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The Quest For the Ultimate Vacuum Tube (ieee.org)
An anonymous reader writes: IEEE Spectrum reports on progress in the development of vacuum tube technology, which remains surprisingly relevant in 2015. "In the six decades since vacuum tubes lost out to solid-state devices in computers, receivers, and power supplies, vacuum technology has continued to evolve and branch out into new terrain, sustaining a small but skilled corps of engineers and scientists around the world, as well as a multibillion-dollar industry. That's because the traveling-wave tube and other vacuum devices continue to serve one purpose extremely well: as powerful sources of microwave, millimeter-wave, and submillimeter-wave radiation. And now, ongoing research into a new and potentially revolutionary kind of traveling-wave tube—the ultracompact and ultraefficient cold-cathode TWT—looks poised to deliver the first practical device by the end of this decade."
EMPs are the death of solid state devices. But, due to their nature, vacuum tubes can weather EMPs fairly easily.
I usually delete those spam emails
Light travels faster than sound. This is why some people appear bright until you hear them speak.........
Could learn a thing or two from studying vacuum tube technology. Unlike most everything casts from silicon, you can actually "see" electron flow, with enough certainty to end the conceptual debate between hole flow and electron flow.
Nothing evolves faster than the word of god in the minds of men who think themselves divinely inspired.
Vacuum tubes use the integrated face system to compute data.
The local PBS station in Silicon Valley had to shutdown and merge with a distant PBS station in the 1990's because the station couldn't afford the $50,000 replacement cost of the vacuum tube in their transmission tower.
https://en.wikipedia.org/wiki/...
You are all cows. Cows say moo. MOOOO! MOOOO! Moo cows MOOOO! Moo say the cows. YOU WARMER, MORE NATURAL SOUNDING COWS!!
In my experience, when someone feels the need to insist that something is "surprisingly relevant", it's usually unsurprisingly irrelevant.
In my experience, when someone feels the need to insist that something is "surprisingly relevant", it's usually unsurprisingly irrelevant.
What a surprisingly relevant insight...
Do not look into laser with remaining eye.
I worked with TWTs in the 70s, airborne systems not space. We could admit to Ku band capabilities, and the real limiting factor we were concerned with was the high voltage required. And vibration.
Fabulous devices. Lots of power output. Ours were tough. Radar systems relied on them mostly exclusively, replacing magnetrons. Very difficult to adjust though, and a finite life.
Now, can we get cold cathode tech into 12AX7s and 6L6s?
deleting the extra space after periods so i can stay relevant, yeah.
The other place vacuum tube technology in a big way still exists is Photomultiplier tubes. Photodiode technology has come on significantly, but for very low light level applications PMTs win. They lose out in quantum efficiency to silicon and ingaas photodiodes at almost all wavelengths of light PMT are actually useful at. But the internal amplification of the tubes means dark noise is very low at low light levels. To the point that PMTs can detect single photon events (photon counting) with a collection area of an inch or larger. Avalanche photodiodes (photodiodes with internal amplification) can do photon counting but only on devices less than a mm, which limits their applications.
Of course PMTs have their weirdnesses. The gain you apply is not able to be known accurately. The devices have weird non-linearities at low gain. They have a polarisation bias. And many more.
In my experience, there's a corollary which applies to the reverse of all such statements. Especially on the interwebs.
Just sayin'. ;-)
Lost at C:>. Found at C.
So you goggle "vacuum tube nanotechnology" and...
http://www.newelectronics.co.uk/electronics-technology/how-vacuum-tube-technology-is-being-deployed-at-the-nanoscale/45695/
.
Prisencolinensinainciusol. Ol Rait!
Getting >50% efficiency from a TWTA at microwave frequencies is easy. Getting >25% from a solid state amplifier at the same frequency is hard, particularly as you get above 30 GHz.
That's "wall plug" efficiency, and for a decent amount of gain.
