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From: mike@amdcad.UUCP (Mike Parker)
Newsgroups: net.consumers
Subject: Re: Ion Generators (CRT's actually)
Message-ID: <1470@amdcad.UUCP>
Date: Thu, 30-May-85 15:31:21 EDT
Article-I.D.: amdcad.1470
Posted: Thu May 30 15:31:21 1985
Date-Received: Fri, 31-May-85 06:34:28 EDT
References: <2366@decwrl.UUCP>
Organization: AMDCAD, Sunnyvale, CA
Lines: 39

> >cathode at a very high negative potential and the phosphor grounded to
> >minimize this effect (as you wouldn't want to get a serious shock from the
> >alternative arrangement of putting the cathode at ground potential and
> >raising the screen to a large positive potential).  
> 
> Not quite true.  Almost all CRT's have the cathode at about ground and a
> very large positive charge on the anode, since the alternative requires some
> tricky electronics.  You don't get a shock from touching your screen since
> glass is a very good insulator.  I don't know myself whether the static charge
> that accumulates on the screen is from the negative electrons hitting the
> screen or stray positive charge from the anode, since glass isn't a perfect
> insulator.
> 
> "There's a madness to my method."			Mike Moroney
> 						..decwrl!rhea!jon!moroney

I worked in a tv shop as a youngster, I didn't understand much
of what we did at the time, but I remember a few things that might 
shed some light on the subject.

First, the static is caused by the electron beam from the cathode.
When we got a set with absolutely nothing on the screen, not even 
static, we would feel the screen. No static meant no drive to the
cathode, bad amplifier. Static meant that there was no drive to the
anode, bad high voltage power supply.

Second, I know that the cathode is not at ground. We used to measure
cathode voltage with a high voltage probe using the chassis ( ground )
as a reference. Old B+W sets measure over 15,000 volts, new color
sets measure as high as 35,000. For those who question my terminology,
the cathode voltage is measured at one of the pins on the back of
the neck, the anode is under the suction cup. The anode is also
not at ground, it's the part that Dad always said would kill you
if you didn't know what you were doing. 

So, let's move the discussion to net.analog and see if someone
can explain the facts.

Mike