Nanoscale vacuum transistors – way cool, but still not as pretty as a glowing 12AU6

The venerable 12AU6 vacuum tube, still in use by audiophiles today – I used many like this in my youth

From AAAS, news of a super tiny vacuum-tube transistor hybrid that can operate up to .46 TERAHertz (thats 460,000 megahertz or 460 gigahertz):

Return of the Vacuum Tube

by Jon Cartwright

Peer inside an antique radio and you’ll find what look like small light bulbs. They’re actually vacuum tubes—the predecessors of the silicon transistor. Vacuum tubes went the way of the dinosaurs in the 1960s, but researchers have now brought them back to life, creating a nano-sized version that’s faster and hardier than the transistor. It’s even able to survive the harsh radiation of outer space.

Developed early last century, vacuum tubes offered the first easy way to amplify electric signals. Like light bulbs, they are glass bulbs containing a heated filament. But above the filament are two additional electrodes: a metal grid and, at the top of the bulb, a positively charged plate. The heated filament emits a steady flow of electrons, which are attracted to the plate’s positive charge. The rate of electron flow can be controlled by the charge on the intervening grid, which means a small electric signal applied to the grid—say, the tiny output of a gramophone—is reproduced in the much stronger electron flow from filament to plate. As a result, the signal is amplified and can be sent to a loudspeaker.

Vacuum tubes suffered a slow death during the 1950s and ’60s thanks to the invention of the transistor—specifically, the ability to mass-produce transistors by chemically engraving, or etching, pieces of silicon. Transistors were smaller, cheaper, and longer lasting. They could also be packed into microchips to switch on and off according to different, complex inputs, paving the way for smaller, more powerful computers.

But transistors weren’t better in all respects. Electrons move more slowly in a solid than in a vacuum, which means transistors are generally slower than vacuum tubes; as a result, computing isn’t as quick as it could be. What’s more, semiconductors are susceptible to strong radiation, which can disrupt the atomic structure of the silicon such that the charges no longer move properly. That’s a big problem for the military and NASA, which need their technology to work in radiation-harsh environments such as outer space.

The new device is a cross between today’s transistors and the vacuum tubes of yesteryear. It’s small and easily manufactured, but also fast and radiation-proof. Meyyappan, who co-developed the “nano vacuum tube,” says it is created by etching a tiny cavity in phosphorous-doped silicon. The cavity is bordered by three electrodes: a source, a gate, and a drain. The source and drain are separated by just 150 nanometers, while the gate sits 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. In their paper published online today in Applied Physics Letters,

Full story here at AAAS, here’s my concept pictorial image (may not be fully accurate – I don’t have access to their paper diagrams) of what it looks like compared to the traditional vacuum tube (triode) based on what I’ve been able to find on the design:

The paper from AIP:

Vacuum nanoelectronics: Back to the future?—Gate insulated nanoscale vacuum channel transistor

Jin-Woo Han1, Jae Sub Oh2, and M. Meyyappan1

1Center for Nanotechnology, NASA Ames Research Center, Moffett Field, California 94035, USA
2National Nanofab Center, 335 Gwahangno, Yuseong-gu, Daejeon 305-806, Korea

(Received 24 February 2012; accepted 22 April 2012; published online 23 May 2012)

  • A gate-insulated vacuum channel transistor was fabricated using standard silicon semiconductor processing. Advantages of the vacuum tube and transistor are combined here by nanofabrication. A photoresist ashing technique enabled the nanogap separation of the emitter and the collector, thus allowing operation at less than 10 V. A cut-off frequency fT of 0.46 THz has been obtained. The nanoscale vacuum tubes can provide high frequency/power output while satisfying the metrics of lightness, cost, lifetime, and stability at harsh conditions, and the operation voltage can be decreased comparable to the modern semiconductor devices.
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120 thoughts on “Nanoscale vacuum transistors – way cool, but still not as pretty as a glowing 12AU6

  1. Wow, very interesting. AS I recall, those old tubes were resistant to EMP damage as well.

  2. Very interesting how we can make old stuff better rather than just replacing it.

    I remember my old valve amp very well. I suspect my neighbors at the time still do too, and they lived about 500m away!

  3. Vacuum Tubes have always been superior to transistors at RF.
    Check any TV or Radio station transmitter.

  4. Tubes were naturally suited to analog uses because of their response curve. I wonder if this technology will finally make super-complex analog computers … i.e. true neural equivalents … more feasible?

  5. EMP resistive, Gama resistive, and need little shielding in space..

    great achievement… and one that will push out telecommunications abilities to great lengths by reducing weight needed in space for them to operate…

  6. 460GHz, amazing, Bye-Bye travelling wave tubes. Not sure the diagram is quite accurate. Of course, first you need a vacuum and are able to keep it.

  7. As an avid ham radio operator – I collect 1950’s era tube transmitters and receivers. I have always loved the warm glow of vacuum tubes. I use a transceiver that has 3 vacuum tubes in it daily. Tubes are able to take abuse that solid state devices cannot – plus they have made a huge ‘comeback’ with audiophiles because they have a much better ‘sound’. Don’t get me wrong, I deal with digital devices on a daily basis & they are indeed wonderful, but if you want a device that can literally take some serious abuse and ‘keep on ticking’ – vacuum tubes win every time. Great stuff!

  8. BTW I remember meddling with my valve radios and amplifiers.

    BBTW There is a company in the UK named E2V which makes blazingly fast (and yes, they are also hot) analog-to-digital converters. They used to be The English Electric Valve Company. (Ed Note: The Brits call a vacuum tube a “valve”).

    KT66 anyone?

  9. At the first glance, this appears to be a solution looking for a problem. The speed of integrated circuits is determined mostly by delays in “wires”, not by delays in individual transistors.It could become important in true 3-dimensional circuits; the vacuum should generate much less heat.

  10. I think the structure may be more like a vacuum between source and drain and the metal gate physially on top of the vacuum space between the two, insulated by SO2.

  11. The concept is not new, the basic idea was being bandied around physics depts here as early as the late 1960’s. The essential problems are current density, low, dissipation of waste heat, and of course engineering the blighters to close enough tolerances.to operate. I forget the order of voltage gradient you need for what were then called cold cathode valves, and I am not going to look up my notes, but I seem to remember it is really rather high which causes other engineering problems.

    But of course the truth is at that time the transistor had become incredibly cheap, the integrated circuit was starting to appear and nobody was much interested. There was a revival in the mid eighties with much better field computation techniques but nothing came of it, the engineering was still too difficult.

    Time will tell whether these new fabrication techniques work well enough to produce a commercially viable product.

    Still I have a certain nostalgia for glass bottles with fires in, UK and US designations were not the same, but my particular favourite was the mighty KT 66.

    Kindest Regards

  12. A NEW TOY! YAAAAAAAAY!

    I suspect it will be a few years, but I look forward to seeing them in action.

    One wonders if they will be able to replicate the more subjective differences in things like Amp output frequencies that cause people to keep building tube amps, and if they will actually be EMP-hard or if that is too dependent on everything *else* in a circuit.

  13. I just never know what to expect on WUWT. It will surely be the cutting edge of science and/or technology.

    Thanks Anthony.

  14. A little background (and more info) on “Vacuum Transistors”, as they have been tried before (processing technology has advanced a lot since then, however, perhaps making this practical now):

    http://tikalon.com/blog/blog.php?article=2012/vacuum_transistor

    In 1973, Charles Spindt and his colleagues at the Stanford Research Institute (Menlo Park, California) fabricated miniaturized vacuum tubes by a planar process. These vacuum tubes solved two vacuum tube problems. They worked at a lower voltage, and they didn’t need a heater for thermionic emission.

    The “Spindt” cathodes generated electrons by field emission, the idea that electric fields are concentrated at sharp points. This idea was improved in a recent device that used diamond as the field emitter. Diamond works well in this application, since it has an extremely low work function, so it will produce field emission electron beams at low voltage.

    A different vacuum transistor has been designed by an international team of scientists from NASA’s Ames Research Center (Moffett Field, CA), and the National Nanofab Center, Daejeon, Korea. This transistor, details of which are soon to be published in Applied Physics Letters, uses a vertical architecture like the geometry of a standard MOSFET to mitigate these problems (see figure). The device characteristics of this so-called “vacuum channel transistor” are similar to those of a field effect transistor transistor.

    .

  15. Cool.

    That’ll open up more radio spectrum. When do we get to use 460GHz ham band? :-)

  16. Bill Marsh says:
    May 24, 2012 at 4:04 pm

    Wow, very interesting. AS I recall, those old tubes were resistant to EMP damage as well.

    Which made the Soviet systems much more survivable than US systems since they had mostly vacuum tube systems long after we had switched to transistors. Audiophiles that I knew also prized “Red” tubes since they had really refined their manufacturing techniques.

  17. Steve in SC says May 24, 2012 at 4:27 pm

    Vacuum Tubes have always been superior to transistors at RF.
    Check any TV or Radio station transmitter.

