It's well known that if you've got tubes running in the 10's of kV range then X-Rays become a concern. Obviously this is of no concern or worry whatsoever for every day audio and radio tube voltages.
But here's what I was wondering: Since visible light is only around 2-3eV and tubes run in the 100's of volts range, are there technically high energy photons as a result of this? Obviously they aren't getting through the glass but technically, do you get super short wavelength photons from the typical acceleration in say an output valve? Obviously not typical x-ray wavelengths but somewhere at the end of the UV spectrum. I simply don't know the physics around this and whether or not this happens proportionally or you have to get over some threshold for things to get interesting!
But here's what I was wondering: Since visible light is only around 2-3eV and tubes run in the 100's of volts range, are there technically high energy photons as a result of this? Obviously they aren't getting through the glass but technically, do you get super short wavelength photons from the typical acceleration in say an output valve? Obviously not typical x-ray wavelengths but somewhere at the end of the UV spectrum. I simply don't know the physics around this and whether or not this happens proportionally or you have to get over some threshold for things to get interesting!
You do get UV photons out of any regular tube.Some of the old tubes had radioactive coatings too on the anode in order to absorb higher velocity electrons releasing other high velocity electrons or UV...gamma ray photons ... while some tubes might be really dangerous to be used in your home on a regular basis , but fortunately they aren't used in audio : My vintage vacuum tubes are radio-active! - YouTube
Interesting - I presume you mean the UV photons are inside the envelope? I would guess that the glass pretty much attenuates them 100% as they'd struggle to even get through much air, given that below a certain wavelength UV and even very soft X-rays are pretty much stopped by air.
Obviously none of this of any actual health concern, I am just curious about whether or not this is actually happening inside, fun to imagine if there are "exotic" light wavelengths in there!
X-ray emission lines are due to inner electrons being booted out of an atom and then being replaced by another electron from that atom. There's also a continuum spectrum from bremsstrahlung (abrupt electron deceleration).
There's no clear boundary between hard UV and soft X-ray so I expect all sorts of energies are produced, although at what intensity I know not. Glass being amorphic may filter out wide bands rather than precise absorption lines.
One datapoint I have is some of the VHF high-power tetrodes I have use alumina as the envelope (well much of the envelope is the copper anode really), and the alumina lights up bright electric blue in operation, fluorescing strongly in the visible and presumably other wavelengths too (at about 1kV IIRC)
There's no clear boundary between hard UV and soft X-ray so I expect all sorts of energies are produced, although at what intensity I know not. Glass being amorphic may filter out wide bands rather than precise absorption lines.
One datapoint I have is some of the VHF high-power tetrodes I have use alumina as the envelope (well much of the envelope is the copper anode really), and the alumina lights up bright electric blue in operation, fluorescing strongly in the visible and presumably other wavelengths too (at about 1kV IIRC)
I am sure I have seen x ray warnings inside old TV sets.
The last hybrid tube amplifier I designed ran off +/-24 volts so that should be pretty safe.
The previous valve headphone amp design ran off 12 volts B+.
The last hybrid tube amplifier I designed ran off +/-24 volts so that should be pretty safe.
The previous valve headphone amp design ran off 12 volts B+.
You need to accelerate the electrons and bash them into a target metal.
A 19" CRT is designed for this - electron gun with focusing anodes, then a high potential to accelerate them into the screen. Not sure many vacuum tubes are constructed in a such a way to get the electric field intensity high enough to get the energies needed. However, CRTs were defacto particle accelerators.
Electrons at the needed kinetic energy to produce X-rays are available at all temperatures and all electric field intensities. Boltzmann's Thermal Distribution. It's just the probability is so low, that the radiation is part of the background radiation. In fact, you can get deuterium to fuse in a simple plasma in a home-made tube - and observe the neutron flux that proves you have fusion. In effect, you have a thermonuclear reaction you can run in your basement. You can do this again because of Boltzmann's Distribution. You dont need a Tokamak or a Fission Primary get a population of particles that can fuse in normal conditions. It's just getting a reasonable density of deuterium to get to a high enough temperature in a plasma and it will happen for you! Weaponizable? No. Practical? Not really - but a nice safe source of neutrons to play with.
A 19" CRT is designed for this - electron gun with focusing anodes, then a high potential to accelerate them into the screen. Not sure many vacuum tubes are constructed in a such a way to get the electric field intensity high enough to get the energies needed. However, CRTs were defacto particle accelerators.
