Long Live Vacuum Tube Amps

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Commentary on the long life of vacuum tubes.

Vacuum tube amplifiers just won’t go away.  I am speaking more of audio vacuum tube amps than I am of microwave amps like magnetrons, klystrons, TWTs and the like.  Most other audio gear is solid state so why are there still vacuum tube amps?  My grandson asked me that recently and it was hard to explain this phenomenon.   What I basically said is that vacuum tubes amps sound better than solid state amps, to some people.  I had no way to follow up or demo this effect.

I have actually compared solid state audio power amps to the vacuum tube equivalents several times and using the same speakers.  (It seems to me that the speakers would have more of an effect on the sound than the type of amplifier.)   I could discern a difference between the two.  I do not have the words to describe the difference.  It is akin to comparing wines in a tasting.  There are words for that but they are also vague and subjective to be sure.  So it is with audio sounds.  I have actually heard people say they can tell the difference between two different sets of speaker cables and connectors.  I still don’t believe it.

So are vacuum tubes amps better?  I’m not sure.  They do still sound very good and for me it also depends on the music being played.  Guitar players almost universally favor vacuum tube amplifiers.  There are certainly enough vacuum tube audio power amp manufacturers to support the niche.  I ran across one called Frenzel Tube Amps in Texas.  No relation to me. These guys build custom amps for audio systems and musicians.  And there are a dozen or so other tube amp companies.  Amazing.

Not only that, I recently discovered a new book Building Valve Amplifiers, 2nd edition by Morgan Jones.  It is a highly detailed book on the actual design and construction of tube amplifiers.  Published by Newnes/Elsevier, the book covers planning, metalworking, wiring and testing.  A real nitty gritty book for hobbyists and serious manufacturers.  For example, the book details things like how to orient audio and power transformers to avoid problems of magnetic flux leakage from affecting other transformers or the tubes themselves.  The test section is excellent.  You may even learn where to find a loctal socket for a 7N7.

Incidentally the book is a companion to the book Valve Amplifiers, 4th edition also by Morgan Jones and published by Newnes/Elsevier.  This is a serious design book with details on audio circuit design, equations and related topics.  A 4th edition means that the book has been around for a while and is being updated and there is a real market for it.

Anyway, I no long have any tubes or tube equipment around.  Very early in my career I worked as an engineer in industrial electronics and I recall that I could make almost anything I needed with a 12AU7, 12AX7 and/or a relay.  The early germanium PNP 2N1305s did not cut it. Those days are gone for good.  And even my ham gear is solid state although one can still buy RF power amps with multiple kinds of vacuum tubes.  It is hard to beat them for power RF in the HF range.  LDMOS amps are available too but more expensive. And I suspect we will see some GaN ham power amps at modest prices in the near future.  But I am not betting on the demise of the vacuum tube.

Discuss this Blog Entry 29

on Mar 18, 2014

Holy Cow! I remember loctal tube sockets. I once had an old car radio that I was scavenging for parts, and all the tubes were loctals. I had a lot of fun with tube circuits, but don't miss them all that much. All in all, I agree that they will still be around for quite a while.

on Mar 19, 2014

I missed out by a year learning anything about vacuum tubes in college -- they had just deleted them from the curriculum (1966) -- though we still had a course in analog computers. Now as I approach retirement I find myself fascinated with them, though mostly as used in antique radios and Ham gear. I'll have to look up those books you cite.

on Mar 19, 2014

Despite my user name (yes, I have a Moog synth...), I'm somewhat of a young pup. The CD, not vinyl, was the music format of my youth. That said, all of my amplifiers over the years have been BJT, or more rarely, MOSFET. Vacuum tubes were something my dad listened to!! Several years ago, after reading so many positive comments on the Internet about tube amplifiers, I had it in my head to obtain one. Reality hit after realizing I was going to part with many, many Franklins to purchase even a vintage tube amp. So piece by piece (financially a little easier to handle), I obtained the parts to build one. In the first few minutes of those glowing bottle's operation the difference was immediately apparent. More detail, more "air," better imaging and staging, more presence, an effortlessness, more "alive..." Simply unbelievable and awesome...I was hooked (line and sinker)! I still own several "transistor" amps/stereos in various rooms, but currently, any serious listening is done on the "tube stereo."

BB
on Mar 19, 2014

Although my electrical engineering career has taken me on a journey through the evolving state-of-the-art over the decades, I still insist on a good tube gear in my audio system. At their best, great tube amps, tube preamps and even tube DACs come closer to the sound of the live event. There are some "sound" technical reasons why this is so, but I won't get into that here since I may publish on the topic soon. Suffice it to say that it's not about euphony, but about accuracy vis-a-vis the sensitivities of human perception.

