Output tube radiation exposure - thoughts?

Doesn't seem like a concern at all, to me, in the context of an audio system.

The key distinction with respect to the situations you mention about shipboard equipment being that in the audio application the frequencies involved don't radiate through the air (at least to any degree that is remotely significant, considering the power levels that are involved), while of course radio frequencies do.

Regards,
-- Al

Honest1: I thnk it has more to do with the voltage the tubes operate at, rather than the frequencies they are amplifying. I don't think there is a problem until you start getting into much higher voltages than any audio amplifier uses, But at those voltages, tubes can emit Xrays. May be an issue with CRTs, not sure.

Lonestarsouth: This is utter nonsense!! Ionizing radiation only can occur when sub-atomic particles are excited by a high energy, high frequency power source. If your statement was true then electrostatic loudspeakers would have been ultra-deadly.

Actually, I believe that Honest1's statement about x-rays potentially being generated by high voltage tubes (much higher than any audio tube would use) is correct. As I understand it, an x-ray tube functions by bombarding the material in its plate with electrons that are emitted by a heated cathode, and then accelerated to high energy levels by means of a very high dc voltage applied to the plate. The voltage is typically in the range of 30,000 volts or more.

The analogy to electrostatic speakers is not applicable. While several thousand volts may be present between the elements of an esl, there is no electron emitter, no vacuum, and no plate being bombarded.

X-ray emission was definitely an issue with early tv sets, both from their crt's and from the tubes in their high voltage power supplies. Modern tv's and crt monitors use solid state power supplies, and presumably/supposedly limit x-ray emission from crt's via lead shielding which is impregnated into the glass.

See this wikipedia article for further information:

http://en.wikipedia.org/wiki/X-ray_tube

Regards,
-- Al

Well A1marg... what amplifies operate at 30 kVa? Not even the huge WAVAC amps run near that.

Both Honest1 and I said very clearly and explicitly that the concern about X-rays would only arise in the case of tubes that operate at far higher voltages than are used in audio applications.

If the above were true then we all would have been dead a long time! Tubes are around quite a while - long enough to have wiped out the entire earths population.

I'm not totally certain as to what you are referring to by "if the above were true," but I assume it is my reference to early tv sets having an issue with X-ray emissions.

For starters, please read the last section in the Wikipedia writeup I linked to in my previous post, which is entitled "Hazards of x-ray production from vacuum tubes." Then please do some Googling on the subject and you will find additional commentary to the same effect.

I am an antique radio collector, and as such I have had occasion to accumulate significant knowledge about early tv sets as well (ca. 1946 to the 1960's). The issue was not that they would "wipe out the earth's population." The problem was that those sets, when viewed from close distances (such as children are often known to do), for considerable amounts of accumulated time, would pose unacceptable long-term health risks. As I said, those risks have presumably been eliminated in more modern sets.

Regards,
-- Al

Lonestarsouth -- I think that the comments provided by your EE friend are good, and are likely to be completely correct.

I too, btw, am an experienced electronics engineer.

In regard to my comments about OLDER televisions, though, I would like to offer the following quote from United States Patent number 3562518, which was applied for in 1967 by National Video Corporation, and granted in 1971. National Video Corp., btw, had in 1963 developed the world's first truly rectangular color tv picture tube, in conjunction with Motorola.

Ordinarily, the electron beams which scan the viewing area in a color television kinescope are energized by an accelerating potential of 25,000 volts. At this limit of accelerating potential, there is little or no danger of generating harmful X-rays. Further, since the faceplate panel of conventional color kinescopes are usually quite thicker than the rest of the tube and comprise a lead type of glass, whatever X-rays are generated within the tube are absorbed in the faceplate panel. However, if the accelerating voltages exceed by as little as 2,000 volts the 25,000 volt specified accelerating potential, the safety limit for X-ray generation may be exceeded with resulting hazardous generation and escape of X-rays. At this level, the X-ray penetration at the back of the tube becomes considerable, and additional protection must be provided ....

The present invention provides for coating the shadow mask mounted within the peripheral flange of the faceplate panel of a conventional color kinescope with a thin layer of bismuth thereby substantially reducing the penetration of X-rays generated by high energy electron beams impinging on the phosphor screen escaping through the rear of the tube. In addition, the constricted neck portion of the tube is encompassed with a paper pulp sleeve impregnated with bismuth trioxide; and the external surface of the funnel from the paper pulp sleeve to the flange of the faceplate panel is coated with a nonconducting mixture of bismuth trioxide and sodium silicate. It has been found with this particular arrangement of means for protecting against X-ray penetration, there is provided sufficient safety for personnel even if the accelerating potential rises to the 30,000 volt level.

Note too that this was more than 20 years after tv was first introduced on a widespread basis, and I believe that the earliest crt's used glass that was either unleaded, or at least not as heavily leaded, as in the later ones.

And re your comment that

"It is useless to stress about such things. Sit back and enjoy the music!!"

I agree, and even more so because we are all agreed that the answer to the op's question about radiation from audio tubes is that there is no problem whatsoever.

Regards,
-- Al