Getting 40-60 dB from a TWTA is easy (1 mW in, >100W out). Getting 50 dB of gain from solid state amps, with 8-10 dB/stage is really hard, particularly at the higher powers. If you want 100W at 30GHz, you're probably ganging up a lot of 4W MMICs, so you have lots of divider/combiner losses too.
Vacuum tubes make excellent high-power switches (talking the size of a 55-gallon barrel, here), and there are ultra-high-speed switches called Krytrons that are technically a type of vacuum tube, too. Also so far as I know vacuum tube final amps for very high-power transmitters.
Are YOU using the TOOL, or is the TOOL using YOU? Think about it!
Yup- ratio of transistor applications to tube applications is probably million to one
love is just extroverted narcissism
The root problem here is that every time you think you've found the ultimate vacuum tube, you find one more.
Obliteracy: Words with explosions
"And now, ongoing research [...] looks poised to deliver the first practical device by the end of this decade."
So up until now the multibillion-dollar industry has been founded entirely on impractical devices? Or if they mean the first practical vacuum tube of that particular type it might be useful if the summary gave some kind of brief explanation about what makes it different from/better than other vacuum tubes.
(The TFA probably explains it, but the site is blocked for me.)
This Space Intentionally Left Blank
About 70 years ago, E. E. "Doc" Smith wrote a series of books that are wonderful space opera: the "Lensman" series. The space battles just keep escalating throughout the series, getting more over-the-top.
My favorite plot point: they used the principles of a vacuum tube to make a device whose pieces included grids mounted in the asteroid belt, with more in other orbits closer in to the sun. In effect they turned the inner Solar System into one honking big vacuum tube, and created a weapon that could concentrate a significant fraction of the sun's output onto attacking enemy fleets. This was called the "Sunbeam". (Believe it or not, this wasn't the end of the escalation. The battles got even bigger after that.)
When you say "ultimate" vacuum tube, I think that one is pretty hard to top.
P.S. 200-word crossover fan fiction: what would have happened if the Battlestar Galactica reboot show had found Earth, and it was the Earth of the Lensman series?
http://archiveofourown.org/works/495034
When I was a teen and read those books, I just enjoyed them, but now I'm thinking that it would take a lot of trust to allow Kimball Kinnison to run around acting as judge, jury, and executioner. As readers of the books, we know that he was vetted as deeply as anyone could be by the Arisians, so he can be trusted with that kind of power; but it would be hard for the ordinary people in the world of the books to trust him that much.
lf(1): it's like ls(1) but sorts filenames by extension, tersely
As an aside, never forget that microwave emissions are a natural, expected result of plasmas conducting electric currents. The point seems to have been completely lost on cosmologists who seem to believe that a microwave background signal coming at us from all directions can only be explained in metaphysical Big Bang terms. Actually, there would be nothing particularly difficult about explaining the CMB with plasmas, the most common state for observable matter ...
It is simply a matter of explaining why the spikey synchrotron microwaves would become thermalized into a smooth bell curve.
Could this possibly be used to produce a more efficient vacuum tube oscillator such as what were used in early BFO design detectors, allowing for better metal searching capabilities?
Back around 1980 I did some preliminary work on making vacuum tubes on a chip. It was a sideline idea I had as part of another project I was involved in - we were also making micro gas valves, pumps, and thermal conductivity sensors on a chip, all without moving parts, as part of this project. We etched channels and put in cathodes and anodes and sealed in the vacuum with a cover plate. It was promising, as the small sizes and distances eliminated the need for heaters plus the response times were exceedingly fast. Unfortunately, the main project was killed and a few months later the entire department was disbanded. I don't believe any more has been done after that.
Before I got a BSc in CS, I got an AD in Electronics Engineering. I took an avionics course and it included microwave landing systems and radar systems. The radar systems used tubes (mid 1990s), because there were no transistors that would operate at that power (2kW) and at that frequency (6-7 GHz). They would tolerate running 'up to cherry hot' (the glass envelope glowing a nice reddish color). Its interesting to see too that travelling wave tubes (I studied their use in C and Ku band satellite systems), are a lot like free electron lasers. Not stating a military application, just sayin'.
