Ask Slashdot: How Do You Build Your Own Vacuum Tubes?

Could you beat wireless headphones by creating your own DIY home audio system? Two weeks ago one Slashdot commenter argued, "to have good audio that is truly yours and something to be proud of, you need to make your own vacuum tube amplifier and then use it to power real electrostatic headphones over a wire." And now long-time Slashdot reader mallyn is stepping up to the challenge: I want to try to make my own vacuum tubes. Is there anyone here who has tried DIY vacuum tubes (or valves, to you Europeans)? I need help getting started -- how to put together the vacuum plumbing system; how to make a glass lathe; what metals to use for the elements (grid, plate, etc). If this is not the correct forum, can anyone please gently shove me into the correct direction? It needs to be online as my physical location (Bellingham, Washington) is too far away from the university labs where this type of work is likely to be done.
Slashdot's covered the "tubes vs. transistors" debate before, but has anyone actually tried to homebrew their own? Leave your best answers in the comments. How do you build your own vacuum tubes?

Comments

Covered in the past.

[Pikoro]

Here's a good one with links to more: http://hackaday.com/2016/05/04...

Re:Covered in the past.

[Pikoro]

And here's another: http://hackaday.com/2014/11/21...

Re:No no no.

[Anonymous Coward]

The reason real guitarists prefer tubes is because of the distortion. Solid state just doesn't compare.

Re:No no no.

[KingOfBLASH]

Actually that's not true, just ask a guitarist (and IAAG - I Am A Guitarist!)

Vacuum tubes create a noisy signal, but in a weird coincidence, they do it in a way that is pleasing to the ear. The clipping and distortion sounds "warm," and there's an added depth in the sound (harmonics) that you don't get via transistors -- unless you create circuits that mimic the behavior of a vacuum tube.

Metallica? Tube amps. John Mayer? Tube Amps. Clapton? Tube amps. BB King? Tube amps. Eric Johnson? Steve Vai? Garth Brooks? All tube amps.

Of course, much of the "tone" we guitarists revere comes from overdriven and abused guitar tubes -- cranking up the volume on the tube so that there's massive distortion and noise -- which again sounds pleasing to some people.

Now, it's one thing to overdrive a tube or change the bias on it to get a particular sound from your guitar, what about building a tube amp to just listen to music?

Well, I suspect this is essentially "remixing" songs. Adding a bit more depth, dirt, or warmth (from the noisy tube) might sound better but that's subjective, and it's all about personal preference.

So, sir, you might argue that you dislike what a noisy tube does to your signal, but you can't say some people won't perceive it as improved, as it's about personal taste.

Re:No no no.

[Anonymous Coward]

So they waste your money sticking vacuum tubes in the circuit, then use solid state amps in the actual headphones. I'll stick with my original Koss ESP-9 electrostatics - they've stood the test of time without the vacuum tubes raising from the interior gimmick.

Re:No no no.

[Anonymous Coward]

You cannot measure or quantify sound quality.

Yes you can. Hi-Fi equipment is suppose to *reproduce* the original as accurately as possible. This is something you can and people do measure. Hence the name Hi-Fi an abbreviation of High Fidelity.

Yeah, no

[fyngyrz]

Okay, we need to discuss classic amplification (IOW, not digital) and tube vs. transistor distortion. Applies to all audio reproduction systems - receivers, preamps, amps, headphone amps.

When run entirely in their linear range, which is to say, in class A amplification, where very expensive and/or high end analog musical system designs sometimes run, analog devices, be they tubes, fets or bipolar transistors, all follow the input signal faithfully, plus or minus total system noise and phase shifts -- no "warmth" or other characteristics are inherent in even a half-decent design, unless you add it yourself with tone controls or the like. *NONE*. For the record, tubes make the most noise, bipolar transistors next, various field effect transistor types the least. Analog integrated circuits tend to use bipolars and/or FETs; look the specific IC up to see, there's no telling otherwise.

