Return of the Vacuum Tube

sciencehabit writes "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 (abstract). It's even able to survive the harsh radiation of outer space."

Comments

Amps

[Aeros]

These are still widely used in some of the best amps out there.

Re:Amps

[jenningsthecat]

Yes, transistor audio amplifiers are "way more linear" with gobs of negative feedback applied, if THD, (Total Harmonic Distortion), is your measurement criterion. ANY amplifier is more 'linear' with correctly applied negative feedback. The basic premise is that added harmonics are bad - if you feed a pure sine wave into an amplifier, you want a pure sine wave at the output. The problem is that in audio, THD is a fundamentally flawed measurement with very poor correlation between lab measurements and listening tests.

THD measurements are taken as the ratio of the total power of all harmonics to the power of the fundamental, with no weighting of any kind applied. The trouble is, human hearing doesn't respond to harmonic distortions in this linear fashion - our ears find higher order harmonic distortions much more apparent and objectionable.. This deficiency was noted by prominent BBC engineers D.E.L. Shorter and Norman Crowhurst in the 40's and 50's, when they proposed weighting harmonics by the square or the cube of the order; but their voices were drowned out by market forces that wanted a simple, flattering figure of merit that made the newer, more powerful pentode-based amps, (with lots of negative feedback), look better on paper than their lower-powered triode predecessors. The market won out over scientific and technical accuracy, (it usually does), and today engineers the world over, ignorant of this history, mistakenly believe that low THD is the gold standard for measuring and defining audio amplifier quality. (For a good technical analysis of distortion and the sound of an amplifier, see Lynn Olson's excellent investigation.

By the way, in the 'tubes vs transistors' debate, good triodes have the advantage of being more intrinsically linear than transistors. This means that they require less negative feedback to tame their distortion, and often sound wonderful with NO negative feedback. The THD figures of amps built this way are often quite poor, but look at their spectra and you'll see predominantly second- and third-order, with a smooth and rapid falloff of higher order harmonics. Occasionally solid-state amps can give this kind of performance, but tubes have an easier time of it. Designing a good-sounding, (as opposed to good-measuring), audio amp, requires a lot of skill, and a lot of knowledge about distortion mechanisms and how to counter them. Unfortunately the prevailing practice in HiFi is to add more gain, throw most of it away with additional NFB, get a nice low THD figure, and call the job done. Amps designed this way generally sound like shit, if not initially, then after 20 minutes or so of listening, at which time listening fatigue sets in.

Reel to reels as well

[John3]

And they are used in some of the best old-school reel-to-reel recorders. I don't know if they are making new components with tubes, but older tube pre-amps for Ampex and Scully tape recorders are prized by some audiophiles for their "warm" sound. They are also great for creating distortion...over-driving tube pre-amps creates some nice distortion effects which digital components would just clip.

But (and I'm speaking as someone who has been out of radio and audio for many years...I own a hardware store), from what I've seen and heard there are some pretty awesome digital programs that can duplicate nearly any pre-amp ever made. Based on what my daughter can do with her Mac (Protools, FInale, etc) I am pretty impressed at the sounds that can be processed even in a home environment with no need for tubes.

On the other hand, my tube pre-amps do keep the basement warm. :)

Re:Vacuum tubes have never left!

[Anonymous Coward]

Uh... Microwave ovens use a magnetron http://en.wikipedia.org/wiki/Microwave_oven#Design I've repaired many a Microwave ovens and I have never seen any vacuum tubes.

Too smart for your own good. A magnetron is a vacuum tube. Not all vacuum tubes are transparent. Hell, the "vacuum tube" in the article has neither a tube or a vacuum!

Re:Vacuum tubes have never left!

[digitig]

Uh... Microwave ovens use a magnetron http://en.wikipedia.org/wiki/Microwave_oven#Design

I've repaired many a Microwave ovens and I have never seen any vacuum tubes.

Nathan

Indeed they do use magnetrons. And to quote from the first line of the Wikipedia article on magnetrons" "The cavity magnetron is a high-powered vacuum tube..." (my emphasis). Do you repair the microwaves with your eyes closed?

Re:Vacuum tubes have never left!

[Bill, Shooter of Bul]

1960's?

The amplifying triode vacuum tube was invented near 1907.
The transistor itself in 1947.

