[rescue] Old Monitors

John Hudak jjhudak at gmail.com
Wed Feb 14 23:52:50 CST 2018

I thought that the AquaDAG also acted as a collector for both the electrons
in the initial beam after the hit the phospos coating on the screen and are
redirected, as well as collecting the secondary electron emissions,
returning them to the annode of the power supply.  If not, the accumulation
of electrons would distort the electron beam.

On Wed, Feb 14, 2018 at 10:49 PM, Ron Wickersham <rjw at alembic.com> wrote:

> On Wed, 14 Feb 2018, Patrick Giagnocavo wrote:
> > Yes, the interior of the CRT is coated with lead oxide. Breaking a
> > tube will release this.
> not in any CRT manufacturing process I'm aware of.   the coating both
> on the inside and the outside of the conical glass portion of the
> envelope is Aquadag, a water-based graphite coating.   the two coatings
> form a capacitor, with glass as the dielectric as in the Leyden jar which
> used metal foil conductors rather than the conductive graphite Aquadag
> coating.   the Aquadag coating on the inside of the CRT is required to
> form the uniform accelerating electrostatic field for the electron beam
> to strike the phosphor coating on the inside of the face of the tube.
> the Aquadag coating on the outside makes the second plate of an inexpensive
> high-voltage capacitor for the high voltage supply.
> as the accelerated beam strikes the face of the tube with high velocity,
> X-rays are produced.
> the lead content of the CRT is primarily in the face-plate glass of the
> tube to shield the user from these X-rays.   the lead is bound in the
> glass, like in lead "crystal" glass vases, pitchers, and goblets.  the
> lead content in lead "crystal" is 35-40 percent PbO, lead oxide, by
> weight, and in CRT the lead content is slightly higher at 50-55 percent.
> -ron
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