the internals of a few, and would hesitate to guess what exactly is being
done internally.


John W. Jabusch
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