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Analog Angle Blog

Is There Still a Vacuum Tube in Your Future?

For most electrical engineers, the vacuum tube or, more formally, the vacuum electron device (VED), is a quaint curiosity and artifact of the past, and with good reason: The world of solid-state transistors and ICs is where most electronics is these days. Advanced versions and extensions of Lee DeForest's 1906 Audion triode — the first electronic analog amplifier — were critical to making our industry the powerhouse it became. Look at the products of the first half of the 20th century: It's astonishing what skilled scientists, engineers, and manufacturers accomplished using these devices. Even the classic five-tube AM radio, which brought wireless to millions, is an outstanding example of design, cost-effectiveness, and performance.

Various 12AU7 (ECC82) Vacuum Tubes / Valves (Courtesy of Diy Audio Projects.com)

Various 12AU7 (ECC82) Vacuum Tubes / Valves (Courtesy of Diy Audio Projects.com)

Though no one today is going to build a VED-based computer or cellphone, there are still plenty of VEDs in widespread use. Start with the ubiquitous microwave oven in almost every home: It has a 2.4 GHz, 1 kW magnetron (a typical unit's maximum power) to excite the water molecules in the food.

But the use of VEDs goes well beyond that single mass-market application. I was surprised to read a summary of a report “Microwave and Millimeter Wave High-Power Vacuum Electron Devices: Changes Are Looming on the Horizon” from ABI Research, which claims the annual market for specialized VEDs for military/aerospace markets is over $1 billion annually. Depending on where you sit with respect to the active-electronics components business, that's either a big chunk of money or too small to really think about. The key sentence from the summary is this: “These tubes remain essential elements in specialized military, scientific/medical, and space communications applications.”

Reality is that if you need tens of RF watts, at frequencies in the GHz range and higher, or kilowatts for your TV broadcast transmitter in the 100-to-500 MHz range, you're looking at a VED solution. If you are working with microwave and millimeter waves and need high power, you don’t have much choice — at least, not yet.

But what about the future of VEDs? Predictions about the future are always risky, as any look back at predictions made in the past shows. Still, the report notes that devices based on gallium nitride (GaN) may make significant inroads over the next few years, judging from products that are available now from many vendors or in the immediate pipeline. Perhaps that magnetron in your microwave oven will go GaN solid state before too long?

Nonetheless, for the foreseeable future (which is an unknowable period in the high-tech world), VEDs are here to stay in one form or another, with their wonderful names such as klystron, magnetron, traveling wave tube (TWT), crossed-field amplifier, to cite just a few of their many versions. I just hope that as their use declines, we don’t lose the manufacturing “secret sauce” it takes to make these complex marvels of glass, metal, and ceramic, which can calmly produce and dissipate kilowatts and more.

Are there any other products you know of that we might naïvely assume are “obsolete” (such as the electromechanical relay) but which are actually still going strong?

27 comments on “Is There Still a Vacuum Tube in Your Future?

  1. RedDerek
    June 26, 2014

    I would say the market would cover the following categories:

    1. High-end audiophiles – those that believe the only true sound comes from a vacuum tube. (Bob Pease had stuff to say about this)

    2. Old ham radio operators that like to keep nostalgia.

    3. Military and space applications to ensure good rad-hard circuitry.

    Curious to know others.

  2. vbiancomano
    June 26, 2014

    It's often more than nostalgia for old ham operators. Unless it's a well-designed (and usually much more expensive) and carefully driven solid-state high power amp, the voice-modulated output of a vacuum-tube amp will sound much cleaner. In recent years, that's changed a bit, but high-current, solid-state amps that produce any degree of power still tend to clamp and their output will often be noticeably muddy, distorted. Transistors may be “more linear” than vacuum tubes, as has been stated over the years, but in engineering practice it doesn't necessarily work out that way—i.e., it's not automatic. 