    Not so much anymore; all your AMs are now solid state (saves TONS on cost of electricity), and everything except the PA stage in your UHF TV transmitters are tube/thermionic-emission devices …

    As an example, take a look at the AM broadcast transmitters in the 3DX Transmitter Family from Harris, all solid-state with output power levels of 25, 50 and 100 kW (Kilowatts) and HD (digital) capable out of the ‘box':

    Overview – http://www.broadcast.harris.com/media/3DXTransmitterFamily_25-20445.pdf

    Datasheet – http://www.broadcast.harris.com/media/3DXAMTransmitterFamily_25-20959.pdf

    Note that overall “AC” (input power conversion to RF) efficiencies are better than 85%.

    .

  18. Operation up to 460 GHz is mind boggling, but there will be the same (or greater) power limitations as with all solid state devices. They are only around 50 % efficient, so a lot of heat has to be conducted away with heat sinks. High power devices are therefore impractical. I use a homebrew pair of 4-400s for a KW PEP out on 3.8 MHz and some other bands. I use a pair of 3CX800A7’s for legal 1500 watts out on 144 MHz and 432 MHz. Tubes are a little more efficient, ~ 65%, and not going to be replaced any time soon for high power applications. With low power, even 5 watts, you can be heard all over the world. With high power you can do things that you can not do with low power- like hear your echoes off the moon! There is very little ham radio operation above 10 GHZ. With the described device we can, I suspect, investigate the frequency spectrum 142-149 GHz, 241- 250 GHz, and everything above 300 GHz, all of which has been allocated by the FCC to ham radio. We pioneered the exploration and use of much lower frequencies in the 20th century. Maybe we can again!

  19. WOW, this is an interesting one, but it will need more research to see how best to use it. Like many other technologies, I’m sure this will do well in some areas and other technology will do well in other areas.

  20. So now we have the possibility of large scale integration of analog circuits? I’m thinking, emergent properties. Uh oh. Skynet.

  21. I remember rebuilding a 1950s radio designed around vacuum tubes in the early 1980s, the local electric still had spare ones in stock. The whole thing was bigger than a microwave oven and made out of wood.

  22. BarryW says May 24, 2012 at 5:05 pm


    Which made the Soviet systems much more survivable than US systems since they had mostly vacuum tube systems long after we had switched to transistors.

    But never mind the reliability of a vacuum-tube based radio or control system in a high-vibration and dynamic environment like a jet fighter aircraft (where the BIG advantage in “solid-state” shows up) eh?

    Full disclosure: Our project in the day would test our ‘black boxes’ for that environment (fighter aircraft platform); some of the testing included a repeated sharp impact force called ‘gunfire vibration’ (simulated the impact force that cannon fire produced on the ‘black boxes’ through the A/C frame) and of course, ‘sine vibe’ (vibration) over a wide frequency range …

    .

  23. The problem with vacuum tubes is vacuum. Glass envelopes can be pumped down to ten to the minus six mm of mercury, heated to outgass the glass than fire a small pelet of gettering material to keep absorbing any gas molecules. This works for quite a while. As anybody who has used vacuum tubes knows. I don’t hold out much hope that this device will maintain vacuum for any lenth of time.

  24. I have just read the article. There is no vacuum . Just air. They are hoping that the small distance reduces the chance of an electron hitting an atom. It depend how many atoms there are.

  25. Billy Liar says May 24, 2012 at 5:11 pm

    I like these small atomic clocks too:

    Nice; but you’ll have to drive it (with a 1PPS pulse) with something like this for use in anything except a free-standing* application:

    http://www.semiconductorstore.com/cart/pc/viewPrd.asp?idproduct=41718#Description_sec

    .

    * An application not synchronized time-wise with a larger external network, e.g. in WiMAX or other TDD (Time Division Duplex) GPS 1PPS time-synchronized system.

    .

  26. The Vacuum Tube has never really died. I worked with niche communication equipment that was almost all VTs and relays (except one huge FET) during the final days of the cold war. VT technology has continued to advance under the radar (umm inside the radar). This is just the latest chapter in a very exciting story. I ought to dig up and dust off a paper I wrote in the mid 90’s on the history of the Vacuum Tube in relation to the Bi-polar Transistor and how it compared to the history of European bronze metallurgy in relation to iron metallurgy.

  27. Oh, Anthony, you’ve done it again – stirring up all us old geezers. I had my father’s Hallicrafters shortwave radio. The power supply rectifier was a tube 80, all the others had the new naming convention, and tube 80 became 5U4 (5 volt filament, “U” model ID, 4 elements).

    But transistors weren’t better in all respects. Electrons move more slowly in a solid than in a vacuum, which means transistors are generally slower than vacuum tubes; as a result, computing isn’t as quick as it could be.

    Given today’s tech, with a billion transistors on a 1 cm^2 chip, signal delay in a model made from vacuum tube tech would be a major impediment. Not to mention the power required to heat the cathodes. At least tube tech would have shrunk, so maybe just 1 W per cathode, so a gigawatt for the CPU.

    When I was 12 or so, I picked up an English language broadcast on Radio Moscow one day. I learned more about propaganda in 30 seconds than I did in any classroom lesson!

  28. For an analog computer you don’t need vacuum tubes. Just operational amplifiers. Transistors can do that very well. In addition you can emulate an analog computer using a digital computer. No, the problem is scale and programming. Analog computers are programmed differently.

  29. George Steiner says May 24, 2012 at 5:42 pm

    The problem with vacuum tubes is vacuum. Glass envelopes can be pumped down to ten to the minus six mm of mercury, heated to outgass the glass than fire a small pelet of gettering material to keep absorbing any gas molecules. This works for quite a while. As anybody who has used vacuum tubes knows. I don’t hold out much hope that this device will maintain vacuum for any lenth of time.

    George, Dev Gualtieri, who has had an advance look at the paper (courtesy of one the upcoming paper’s authors) says at the referenced link above the following regarding the ‘vacuum’ aspect:

    Not only that, but a vacuum is not required. The channel dimension is less than the mean free path of electrons in air, and the low operating voltages are below the ionization potential for molecules in air. High frequency operation is assured, since the velocity of electrons in vacuum is 3 x 10^10 cm/sec. The electron velocity in semiconductors is only as high as 5 x 10^7 cm/sec.

    .

  30. Remember how long it took the radio or TV to warm up and function? How about the circuit breaker on the back of the set and horizontal and vertical adjustments?

    I’m still waiting for a good solid state replacement for photomultiplier tubes.

  31. I enjoy the plasma burst from the quartet of 6L6’s in my Fender Twin Reverb…as I flip the standby switch. The smell of phenol in the evening…..mmmmmmmm! Moments later, the fuzzing and fritzing of the preamp-stage 12AX7’s, slightly microphonic. Yep!

  32. hmm. It will be interesting to see what the transfer curves look like …. definitely a new toy!

  33. Doug Allen says May 24, 2012 at 5:34 pm
    ..
    I use a pair of 3CX800A7′s for legal 1500 watts out on 144 MHz and 432 MHz. Tubes are a little more efficient, ~ 65%, and not going to be replaced any time soon for high power applications

    You guys keep saying that, and yet commercial products put out by the likes such as Harris continue to supersede that oft-repeated “Solid-State Power Amplifiers are Limited” saw.

    Okay, maybe for ‘ham’ apps for awhile, but in the commercial world they have entered the 21st century already. An example: Harris 16 kW SS Analog VHF TV transmitter. The liquid cooling they refer to is for the solid-state PAs (and not a PA tube with an external anode!) The 16 kW transmitter in conjunction with a modest 10 dB gain transmit antenna array yields a quite respectable 160 kW ERP signal!

    .

  34. 12AU6’s are so… ’60s.

    Real vacuum tubes had a shapely envelope outlines and Bakelite bases, the filament WAS the cathode and they had a really cool electrode caps at the top of the tube. Real vacuum tubes had 3 or less characters for a part number like ’30’ or ‘1A6′ or 6Y5.

  35. Alec Rawls says:
    May 24, 2012 at 5:40 pm
    “So now we have the possibility of large scale integration of analog circuits? I’m thinking, emergent properties. Uh oh. Skynet.”

    There’s not really a qualitative difference between analog and digital computing. Think genetic programming in digital computers; if you want your computer to come up with some surprises, use that.
    You might get a qualitative difference if quantum entanglement works the way it’s always advertised. There’s allegedly already a quantum system simulator with 320 qubits. Works with entangled spins.

    http://www.nature.com/nature/journal/v484/n7395/full/nature10981.html

    And Prof. Gerlich has managed to entangle a whole 340 atom hydrocarbon molecule.

    http://www.slideshare.net/lewisglarsen/lattice-energy-llcnickelseed-lenr-networksapril-20-2011

    What you would get with working quantum computing systems is an Oracle; a system that can solve an NP-complete problem in deterministic time – in other words, in a fixed number of steps deliver the optimal solution for a problem that has an exponentially exploding number of possible solutions. At the moment, the best algorithms can only approximate the solution even when running for a long time.

  36. Steve in SC wrote;

    “Vacuum Tubes have always been superior to transistors at RF.
    Check any TV or Radio station transmitter.”

    Careful there, the term ”superior” needs to be carefully applied in this case. A transistor can do everything a vacuum tube can do, and just as well. The simple fact that vacuum tubes are still prevalent in high power Radio Transmitters is more a market force effect than a technology effect. The number of “really high” power radio transmitters (10’s-100’s of kiloWatts) is relatively small (100’s-1000’s). Thus, semiconductor manufacturers have never bothered to go after that market. The tube manufacturers have the processes and plants inplace to make the few (100’s) of replacement tubes necessary each year.

