
The Vacuum Tube’s Many Modern-Day Uses - zdw
https://tedium.co/2018/11/13/vacuum-tubes-modern-day/
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i_am_proteus
What this article doesn't mention is why vacuum tubes are still used in guitar
amplifiers:

The "distorted guitar" sound common in rock music is a direct result of
nonlinear characteristics of tube amps (both the tubes themselves and the
coupling transformers necessary to connect an output tube to a speaker). Tubes
exhibit "soft clipping" when pushed to their limits, which has the effect of
producing the harmonic content associated with distorted electric guitar. Rock
and roll pioneers got their sound principally from driving tube amps past
their limits. "Overdrive" pedals are usually just voltage boosters that make
the amp's input signal louder, but this pushes the amplifier past its clean
linear section into the nonlinear crunchy overdrive that guitar players want.

Modern tube guitar amplifiers, even "new" designs, generally follow one a
handful of basic circuit topologies, all derived from a few classic designs.
Even the iconic Marshall "Plexi" amp was a close copy of an earlier Fender.
These circuits are extremely simple; a handful of tubes, transformers, and
passive components, often less complicated than the internals of a single
LM741. Here's an example:
[https://www.thetubestore.com/lib/thetubestore/schematics/Fen...](https://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-
Deluxe-5A3-Schematic.pdf)

It's possible to mostly recreate this sound with digital signal processing or
carefully-tuned solid-state analog circuitry, but players like the sound of
tube amps and are willing to pay for them, and so the market exists as it
does.

~~~
hamiltonkibbe
I’ve found that a really good proxy for how good an amp sounds is the number
of line-items in he BOM. The fewer the better.

A lot of the classic designs that sound good and still sell have exactly what
they need to get the job done well and no more. It’s almost like all the major
(and boutique) amp manufacturers took one of three or so amp designs and just
threw components at the schematic until you couldn’t recognize it right away,
and sell it as some revolutionary design. I wouldn’t be surprised to find that
it it all came from some RCA reference design in 1950

~~~
exabrial
There some truth to that, but not always.

Ideally you would want each time to be fed with a noise free constant current
supply. Having each tube on its own power supply would be incredibly expensive
but sound awesome.

Buffering the output of each tube would prevent blocking Distortion, but would
also be fairly expensive (although now we have mosfets that can handle 500+,
so that might not be as bad).

Split audio path about, where the bass goes through cleanly and the treble is
overdriven would also sound incredible, but be expensive.

Designs end up being about compromise: the above features will add $5-$35 to
the bom per tube, and in the end, a lot of people just end up buying on brand.

My Laney Lionheart L5T has a really cool preamp that uses solid state surface
mount components where they don't affect the signal. This drives the bom cost
down but sounds incredible (fully buffered fx loop, fully buffered reverb
tank).

~~~
i_am_proteus
And further counterpoint: some guitar players like the sound of overdriving a
tube power supply (the attack on a loud note reaches current limits for the
p/s rectifier tube, dropping rail voltage, increasing harmonic content). Mesa
"dual rectifier" amps made this an option, letting players switch between tube
and solid-state rectifiers.

There's definitely room for "improving" guitar amplifiers; I personally think
that many guitar players like classic sounds, buy on brand as you said, and
the brands just try to reproduce classic designs with any deviations made for
cost more than for any other reason.

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walxor
The article briefly mentions magnetrons and X-ray tubes, the former of which
is made in massive quantities today for consumer appliances. Other vacuum
tubes in current use include the vacuum fluorescent display, the
photomultiplier tube and the electron multiplier tube. I believe old school
vacuum tubes also still have application in high-wattage class-C RF power
amps. Vacuum tubes for audio receive a lot of lip service, but they really are
botique, lunatic fringe stuff in that application. Magnetron tubes are the
only practical choice for microwave ovens; in contrast, power output tubes for
audio amplifiers are inferior to semiconductors in every way.