The Morgan Jones books are excellent and I heartily recommend them too.

on Mar 19, 2014

I remember loctal tubes, yes, I'm that old. My grandmother had a version of the "All American 5" radio that eventually was replaced by a newer miniature tube model. I got to salvage parts from the older radio somewhere back in the mid 50s.

All my ham equipment that I use regularly is solid state, but I still have the Heathkit DX-40 I built at age 11 when I got my Novice ticket. I also have a couple of tube receivers from Collins and Hammarlund as well as a Collins KWM-2, all in working order. I still homebrew some tube transmitters for the fun of it.

73 K9LJB

on Mar 19, 2014

There are many dozens - if not hundreds - of tube amplifier companies, guitar, musical, car/mobile, and home audio.

This is pertinent, particularly the part about "Mr. Dumble's Good Tone via Hot Plasma":
http://milbert.com/tubes_vs_transformers

Also good, tubes vs transistors, reprint from AES:
http://milbert.com/Files/articles/TvsT/tstxt.pdf

Also quite interesting:
https://www.youtube.com/watch?v=84W72Ux3IBE
listen from 3:15 into interview w/ Preston Nichols (of Montauk / Philadelphia Experiment infamy), regarding electrons in a vacuum tube.

on Mar 19, 2014

I have used and designed tube guitar and recording gear for many decades. The tube guitar amp must be viewed as an extension of the instrument, the electronic 'sound box'. Therefore specs are dependent on the subjective desires of the player. Many times I will design guitar tube circuits and never turn on the Audio Precision analyzer until the end of design. Design is done 'by ear', then verified.

Recording gear is the opposite. Specs are examined during the entire design cycle, noise and THD are tweaked to lower those specs. I have found a very linear tube design void of coupling transformers to sound very close to fast, low THD transistor gear. Use a bipolar power design and dircect couple those optimized tube stages and many can't tell the difference anymore.

I have found many listeners are fond of second harmonic generation, typical of home hi-fi gear. To me they sound like there is an "aural exciter" going on and there is, second harmonics add a sense of 'life' and a 'breathing' quality but don't be fooled, it's a pleasant form of distortion many have grown to like.

on Mar 19, 2014

I thought we've been through this... or maybe the definitive article was in EDN, I forget. Anyway, the "tube sound" is mainly from the filtering effect of an output transformer, as opposed to the stiff voltage source of a transistor direct coupled amp.

I'm a high powered tube transmitter engineer, and those will not go out of style for a looong time. I bet there is probably a fairly low-powered S band magnetron in your kitchen right now. As for tube audio gear, as long as there are suckers with "golden ears" and roadies to carry heavy, expensive amps for rock stars, the silliness will go on.

on Mar 19, 2014

Yes, we've been through this before. I have no doubt that a DSP with enough bits coupled to a clean solid state amplifier is capable of generating sound no golden ear could tell from his favorite tube amplifier (if you can find one foolish enough to submit to a double blind study--that's a big if). The only exception I can think of is that solid state amplifiers have extremely low output impedance, which produces high dampling (tube amplifiers do not). This can have an impact on the behavior of the cone of the loudspeaker. I'm not sure if the DSP can simulate that, or if the high damping would result in distortion in the speaker. So, the test might have to include some series resistance between the amp and the speaker (with a resulting loss of efficiency).

on Mar 19, 2014

Lou, we (engineers) have had this argument a countless times. Tube afficionados never measure distortion, they are happy to accept the second harmonic that comes as a natural course of the device and use a wine vocabulary to describe the result. Odd harmonics simply don't sound as good, our senses are not tuned for it. If you really want to feel the "presence" of the music, learn to play an instrument and join a band. I started playing over 50 years ago and still enjoy every musical experience.

on Mar 19, 2014

The founding engineers effectively assumed human hearing does not produce harmonics on its own. But it does. That is mathematically handy as it allows analysis. However it set the stage for "objective" testing. This objectiveness is "better" than the subjective listening. And it would be if there were not for one little problem - the errant assumption.

Fundamentally engineers wish to make amplifiers that replicate their inputs without any embellishments. But those who listen with their ears instead of their distortion analyzers pick their amplifiers based on these embellishments.