    On the other hand, the market size for high power switching semiconductors (SCR’s, TRIACS, etc.) is very large (10,000s-millions) everything from light dimmers, variable speed motor drives, CFL lamp ballasts all the way up to railroad locomotives are just chock full of “high” power (1000’s-100000’s of kilowatts) semiconductor switches.

    And at the lower power levels, (1-100mW) we have every cell phone (100’s of millions) which have lots of cheap transistors operating everyday in the GigaHertz range.

    While this is an “interesting” development, the transistors in use today are on the 1 nanometer scale, this hybrid semiconductor vacuum tube is still in the 100 nanometer scale, a factor of 100x larger. So at this point in time they are not faster or smaller, although they might be in the future.

    Regarding radiation “hardness”, that’s more of a “how small is the device” concern. If they shrink the contacts (implemented in semiconductor materials) to make the total device smaller, then the risk that radiation will “blow out” the device may be the same. So we have a device that is larger overall and may be “harder” from a radiation standpoint versus a smaller device. BUT you can just put some more radiation shielding around the smaller device. It maybe a total wash. You can just put a smaller device inside a thicker steel “can” and get the same level of radiation “hardness” in the same volume.

    Cheers, Kevin (MSEE, working in the space qualified electronics business)

  37. I still run several tube radios from the 30’s and 40’s on a regular basis including a 1935 Hellicrafter’s Super Skyrider receiver. The sound or static, as the case may be, from the old tube receivers was and still is special.

  38. KevinK says on May 24, 2012 at 6:53 pm

    … The simple fact that vacuum tubes are still prevalent in high power Radio Transmitters is more a market force …

    As detailed above, Kevin, not so much these days in contemporary broadcast ‘products’ today; one finds some prevalence of high-powered tubes in use in the cheaper shortwave operations though (by some of the ‘religious broadcasters’ e.g. WWCR with facilities for hire; one can literally buy airtime and air one’s own program for a reasonable two-figure fee per hour for instance) since the acquisition cost of a used/surplussed 200 kW transmitter was low and the cost for electricity is paid for in the per-hour airtime fees that are charged …

    .

  39. KevinK says:
    May 24, 2012 at 6:53 pm

    Steve in SC wrote;

    Regarding radiation “hardness”, that’s more of a “how small is the device” concern. If they shrink the contacts (implemented in semiconductor materials) to make the total device smaller, then the risk that radiation will “blow out” the device may be the same. So we have a device that is larger overall and may be “harder” from a radiation standpoint versus a smaller device. BUT you can just put some more radiation shielding around the smaller device. It maybe a total wash. You can just put a smaller device inside a thicker steel “can” and get the same level of radiation “hardness” in the same volume.
    ————————————-
    Aside from the mechanical robustness problems of tubes they are superior from both a overvoltage and a radiation perspective. Lots of old time plasma physicists try to keep around old tube powered scopes because that accidental 10kV zap is probably survivable with that old scope whereas that nice new 30GHz Lecroy scope just became a pricey boat anchor. Can you protect these devices? Sure, but the tube devices are inherently more robust. Short of melting an electrode or sputtering material away there’s no channel to be permanently damaged as it’s a vacuum.

    Similarly, tubes are intrinsically rad hard compared to any semiconductor. They’re not really susceptible to upset due to energetic particles passing through which is going to be the practical problem you have to deal with. Again, you can shield semiconductors to provide rad hard and you can play games like SOI and oversizing channels and such to make them more robust, but a tube is generally immune to such problems not counting truly massive energy bursts capable of melting components.

  40. I’m running matched 12ax7’s and 6550’s in my Bud Wyatt (of Sheffield Lab fame) modified Mac 60’s. They’re big, and fat, and warm… and soothing to listen to, with shimmering highs and in-your-face mids. Love ‘em.

    …..Mariss…. pm fizzissist at CNC, I’ll tell ya more!

  41. KevinK
    May 24, 2012 at 6:53 pm

    Cheers, Kevin (MSEE, working in the space qualified electronics business)
    ###

    Cool, I also worked in the field also, starting as an engineering tech working up to a software architect. On top of that, after the blood letting of the late 80’s early 90’s I ended up working for a division of my company that was designing those revolutionary semiconductor devices that are now used in the high-powered applications you mentioned.

    What many don’t realize is that semiconductor devices for space and defense applications use an array of techniques that yield them rather immune to the effects of radiation and to EMP. Testing showed that the semiconductors we were producing were just as hard as those Soviet VT’s that other posters mentioned.

    Regardless, I still think Vacuum Tubes are cool :)

  42. KOOL, and very important (once upon a time, a long time ago, I designed some vacuum tube based aps.).

  43. I worked navigation radar in the USAF in the 80s and early 90’s and we didn’t replace all our old tube sets until right before I left the field for other endeavors. The first troubleshooting step was always to take the covers off, flip off the lights and look for the nonglowing tube. Worked about 90% of the time. Then the hard part came…removing the tube without touching one of the high voltage capacitor arrays. They bite!!! (The technical manual said to discharge them first, but that was for wimps.)

  44. Even my ground radar contemporaries had solid state up to the final power stage, then most of them had some combination of travelling wave tubes for the final power output stage.

    For the high GHz devices we always had trouble because all the solid state stuff was very exotic and expensive and the first thing we did in any receiver was knock the frequency down to a reasonable intermediate frequency that didn’t get into the nonlinear range of the transistors since sometimes the return frequency offset was the important bit of information we were trying to process. In the process we lost some phase information that could have been used to improve resolution. If you have receiver parts that can operate at the received RF, you don’t lose anything in translation, and might be able to do some pretty nifty phase and edge comparisons to separate closely spaced targets or even get single or few pulse imaging techniques. It could open up many things.

  45. The missile I repaired in the Army, the Hawk Misslie had one transistor and boat loads of electron tubes, mostly 5703, 5704 and 5707s. The radars were basically all electron tubes too, they used a 4CX1000 as a voltage regulator!

  46. curious george says:
    May 24, 2012 at 4:36 pm

    At the first glance, this appears to be a solution looking for a problem. The speed of integrated circuits is determined mostly by delays in “wires”

    Well, george, with the speed of light being about 1 ns per foot (1 x 10^-9 ns/foot), the propagation delay time for a typical ‘gate’ implemented in the following device technologies results in these propagation delay times:

    a) ECL = 2ns

    b) TTL = 1.5 – 33ns depending on type: conventional TTL ~ 9ns, Advanced Schottky ~1.5ns

    c) RTL = 25ns

    d) CMOS = 5 – 20ns depending on type: conventional CMOS, TTL pin compatible CMOS, high speed TPC CMOS or TTL compatible CMOS

    So, we still have various ‘delays’ far exceeding a foot’s worth of wiring in most ‘gates’ (whose dimension we will stipulate is on the order of half an inch). Now, a gate is comprised of between 1 and 5 internal stages, with CMOS being probably the simplest for an inverter ‘gate’ at 1 stage. Fewer internal stages with faster switching time transistor reduces the overall ‘delay propagation time’ in a ‘gate’ then.

    .

  47. Some of these old valves were veritable works of art – true sculptures. My brother still uses an old valve wireless.

  48. Tsk Tsk says;

    “Similarly, tubes are intrinsically rad hard compared to any semiconductor.”

    Yes, BUT, you need to consider the VOLUME, yes they are more intrinsically rad hard, but they are BIGGER, so I can stuff more stuff that is less RAD HARD in a smaller “shielded can” and still get the same performance out of the system. This is what’s called a “trade study” in the industry, do I use a radiation hard device with no shielding, or do I use a “less” radiation hard device with some shielding ??? This is why you can make big bucks in the aerospace industry.

    Boy, I never thought I could start a “RADIATION HARDNESS” debate on the “WUWT” website, I work with a Senior IEEE Fellow that has DEDICATED 30 plus years of his career to this topic, I consult him when I need advice on what SHOULD work out there in space. A whole bunch of those satellite images that are enjoyed by us have all been been produced by systems that he helped certify as “space ready”.

    Man, I bet I could talk to 1,000,000 folks on the street and I could not find more than one who even knows what the heck “radiation hardness” even means……….

    Cheers, Kevin

  49. Once upon a time far away it was interesting to listen to the SW overseas broadcasts from the UK and the USA. We would sit many evenings in a darkened room intently listening to the radio as it faded in and out. The radio tubes would glow in the dark like little coals in the fire place and provide some warmth. The tubes seemed magical in that they could bring news from far away. Winston Churchill and Harry Truman would give encouraging speeches.

  50. My favorite tube was the EF50 but when transistors came along vacuum tubes were supplanted by solid state devices for small signal applications.

    Vacuum tubes still dominate at high power. The best way to provide 50 kW CW at 178 MHz for a 1 GeV storage ring (Duke University Free Electron Laser, 1995) was the 4CX100000 tetrode. When an upgrade to 200 kW RF output was needed (2005), larger tetrodes made in Russia were the obvious choice.