So what you want, ideally, is the very minimum of distortion, noise, and as close to perfect signal reproduction as you can get. What goes in equals, as closely as possible, what comes out. But class A is an expensive and power-hungry way to do anything. So most reasonably priced tube and transistor linear amplifiers tend to run in class AB, which uses two devices or sets of devices at the high levek output, where one set amplifies the negative excursions of the signal, the other the positive set. The idea is that the devices are slightly on all the time, and when they begin to amplify their part of the signal, there won't be much distortion from moving into the linear part of their amplification curve from the non-linear, off, part, because the device isn't switching from off to on, it was already on. This works really well, and some very high end tube and transistor equipment works this way. Uses a little extra power, but it's a great compromise.

So what's different in a useful and interesting way between tubes and transistors? Well, when a tube is pushed into its nonlinear range, the gain transfer curve bends over comparatively smoothly so that what would be a sharply clipped (squared off) signal in a device like a bipolar transistor, turns first into a compressed signal, and even later down the curve, begins to evidence harmonic and other distortion that somewhat resembles that produce by hard clipping, but has, because of that still-somewhat-gentle curve, an entirely different set of dominant harmonics as compared to, for instance, a bipolar transistor at or near saturation. So the distortion, when the system is run so hard it distorts, sounds quite different.

That characteristic is why (knowledgeable) musicians who use distortion as a tonal tool often choose tubes; specifically because these musicians *do* run the tubes out of the linear area of the transfer curve, and the result is interesting -- and often pleasing. When the distortion is the result of a transfer curve that abruptly goes from highly linear to highly nonlinear, as is the case with bipolar devices, the result is most unpleasant. Edgy. Sharp. Dissonant. It isn't very often that such a thing is well received in a musical performance.

However, this choice does not *ever* hold true for a musical reproduction system based on tubes that isn't running in a range that will distort the music. You'd have to turn it up so far that one or more elements of the preamp or power amp is pushed past the linear part of its transfer curve, and then all of the music distorts -- and that's not a "warm" sound, that's a "hey, your system sounds awful, turn that thing down before I puke" sound.

So, for example, if I get out my Les Paul or my Strat and plug it into a tube amp and turn that bizatch up, I'm doing so because the amp's distortion is going to very significantly color the reproduction of what I play. I'm going to adjust the amp specifically so I *get* distortion. It'll sound fabulous. I'll get feedback, there will be awesome weirdnesses when I hit harmonics on my strings, pick and fretting artifacts will sound very different,

Re:Yeah, no

[Anna Merikin]

Wow! Exactly what I've learned in fifty years of audio/broadcast production. I wish I had written it; I certainly wanted to.

I would give the speakers/headphones more emphasis, however. No matter how expensive your rig is, speakers as good will be more. Much more. Including the speakers (especially cheaply-made and poorly designed) in the system evasluation gives an edge to the way bipolar transistors handle transients or square waves. A high power-to-cone mass speaker will follow the sharply cut off curve of a transistor well enough to make a listener's ears bleed, that's true, but a low power-to cone mass cheapie will not; its physics actually complements the transistor's characteristics by not following its sharp peak, but taking its lazy time returning to its accurate excursion limit. In effect, a cheap speaker "smooths' the spikey output of an overdriven bipolar transistor or IC.

But wait, there's more! Psychology is the number one influence. We like what we are used to hearing. We get used to good audio over time, and we become more selective. Or, if we have only heard distortion all our lives, we get to miss bad production if it is absent.