We should pick our amplifiers based upon our subjective hearing because most all of music is subjective from the choice of mics to the playback tone control settings.

on Mar 19, 2014

I built tube amps for my Dad back in 1960 and had quite a collection of tubes and parts. I served Uncle Sam in the USAF for 4 years and when I returned the transistor had replaced tubes in most guitar amps. I stored my collection and nearly forgot it. Five years ago my kids helped me move and urged me to do something with all that junk. I started building tube amps again using my original designs and everyone was amazed at the rich tube amp tones I get. Tubes may never replace solid state devices for the purest audio amplification but they add rich depth and overtones to instruments like the guitar. A guitar played through a fine high fidelity amplifier sounds sterile and empty when compared to a good old fashoned tube amplifier.

on Mar 19, 2014

It must really be nice to have something coincidentally named after you, specially when both of you are famous (though it gets annoying in the long run - like people keep calling me Justin Bieber even though I look better than him).

I think the competition between vacuum tubes and solid state technology lies more on application, rather than quality (as also implied near the end of the article). "Voice of America" has a station here in the Philippines and they still use vacuum tubes due to their robustness in high power RF application.
I'd also like to reference a blog post I made on this (though it spans a more general concept) a year ago:
http://www.schematicanalysis.blogspot.com/search?q=vacuum+tube

A 2n1305 certainly won't cut it because industrial electronics deals with high power (unless you wanna barbecue transistors). Sadly, Jacques Arsene d'Arsonval's PMMC concept is quite outdated and SCR's, thyrectors, PUTs (they say UJTs are too expensive) are dominating the industry (though they are still good in meters because they don't introduce noise to your circuit).

on Mar 19, 2014

Three points: (keeping it simple for brevity)

1) today's tube amps are not quite the same things as were the tube amps of the classic tube era, at least not the best of the class. A variety of reasons, all of which add up.

2) the divergence or convergence of the best tube gear with low distortion solid state amps will not be known or be clear until much higher fidelity and sample rate digital source is widely available. 24/192 seems clearly to be more "natural" than earlier digital source.

3) Go to http://www.diyaudio.com and see what is possible in the world of both solid state and tube. Many top engineers participate (for those of you who are focused on theory and measurement, don't think this is about "tweaks" at all). So, as far as any amp costing a huge amount of $$, not if you can build ur own!

4) We have a major *crisis* in THROUGH HOLE DEVICES!! Almost all of the solid state through hole gear is quickly becoming unserviceable due to the vacuum in parts availability!! Whereas tubes that are seemingly obsolete by 60+ years now are in reasonably ready supply (both new and NOS), through hole devices have vanished from the face of the earth in about 10 years time! Go ahead try to find a Toshiba JFET, and other bipolar devices that formerly cost pennies. Unobtainium. CRISIS!

tnx for reading...

on Mar 20, 2014

I agree finding through hole parts is sometimes a challenge. I am still designing mixed through hole and surface mount devices. It often takes me a long time to write the bill of materials because I check for each part at Mouser and Digikey and a few other sources. High voltage surface mount capacitors are too expensive, so I still use through hole there.
Best regards,
Stan Hubler

on Mar 20, 2014

I agree finding through hole parts is sometimes a challenge. I am still designing mixed through hole and surface mount devices. It often takes me a long time to write the bill of materials because I check for each part at Mouser and Digikey and a few other sources. High voltage surface mount capacitors are too expensive, so I still use through hole there.
Best regards,
Stan Hubler

on Mar 20, 2014

I agree finding through hole parts is sometimes a challenge. I am still designing mixed through hole and surface mount devices. It often takes me a long time to write the bill of materials because I check for each part at Mouser and Digikey and a few other sources. High voltage surface mount capacitors are too expensive, so I still use through hole there.
Best regards,
Stan Hubler

on Mar 20, 2014

* Power tube amps were push-pull class B producing pleasant sounding even harmonics. "Totem pole outputs used in transistorized equipment (if not perfectly ballanced) generates odd harmonics (and no even harmonics at all). Add the 'required' transformers that also changed sound qualities.

on Mar 20, 2014

you can produce the same harmonic ratios using solid state as tubes for the most part, class A tube and class A solid state are very similar in that regard. The issues, it has been found, are not so much in the absolute value of THD or IM but in the ratio of harmonics - the spectra. Very low THD amps are capable of not sounding "good" at all. Others are.

The through hole device problem is not mere a "challenge" - it's a *CRISIS*. Many devices are simply not available at any price from any source. Other devices are being supplied from Asia are bogus, fakes, junk that is rebranded. Even the larger distributors don't usually test (much less strip open or x-ray) the devices, but still sell them anyhow. BIG problem.

on Mar 24, 2014

I don't know if the problem finding through hole semis is as bad as you represent it, I'm sure many of the old RCA or Motorola (now On Semi) proprietary part #s/packages are gone but lots of times there are alternatives available. For example if you had a circuit that used a garden variety "traditional" pair like 2N2222/2N2907 you can still get PN2222 etc. Maybe junction FETs are getting hard to find, don't know, maybe there's a depletion MOSFET with a similar gate characteristic? At least modern devices mostly have lower "flicker" noise than back in the day! Give a more precise example so I can tell if I'm in general agreement, my observation is if the package is still current you can usually find something that'll work but I could be wrong for some cases.

on Mar 24, 2014

Another good article Lou.
Keep up the good work!

on Mar 24, 2014

Tube amplifiers don't sound /better/ than transistor amps -- they sound different.