    Klystrons vacuum tubes with over 50 MW of pulsed RF output are available for L-band (~1.5 GHz), S-band (~2.8 Ghz) and X-band (~11 GHz). You can even get 2 MW CW at 350 MHz.

    When it comes to fast switching, the krytron (radio-active cold cathode) is the best option when you need a few Mega-Watts with sub-nanosecond jitter times. While my work had nothing to do with weapons technology it was really difficult to get supplies of these devices owing to their applications in Plutonium based weapons.

    It looks as if vacuum tube technology will have application in small signal high bandwidth devices, once again. Now what did I do with my lecture notes from A.H.W. Beck’s classes?

  51. Mike Bromley the Canucklehead says:
    May 24, 2012 at 6:04 pm
    “I enjoy the plasma burst from the quartet of 6L6′s in my Fender Twin Reverb…as I flip the standby switch. The smell of phenol in the evening…..mmmmmmmm! Moments later, the fuzzing and fritzing of the preamp-stage 12AX7′s, slightly microphonic. Yep!”

    “Right on! I have solid state Pevey’s and Marshall’s, and nothing screams like my ’64 Fender Super Reverb. And no complement is more satisfying than have someone aproach and say, “What the hell have you got there.” Yes – there are somethings that can’t be replaced, at least on earth.

  52. As an AGW skeptic who happened to make and sell tungsten light bulb based vacuum-tube-look “Tube Lamps” in danger of being banned I had to be careful not to be biased indeed but extra motivation was certainly there to get the word out, online. The way the eye works, exposed filaments that glow like vacuum tubes cause psychological pain due to glare, in that the eye cannot adjust the iris down to protect it from the glare. So! I learned to stick with designs that placed several exposed bulbs next to each other, providing a large enough area on the retina for the eye to get the message that it was O.K. to close the iris a bit since there was enough light to still see the room safely. My WWII veteran father who repaired aircraft instruments in Alaska used to try to teach me vacuum tube physics on paper in the era of the transistor. The take home message was that the inner design of the tubes themselves involved mostly hocus pocus! The physics was the simple part.

  53. Mike Bromley the Canucklehead says:
    Paul Marko says:

    Exactly- My Mesa Boogie sounds better than any solid state on the market. 2x12AX7 pre-amps RULE!

  54. Does this mean the Met Office will be able to work out how much hotter it’s going to get faster than they do now?
    James Bull

  55. “The nanoscale vacuum tubes can provide high frequency/power output while satisfying the metrics of lightness, cost, lifetime, and stability at harsh conditions, and the operation voltage can be decreased comparable to the modern semiconductor devices.”

    High frequency?!?!?! Tesla would approve.

  56. Nano vacuum tubes could be useful in digital x-ray cameras where radiation damage is a problem.

  57. “””””

    Marian says:

    May 24, 2012 at 5:03 pm

    Cool.

    That’ll open up more radio spectrum. When do we get to use 460GHz ham band? :-) “””””

    Why would you want to waste your time Hammimng in those “dc” bands below 460 GHz. A ham former colleague of mine already recorded a communication with another ham on some field day exercise, back around 1990, at a carrier frequency of about 458 THz; and I myself demonstrated voice and music transmission over exactly the same frequency, back in 1967. My transmission was quite low tech; all done inside the lab to show I had nothing up my sleeve; but the 1990 exercise was quite high tech, and employed a silicon CMOS receiver chip, that I designed. The CMOS chip itself was quite small, only 500 x 600 microns; most of which, was the three connection pads. (but still a very primitive 800 nm technology, compared to today’s 22 nm chips). That transmission was across the whole of SF Bay, and that was far from max range at 458 THz.

    The transmitter chip was actually an off the shelf transmitter. Today, you can get over 700 THz chips.

  58. And as distinct from the Gore/Hanson CO2 propaganda, vacuum tubes really were susceptible to feedback initiated “tipping points”. Maybe we should be careful before we go too far down this track?

  59. There’s a lunatic fringe of so-called hi-fi nutz, who still believe that valve amplifiers sound better than transistor ones; the sound is “warmer” they claim. Well I never ever heard, a “warm” symphony orchestra, and the 4-manual pipe organ I used to play in Palo Alto never was warm. I know valve amplifiers can be warm; I burned my nuckles many times, on those 807s in my early Williamson Amplifiers. The distortion in even the best speakers, is orders of magnitude higher, than a well designed solid state hi-fi amp; so there’s no way a valve amp could be lower in distortion or noise. Yes they sound different; it’s called “hiss” and is much like tonitis. You can go into Fry’s and watch all the yuppies going gaga over some “matchbox Bose” system; but how do you tell if it sounds good if all they play on it is that Canadian shrieker; no offense to Canadians; but I would much rather listen to the amplified sounds of a fine Swiss mechanical watch with sand in the gears.

  60. Not a new idea. 30 years’ ago I was developing nano-engineered cold cathodes ad went to a field emission conference in Paris.

    The technology lives on as cold cathodes in the miniature florescent lamps.

  61. Nice! But as another old-timer who remembers firebottles fondly (including most of the type numbers mentioned here!), I’m holding out for a glass top on the chip, so that when you overload the thing you can see the pretty purple plasma light show!

    The biggest “bottles” I ever had I donated to the UK’s National Valve Museum. Look ‘em up – type MZ2-200. Hand-built beauty from another age.

  62. The death of the vacuum tube described in the article in the 1960s is premature. In 1980 I still had callouses on the pads of my right thumb, forefinger, and middle finger from pulling hot vacuum tubes out of television sets. Transistorized televisions (except the CRT of course) didn’t go on the market until the early 1970’s and vacuum tube models were still be manufactured in the middle 1970’s. Typical service life of a television from that period was 15-20 years. The picture tube would be pretty faded by that time and you’d almost certainly have few tubes replaced and the mechanical contacts on the channel changer cleaned with a solvent once or twice but otherwise they were built like tanks. Vacuum tubes persisted in the form of picture tubes to probably the year 2000. My last set with a picture tube died this year – a 35″ Sony that was about 14 years old. It was actually still working but I got a new larger flat screen and gave away the 200 pound dinosaur and it didn’t survive the trip in the back of a pickup truck to its new home.

  63. gallopingcamel says:
    May 24, 2012 at 9:01 pm

    Vacuum tubes still dominate at high power. The best way to provide 50 kW CW at 178 MHz for a 1 GeV storage ring (Duke University Free Electron Laser, 1995) was the 4CX100000 tetrode. When an upgrade to 200 kW RF output was needed (2005), larger tetrodes made in Russia were the obvious choice.

    Klystrons vacuum tubes with over 50 MW of pulsed RF output are available for L-band (~1.5 GHz), S-band (~2.8 Ghz) and X-band (~11 GHz). You can even get 2 MW CW at 350 MHz.

    ————————————————–

    I was a weather- radar technician in the mid-1970s. As I recall the unit I was qualified on used a klystron for the local oscillator and a magnetron for the final stage.

  64. Ask any electric guitar player: valve (tube) amplifiers just sound better. That’s why they never did go quite the way of the dinosaurs – there remained a small group of dedicated trolls living in caves who have, these past forty years, been hand-carving valves out of granite for the benefit of us old rock ‘n’ rollers. Marshall, Orange – I’m a Laney man myself – still make proper amplifiers.

  65. My old high school electronics instructor was right. Transistors, and integrated circuits are just a fad after all, and having to construct a two tube superheterodyne AM receiver when every other high school kid in the country was playing around with op amps, and 555 timers, is now apparently going to pay off for me. Right?

  66. George E. Smith, a very large portion of professional (studio grade) recording equipment still contains at least one vacuum tube. I’m sitting right beside both a microphone and a pre-amp that both have tubes, and they’re not old. There IS a warmer sound, and in truth there’s no good reason they couldn’t simulate the sound with solid state. The reality is the solid state guys get so obsessed with the accuracy of signal that they forget the vagaries of art.

    One of the more popular plug-ins for digital recording software was the tube-sound.

    The Abbey Road plug ins simulate the beautiful and highly inaccurate tube-driven compressors of the 60s.

    Warmth is subjective. I can recognize it but I can’t describe it. My own voice through tube equipment (or a competent simulation) sounds better to my own ears than when it’s as accurate and precise as possible.

    The standard “fuzz” effect for electric guitar will always be most pleasing when it’s an overdriven tube… and whether you like that sound or not (I know my parents hate it, like nails on a chalkboard to them), it’s a warmth that still hasn’t been accurately reproduced with solid state.

  67. AJB says:
    May 24, 2012 at 5:25 pm

    Neat!
    BTW, valve audio amps are still being produced in the UK.

    What do you mean “in the UK?” They’re still being produced all over the world, and never went away. My most recent valve amp was Chinese, like everything else these days.

  68. Steve in SC says: May 24, 2012 at 4:27 pm “Vacuum Tubes have always been superior to transistors at RF. Check any TV or Radio station transmitter.”

    Too much of a sweeping statement. It depends what you want to do at RF. A fixed ground installation where you have plenty of space and lots of power available might favour electron tubes. However, a sophisticated mobile military air defence system with a phased array radar would be a different story.

  69. Vacuum tubes didn’t “go the way of the dinosaur”; they continue to be used in applications where they are better than transistors, like high-power transmitters. Also transistors are definitely not “generally slower than vacuum tubes”, since transistors are generally much smaller (until now apparently) which makes them faster.