Electrons at the needed kinetic energy to produce X-rays are available at all temperatures and all electric field intensities. Boltzmann's Thermal Distribution. It's just the probability is so low, that the radiation is part of the background radiation. In fact, you can get deuterium to fuse in a simple plasma in a home-made tube - and observe the neutron flux that proves you have fusion. In effect, you have a thermonuclear reaction you can run in your basement. You can do this again because of Boltzmann's Distribution. You dont need a Tokamak or a Fission Primary get a population of particles that can fuse in normal conditions. It's just getting a reasonable density of deuterium to get to a high enough temperature in a plasma and it will happen for you! Weaponizable? No. Practical? Not really - but a nice safe source of neutrons to play with.
When electrons strike the anode in a vacuum tube, most of the energy is converted to heat.
However, some of the incident electrons excite electrons in the atoms of the anode material to higher energy levels. As the excited electrons fall back to their unexcited states in the atoms, they emit photons of radiation.
The excitation energy required for the incident electrons to produce photons depends on the electron binding energy within the atoms, which increases with the atomic number of the anode material.
To produce high energy photons in an X-ray tube, the anode is commonly made of tungsten with its high atomic number of 74.
However, some of the incident electrons excite electrons in the atoms of the anode material to higher energy levels. As the excited electrons fall back to their unexcited states in the atoms, they emit photons of radiation.
The excitation energy required for the incident electrons to produce photons depends on the electron binding energy within the atoms, which increases with the atomic number of the anode material.
To produce high energy photons in an X-ray tube, the anode is commonly made of tungsten with its high atomic number of 74.
A lot of high powered vacuum tube Amateur Radio transmitters run at 2kV or more.
And a 2kV B+ means the plate may go to 4kV, but will little or no current at that voltage (so consider 3kV at moderate current for example?).
If x-ray radiation is a problem for those transmitters, I suspect that we would have a lot more SK (Silent Key) Amateur Radio operators.
However, there are materials used in certain vacuum tubes that are not good for you, inside the tube,
and even outside the tube including beryllium oxide.
The main dangers are when you crush, open, pull apart, etc.; and touch, ingest, breath in.
Some old photographic lenses are also radioactive.
For the most part, levels are quite low.
If you stay awake at night worrying about all those things, your life will be shortened.
Just My Opinions
And a 2kV B+ means the plate may go to 4kV, but will little or no current at that voltage (so consider 3kV at moderate current for example?).
If x-ray radiation is a problem for those transmitters, I suspect that we would have a lot more SK (Silent Key) Amateur Radio operators.
However, there are materials used in certain vacuum tubes that are not good for you, inside the tube,
and even outside the tube including beryllium oxide.
The main dangers are when you crush, open, pull apart, etc.; and touch, ingest, breath in.
Some old photographic lenses are also radioactive.
For the most part, levels are quite low.
If you stay awake at night worrying about all those things, your life will be shortened.
Just My Opinions
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As I said, this wasn't a worry of mine in the slightest, just curiosity as to the physics of electrons hitting the anode at lower voltages. I realise people do occasionally worry about x-rays on tube forums but I am fully aware that this isn't a problem in the slightest, I was just wondering if they existed inside the envelope to any degree. Just genuine idle curiosity!
That's right, and it's related to old colour TV sets with acceleration voltages of 25 kV and more.
I've pulled tubes form such TV's with X-ray warnings printed onto their gkass envelopes. Those are GY501's, the HV rectifier diode, and I'll never understand the intention. The rectified current is 1 mA at it's maximum, and the GY501 datasheet reads jaust about 1 V plate voltage for that current. So, why hsould these tubes emit X-rays?
The others are the PD500 and PD510 parallel regulator tubes. Quite another thing, as there's indeed high voltage of 25 to 27.5 kV betweeen cathide and anode.
As a precaution the HV cage is mechanically connected to a switch that disables the sweep tube's screen grid voltage if the cage is opened to prevent from radiation. A repairman had to deliberately circumvent this security device if necessary.
Best regards!
The threshold is the electron binding energy of the atoms of the anode material.
To produce high energy, high frequency photons requires an anode material with a high electron binding energy and a high enough anode voltage to overcome it.
I would hazard that photon production may well exist inside an audio vacuum tube, but to no large degree.
At common B+ voltages head on collisions with electrons of the plate at rest and complete transfer of the kinetic energy into a photon is a very, very rare event.
The typical sequence of events would be that our electron bumps into an atom of the plate, gets deflected by the electric field of the outer electrons of said atom, bumps into another atom, and so on, and so on, penetrating deeper into the material until its kinetic energy is dissipated.
With each bounce it looses just a tiny fraction of its total kinetic energy, causing the atoms it has hit to vibrate just a little more than they did before.
Such increase in vibration level is what we measure as increase in temperature, aka heat.
