HOWTO build a tube amp and "Electrons on Parade" 1942 video

Tom Hobson posted an enticing Instructables HOWTO on building a stereo tube amplifier. I haven't built the project, but I love the bonus video he linked to, a 1942 RCA promo for vacuum tubes titled "Electrons on Parade." From Tom's Instructable intro:
 Files Deriv Fff Rdx8 Finoaot7 Fffrdx8Finoaot7.Medium Ever wanted to build a highly dangerous, inefficient, and essentially obsolete piece of electronics? Well, I have. That's pretty much what a tube amp is. Vacuum tubes are old electronic components that act like transistors, controlling a lot of current with a little current. You usually hear about tubes being used in guitar amplifiers, because they distort in a way that suits guitar playing. However, tubes can also be used to amplify a stereo signal from another audio source such as a CD or MP3 player. Tube amps, unfortunately, aren't the most practical things in the world; they consume a great deal of power, get very hot, and are big. That being said, they look damn cool, and some people seem to think they sound pretty nice too.

You can learn a lot about electricity and electronics from a project such as this.
Building A Stereo Tube Amp


  1. One of my first stereo’s was from a kit (though I didn’t build it). It was a Dynakit tube preamp that worked, but was built incorrectly, giving a lopsided stereo image, eventually I had it fixed and it sounded great. I kinda miss it actually; it had “reverse” stereo, and an A/B switch that would make both speakers one side of the image alone (great for listening to two-channel recordings like the Beatles “Day Tripper” or some Coltrane sides).

  2. Meh, you can keep your new-fangled “electronic” vacuum tubes. Those looking for truely old fashioned radio should stick with spark-gaps and coherers.

  3. Curse my indolence. Am I the only person that sees these things and thinks “w00t, DIY electronics FTW! Must do that”, but never ever does?

    Still…nice video and post!

  4. I’ll put my old 100 Watt Fender Twin against a modern solid state amp any day of the week. I can kill cockroaches at 50′ using the rear pickup on my Tele – GRIN!

  5. #9 posted by redrichie:

    Curse my indolence. Am I the only person that sees these things and thinks “w00t, DIY electronics FTW! Must do that”, but never ever does?

    Yep, just you. The rest of us are posting on updated homebuilt versions of UNIVAC with hand-blown CRTs. And brass. Lots of it.

  6. Believe me, it’s very satisfying to listen to some tunes through an amp you’ve built yourself. A certain warm smugness best describes it.

  7. OK, whoever wrote the original misread the nature of this kit.

    Almost all audiophiles have a deep craving for tube amps, which is why so many companies make them. Moreover, single-ended triode tube amps are now old enough (since Carey Audio introduced them in the early 90s) to be past the fad stage.

    What’s this kit is NOT is a kit to build something old and obsolete. Rather, this is (and is supposed to be) a kit that allows those of moderate income to build a tube amp.

    Tubes boost the even-order harmonics and allow music to sound far more sweet and beautiful, arguably more like real music.

  8. You rarely ever see old technical books at 2nd hand stores but should you come across a large volume with a red binding with the title “RCA Radiotron Designer’s Handbook” grab it. It was actually compiled in Australia. It is the best collection of tube circuits ever put together with plenty of design examples.

  9. Yeah, what 13 said. A good tube amp sounds amazing reproducing stereo program. I think Tom is a robot sent from the planet Transistron. @ #5, yeah and a piece of mutton cooks just like a prime steak, it don’t make them equal.

  10. Hey guys,

    I think you’re probably right about the whole obsolete thing, but can you really blame a guy for trying to write a snappy intro? Consider the wrong righted, and thanks for all your interest!

  11. Bah. I spent 6 hours of my Sunday rehabbing 2 old tube amps and a tube preamp for a client. I don’t even remember what they were, and it was yesterday. It’s fun until it’s a job.

    Tube amps are about 5% as complex as a transistor amp. They’re the lawnmowers of the audio world. No matter how well they’re made they will still be simple, hot, inefficient and impossible to perfect.
    My favorite vintage tube amp of all time is the Heathkit W5M power amp. Absolutely amazing sound, but a distressing tendency to burn out their potted power and output transformers. I’ve been collecting and rebuilding them for years. I think my collection of those is down to about 24 or 25.
    If you’re interested in tube audio, I’d recommend browsing the very active tube audio discussion forum at Audio Karma.
    Even a modest tube amp, and all but a few elite designs are very modest, will open your ears to a new kind of sound. Listen to a tube amp for a while and conventional audio will start to sound hard, grainy, irritating and ‘cold’.
    The sound of tubes can be very habit forming.
    As a hobby, it’s pretty straightforward. The parts are all pretty inexpensive. Components are large enough that assembling a circuit is requires no more than ordinary dexterity. The possibility of electrocution adds an extra frisson of excitement.

