X-ray danger whilst working on TV?

It certainly used to be a real problem in the old days, when a PD500 shunt regulator valve ( tube ) was used in the EHT supply. When working with the deflection stage cage open, a lead glass shield had to be placed over this device.

X Rays are easily created by accelerating a stream of electrons, and slamming them into some kind of anode, and the 25 kV used in a CTV is plenty enough to generate an electron beam with enough energy to do just this.

However, the electron beam should not actually ever touch the anode inside the picture tube - otherwise no electrons would ever reach the faceplate to light up the phosphor. The electrons do, however, dissipate large amounts of their energy, when they collide with the slotmask inside the CRT. As far as I know, this manifests as heat, but possibly, some soft x rays may be generated. You are right that any generated to the rear or sides would probably escape through the plastic cabinet, but the inside of this, or even the plastic itself, may be treated to prevent EM radiation of all wavelengths, as there is paranoia these days about such things.

I don't think that there is any significant danger from x rays any more from CTVs. I would guess that as there is high voltage present, and high energy electron beams present, the manufacturers err on the side of caution and warn of the possibility of random x ray generation. As an addition, no x rays would escape from the picture tube faceplate, as this is made from lead doped glass to be sufficiently conductive to form the return path for the spent electrons.

Geoff

Also keep in mind that the same warnings are on 1/2 inch camcorder viewfinder CRTs. :)

And, as noted, the plastic won't block the X-rays so it's not much different than with the back on.

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Most television sets are designed to be watched from the frontside. And in case someone forgets, there is that warning on the back.

But in practice: if you work on a life color-tv, X-ray radiation is probably the least of your worries.

--
Kind regards,
Gerard Bok

There is a slight danger from X-Rays. There is also a slight danger from repairing the set while in a swimming pool. Tobacco smoking is a REAL danger.

N

Thanks for all the input. I guess, for the person who only looks into the back of an operating TV once or twice a year, the hazard is minimal. However, if my job were to be looking into the back end of operating color TVs all day long, day after day, year after year, that might be a different story. I wonder if there are any full-time TV servicemen (women) who follow this NG who could give their input?

Cheers

Just a quick FYI. The KV sets the energy level of the x-ray and the current sets the quantity of x-rays produced. 25KV is right at the threshold for x-ray generation capability of any significant level. Hence the critical nature of the x-ray protect circuits.

The energy level would indicate how thick of an xray stopping material would be required to protect you. At 25KV the lead in the glass is enough to stop virtually all errant x-rays produced. The mA is the amount of electrons flowing and the greater the electrons hitting the surface, the greater the quantity of x-rays.

The dosimeters only measure the exposure to the quantity of x-rays, but not the energy level. The higher the energy level the greater the chance of causing a DNA mutation. The higher the dose over time, the greater the chance of causing a DNA mutation.

I've been in the business 27 yrs, back in the old days of tube sets, and early solid state there was no safety protection. Anybody remember the old Zenith 20Y1C50 type set with a bad VDR? The HV would run

35-40KV all day, pe> Thanks for all the input. I guess, for the person who only looks into

Thanks for your input!

How exactly would you know if it hurt anyone? It's not like you would glow in the dark. Cancers can appear decades later....

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Ditto: same question. You do not know if xrays injured you, unless it was prolonged exposure of minutes or hours to an extremely high dose where you will have xray burns.

Cancer and DNA damage may not show up for years later.

You're not supposed to glow in the dark? Oh crap!

N

Send your application to Jeff Probst for the next Survivor. Outwit, outplay, outglow :)

Ken

Unless you've got a set like my old CTC-7, where the X ray protection circuitry is just that the darn thing can't make the full 25kv most of the time :(

Mine's got a 21FBP22 in it. I can't imnagine what the 21CYP22s were like, . since this one's a rare earth. Reds so red they're orange...

Oh yeah, the remote acts funny. Yep, 4 function (on/off/mute/channel). Sometimes just goes bonkers on its own accord. Thankfully, you can turn it off...

On a modern TV, zero risk, I've seen people *try* to make Xrays with a TV CRT and have very little success, there's just too much lead in the glass.

Better to look at "The Amateur Scientist" in "Scientific American". I'm sure they have had a do it yourself X-Ray generator.

N

Typically they use an old high voltage rectifier tube. Never heard of using a CRT.

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That's my recollection too.

N

TV

glass.

sure

It was more of an experiment just to see if Xrays could be produced with a CRT, as I recall about all it did was melt a big hole in the shadow mask.