The preference of guitarists for tube amps is that the clip more graciously -- mostly because they don't use as much overall feedback. (Doesn't anyone remember Sylvania's introduction of new tubes for guitar amps back in the early 70s?)

Someone once cracked that we've never heard what a tube amplifier /really/ sounds like -- what we hear is the output transformer.

If there is a tube amp that "sounds better" (that is, is more accurate) than transistor amps, it would have to be the Futterman. Unfortunately, no one manufactures it.

on Mar 24, 2014

Having a wall full of gold & platinum albums makes me NO more qualified to comment on this than a 6 year old who only knows what he likes to hear. I have had so many double blind tube vs solid state amplifier shoot outs over the years & I can only tell you the results - - the high quality tube amps ALWAYS won! Across the board from golden ears professionals to 6 year old kids just being honest. By high quality I do NOT mean expensive. Many of the new audiofile super expensive gold wire amps would loose to an ebay $250 vintage tube amp. I have lots of opinions as to why, but they are just that - opinions. With respect to guitar amps the vintage tube amps will probably always remain king. Famous transformer designer Deane Jensen was my personal maintenance man at my studio for the first few years of its existence and he was firmly of the opinion that it was the transformers in the old tube amps that made them win the listening tests and even though he & I could go into his transformer factory on a Sunday and wind transformers with MUCH better specs to substitute into old tube amps there was always a loss of perceptible sound quality to the trained and untrained ear. He was of the opinion the the toxic chemicals used in the vintage transformers that were no longer available anywhere were probably responsible for this!! The old toxic insulation materials somehow may have sounded better and that was his personal explanation for why reissues of old vacuum tube recording gear and vacuum tube tube amplifiers never sounded as good as the vintage originals that they were being sold as identical replacements to an new generation of gear heads. There are two definitions of the word OPINION - 1> an expert formal judgment based on experience, education, or training: 2> an uninformed utterance

on Mar 25, 2014

Do push-pull tube outputs suffer from crossover distortion like transistors? Is that one reason they sound different (or better, if you want)?

on Mar 25, 2014

I have recently started restoring vintage radio equipment. I have worked on tube equipment from time to time, but until I took the plunge and purchased a cheap tube receiver for the HF bands (I love the smell of a hot tube!) last November, I had forgotten what I had been missing. The tube receiver is much more pleasant to listen to than any of my solid state HF gear, and just as sensitive, although in most cases, not as selective. Since November, I have bought several Hallicrafters, National and Hammarlund receivers and transmitters and am having a heck of a fun time restoring them all.

Most of the equipment I have been purchasing is pre 1950. This is excellent gear and easy to repair. Even a replacement coil is not that difficult to find, or repair. The things are big enough that they can be rewound by hand if necessary. My earliest is a 1929 Philco High Boy TRF (Tuned Radio Frequency), with original tubes! It works great but is extreemely loud. The volume control is a pot in the antenna line! I am sure it worked well when a broadcast transmitter was 100W and a hundred miles away, but with 50KW transmitters and 50 miles away, if that, the radio is too loud even without an antenna connected. Low sensitivity isn't a problem with this radio.

The tube may be dead in some peoples minds, but they will be around for a long time to come.

on Mar 31, 2014

I've read many of the amplifier construction books. The reason why they say tube amplifiers are preferred among musicians is that the tubes produce even harmonics, insted of odd (solid state). And guess what - the musicians like the even hamonic distortion!

on Apr 9, 2014

When I build a high power RF amplifier, solid state is out of the equations. Ice on an antenna will cause a solid state amp to either shut down or decrease output for protection. Give me 3KV B+ and a good triode for a simple design high power RF amplifier. GU-43B's are rugged, cheap, and good to 1.2 GHz.

on Apr 7, 2014

When I build a high power RF amplifier, solid state is out of the equations. Ice on an antenna will cause a solid state amp to either shut down or decrease output for protection. Give me 3KV B+ and a good triode or for a simple design high power RF amplifier. GU-43B's are rugged, cheap, and good to 1.2 GHz.

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Lou Frenzel

Lou Frenzel is the Communications Technology Editor for Electronic Design Magazine where he writes articles, columns, blogs, technology reports, and online material on the wireless, communications...
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