  12. Am I the only one who finds the whole: vinyl sounds better, warmer, fuller, etc., than CDs, & tube amps sound better than solid state, etc. confusing to the n’th degree?
    Without getting too nuts, what is the difference? What should one listen for? It seems like CDs sound real good to me, adjust the treble and bass, sounds fine. I can’t pick up on the sounds I’ve heard described as “brittle”, “cold”, etc.
    How much of it can a layman discern, and how much of it is audiophile one upsmanship?
    So much of what is available, from amps to effects boxes, etc., is digital anyway.
    What #13 Keeper said, “even order harmonics”, what does that mean?
    I’ve heard folks say they want to record and play back on analog gear, etc. etc. But I’ve heard stuff recorded digitally and then ‘dirtied up’, that makes it sound like it was analog.
    Confusing as hell.

  13. Hearing is complex. People have been trying for over 100 years to quantify the correlations between signal and perception. Some of what they have learned is useful in providing satisfying reproduced sound and some of the research has yielded confounding contradictions.
    If you like the sound of a 48K MP3 through earbuds, don’t bother with tube amps. The differences won’t matter to you. If you have modest needs for power output and want to explore a technology that might return a little warmth and presence to many recordings then tube amps might be worth a listen.
    Anyone in the upper Midwest can find a huge range of tube audio on display at the 2009 Audio Karma AKFest near Detroit. It’s a blast.

  14. hey hey Hey HEY!

    Grandma’s going to be mighty unhappy when she sees what you’ve done with her breadbox there!

    Amplifier? Pffft! When I was your age I used to have a *lot* of fun with a cat’s whisker and hunk of galena!

  15. @ #18. Each sound has a fundamental frequency, that is a frequency where the most energy is. When that frequency and odd orders of magnitude (x3,x5,x7 ect) are amplified it sounds like added presence, but can also be harsh sounding. When even order harmonics are amplified (x2,x4,x6,ect) the result is an added “warmth”, too much is kinda artificial sounding. When a solid state amplifier is over driven it tends to accentuate the odd harmonics because it’s much more linear and tends to clip the signal harder. A tube amplifier tends to accentuate the even harmonics because it essentially compresses the peak energy (odd harmonics) when overdriven allowing the ratio of even to odd harmonics to be raised. That’s why solid state amplifiers have a bad rap. A FET type solid state amplifier acts more like a tube amp. A well designed solid state amp with plenty of head room can be outstanding, but an equally well designed tube amp is like listening to candy. Tasty candy.

  16. @#22 The story on distortion is that even harmonics are generated if the waveform is flattened at one extreme (positive or negative but not both) while odd harmonics are generated if it’s flattened at both positive and negative extremes equally.

    The best “warm tube sound” comes from underpowered single-ended triode amplifiers because they produce a buttload of even harmonics. The triode is inherently non-linear in the right way, and the underpowered amp saturates quickly, and the single-ended design ensures that saturation affects one peak of the signal much more than the other.

    To see this in audiophile terms, type “300b amplifier” into Google.

  17. It always amuses me that folks who like tubes (as I do) feel the need to justify them to the uninitiated. As if you needed a reason to like them. People who enjoy tubes usually just do, without needing a reason. Something about glowing glass is really special and awesome. I do acknowledge that they are considered to be a little heavy on the electricity use, but then again, the enjoyment they provide is worth it. If your television stays off because you are getting more out of your music listening then you are probably not using any more power.

    Also, they sound better when they are called “valves”. :)


    “Tube amps are about 5% as complex as a transistor amp. They’re the lawnmowers of the audio world.”

    That’s exactly the reason why I miss my old VW bug.

    Some people can’t notice a difference, some can. With respect to guitar amps I think it’s much easier to tell the difference: solid state amps tend to sound harsher when overdiven, however some people prefer that (Greg Ginn of Black Flag always preferred solid state amps, in fact his record company SST stood for Solid State Transmitters, as it was originally a mail order electronics company he founded). My old Supro amp sounds sweet, like saxophone, when overdriven. My modern Peavey sounds, well, like a piece of electronic equipment (which fits in well with the “5% as complicated” theory– I’ll take the uncomplicated saxophone, thanks).