  70. Steve in SC says:
    May 24, 2012 at 4:27 pm

    Vacuum Tubes have always been superior to transistors at RF.
    Check any TV or Radio station transmitter.

    You are correct. In fact, a company in the Czech Republic is still making vacuum tubes used for superior sound reproduction. Here’s a How It’s Made rendition of that (mostly hand-made) process:

    Wish I could afford a high-end system like that.

  71. Way back when I was working in electronics I found signal to noise ratio from a front end valve amplifier much better than a transistorised front end. As far as the final audio amp is concerned, a transistor push-pull output was just as good as a valve, especially as you could power it with a car battery.

  72. More than 50 years ago I used to design and build transmitters, receivers and amplifiers with vacuum tubes or valves. I bought my first transistor more than 50 years ago. My old homemade 1500W linear amplifier for 3.5 to 30 MHz uses a pair of 813,s operating at 3000 volts 0.5 ampere peak. I got my ham license in 1964…

    Tempus fugit…
    73
    Agust, TF3 OM

  73. How did this get published?
    It doesn’t give the obligatory acknowledgement to the dangers of climatechange.

  74. One minor correction. Transistors are slower than vacuum tubes of the same size. But since transistors could be made millions of times smaller than a vacuum tube, they ended up being faster. I’ll watch this development of micro-vacuum tubes with interest.

    Another advantage to transistors was they used much less power and could operate at lower voltanges.

  75. DirkH says:
    May 24, 2012 at 6:40 pm

    Alec Rawls says:
    May 24, 2012 at 5:40 pm

    “So now we have the possibility of large scale integration of analog circuits? I’m thinking, emergent properties. Uh oh. Skynet.”

    There’s not really a qualitative difference between analog and digital computing.

    Actually…

    Well it depends how you set up your computer. Digital computers use voltages to determine whether something is 1 or 0 and they tend to fall within ranges of the ideal on or off voltage state, so in that sense they’re not qualitatively dissimilar from a computer built from discrete analogue components, if that computer also operated in binary. The early computers were huge valve-built monstrosities and had no emergent properties.

    However, part of the implication of “analogue computing” is the idea that it doesn’t operate in binary, using discrete voltage levels to determine on or off, but instead operates along a continuum of states. It would be difficult to impossible to replicate this using current digital hardware (though it could be simulated in any turing-complete device but, as anee fule kno, simulations are always missing something and any digital simulation of an analogue system would be quantised by its nature, thus introducing subtle “error” in how its components interact).

    In analogue computing the emergence would likely come as a result of propagating waveforms within the circuits of the computer interacting in unpredictable ways. It’s been speculated that human sentience is an emergent property of the pattern-recognising aspect of the human brain turning inwards to recognise patterns within itself so it seems likely to me that any non-digital device with sufficient capacity would spontaneously generate emergent phenomena, which might be as comparatively simple as the motions of a flock of birds or might amount to a rudimentary intelligence.

    I’m not sure quantum computing would produce that. It is an incredible concept, but it is still essentially operating within a digital paradigm of “on” and “off”, “true” and “false”, it’s just skipping a few steps to get to the answer, chucking out the occasional “maybe” that eventually resolves to either “true” or “false”.

  76. I love the ruddy glow from the graphite plates of a pair of 813s. And they can keep the ham shack nice and toasty in the winter time. At RPI’s ham station W2SZ they had a single HV supply for all of the HF amps. It was in a caged room using a pole peg feeding 866 mercury rectifiers. Quite colorful.

    Tom Bakewell KE7AVZ ex WB6HLR

  77. The IGFET has been around for a long time. No breakthrough here just evolution as with any other semiconductor device. I remember the days when Ico was the bane of all transistor circuit designers.
    Tube lovers:the transistor is here to stay. Get over it.

  78. And don’t forget printed circuits are susceptible to static electricity. Once zapped their reliability goes out the window.

  79. I’ve invented a vacuum tube filled with CO2. It operates at infra red and dosen’t need a heater.
    It warms up due to back radiation which also produces the amplification.

  80. Ok, just one more note about vacuum tubes;

    Back in WWII (the BIG one per Archie Bunker) the USA developed (Lincoln Labs, MIT) a far superior fuse for the shells used in our big Army guns and Navy AA guns. This was a radar proximity fuse that sensed the approach of metallic or dense materials (i.e. Japanese Planes or the ground that German troops were standing on). Once the proximity to target was sensed the shell exploded.

    Our enemies (friends now) only had time delay fuses and they actually adjusted them before firing for the altitude they thought our planes were at.

    Our fuses were vastly superior, once we introduced them our rate of hits on the planes attacking our Navy went from a plane every few ten thousand shells to every hundred shells, or so.

    The interesting thing is; those fuses had several miniature vacuum tubes inside. These were really tough tubes, the G forces from being fired out of a gun is tens – hundreds of G’s. But they survived the launch. All over the country people were assembling portions of these tubes without any idea what they were for.

    So, in part we defeated the Japanese and Germans by firing vacuum tubes at them…………

    Cheers, Kevin

  81. Vacuum tubes live on! The venerable HW101 in my “3-generation shack”, on the left, and the signal scope above it are all tubed. 22 of them in the HW101. Other than having to replace the rubber drive belts in the mechanical tuner section from time to time, and try to remember how to properly “dip the finals” on tune up, it still warms the shack and tickles the neighbourhood.

    http://ephemerata.wordpress.com/2009/09/01/beautiful-noise/

  82. Mike Bromley the Canucklehead says:
    May 24, 2012 at 6:04 pm

    I enjoy the plasma burst from the quartet of 6L6′s in my Fender Twin Reverb…

    Indeed, Mike, I had an old ’64 Fender Bassman head that was fantastic. I liked the look of the tubes as the 6L6s would die, they’d get all blue and plasma-y all the time. Unfortunately, they started sounding like crap about the same time. ;)

    Couldn’t see the 12AX7 tubes in that amp, as they all had springloaded metal covers.

    The only drawback was the REALLY BIG zap I got one time playing outdoors in the summer. I happened to be barefoot on concrete, and grabbed my guitar… ouchie. Got a couple of those through the lip grounding out on a microphone too, but not nearly as bad.

    …. ahhh, the good old days.

    That said, my back really appreciates the new technology that gives me a 300w rms power amp in a 2.5lb package, not to mention the neodymium magnets on speakers now…. Where’d my Doan’s pills go?

  83. I haven’t had time to read the (amazingly heavy) barrage of responses
    to the initial post, but of those I did read, I agree most strongly with
    curiousgeorge. It has been some time now since SYSTEM speed was
    dictated by DEVICE speed. The real challenge these days is getting a
    ‘fast’ signal from one place (say, the output of a gate) to another (the
    input of the next gate, or – far worse, an output pin on an IC). That’s
    to say, we live in an era in which electro(magnetic) propagation is in
    the driver’s seat.

    Years ago, I proposed planar triode, standing on the shoulders of all
    the advances in CMOS technology. It’s a ‘low-hanging’ plum and not
    very remarkable at all. But I knew very well that the only ‘good’ use
    to which such a device could be applied was in space applications,
    and that is still true- although, even THAT is a stretch, since modern
    CMOS transistors using hafnium-doped gate stacks are also rad-hard.

    Nevertheless, the realization of this idea is welcome news, even as a
    curiosity. And it will doubtless have some uses.

  84. My late father was an audio electronics engineer from the era of vacuum tubes all the way to solid state. Sadly he sold off all of his older tube audio stuff which is now sought after by collectors.

    All my ham gear is solid state but one of these days I’m going to arrange to have Dad’s kilowatt Heathkit linear shipped to me. I mostly play acoustic guitars but I have a couple of electrics. I have a little solid state Fender amp. While back at my parents house several years ago I found the head unit of a 60s era Silvertone Twin Twelve tube amp. The speakers and the case were gone so I shipped it back home. I think it cost me a little over $150 to replace all the tubes. I even bought a pair of the (new) original 12″ Jensen speakers for authenticity. I have yet to find an original spring reverb. But it works and sounds great. It’s got that same sound I remember as kid when I was learning to play guitar. What really surprised me is the interest other musicians have in this amp. Must be that “tube sound.”

  85. Jim says,
    “You guys keep saying that, and yet commercial products put out by the likes such as Harris continue to supersede that oft-repeated “Solid-State Power Amplifiers are Limited” saw.”
    True enough at HF and VHF frequencies such as VHF TV which is pretty much obsolete, but those commercial products use parallel of other configurations solid state devices to develope, say, 10 KW, whereas a single tube can easily provide many times that amount of power. Also, in the UHF and microwave range, solid state devices are much more expensive for high power applications, such as UHF TV, than are tubes. I sure have enjoyed the walk down memory lane with many of you here. I remember the “romance” of listening to far away short wave stations when I was 12 in 1952, and of getting my Novice ham ticket a couple years later. I don’t think young people have any sense of that kind of “romance” or anything comparable- or am I wrong?

  86. Does not appear to be a vacuum tube. Merely a FET with a vacuum isolated gate.
    Vacuum tubes emit electrons across the vacuum and steer them with space charges. This device appears to inject electrons from source silicon to drain silicon and controlled via charge in the gate channel silicon.