With rising acceleration voltage the probability for more harder collisions also rises, this is why there is no hard threshold for when dangerous radiation levels begin to occur.
The typical sequence of events would be that our electron bumps into an atom of the plate, gets deflected by the electric field of the outer electrons of said atom, bumps into another atom, and so on, and so on, penetrating deeper into the material until its kinetic energy is dissipated.
With each bounce it looses just a tiny fraction of its total kinetic energy, causing the atoms it has hit to vibrate just a little more than they did before.
Such increase in vibration level is what we measure as increase in temperature, aka heat.
With rising acceleration voltage the probability for more harder collisions also rises, this is why there is no hard threshold for when dangerous radiation levels begin to occur.
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I suspected something along these lines might've been the case (i.e. it's a rare and negligible event) , but that's no fun is it 😀
Part of me wants to experiment with actual x-rays but as a chronic worrier I'd never stop worrying about any accidental exposure so probably for the best I don't go down that road 🙄
I saw a cool youtube video where you can generate relatively harmless amounts with a wimshurst generator and a commonly available vacuum diode. The only trouble is you need an expensive image intensifier tube to image them, but I must admit it did look fun. Probably a bad idea.
There is something compelling about such high energy photons that can just sail through things, 0.1nm light? Crazy.
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Well, 7 years of 2.3kV plate voltage at 160mA in my amps and I'm not suffering any radiation burns as of yet...
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Color TV CRTs pulled hard enough on the electron stream that they had relativistic mass gains of several percent. The backs of the CRTs were wrapped in lead sheet for Xray absorption. HV rectifier and shunt regulator valves were also shielded for Xrays. Several pounds of lead for every old TV in landfill.
Mercury vapor rectifiers in the 866 class make lots of UV, and later 866A family have internal shielding specifically for that.
All good fortune,
Chris
Mercury vapor rectifiers in the 866 class make lots of UV, and later 866A family have internal shielding specifically for that.
All good fortune,
Chris
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But this doesn't happen by electrons hitting the anode, but within the gas filling (recombination of Hg ions).
Best regards!
Best regards!
When I was very young, in the early '70s, one nearby town's library had a section of science and experimenter books from the '30s, '40s, and '50s that they had not culled and that I used to love to go pore through, because they had all sorts of interesting electronic and chemistry how-to experiments and projects that no one in later years would have remotely dared to actively encourage kids to fool around with. Even though many seemed ill advised they were really illuminating on how things worked. One of them, I wish I could remember any details that would let me find my way back to book title or author and find a copy, had one project with step-by-step how to DIY your own x-ray machine with a particular vacuum tube and power supply, and how you could then set up film to capture images using the x-rays. It was fairly specific as to what parts you needed to use and they were "not just any combination of parts, but nothing that you wouldn't have been able to get from '40s/ '50s TV and radio repair parts/ junk bin." I subjected myself to a fair range of hazards during those years ("I wonder what's inside this pyranol capacitor....")(and who knows how many tubes of all types I dissected with no precautions for what I was handling and inhaling) but somehow even the fourth grade me knew that the DIY x-ray rig wasn't a terribly safe idea based on increased understandings of X-rays in the intervening decades.
I've always proceeded on the imprecise but reasonably confident understanding that unless you are getting into kilovolt+ of anode voltage or being strangely proximately intimate for long intervals with your vacuum tubes, the risk is probably usually pretty negligible.
Lo and behold, thanks to the internet, the not so well advised idea still lives (the person who describes this does describe and recommend precautions that were conspicuously and completely absent in the library book)
Homemade Xray Machine : 6 Steps - Instructables
And I think the 2x2 tube or something similar was what was used in that old library book's project.
I've always proceeded on the imprecise but reasonably confident understanding that unless you are getting into kilovolt+ of anode voltage or being strangely proximately intimate for long intervals with your vacuum tubes, the risk is probably usually pretty negligible.
Lo and behold, thanks to the internet, the not so well advised idea still lives (the person who describes this does describe and recommend precautions that were conspicuously and completely absent in the library book)
Homemade Xray Machine : 6 Steps - Instructables
And I think the 2x2 tube or something similar was what was used in that old library book's project.
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> x-ray rig wasn't a terribly safe idea
In the early 1960s, shoe stores still had a fluroscope (continuous X-rays, unregulated) but were no longer using it. In the early 1980s it was standard for chiropractors to take a whole-body X-ray snapshot. (And dentists, but they learned early that your finger can fall off.)
In the early 1960s, shoe stores still had a fluroscope (continuous X-rays, unregulated) but were no longer using it. In the early 1980s it was standard for chiropractors to take a whole-body X-ray snapshot. (And dentists, but they learned early that your finger can fall off.)