X Ray issue ?

stargatekeep

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Hi, just bought an upright Defender game. Game works great...but I noticed that the CRT tube and the chassis are not of the same manufacturer or date. I'm a little worried about whether the high voltage specs were properly maintained when this chassis/tube combination was put together. I don't want to be getting X ray'd every time I play the game. How can I be sure ?
 
You you can check with a high voltage probe rated for 40kV. I think 35k is where you get x-rays.
 
Do arcade monitors use voltage multipliers ? What is the chance that a mismatch between chassis and tube could create the kind of high voltage that would emit x-rays ?
 
Don't worry about X radiation. All modern (and by modern I mean, after the late 60's or so) monitors have integral x-ray protection circuitry that shut the HV down if it goes too high. The HV ranges for any 19" CRT is about 19kv. Mismatching a picture tube won't cause any X-ray problems - they all operate in the same ranges.

Also, the amount of X-radiation that it's even physically possible to produce by a picture tube is SO far below what you'd get through normal means (like, for example, a commercial airline flight), that it's not even beginning to be an issue.

Back in the old days, there were theoretical issues with high voltage regulator tubes in color TV's (6BK4 tubes), but then they switched to increasingly thicker leaded glass in the tubes (6BK4B and finally 6BK4C) and that was that. Even back then, the exposure risk was primarily to servicemen working on the sets with the metal HV cage covers removed.

While it's theoretically possible to get X-radiation from a color picture tube, the amount is very, very low. To generate even tiny amounts of harmful radiation, you'd need to run the thing at much higher voltage than normal - probably higher than the flyback is capable of producing without burning up.

Also, all modern color picture tubes are also made of leaded glass.

-Ian
 
thanks Ian...I feel better now.....follow up

The monitor in my Defender cabinet isn't surrounded by a metal
cage...the yoke is pretty much in the serviceman's face. So,
no x-ray worries back there either ? just don't touch the hv spots,right ;)
 
Mabye you dont know, but tube maker and chassis maker are almost always different.

Wells gardner, electrohome, all the big name guys BOUGHT tubes from other manufacturers.

thats why you always seem to see tv names on tubes( rca, zenith, phillips, etc) and never see a walls gardner tube for example, they dont exist.
 
Mabye you dont know, but tube maker and chassis maker are almost always different.

Wells gardner, electrohome, all the big name guys BOUGHT tubes from other manufacturers.

Ah, yeah, I didn't pick up on that in his post - I just assumed he knew the tube came from one chassis originally and was transplanted. Yeah, Wells Gardner never made picture tubes, neither did any of the monitor manufacturers. Just like Dell doesn't make processor chips or hard drives.

-Ian
 
Where would you measure the high voltage ?

If using a high voltage probe, where would you measure the high voltage?
Where do you place the probe's ground ? Is it a dc or ac voltage ? Does
it change depending on what's being fed to the tube signal-wise ? thanks.
 
You measure the HV at the tube's anode connection. That's the thick red wire that plugs into the tube with the suction cup. On a 19" monitor, it should be around 19.5kv or so - give or take a thousand volts. The probe's ground connection just gets clipped to the metal frame of the monitor.

HV can change slightly with beam current, which can cause the power supply to sag and thus affect the HV. But it won't fluctuate much. In most monitors the B+ is directly tied to the HV, so if the B+ is right on, then the HV will be too. Raster monitors don't usually have a HV adjustment, it's all pretty fixed - this is because the operating frequency of the flyback is tied to the horizontal scan frequency. In a color vector monitor, the HV can be a lot more variable, and that's the only place I ever use the HV probe. On a monitor like the WG6100, the HV can jump around a lot, depending on how well the circuit is working, and if the regulator transistors are good. It's still pretty tightly tied to the B+ though - on a 6100 when I dial the B+ to 180v, the HV is spot on.

If you're really paranoid, then sure, get a HV probe and measure the HV. But again, I don't think it's physically possible to produce damaging radiation from a modern monitor. The protection circuits will cut it off way before it gets that high, and even if they didn't, the picture wouldn't even come close to fitting on the screen because the B+ would be so high. You also get weird blooming if the HV regulation is shot. When the HV diode fails on a black and white vector, the HV gets screwed up and the picture gets huge and washed out. Of course, this is a black and white monitor - obviously there's no possibility for X radiation with a black and white picture tube.

-Ian
 
I have yet to see a monitor that could even generate over 25k where I think it is that it begins to emit Xrays. And even then, you would have to be right up on that tube. I was told that standing back at arms length from a game as if you were playing it, the voltage would have to be higher to do anything. Like closer to 30k or so.
 
I was told that standing back at arms length from a game as if you were playing it, the voltage would have to be higher to do anything. Like closer to 30k or so.

It's the old inverse-square law for those of you who had to take a physics class. The intensity at 2 feet is 1/4 the intensity at 1 foot. Or the other way around, the intensity at 1 inch is 144 times stronger than the intensity at 1 foot.

-Jim
 
It's the old inverse-square law for those of you who had to take a physics class. The intensity at 2 feet is 1/4 the intensity at 1 foot. Or the other way around, the intensity at 1 inch is 144 times stronger than the intensity at 1 foot.

-Jim

Yes, and don't forget the distance is the distance from the point source. And the source is the electron gun, not the screen. Ratio between 1 inch from the screen and 1 foot from the screen isn't 144. The screen is ~1 foot from the gun, so 1 inch from the screen you're still about 1 foot from the source. Moving to 1 foot from the screen (~2feet from the gun) makes the ratio closer to 4.
 
Nice one Chad! :)

BTW, did you ever get the email I sent you asking about combining shipping on 4 Sanyo flybacks? I ended up ordering them anyway but I'm curious if my email got bumped or something...
 
Yes, and don't forget the distance is the distance from the point source. And the source is the electron gun, not the screen.

X-rays are generated when the high energy electrons impact an atom causing the valence electrons to jump to a higher state. When the electrons decay back to a lower (stable) state, the excess energy is be emitted in the form of electromagnetic radiation (X-rays typically for CRT's). This takes place at the screen mask, tube face, and even the rear of the tube.
 
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