  3. yalanand
    June 27, 2014

    VED technology is useful even today. Its uses are still known by the military and something that can be used to make military operations efficient is something that is worth investing in and using. This is because they are use I specialized military. Scientific, medical and space communications applications. Meaning they can act as a backup for the kind of communication systems ha we currently use right now in case of any catastrophic calamities.

  4. SunitaT
    June 27, 2014

    NASA researchers have figured out how to make vacuum tubes on the nanoscale.

    The exciting part is making a vacuum tube that is as small and easy to fabricate as a transistor. With the shrinking size of present day transistors its very difficult to build a lazer to etch them. The further shrinking technology will be a reason for nanoscale vacuum tube.

    Researchers says, the new nano vacuum tubes have a filament and a plate that are separated by just 150 nanometers, which is a small enough distance that the electron colliding with an air molecule is pretty much zero, even without an actual vacuum going on.

  5. SunitaT
    June 27, 2014

    Super hardcore stereo systems sometimes still use vacuum tubes for amplification because of the warmer sound they produce and are claimed to be more musical.

    Vacuum tubes are also better than transistors as electrons move faster through the nothing in a vacuum tube than they do through the material of a solid-state transistor. The vacuum tubes make for significantly faster processors than transistors.

  6. Netcrawl
    June 28, 2014

    @SunitaTO you're right about NASA's work on vacuum tube, I think vacuum tube could make a strong comeback. Researchers at NASA are lookingto use nanoscale techniques to exploit the power of vacuum. Vacuum tube went away not because they're bad, that's because with silicon we could make everything much smaller and build things cheaply. Nanoscale vaccuum tubes has huge potential, it can provide high frequency and power output while meeting the metrics of cost and lifetime. 

  7. Netcrawl
    June 28, 2014

    @SunitaTO I agree with they're widely considered more musical as transistors, vacuum tubes also sound louder and have a better signal-to-noise ratio because of their extra subjective headroom that transistors amplifiers simply don't have.

    Vacuum tubes suffered a slow death just like the great dinosaurs of the Jurassic era, but researchers from NASA have now brought them back, creating something much faster and more hardier than -transistors. You know why NASA like them? because tubes can survive the harsh condition of outer space. NASA need something good, able to work in radiation-harsh environment such as outer space.   

  8. SunitaT
    June 28, 2014

    @NetCrawl, transistors are sensitive to noise and distortion as the carriers(electrons) travel through silicon lattices. Whereas in the vacuum tubes, electrons ballistically travel through the vacuum, so do the high signal-to-noise ratio. Hence vacuum tubes are still used in sound systems.

  9. SunitaT
    June 28, 2014

    Nano vacuum tubes are fabricated using the semiconductor industry's well established silicon technology, which will have a vital cost benefits.

    Vacuum went away because with silicon we can make everything much smaller and manufacture the same in billions with very low cost. By combining vacuum tube concepts with cmos fabrication process we get nanotubes satisfying lightness, cost and stability.

    The thing is that vacuum tubes went away not because they were bad but because, with silicon, you could make everything so much smaller, and manufacture devices in the billions very cheapl – See more at: http://www.newelectronics.co.uk/electronics-technology/how-vacuum-tube-technology-is-being-deployed-at-the-nanoscale/45695/#sthash.GWVv8y4p.dpuf
  10. Victor Lorenzo
    June 29, 2014

    One tube's disadvantage in front of solid state devices is power consumption as tubes need the heating filament.

    For HiFi audio and high power broadcats applications VEDs are still providing best overall performance. In HiFi applications it is perhaps a little bit more difficult for most non trained ears to account for the difference with respect to solid state amplifiers (under the same high quality speakers conditions)

  11. Netcrawl
    June 29, 2014

    @Sunita I agree with you about vacuum tube, its went away because of silicon's presence but its making a strong comeback. NASA researches have now figured out how to make vacuum tubes on nanoscale, which means better batteries, better memories, more reliable and much faster computers. We are now in a race to find an alternatiuve solution or replacement for transistor technology, to address technological challenges and needs. 