Re:Ahistoric Hyperbole Rant Warning

[scharkalvin]

Actually an open heater was NOT the way most tubes died. The coating on the cathode that emits electrons when heated gradually decays and emission drops off to the point that the tubes transconductance is too low for it to operate. But the heater rarely burns out, at least not in indirectly heated tubes. Another way they die is that air gradually leaks in and the vacuum becomes too poor. The silver flashing on the side of the tube will then turn a milky white as the chemical "getter" that absorbs air has absorbed all that it can. Once the getter coating is depleted the tube will become gassy. A tube can also die from shorts when closely spaced elements break loose from vibration and touch. Over heating will soften the elements and cause the same effect. Tubes can handle a much higher percent of overload than solid state devices however. Tubes computers were never faster than solid state ones even if the tubes themselves were faster. Because of their size the total wiring in a tube computer is much longer than in a solid state system. In transistors it is the "holes" in the crystal structure that "move" and the speed of light in silicon is lower than in a vacuum for electromagnetic waves. Still these waves have less distance to propergate in an IC than a bunch of interconnnected tubes. Finally note the description of this new tube technology, it is really a "vacuum state" IC. I always wondered when nanotechnology would be applied to thermionic "valves" (as they say across the "pond").

Re:But in outer space...

[compro01]

No, space is a far far harder vacuum than anything we can currently manage on-planet.

A vacuum tube still has between 1 million to 1 billion molecules per cubic centimetre, depending on tolerances. The best vacuum we can currently make has about 100k molecules per cubic centimetre.

Interplanetary space has about 10. Interstellar space has about 1. Intergalactic space has about 1 per cubic metre (10,000 cubic centimetres).

Re:Sweet

[hairyfeet]

They modded you funny but any musician will tell you for guitar amps you can't beat tubes. as a bassist I prefer my Trace solid state (one of the last Brit made before they got bought by Peavey) because its hard to get a truly clean tone out of a tube but frankly that is what makes them great for guitar as even a "clean" tube tone has a warm slightly compressed midrange that is just better than solid state.

Let us just all hope that Russian Sovtek factory never goes out of business or rock would be screwed. I have heard just about every kind of modeling amp out there but none of them compare to the tone of a Marshall Plexi or a Fender Bassman or Concert, hell even a mid 70s Peavey Mace tube head sounds better than the modeling amps. Sometimes the older tech is just better, that's all.

as for TFA I'd love to see something like that filter its way down to musical applications. Can you imagine a tube amp you could just throw in a rack and that would take as much abuse as a solid state? man that would be like heaven.

Re:Vacuum tubes have never left!

[smpoole7]

> At low power levels (e.g. 10kw) transistorised VHF/UHF output amplifiers are fine. Additionally, you can get a higher power output by operating multiple VHF/UHF output amplifiers in parallel - which also gives some redundancy for transmitter maintenance.

See Pentium 100's reply; he hit the high points. But it's essentially a matter of cost-effectiveness. If you tell me, "I need 30,000 watts at 100 MHz (a typical FM arrangement), I'm going to use a tube. Even after paying $5,000 for the tube and building a 10,000 volt, 5A power supply, I'd still come out ahead. Combining enough 100-200W solid-state modules to get that kind of power level would be far more expensive.

There's a practical matter, too -- for example, or 50 KW AM stations *do* use solid-state, and they're done as Pentium100 describes: you combine bunches and bunches of modules to get that power level. That's at a much lower frequency, and they can be made very efficient .. . .. but with full modulation, our Nautel transmitter runs a 300V primary supply and draws in excess of 300 amperes(!). There are giant 3/0 cables (they look like booster cables!) running all over the inside of that thing just to handle the current.

Can't cheat physics: power = voltage times current.

But I'll add this: Some competitively-priced solid state high power transmitters have begun appearing, so I have hope for the future. (We're looking at some of the new Nautel FM units ourselves; www.nautel.com if you're curious.) But seriously, even as recently as 2 years ago, there was no question that a 4CX20000 tube in a tuned cavity was far more cost-effective than trying to do it with solid-state.

Re:Pure marketing

[Ellis D. Tripp]

The tube on the AOpen mobo was a 6DJ8/6922, not a 12AX7.

The 6DJ8 is also a dual triode, but it has much higher transconductance because it is a frame grid design. Those tubes were widely used as input amplifiers in vintage Tektronix scopes because of their low noise and high linearity.