I have never heard of a vacuum tube before. Thanks for posting the link. I thought the article was talking about a part used in vacuum cleaners.
https://www.youtube.com/embed/Imsc_J25QmE
https://www.youtube.com/watch?v=Imsc_J25QmE
Actually, the electron beam is a lot slower, and there's lots of wavelengths in a typical TWT. A klystron (not a travelling wave, but still a crossed field amplifier) may have a couple of "wavelengths" (or more properly coupled resonators).
A coupled cavity TWTA might have 30-40-50 cavities.. A helix tube might have 50 turns (although it's continuous, not coupled cavity).
Typical cathode voltage might be 10-20 kV on a tube that's up to a few hundred watts, so the electrons have 10-20 keV energy
I'm too lazy to calculate it for 10-20 keV, but 30 keV is about 5% of the speed of light. So, a typical 8-10 GHz (3-4cm wavelength) tube that's a foot long (external package), with a "delay line" that's 25 cm long has an electrical length of 20*25 cm or about 5m. That's easily more than 100 wavelengths long.
Another vacuum tube technology with current applications and substantial advantages over semiconductor approaches to the same problems is the Thermionic Converter. This is a vacuum-tube technology heat engine that turns temperature differences into electric power - by boiling electrons off a hot electrode and collecting them, at a somewhat more negative voltage (like 0.5 to 1 volt), at a cooler electrode.
Semiconductor approaches such as the Peltier Cell tend to be limited in operating temperature due to the materials involved, and lose a major fraction of the available power to non-power-producing heat conduction from the hot to the cold side of the device. Thermionic converters, by contrast are vacuum devices, and inherently insulating (with the heat conducted almost entirely by the working electrons, where it is doing the generation, or parasitic infrared radiation, which can be reflected rater than absorbed at the cold side.) They work very well at temperatures of a couple thousand degrees, a good match to combustion, point-focused solar, and nuclear thermal sources.
Thermionic converters have been the subject to recent improvements, such as graphine electrodes. The power density limitation of space charge has been solved, by using a "control grid" to encourage to charge to move along from the emitter to the collector and magnetic fields to guide it (so it doesn't discharge the control grid and waste the power used to charge it).
Current thermionic technology can convert better than 30% of the available thermal energy to electrical power and achieves power densities in the ballpark of a kilowatt per 100 square cm (i.e. a disk about 4 1/2 inches in diameter). That's a reasonably respectable carnot engine. This makes it very useful for things like topping cycles in steam plants: You run it with the flame against the hot side so it is at the combustion temperature, and the "cold" side at the temperature of the superheated steam for your steam cycle. Rather than wasting the energy of that temperature drop (as you would with a pure steam cycle) you collect about a third of it as electricity.
It also beats the efficiency of currently available solar cell technology (and the 33.4% Shockleyâ"Queisser theoretical limit for single-junction cells), if you don't mind mounting it on a sun-tracker. Not only that, but you can capture the "waste heat" at a useful temperature without substantial impairment to the electrical generation or heat collection, and thus use the same surface area for both generation and solar heating. (Doing this with semiconductor solar cells doesn't work well, because they become far less efficient when running a couple tens of degrees above room temparature.)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Pseudonymous Powers, may I introduce You to my friend, Augustus De Morgan.
As mentioned previously, my mental model of semiconductors and the like is a fireman's water brigade, were either the majority of the line has buckets or empty hands.
It helps if, instead of a line, you think of a LOT them standing in a two-D array (like in the yard of the burning building, or a section of a parade that's stopped to do a little demo). It's really three-D, but we'll want to use up/down for something else in a bit...