  87. “Steve in SC says: May 24, 2012 at 4:27 pm Vacuum Tubes have always been superior to transistors at RF.
    Check any TV or Radio station transmitter.”

    Part of the reason for this is power. Bipolar transistors have always been able to handle more power than the more common MOSFET devices which actually operate similar to a vacuum tube. You will almost always find bipolar output transistors in high power solid state designs. And solid state microwave devices have been around for years. Even so, manufacturers continue to increase the power range of both bipolar and MOSFET devices and developing new devices that can handle more power such as BiCMOS which combines the advantages of both technologies.

    Also, the device you show a cross section of still looks like a solid state device to me with a couple of vacuum wells. Other than breakdown voltage, I don’t know why that might be any better than a P/N junction.

  88. Vacuum tubes. I remember Grandpa trying fix our TV in the early ’60’s. He pulled a few of the tubes out and let us go with him to Woolworths. They had a tester. You just plugged the questionable tube into the right socket to find out which one was bad. Replacements were on nearby shelves.

    I also remember my brothers and I had an old phonograph in our room that had vacuum tubes. If we turned it a certain way and fiddled with one of the knobs, we could get WLW radio on it!

  89. In The high tech world, we use an expression to explain the workings of some gadget that we don’t fully understand. We say: Oh, It works by FM. (the M stands for magic.)
    Seriously though. These frequencies are very high. This is a switching device. on and off, 1 and 0, data.
    Soon, the drivel of the internet coming to you even faster

  90. Thanks Anthony!
    You brought back some nice childhood memories, mostly forgotten! In the late 60’s, my folks acquired a color television, when the old black-and-white set was getting cantankerous. After a bit of negotiating, they agreed to let me delve into the old B&W set, I’m sure with the caveat “He can’t make it much worse!” I was 13-14 years old then.

    I had already caught on to the simple tube diagnostics of “look for one that isn’t lit, has a broken filament, or has a lot of grey/black soot on the inside of the tube glass” from exploring a couple of old tube radios. When my folks would go into the nearest ‘town’ (Markesan WI, about 8 miles) once a week to get groceries, I’d tag a long so I could get to the local TV sales and repair shop, to test and replace ‘suspicious looking’ tubes on their tube tester. It took a few weeks and several discussions with the really nice old fellow that ran the TV repair shop, but eventually I had the old set working reasonably well again! I now had a TV in my bedroom, much to the surprise of my older brothers and sisters!

    If the folks were watching some ‘serious’ show (The Evening News, with Walter Cronkite…), we would pile into my room to see if we could get something ‘better’ on the old B&W (Daniel Boone?!). Mind you, the ‘deep fringe antenna’ had to be aimed at either Green Bay WI or Madison WI with the antenna rotator, to receive any of the 3 or 4 stations we could usually receive! On one occasion, the ‘new’ color TV went on the fritz and I ended up with Mon, Dad, and the rest in my room watching ‘Gunsmoke’, a family favorite!

    Thanks for shaking some nice memories loose again!
    MtK

  91. @George E Smith

    “There’s a lunatic fringe of so-called hi-fi nutz, who still believe that valve amplifiers sound better than transistor ones; the sound is “warmer” they claim. Well I never ever heard, a “warm” symphony orchestra”

    By coincidence I’ve spent the last few days on the internet researching which tubes to buy for a mic preamp I’m building (settled on some 80s military Mullards in the end). In the process I discovered that there’s no bore like a hi-fi bore, and that some do talk a lot of bull. The ‘superior’ and ‘warm’ sound quality of tubes which they perceive as accuracy most likely comes from even order harmonic distortion introduced by the tubes and other analogue circuitry in their amplifiers, giving some instruments a more human voice like quality (and also maybe emulating sound reflections in an enclosed space which can add depth). In reality a lack of reproduction accuracy but sometimes pleasing nonetheless.

    Looking forward to getting the amp finished, but it’s probably 50/50 as to whether me or the tubes light up when I switch it on..

  92. I’m amused that no one has picked up on the fact that the tube referred to at the start of the article (12AU6) is in fact a pentode, not a triode as used in the following explanation about how the vacuum nanotransistor works.

    The triode 12AU7 (+variants) however has been used in numerous audio/hifi and guitar amplifiers.

  93. My boss is a vacuum tube amp fanatic, and I’ve talked to him about the difference between audiophile solid state amplifiers and tube-amp guitar amplifiers. Yes, there is a big difference, and musicians rightfully love the tube amp sound. Tubes are 3/2 law devices, so they naturally introduce harmonic distortion into the waveform. They also tend to be smoother at the clipping point; distortion increases smoothly rather than just hitting the wall like solid state amps do. So…. an electric guitar with a tube amp constitutes a musical instrument, and the sound of that instrument is compelling.

    But hi fidelity sound reproduction is a different problem. There, the object is to be absolutely faithful to the original source material. Harmonic and inter-modulation distortion are killers for transparency and accuracy. Distortion is eliminated by having lots of head room; one simply uses an amplifier with so much power capacity that you never get close to clipping. You don’t want a hi-fi amp to sound warm. You want it to acoustically disappear.

    I built my first audio amp back in the late ’60s using 6V6 outputs with A-B biasing, and a 12AX7 phase splitter. It was good for about 15 watts. It sits in my basement now, gathering dust and memories.

    -BillR

  94. “”””” JJB MKI says:

    May 25, 2012 at 5:24 pm

    @George E Smith

    “There’s a lunatic fringe of so-called hi-fi nutz, who still believe that valve amplifiers sound better than transistor ones; the sound is “warmer” they claim. Well I never ever heard, a “warm” symphony orchestra”

    By coincidence I’ve spent the last few days on the internet researching which tubes to buy for a mic preamp I’m building (settled on some 80s military Mullards in the end). In the process I discovered that there’s no bore like a hi-fi bore, and that some do talk a lot of bull. The ‘superior’ and ‘warm’ sound quality of tubes which they perceive as accuracy most likely comes from even order harmonic distortion introduced by the tubes and other analogue circuitry in their amplifiers, giving some instruments a more human voice like quality (and also maybe emulating sound reflections in an enclosed space which can add depth). In reality a lack of reproduction accuracy but sometimes pleasing nonetheless.

    Looking forward to getting the amp finished, but it’s probably 50/50 as to whether me or the tubes light up when I switch it on. “””””

    My point is JJ, that ANY competently designed audio Amplifier, uses so much negative feedback, that the amplified INPUT SIGNAL couldn’t possibly have enough harmonic distortion to hear over the distortion introduced by THE INPUT AND OUTPUT TRANSDUCERS; namely, microphones, phono pickups, loudspeakers, not to mention speaker enclosures.

    The rush to tiny matchbox speaker enclosures, which drive down the low frequency response corner frequency by accoustically loading the speaker to the point that the efficiency drops radically, and every six dB of conversion efficiency, you throw away, gets you another octave of low frequency response, at the expense of having to double the drive power. The resut is that whereas a 1960 era speaker system could level the house walls with five Watts, of Amplifier power in a high efficiency speaker, today you need 500 Watts, to put in the Bozo et al full six inch cone sub contra base WOOooofer.
    The other modern problem is the penchant for using “opamps” for audio preamps. A typical opamp feedback amplifier, is actually an integrated input signal ATTENUATOR and feedback amplifier, and that attenuator formed by the two gain resistors, throws away input signal power, so the result is unavoidable input circuit noise.
    In addition, typical integrated op amps, have high frequency cutoff frequencies, in the 1 to 100 Hertz range (open loop), so the neagtive feedback starts dropping, almost before you get into an actual audible signal frequency.

    If your preamp doesn’t have an OPEN LOOP BANDWIDTH of at least 10 kHz to 20 kHz BEFORE, you apply negative feedback around it, then it DOESN’T have low distortion for high audio frequencies.

    Phono preamp amplifier designs ALMOST INVARIABLY throw MOST of the tiny signal power, down the drain in the (47 kOhm) cartridge “load resistor”; and then try to low noise amplify the few dregs of signal power that remains, as a Voltage across that resistor.
    Well I don’t have time to describe all the better low noise low distortion architectures, that were thoroughly researched by engineers at Tektronix (and other places) back in the 1960s.

  95. Make that four times the power for each octave lowering of the low frequency cutoff frequency of the speaker cone.

  96. Thankyou KevinK, I have been pondering for a while how the radar proximity fuses were possible at such an early date.

  97. An odd thing that science noticed long ago, is that a simple vaccum tube like an xray tube that consists of two plates in the opposite ends of a glass evacuated tube. Electrons randomly and spontaneously appear in the vaccum. A large computer made with these new nano tubes may give some surprising outputs!!!!

  98. “”””” William C Rostron says:

    May 26, 2012 at 12:14 am

    My boss is a vacuum tube amp fanatic, and I’ve talked to him about the difference between audiophile solid state amplifiers and tube-amp guitar amplifiers. Yes, there is a big difference, and musicians rightfully love the tube amp sound. Tubes are 3/2 law devices, so they naturally introduce harmonic distortion into the waveform. They also tend to be smoother at the clipping point; distortion increases smoothly rather than just hitting the wall like solid state amps do. So…. an electric guitar with a tube amp constitutes a musical instrument, and the sound of that instrument is compelling.