    Things have changed fast, today's transistor technology has approached fundamental physical limits that could prevent further improvements and progress if we don't find alternative technology. What we really need is something more capable. NASA wants more, transistors are fragile they tend to easily fried by radiation when send to outer space. Not with vacuum tubes, they're much more radiation-resistant, able to survive the harsh enevironment.

     

  12. Netcrawl
    June 29, 2014

    I think the solution is to learn how to make vacuum tubes smaller and easy to fabricate as a transistor. The new nano vacuum tubes offers huge potential and could be the answer.

    @Victor vacuum tubes are still better than those transistros for one good reasons- electrons moves faster through the nothing in a vacuum tubes than they do through the materials of solid states transistors others. 

  13. geek
    June 29, 2014

    “vacuum tubes are still better than those transistros for one good reasons- electrons moves faster through the nothing in a vacuum tubes than they do through the materials of solid states transistors others. “

    @Netcrawl: Performance-wise vaccum tubes must be better and I guess there's no disagreement on that. But what about the cost factor? Does the high cost still justify their use?

     

  14. geek
    June 29, 2014

    “Scientific, medical and space communications applications. Meaning they can act as a backup for the kind of communication systems ha we currently use right now in case of any catastrophic calamities.”

    @yaland: What's the main reason vaccum tubes are being used in these areas? Does it have to do with the reliablity factor as these are critical areas? Or, does it have to do with the fact that legacy systems have been built using these and it's difficult to upgrade/migrate?

  15. geek
    June 29, 2014

    “Vacuum went away because with silicon we can make everything much smaller and manufacture the same in billions with very low cost.”

    @Sunita: I think the discovery of silicon in a very abundant quanity which could cheaply be refined was the main factor in driving vaccum tubes out. I believe that brought about a drastic change in the electronics world. Unfortunately not many people regard that as an important incident.

  16. SunitaT
    June 30, 2014

    @tzubair, Nano vacuum tubes are fabricated with the present day semiconductor fabrication process like source and drain, optical lithograpghy, etching etc. Source and drain are separated by 150nm with the gate on top. Electrons are generated by source due to voltage applied across source and drain, while the gate controls electron flow through the vacuum.

    Here vacuum(between source and drain) is not necessarily vacuum, since electrons needs to travel 1um(mean free path) before it collides to any air molecules. So vacuum is generated automatically no need to create the vacuum.

    The source and drain are separated by 150nm, with the gate on top. Electrons are emitted from the source, thanks to a voltage applied across it and the drain, while the gate controls the electron flow across the cavity. – See more at: http://www.newelectronics.co.uk/electronics-technology/how-vacuum-tube-technology-is-being-deployed-at-the-nanoscale/45695/#sthash.JFnLq3uR.dpuf
    Everything is done using silicon based technology – a conventional source and drain, standard optical lithography – See more at: http://www.newelectronics.co.uk/electronics-technology/how-vacuum-tube-technology-is-being-deployed-at-the-nanoscale/45695/#sthash.JFnLq3uR.dpuf
    Everything is done using silicon based technology – a conventional source and drain, standard optical lithography – See more at: http://www.newelectronics.co.uk/electronics-technology/how-vacuum-tube-technology-is-being-deployed-at-the-nanoscale/45695/#sthash.JFnLq3uR.dpuf
  17. samicksha
    June 30, 2014

    I still remember when i was kid and first saw vaccum tube in television at my home, i use to think that this is bulb and when this will glow then only i will be able to see some something. LOL. But now most small signal vacuum tube devices have been superseded by semiconductors, although we can still find some vacuum tube like magnetron microwave ovens.

  18. Netcrawl
    June 30, 2014

    Vacuum tubes have almost disapeared from our life, they suffered a slow death, their nemesis and replacement -solid state transistors are easier to manufacture, much cheaper, last longer, much smaller, consumer less power and can be packed into microchips.  