    The bottom line is you shouldn’t worry about it. If you like listening to cassette tapes, that’s fine. R. Crumb and others insist 78rpm records sound the best, and there’s a whole subculture of people that love 8-track tapes. Whatever. I think MP3’s do sound kind of dull compared with LPs or CDs, but they make up for that with convenience. I would prefer to listen to a pristine vinyl recording on a fine tube stereo, but a cd on a similarly fine non-tube stereo is just as good; with high end equipment the difference is negligible even for snobs. There’s an old argument I use: would you rather listen to Charlie Parker on a plastic sax, or some hack on a nice Selmer? Good music always shines through, even on crappy equipment.

  19. Different people hear different things in sound, and in music. A great deal of it’s genetic. If mp3s sound as good to you as a high quality system with better input, then you get to save a lot of money. But if someone says something sounds better, give it a listen; maybe you just never heard really good sound.

    Transistors are indeed current amplifiers, but tubes are voltage amplifiers.


  20. Transistors are not current amplifiers. That’s a mistaken explanation for how they work. The Collector current in a transistor is controlled by the thickness of the Emitter/Base depletion region. The thickness of the Emitter/Base depletion region is determined by the emitter-base voltage, not by the base current. The emitter/base depletion region also controls the base current, which is why the base current and the collector current change correspondingly. But the transistor does not amplify the base current and present it in the collector circuit.

  21. You can think of a tube as a Thermionic Field Effect Transistor. The film above actually does a pretty good job of explaining the ‘valve’ action of the grid voltage controlling the current from the cathode to the plate.
    It’s almost impossible to exaggerate how important the development of the vacuum tube was to the modern world. Almost every complex electronic technology that we have originated with vacuum tubes, including digital computers. Television and radio broadcast, microwave ovens, RADAR, garage door openers and a thousand thousand other functions. Yesterday a neighbor came over to test the 25CD6 vacuum tubes from his ultrasonic jewelry cleaner. CRT television or computer monitor? That’s a huge vacuum tube.

  22. @23 NIXIEBUNNY. Something important to consider when looking for the warm tube sound of even harmonic distortion signature: It really only happens with single ended designs. Once you get fancy and start using differential or push-pull circuits to improve the efficiency (around 20% for single ended, up to 50% for Push Pull), you lose the even harmonics because the… uh… there’s no other way to put it: the transfer functions of the opposing tubes cancel out the ‘good’ even harmonics and increase the ‘bad’ odd harmonics.
    Most tube power amps are push-pull and have a little of the harmonic magic due to their single ended driver stages and graceful clipping characteristics but the real psychedelic harmonic loveliness comes from a no-feedback pure single ended triode amp with a classic output tube like a 2A3, 300B, 845, 211, 71A, 45 or 801A.

  23. One obstacle that hobby amp builders run into is how to acquire parts economically. Particularly difficult are the power and output transformers. They’re available new from a number of sources like Hammond Transformers but even modest ones cost a lot. Also difficult to accumulate are tubes, sockets and chassis. Many good amps have been built with parts repurposed from defunct vintage consumer audio electronics. Stereo consoles are popular sources for amps to tear down for parts. Yank the amp chassis out and toss the cabinet. Defective tube tape decks are cheap and common. Many have the capability to drive speakers and the amplifiers in them can be easily removed. With a salvaged chassis/transformers/tubes your project is 70% done for you.

  24. While I cannot comment on much of this post because I just don’t have the ear for it. (or have not been educated to have the ear for it, the debate rages) I did want to mention what for me was an interesting article that is exploring the perception of “heard” or “listened to” music. Many of you have probably read it, but if you have not, check it out.

    “The Sizzling Sound of Music” by Dale Dougherty –…d-of-music.html The article builds upon work and tests by a professor of music at Stanford, Jonathan Berger.

    I would also like to comment that for many people a significant degree of education(With this term being used in the broadest since.) accompanies changes in the standards that one has for good and bad. A simple and anecdotal personal example may help. I never appreciated wine until I met and dated a sommelier. It took almost 2 years, 2 breakups, and many sips of water and wine, but for me personally, its not the bullshit I thought it was and I now love [some] wine.

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