    But hi fidelity sound reproduction is a different problem. There, the object is to be absolutely faithful to the original source material. Harmonic and inter-modulation distortion are killers for transparency and accuracy. Distortion is eliminated by having lots of head room; one simply uses an amplifier with so much power capacity that you never get close to clipping. You don’t want a hi-fi amp to sound warm. You want it to acoustically disappear. “””””

    Well it all depends on design decisions. One of which is to run the power output stages class AB. That automatically means that the amplifier draws a non constant power from the power supply. The bigger the signal and power out demand, the more power the amp draws from the power supply, and the more that power supply will sag, and everything goes pear shaped. In addition, the power supplies were seldom regulated on those early Williamson era amplifiers; and even if they had been, it wouldn’t make much difference, because regulated power supplies simply do not have the same transient, and frequency response that hi fi amplifiers do, So when the whole Orchestra suddenly goes Bang !, and your class AB amplifier suddenly DEMANDS more power from the power supply, then the regulated (or unregulated) power supply, simply says; can you hang on a minute while I throw another log on the fire.

    The answer of course is to strictly adhere to class A output power stages, so that the power drawn from the power supply, is absolutely constant regardless of signal level (or irregardless, as the case may be). So if the supply power is constant, the lack of fast transient response is irrelevent.

    Yes class A amps draw maximum power all the time. All the more reason to not use inneficient matchbox speakers, so you don’t need a 500 Watt amplifier, unless you want to play music in Yankee Stadium.

    And if you stay with push pull stages, then you don’t generate even order harmonics; and of course, the vaccuum tube 3/2 power resonse is irrelevent, since the use of negative feedback makes the gain totally independent of the active devices or their transfer curve law. But I forgot; you can’t put much negative feedback around a class B or class AB amplifier, because now the frequency and transient response of the power supply, is part of the amplifier open loop system response, and the power supply will oscillate, if the amplifier itself doesn’t.

    Yes you can design good audio systems; and you can design schlocky ones too, and most people settle for schlocky; after all, if it is a guitar amplifier, or if your input is that Canadian shrieker singer; who can sing all the harmonic distortion anyone can stand, without ANY amplifier system; then who cares if it sounds crappy.

  99. “”””” CodeTech says:

    May 25, 2012 at 4:35 am

    George E. Smith, a very large portion of professional (studio grade) recording equipment still contains at least one vacuum tube. I’m sitting right beside both a microphone and a pre-amp that both have tubes, and they’re not old. There IS a warmer sound, and in truth there’s no good reason they couldn’t simulate the sound with solid state. The reality is the solid state guys get so obsessed with the accuracy of signal that they forget the vagaries of art. “””””

    Well code, I’m all in favor of everybody doing whatever floats their boat. That after all is what the whole “climate catastrophe” business is all about. Some people just FEEL that it is getting warmer, even though the science proves there is no way they could sense that, even if it was true.

    So if your studio judgement is a feel good approach, that’s ok by me.

    Now with my son, his music is ALL about art; he could care less about high fidelity (another way of describing replication of the original). So he makes no effort to preserve reality, and so he artistically creates EVERY SINGLE NOTE of his quite creative music, on his lap top, out of ones and zeros; so his music has absolutely zero distortion or lack of fidelity, and it has all the warmth anyone could desire, or even cold if they feel that way inclined.

    If somebody wants to pay $4,000 for a microphone that has a gold plated can, like one I saw recently at a San Jose guitar center; well I’m not going to get between him, and someone itching to take his money.

    I have NO DISAGREEMENT with anybody who claims that tube (valve) audio gear sounds different, from some (name your poison) alternative. And if that is better for you; enjoy, but don’t expect everyone to agree with you because it sounds “warm.”

    By the way; how does warm sound; is it akin to how “warm” looks in light bulbs.

    If Mark Zuckerberg, can rip off people for over 20 million dollars in one day; selling them 30 plus million “shares”, for $38 that are worth seven dollars less tomorrow; all in the name of conning people into publishing all the information needed by the identity theft industry, for the whole world to see; then perhaps such people deserve to be separated from their money. Well they are depending on someone else being even sillier, and willing to pay even more than they did. I guess you can sell painted human excrementas art, to people who feel good about it. That’s capitalism

    Does anyone come home from a rock concert (held anywhere), and exclaim; gee that microphone with the tube in it sure sounded good ! Like they actually heard anything.

    Right now I’m sitting in a Peeks coffee shop in Mountain View, and they are playing some 17th century string instrument music; have been for hours, except when they play flute music instead. What they are playing, is obscure, and thoroughly deserves all the obscurity it can muster and then some. It was trash when it was written, and it is still trash; but people will pay other people to play it. Well you can’t here it anyway, because in this coffee shop, they grind the coffee with a hammer, and every 20 seconds or so, some worker smashes their hammer on some metal can for some reason, drowning out the ancient substitute for texting. I’m sure if OSHA walked in here with a noise meter, they would cite the place, for unsafe working conditions. But actually, nobody in ere sipping coffee and yakking, seems to even notice.

    Each to his own I guess; that’s capitalism.

  100. George E. Smith; says:
    May 26, 2012 at 1:38 pm

    > By the way; how does warm sound; is it akin to how “warm” looks in light bulbs.

    I’m not sure myself, but a level headed EE audiophile friend explained a couple things that made sense.

    One of the key things seems to be reduced gain at high levels. E.g. where digital would clip and sound horrible, tubes enter a realm where the signal tails off, i.e. a sawtooth wave would have less pointy tops and lose some of the high harmonics of the sawtooth. In digital, the sawtooth would become a trapezoid. The other, (think op amps here) tube circuitry has a limited slew rate, this also limits loud, high frequency sounds. Like record scratches. I assume purists don’t hook up CD players to tube amps. If they do, how can they live with themselves?

    I’d like to see some of that displayed on an oscilloscope, of course, but I can see how limiting loud high frequency sound can be considered warm, and a good thing.

    Me, I’ll stick to my CD player.

    He also told me to use OFC (Oxygen Free Copper) for speaker cables and to ignore anything that refers to skin effect in speaker cable. Which is pretty much what I had figured. Speaker cables just don’t have any issue with skin effect, at least not at frequencies we can hear.

  101. George E Smith

    Does anyone come home from a rock concert (held anywhere), and exclaim; gee that microphone with the tube in it sure sounded good ! Like they actually heard
    anything.

    Not in a rock concert George, but in a recording studio or the proper home listening environment, yes.

    Perhaps the first place to start looking when you want to add warmth to a recording is the microphone — the very start of the audio chain. A valve microphone will
    usually sound warmer than its solid-state counterpart, largely because of the subtle distortions and phase shifts it adds to the signal. These distortions, while quite measurable, are subtle in their effect on the human hearing system, so instead of perceiving them as detrimental, what we actually experience is an enhancement of detail (due mainly to the added harmonics) and an increase in the apparent density of the sound, almost as though gentle compression is being applied. Valves also limit more gracefully than solid-state circuitry when driven hard, so the high end can sound noticeably smoother at high signal levels.

    Source.

  102. “”””” Keith Minto says:

    May 26, 2012 at 6:36 pm

    George E Smith

    Does anyone come home from a rock concert (held anywhere), and exclaim; gee that microphone with the tube in it sure sounded good ! Like they actually heard
    anything.

    Not in a rock concert George, but in a recording studio or the proper home listening environment, yes. “””””

    I’d venture that more microphones are used at rock concerts, than in recording studios or home listening environments. How about at a jazz festival. Two years ago, I attended the Catalina (Avalon) jazz festival, and we had perfect seats in the middle of the amphitheater, listening to a jazz combo of about six players, so we were maybe 30 to 40 feet from the musicians. We never heard a peep out of the musicians on the stage. Their playing was totally drowned out to the point of inaudibility, by the noise put out from the grossly distorted theatre sound system. We tried moving to the back of the hall, to no avail; and eventually had to leave because of that horrible noise. Too bad too, because those musicians seemed very talented.

    And I think I explained why amplifiers crash; specially class AB and class B amps; it’s their power supply that limits. And I’m not responsible for poorly designed amp systems that overload. At home, I can easily crank my stereo system up way beyond realistic listening level; and I am fond of both full bore symphonic or operatic music; as well as French organ music. So I am not your standard flute solo enthusiast. About a year ago, my son accidently switched on a noisy movie DVD, without checking the level, and he tore the cone out of the rim, on one of my JBL speakers.

    Amazingly, I was able to resurrect it slowly, by painting it with several coats of nylon loaded Hard as nails finger nail polish. So my amp just does not limit within the realistic listening level of the loudest stuff I listen to.

    And if it is necessary to add deliberate distortion to the original sound to make it “warm”, then I’ll just make do with my normally cool music, which doesn’t sound distorted.

    So do people think that listening to MP3 music on their cell phone; that the teens like to do, is where it is at ?

    I’ve seen valve amplifiers that cost $20,000 per channel, that you put down on the carpet in your “audio room”, so your friends can admire them; and your taste. Well good for them; they probably have too much money for their own good.

    And as for those “warm” tube mike amps in the recording studio. Note that word “recording.”