    But recent development at NASA, shows great sign of life for vacuum tubes, the new technology from NASA could be the solution in today's challenges- a cross betwwen transistors and the vacuum tubes, its smaller and easy to produce and radiation-proof. A whole new exciting development from NASA. 

  19. Netcrawl
    June 30, 2014

    Vacuum tubes formed the main core of the computing right to the 50s and 60s, but things has changed fast, it suffered a slow death with the discovery and arrival of silicon transistor.

    But silicon has some serious weakness, its slow and susceptible to radiation. This is big deal for NASA because they need a more capable technology, able to survive a harsh environment. 

  20. Sachin
    June 30, 2014

    But silicon has some serious weakness, its slow and susceptible to radiation. This is big deal for NASA because they need a more capable technology, able to survive a harsh environment.

    @Netcrawl, I am curious to know we can improve the reliability of the existing silicon transistor by using more robust packaging techniques ?

     

  21. Sachin
    June 30, 2014

    the new technology from NASA could be the solution in today's challenges- a cross betwwen transistors and the vacuum tubes, its smaller and easy to produce

    @Netcrawl, I think one more advantage of vacuum tubes is vacuum tubes are generally more faster than transistors because electrons move more slowly in a solid than in a vacuum.

  22. Sachin
    June 30, 2014

    I still remember when i was kid and first saw vaccum tube in television at my home, i use to think that this is bulb and when this will glow then only i will be able to see some something.

    @samicksha, I agree with you. It was fun to watch vacuum tubes when it was switched on. Unfortunately LCD and LED televisions have displaces vacuum tube based televisions. I feel vacuum tube based television was more reliable compared to LCD television.

  23. Sachin
    June 30, 2014

    I think the discovery of silicon in a very abundant quanity which could cheaply be refined was the main factor in driving vaccum tubes out.

    @tzubair, Discovery of silicon definitely helped to bring the cost of the transistor down but it was not the reason why transistor replaced vacuum tubes. Vacuum tubes were bulky and it was hard to manufacture them in large quantities. Moreover vacuum tubes required very heavy voltage to operate where transistor require very low voltage to operate.

     

  24. geek
    June 30, 2014

    “Vacuum tubes were bulky and it was hard to manufacture them in large quantities. Moreover vacuum tubes required very heavy voltage to operate where transistor require very low voltage to operate.”

    @SachinEE: Yeah, there were both push and pull factors. What you mentioned was right about the vaccum tubes. They were difficult to use and a little expensive too. But companies had continued to use them because there were no other alternatives available. The discoverey of silicon immidiately made them switch.

  25. Sachin
    June 30, 2014

    But companies had continued to use them because there were no other alternatives available. The discoverey of silicon immidiately made them switch.

    @tzubair, I agree with you. Companies switched from vacuum tubes to transistors when silicon was discovered. I am sure companies would have opted for transistors even if the costs were pretty high compared to vaccum tubes because there are many advantages of transistors over vacuum tubes.

  26. samicksha
    July 1, 2014

    I agree you @Netcrawl, I read about the progress made by NASA  which could make Vaccum tubes way back into computers, their research that has put together nanoscale “vacuum channel” transistors that can switch at more than 400GHz. An article i read says …

    The thing that made vacuum tubes so hot and power hungry was the cathode. Electrons can be encouraged to cross gaps by using very high voltages, but these tend to be difficult to work with. Instead, a phenomenon called thermionic emission is used—heat a piece of metal up enough, and the thermal energy lets the electrons escape the metal. Vacuum tubes have heating elements to make the cathode hot enough to emit electrons.

    Source: http://arstechnica.com/science/2014/06/nasa-melds-vacuum-tube-tech-with-silicon-to-fill-the-terahertz-gap/

  27. Davidled
    July 3, 2014

    I guess that vacuum tubes are still used for music amplifiers, but is getting hot quickly and consumes a lot of power. In the future, I expect that there would be alternative transistor generating the same audio quality with less power consumption.  

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