Re: Yeah, no

[Jfetjunky]

You're pretty spot on. Just a few points to highlight. 1. Bipolar devices have the very lowest broadband voltage noise of widely used transistors, with field effect being a bit higher (but with significantly lower current noise). 2. Modern audio devices correct nonlinearities with excessive open loop gain and feedback. This gives them the knee point after which distortion vs frequency begins to rise (because the open loop gain begins to drop vs frequency). It works well but gives the "audiophiles" one more thing to point at, since most tube amps run multiple stages, each with a fixed amount of local gain. 3. The last is psychological, and it's something I had to force my self to come to grips with as someone who literally used to design extremely high performance audio test equipment: If someone thinks something sounds good to them, it sounds good to them. Just like taste or smell. Which is why the whole audiophile mythos exists. 5. 32bit systems are a joke. None of them have low enough noise. For high end systems the first 20 bits might be useful information , if you're lucky. After that the rest of thr bits are noise, and are, from a physics standpoint, hooked up to a gaussian random number generator. Happy listening.

Re: Yeah, no

[Anonymous Coward]

And one step further - the room the speakers are in can do horrible, or wonderful things to the audio as perceived at your listening position. (Usually horrible in domestic rooms.)

Spend a few bucks on corner traps and absorber panels (I like rockwool/mineral wool absorbers - effective, easy & cheap to build and look decent) and you'll completely transform your listening experience.

Re:No no no.

[BlueStrat]

Of course, modern solid state amplifiers aren't particularly power limited (at least if you have the cash) and should never be driven into distortion. Effects pedals give you whatever distortion you want and have the advantage that you can turn the amplifier some level other than 11 and you still have the distortion you like.

As a pro-level guitarist for 4+ decades and who also has been designing & building tube guitar amplifiers for nearly as long, I have to disagree.

Distortion type effects pedals are attempts to imitate what goes on in a tube guitar amplifier being pushed to (and past) it's limits and some come close (and many more close enough for the average local artist/band in bar/small-gig venues) but it does not sound nor 'feel' the same to play through for a good guitar player.

Nearly all the flagship lines of the major guitar amplifier manufacturers are tube amps. Most pro-level concert/festival guitar amplifier backlines are tube amplifiers. Fender Twin Reverbs, Super Reverbs, and Marshall amplifiers (often vintage '60s/'70s era) are the vast majority of venue-owned backline kit provided for touring acts (and usually specified by the artist/band in the performance contract 'riders' section) at most large venues.

As to making a home-brew vacuum tube, it is doable but not practical. To get predictable performance mechanical tolerances must be exacting and the materials used in commercial tubes are rather exotic and difficult (if not impossible to come close to) for a home-brew vacuum tube maker. What you end up doing is making a tube using 'best guesses' and test/measure the tube's operational parameters and design the circuit around those parameters, rather than the other way around.

The other problem with the inability to make tubes with fairly consistent and predictable performance and operational parameters is that it makes building things like the typical push-pull 2 or 4 tube Class AB1/AB2 power amplifier extremely difficult, as the tubes must be fairly close in there operational parameters or the unbalanced circuit will likely destroy the tube(s) of one side that conduct the most current. It would also be necessary to custom-wind output transformers to whatever plate impedance the tube(s) happened to exhibit

If you love vacuum tubes and spending exorbitant amounts of time & money mucking about with molten glass and exotic metals for fun, have at it. Just don't expect to build the equivalent of a McIntosh MC30 or a 100-watt Marshall using them.

There is an amazing amount of exacting engineering, sophisticated manufacturing processes/techniques, and exotic materials science in the old commercial vacuum tubes even by today's standards and is pretty much impractical and beyond the means for the vast majority of private experimenters to reproduce in a home shop.

Strat

I make tubes!

[Doctorglasseye]

Howdy all, I'm a scientific glassblower (25 years now), and I make my own tubes. I'm at www.incandescentsculpture.com; not much tube info there yet -been a few years in beta mode on them, but some other high-vacuum delights are to be seen. (My handmade incandescent bulbs, my Tesla wireless brush bulbs, the 'fuxie' tube....) Even the production of a simple, low-mu triode is non-trivial; the requisite equipment and knowledge take years to acquire, and a page long essay to even enumerate. OP, I'd be glad to help; perhaps we can compose a FAQ and parts list for kindred spirits.

Re:No no no.

[Solandri]

This whole thing reminds me of the filters people have come up with to modify digital photos to simulate different types of film