    The end consumer is going to listen to that “recording”. Well actually they will listen to what remains of that “warm” music after the “sound engineers” have finished with masticating it and digitizing it so that it has lots of quantization noise, specially in the quiet passages, where the ear can hardly ignore it. The very best “records” I have are actually now 40 year old LPs. Except for a few scratches, and sometimes a little dust, thy sound better than CDs. Yes I do actually have the exact same recorded performance originally cut onto disk, from tapes; and a modern digitally remastered CD release of the same recording. The LPs sound better; can’t tell if they are warm or not.

    Still don’t know what warm music is; something like wine “bokay”, I would venture.

  103. George E. Smith;

    If this sounds like an argument, I can assure you it’s not. But hopefully I can explain some of this for the benefit of anyone wondering about warmth.

    I record digitally. I personally prefer 24bit/96khz for the highest quality I can get with my equipment, with the greatest dynamic range. I lay down the tracks: drums, bass, guitar, keyboards, vocals, vocals, more vocals, and do a mix. The mix is balanced, each track is individually EQd so it stands out in the mix, and the overall mix makes a satisfying downward slant on the spectrum analyzer. That’s part one, and it sounds great here in the studio.

    Trouble is, when I take it from the studio, downsample it to 44/16 for CD quality, and play it in the car, it sounds horrible. It’s cold, lifeless, sterile. Yes, those are subjective terms, and they are terms you will hear virtually everyone in the recording world use. I don’t know the origin of the terms, and probably neither do the majority of people who use them.

    So the first thing that, again, virtually everyone in the recording world does: I add distortion. Or, I take away precision, depending on your perspective. Two voices together in perfect pitch sound bland. Detune one slightly and they merge into a rich blend that looks quite complex on the scope. Instruments should never be perfectly tuned, but obviously also never too far out of tune.

    Vocals are almost always compressed, otherwise the quieter parts get lost in the music. Compression makes the quiet parts louder and the loud parts quieter, to compress the dynamic range. Compression is almost a voodoo art, not enough and your vocals seem to get louder and quieter, too much and they lose power and punch. Overcompression leads to chuffing, and that particular one is at least onomatopoeic. Each track needs to be compressed differently, and the overall mix also gets compressed.

    If you listen to any popular music from at least the 50s, you will hear intentionally introduced distortion, and specific response curves of the compressors and their settings. Some famous compressors limit your range of control and always add a characteristic sound, while current digital ones can pretty much be set wherever you need them to be. I mentioned before that there is an Abbey Road plug-in that faithfully reproduces the actual specific hardware that was custom built just for Abbey Road, using tubes, and exists nowhere else. Those sounds are instantly recognizable to any Beatles fan, or fans of any of the British Invasion bands.

    Every track in a recording has a certain range of compression, EQ, and distortion that defines it as the sound that we are used to hearing. Originally it was done this way live, then the ad-hoc standard was further refined in studios through the decades, and even today very few recordings ever achieve success if they are outside of the norms.

    I noticed your comment before comparing the “warmth” with something undefinable like the AGW people promote, and nothing could be farther from the truth. What we describe as “warm” is a combination of dynamics and distortion, that makes the sound less precise but more like you’d hear sitting beside someone in a comfortable setting, maybe beside the fire. If you wanted perfect quality, the person would have to speak right into your ear. A real comfortable conversation takes place in a room with sound reflecting and absorbing materials and is totally unpredictable.

    Live concerts work entirely differently. I don’t think many people realize it, but after playing an artists’ albums a few dozen (or hundred) times, they literally fill in most of the details when they hear it live. Live music quality can descend to the level of horrid while still elating the audience. This is the trick that gets the showmen going, adding dancing and visual effects (eye candy) to the music that is mostly in the audience’s head. Almost every concert I’ve been to uses non-tube Shure SM58 mics for their convenience and good signal quality, then basically slaps together a passable mix.

    In my recording industry years I often encountered someone who tried to run live sound the way they ran a studio mix, and it never works. Your description of an overly loud and poorly rendered concert is a perfect example. I would always tell these techs to, first and foremost, TURN IT DOWN. 90db is a good volume, anything more annoys your audience.

    For the record (no pun), I love classical music, and nothing has more power than a real orchestra at full volume, pounding out the crescendo for a symphony. Live performances always include the acoustics of the hall they were recorded in, usually some coughs, the occasional mistuned instrument or misplayed note, and that is part of the appeal.

    Imprecision is warm. Precision is cold and sterile.

  104. Oops, almost forgot:

    Almost ANY audio purist, myself included, will agree with you that your 40 year old records sound better than anything new, with the possible exception of the latest high sample rate remasters of analog recordings (the jury is still out on that). And yes, you have thus defined “warmth”.

    It is unfortunate that the current generation are being brought up believing that hiss is an evil sound… they can’t tolerate an occasional click or pop. Then again, they also can’t handle a space between their songs and are more than happy to mix the tail of one to the start of another.

    MP3s are horrible quality, unless the settings are all maxed out at 320, but nobody does that because at 128 they can fit more songs on their disc or device. The end result of this is not so bad, they don’t realize it but 20 years from now they’ll long for the nostalgic sound of a badly rendered MP3, and recording studios will obligingly reduce all their quality to that.

  105. “”””” CodeTech says:

    May 27, 2012 at 6:31 am

    George E. Smith;

    If this sounds like an argument, I can assure you it’s not. But hopefully I can explain some of this for the benefit of anyone wondering about warmth. “””””

    Say CodeTech, thanks for the detail on what YOU do, and what you are telling me (which I certainly believe) is that YOU and your brethren, are as much the ARTISTS, as are the grassed out guys jumping around on the stage, and smashing their guitars, for audience effect.

    I happen to have an almost full set of all ten of the Widor Organ Symphonies; which are rarely performed (in full) and even more rarely ever recorded; so I take what I can get. Now recording a pipe organ is quite difficult, and whoever “did” these recordings, did a lousy job; lousy mike placement (if any) and lousy mixing so they sound like mush; but there they are, virtually the only records of those works you can get. For good measure, some of the organists involved, despite their reputations, also did a really lousy interpretation of the works; but what can one say; nobody else recorded them.

    On the other hand, the sound engineers and recordists, who put together the Georg Solti Decca/London recording of the complete Wagner, Ring of the Nibelung, with a spectacular singing cast in the 1960s made a recording, that likely will never be surpassed.
    Now I should hasten to add, that the music genre is not the issue, I can listen to most anything; although I certainly don’t know a lot of categories. I know nowt about jazz, but my ear and my heart sure as hell knows when it likes it.
    I know nothing about Country and Western music; either one as they say, or Bluegrass, but if I hear something I like, I kow when I like it. Amazingly, when I go to work, these days (I still work) I actually can get to hear some of the best Bluegrass fiddling music on the planet;and am itching to get my hands on some of those recordings. But I’m spoiled rotten; I can actually listen to live artists playing in the next room, including a four time National Grand Champion BG fiddler, and currently an excellent Junior one as well.

    So I don’t have a problem with folks such as YOU creating works of pure fiction, when the result is more satisfying than the “observed facts” ; but a 90 dB reduction for that Certain shrieker would be a great improvement.

    Incidently, your 24 bit A-D certainly should practically fix the quantization noise at low levels. I’m not sure it was available when Decca remastered the “Ring” for CD from the original 16 track tapes from the 60s. The CDs are more convenient to play, but the old LPs still sound better; but then I have to toss the family out of the house to get rid of ambient noises.

    Dunno whether my son’s computer music, will ever make him rich; but at the moment, he is also his own recordist. But then he doesn’t use any mikes, so even a gold plated one won’t help him.

    George

  106. I’d love to here what a silicon tube would sound like in audio application. Oh the sweet sound of the breathing tube amp. Jack Vance’s “Book of Dreams” has interesting comment about how real musicians intentionally don’t play music accurately. A musician plays all these extra things “wrong” to make the music come alive. Sounded like something Minto was saying.

    Someone also mentioned the other great audio technology, the turntable, which is superior because it is analog and is missing the digital pulse. No possible number of digits can beat no digits. Digital music is tiring and stressful: it’s sandpaper on the subconscious. When I listen to records with a non-digital amp I get to go way down into the music, there is no second reality digi-beat.

  107. Audiophiles are nuts. No further proof is needed other than what is written by them in these comments.

  108. Mac the Knife says:
    May 25, 2012 at 4:08 pm
    Thanks Anthony!
    You brought back some nice childhood memories, mostly forgotten! In the late 60′s, my folks acquired a color television, when the old black-and-white set was getting cantankerous. After a bit of negotiating, they agreed to let me delve into the old B&W set, I’m sure with the caveat “He can’t make it much worse!” I was 13-14 years old then.

    In the year 1958, 14 years old, the boss of the local TV repair shop in Germany has begun teaching me TV technology with receivers like this and all that stuff of tubes. In July 1969 I was watching late night on such B/W TV receiver the TV pictures from the Moon. In my last years in research fifty years later in 2008 all that stuff was helpful to design a CT x-ray tube emitting electrons of total 2 Amps from a round cathode accelerated by 75 kV on a rotating tungsten anode spot. Its not problem of high frequency but on power density. It was fun.
    .
    V.

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