Re: RF Shielding for CRTs

["Hank" <bicehous@gso.uri.edu>]

Maybe a lttle history will help the discussion. In the 1960's, the HVR on
some color TV sets went as high as 30 kV and its misalignment and/or
shielding removal led to measurable x-ray production. The press had its
usual "don't let facts get in the way of a good story" field day. Congress
held hearings and passed legislation in 1968 giving jurisdiction to the FDA
and supposedly correcting the problem.
----- Original Message -----
From: Huesgen, Jim <HuesgenJ@health.missouri.edu>
To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
Sent: Wednesday, February 16, 2000 11:00 AM
Subject: RE: RF Shielding for CRTs


> Ok, I have to jump in here.  The radiation produced in old vacuum tube TV
> sets did _not_ come from the CRT.  It came from the high voltage rectifier
> tube which consisted of an electron beam and a target, just like a small
> x-ray tube.  The black and white sets generally operated at a low enough
> voltage that little radiation escaped the tube package, but with the
advent
> of color TV, the HVR operated at around 20 KV.  The anode of the tube was
> dish shaped to partially self shield the produced x-ray beam but as the
> tubes aged, the beam would drift off center with some of it striking the
> edges of the anode and producing a wider x-ray beam.  Most manufacturers
> placed the HVR in shielding of one kind or another but this caused the
tubes
> life to shorten due to heat retention.  Many service technicians would
> removed the shielding during tube replacement and neglect to replace thus
> creating a low energy x-ray source within the TV set.
>
> huesgenj@health.missouri.edu
>
>
> -----Original Message-----
> From: BobCherry@aol.com [mailto:BobCherry@aol.com]
> Sent: Tuesday, February 15, 2000 10:05
> To: Multiple recipients of list
> Subject: Re: RF Shielding for CRTs
>
>
> In a message dated 15-Feb-2000 8:39:33 AM Eastern Standard Time,
> Tad.M.Blanchard.1@gsfc.nasa.gov writes:
>
> > Most of the newer CRTs do not radiate hazardous RF levels.
>
> None of the older ones did either.
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