For metallic electron conduction everybody has TWO buckets, one for each hand, and when a guy by the fire throws a buck of water on it (bucket and all) on the fire, a guy farther back immediately tosses him a bucket, the guy behind him essentially instantly throws HIM a bucket, andso on. Hands are effectively never empty.
For semiconductors, imagine two layers of these guys, the second standing on the firsts' shoulders or on a scaffold right above them, and about enough buckets for each of the guys on the ground to have two and the guys on the scaffold to have none. (There's actually many layers of scaffold, but the rest are so far up that it's hard to get a bucket to them, so they mostly just stand around.)
Usually nothing useful is happening. Everybody on the bottom layer has both hands full of buckets, and it's hard to hand a bucket up to the guys on the top.
- Electron-hole pair creation: Somebody comes up with the energy to heave a bucket up to the guys on the upper layer, leaving a guy with one hand empty in the lower layer. (Maybe somebody (a photon, for instance) comes along with a lacrosse stick and whacks a bucket up to a guy in the top row - dying or becoming exhausted and much weaker from the effort.) Now you've got one guy with a free hand in the lower layer (a hole) and one bucket on the top layer (a free electron).
- Electron conduction in a semiconductor is that bucket on the upper layer. The guys there can hand it around easily, or toss it along a diagonal until it would hit a guy - who catches it. They're all standing on accurately-spaced platforms so the bucket can go quite a way before somebody has to catch it. Suppose there's a slope to the yard, with the fire at the bottom. Then, if tossed too far, the bucket might pick up substantial speed and knock the guy who catches it out of place (electromigration), or fall down to the lower layer and knock another bucket out of somebody's hand and bounce, ending up with TWO buckets on the upper layer and an empty hand below (avalanche electron-hole creation).
- Hole conduction is when you've got an empty hand on the bottom layer: Now it's easy for a guy with two buckets to hand a bucket to a guy with only one, exchanging a bucket for an empty hand. But now the guy whose hand had been empty has two buckets and nobody in the downhill/toward-fire direction to hand a bucket to, while the guy who handed it off has an empty hand and can grab a bucket from somebody farther uphill / closer to the water source - or beside him, or diagonally. So "empty-handedness" (a hole) can move around as a persistent entity while the individual buckets gradually work their way in the general direction of the fire, only making a bit of progress "when a hole comes by". Though the water makes progress toward the fire, the action is all where the holes are making progress away from the fire.
- Electron-hole annihilation: Somebody has a bucket on the upper layer when a guy below him has an empty hand. So he drops the bucket. CLANG! Ouch! Now there's no "free bucket" on the upper layer, no free hand on the lower layer, and the energy of their separation went somewhere else (knocking the guy sideways so he bumps into his neighbor and generally making the guys vibrate, "creating a guy with a lacrosse stick who runs off to whack at buckets", etc.)
- P-type doping: A guy in the bottom layer had a sore hand and only brought one bucket to the fire, thus having a free hand from the start. He can take a bucket when a neighbor pushes it at him (the hole moves
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
....as a vacuum tube (mostly TWT) engineer since 1968:
I don't remember when they started working on cold cathode tubes, must be about the time they started working on fusion reactors. Both are now going to be ready in "another five years". Meanwhile, satellites in orbit run their tubes for 30,000 hours, limited by the amount of barium and unobtanium that boils out of their cathodes at 1000C. Or, the power supply shits the bed.
Nobody uses little tubes any more, except rock star guitar players (and wannabees) with strong roadies, and audio aficionados with golden ears, deep pockets, and low cranial capacity. A series of articles in Electronic Design magazine some years ago pointed out that the "tube sound" is mostly the loose impedance coupling and high frequency smothering of output transformers, not the tubes themselves.
Just about everybody uses an S band microwave power oscillator tube in their kitchen. They can be replaced with Gallium Nitride transistors, and I'm sure rich hipsters will buy them, but physics and economics is still backing the maggie.
And if you still want 10 KW of average power and 100 KW or a megawatt peak in a device a couple people can lift, a tube is hard to beat.