~~~
mmmBacon
I think you mean traveling wave tubes for high power RF amplifiers
[https://en.m.wikipedia.org/wiki/Traveling-
wave_tube](https://en.m.wikipedia.org/wiki/Traveling-wave_tube)

There are also klystrons, which are oscillators, used for high power radar
generation, particle accelerators, etc...
[https://en.m.wikipedia.org/wiki/Klystron](https://en.m.wikipedia.org/wiki/Klystron)

------
CaliforniaKarl
And of course, there's the Nixie tube.

[https://www.youtube.com/watch?v=wxL4ElboiuA](https://www.youtube.com/watch?v=wxL4ElboiuA)

(Previously posted in
[https://news.ycombinator.com/item?id=12623738](https://news.ycombinator.com/item?id=12623738),
the maker's web site via
[https://news.ycombinator.com/item?id=12308974](https://news.ycombinator.com/item?id=12308974),
and covered in an IEEE article via
[https://news.ycombinator.com/item?id=17397133](https://news.ycombinator.com/item?id=17397133))

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sehugg
In 2002, you could buy a PC motherboard with a sound section amplified by a
dual-triode vacuum tube. You can still find them on eBay:
[http://ixbtlabs.com/articles2/aopentube/](http://ixbtlabs.com/articles2/aopentube/)

~~~
dharmab
There's still a market for tube amps, although most are external for both
aesthetic and practicality purposes.

~~~
rolltack
Guitar amps too!

------
dustycat
People who are interested in vacuum tube technology might enjoy the following
youtube channel:

[https://www.youtube.com/user/MrCarlsonsLab](https://www.youtube.com/user/MrCarlsonsLab)

~~~
jhallenworld
A counter channel (hilarious guy revives old TVs sitting out in the desert for
50 years). He's the voice of LA:

[https://www.youtube.com/user/shango066/videos](https://www.youtube.com/user/shango066/videos)

Also, make your own tubes (in Texas while wearing a dress):

[https://www.youtube.com/user/glasslinger/videos](https://www.youtube.com/user/glasslinger/videos)

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exabrial
I recently designed and built my own guitar amp. I highly recommended the book
"Designing Preamps for guitar and bass". Absolutely fascinating read and
software engineers could learn a lot from the writing style! It's very
approachable.

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burfog
I didn't see too many uses listed. Here is one:

[https://en.wikipedia.org/wiki/Active_Denial_System](https://en.wikipedia.org/wiki/Active_Denial_System)

[https://en.wikipedia.org/wiki/Gyrotron](https://en.wikipedia.org/wiki/Gyrotron)

[https://www.sciencedirect.com/science/article/abs/pii/S00422...](https://www.sciencedirect.com/science/article/abs/pii/S0042207X13001516)

~~~
CamperBob2
Other than ADS systems, and the audio and microwave ovens mentioned in the
article:

\- Huge-ass klystrons used to drive particle accelerators (which themselves
can be thought of as the largest vacuum tubes ever made)

\- High-power transmitting tubes used in radio and TV broadcasting

\- TWTs are still used for some satellite communication work, both on the
ground and onboard the space vehicles

\- There's still no solid-state substitute for X-ray tubes. Hard to find a
semiconductor with a 50,000-volt band gap

\- Cesium-beam tubes used for timekeeping (as well as masers used for the same
purpose, for that matter), although entire atoms are emitted in those sorts of
tubes rather than just electrons

If you don't count fluorescent lamps as "vacuum tubes," those are about all
the remaining applications I can think of.

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Aloha
High power RF transmitters are still a notable realm of tubes.

~~~
jhallenworld
True, but apparently not any more in the broadcast industry. To make a 50 KW
AM station these days, you use 50 1 KW solid state amplifiers and combine
their outputs.

[https://www.youtube.com/watch?v=GXh23qrPniM](https://www.youtube.com/watch?v=GXh23qrPniM)

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raintrees
Glad I have not jettisoned the two or three boxes of tubes stored up in our
water tank tower that I inherited from my father in law - Time to go exploring
again!

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hamiltonkibbe
Photomultiplier tubes, still pretty much the only solution for photon-counting
applications.

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WalterBright
Vacuum tubes can't be that hard to make.

