
Say Goodbye to the Last Vacuum Tube Product - tlb
http://electronicdesign.com/blog/say-good-bye-last-vacuum-tube-product
======
ChuckMcM
This story really buries the lede. You can get 250W of radiated RF power out
of a transistor! That is pretty neat. Back in college I got to hear how the
magnetron would not ever be feasible in a solid state device, the free
electron path length was too short. Another impossible thing, now available
from Digikey. Also a bit scary as it makes some previously impractical weapons
more so (like the MASER).

If they are cheap enough (and I suspect they are) they might make a good bird
abatement device as well.

~~~
vonmoltke
A press release[1] indicates the price is $26 - $37 each in 10k lots.

[1]
[http://www.businesswire.com/news/home/20141005005052/en/Free...](http://www.businesswire.com/news/home/20141005005052/en/Freescale-
Modernizes-Microwave-Oven-Appliance-Industry-Solid-State#.VEgwQXW9-V5)

~~~
aidenn0
That puts the cost at over $100 for a 1kW oven though; seems like it will only
be in high-end ovens at first.

~~~
vonmoltke
Basically what happened with LCD panels and televisions. Once Freescale ramps
up and someone else, like Triquint, enters the market the price will come
down.

~~~
ridgeguy
And also what happened with magnetrons in microwave ovens. They were so very
expensive 6 decades ago. Now I can go to Costco and get a 1kw microwave source
for less than $100. It's great for home-brew plasma deposition systems.

------
donatj
I have two tube headphone amps on my desk, one of which I just bought new a
couple months ago right in front of me, and 3 other people in my office have
similar tube amps. Probably not the norm, but still the death of tubes has
been greatly exaggerated.

edit: photographic evidence: [http://jdon.at/15kV9](http://jdon.at/15kV9)

~~~
ska
That was the first thing I thought also, but I guess you can't argue that tube
amps (for headphones, guitars, whatever) is a pretty niche product these days.

~~~
ArkyBeagle
They are not at all hard to find.

~~~
taeric
Not much is, anymore.

~~~
bashinator
They have never been hard to find. Virtually every guitar store has carried a
wide variety of tube amps since rock music went mainstream.

~~~
turnip1979
You know what electronic part is hard to find these days? Variable capacitors!
At the caps needed to make radios. Sure, you can buy them in bulk or at ham
fests, but I've found it frustrating as a hobbyist.

~~~
jacquesm
You can fairly easily build your own.

~~~
turnip1979
You're right. I've followed instructables on how to do it (e.g. some cds and
some foil). However, I am mesmerized by the beauty of some old school variable
capacitors. Wish they still made 'em.

~~~
jacquesm
We used to call them meat mincers :)

If you want good quality variable capacitors then your best source is flea
markets and thrift stores, look for old tube radios that you can scavenge them
out of. And if the radio is nice enough then maybe restore it!

------
wtallis
My perspective, as someone with some experience with truly high power
microwave tubes (multi-MW, not sub-kW): It's great that that a quarter
kilowatt can be done in solid state, but it's not a death knell for microwave
tubes. 58% efficiency at 2.45GHz and 63% efficiency at 915MHz sound reasonable
but aren't a breakthrough, especially for a narrowband application like RF
heating. The big savings come from ditching the strong magnets and high
voltage power supplies. Size _may_ be a significant improvement, but these
devices still need to dissipate more than a third of their power as heat, so
it's not as drastic as pictures may imply.

Solid-state devices have been gradually encroaching on vacuum tubes for a long
time, but vacuum tube tech has been advancing, too. I'm not sure that cathode
lifespan is much of a concern anymore at the power levels that solid-state
devices can reach. The upper limit of how much power you can get out of a
single tube is still growing, as is the efficiency. There's a lot of low-
hanging fruit for the design of microwave tubes now that we can actually do a
3d simulation without a supercomputer.

Solid-state devices haven't surpassed any of the fundamental limitations on
vacuum tube devices except for the entry costs of having a high-temperature
high-voltage cathode, a vacuum chamber, and a strong magnetic field.

~~~
vanderZwan
I kind of wonder what someone with your background thinks of the following
articles:

[http://www.lowtechmagazine.com/2014/06/thermal-efficiency-
co...](http://www.lowtechmagazine.com/2014/06/thermal-efficiency-cooking-
stoves.html)

[http://www.lowtechmagazine.com/2014/07/cooking-pot-
insulatio...](http://www.lowtechmagazine.com/2014/07/cooking-pot-insulation-
key-to-sustainable-cooking.html)

------
kazinator
These sexy things don't seem to be going away:
[http://en.wikipedia.org/wiki/Vacuum_fluorescent_display](http://en.wikipedia.org/wiki/Vacuum_fluorescent_display)

A fluorescent lamp also qualifies as a vacuum tube:

[http://en.wikipedia.org/wiki/Fluorescent_lamp#Principles_of_...](http://en.wikipedia.org/wiki/Fluorescent_lamp#Principles_of_operation)

[http://en.wikipedia.org/wiki/Fluorescent_lamp#Cold_cathode_l...](http://en.wikipedia.org/wiki/Fluorescent_lamp#Cold_cathode_lamps)

 _" Most fluorescent lamps use electrodes that operate by thermionic emission,
meaning they are operated at a high enough temperature for the electrode
material (usually aided by a special coating) to emit electrons into the tube
by heat."_

Thermionic emission is how vacuum tubes work, like the 12AX7's and 6L6's or
whatnot in your guitar amp.

------
j_baker
Ahem... the _last_ vacuum tube product?

[http://www.samsung.com/us/2012-vacuum-tube-
amplifier/](http://www.samsung.com/us/2012-vacuum-tube-amplifier/)

~~~
ori_b
The last _useful_ vacuum tube product.

Tube amps distort the sound more, and clip more gradually. This basically
means that a digital amplifier can perfectly emulate a vacuum tube amplifier
as long as you aren't maxing out the range and clipping the digital amplifier.
(You may need a slightly higher rating on the digital amplifier to achieve the
same volume.)

~~~
morganvachon
I take it you're not a guitarist. Tube amps can generate tones and sounds that
are impossible to emulate accurately via solid state. I've owned some really
nice solid state amps that can do amazing things, but even a shitty tube amp
can do overdriven fuzz better than any solid state amp.

~~~
driverdan
> impossible

Not impossible. Hard, expensive, or currently not available but not
impossible.

~~~
GrouchoDarts
Well, allow me to go into a bit of science detail. The two polar opposites in
amplification technology today are Class A and Class D amplifiers. Class A is
the classic one, and any audiophile and sound engineer will swear by them on
the quality metric. Class D is modern, based on transistors (usually MOSFETs),
and while it dumps the linearity, it has a huge advantage in energy
efficiency. Only in recent years has Class D become competitive in quality
with the lower end of Class A technology, as the linearity of amplification
makes a huge difference in high quality systems at higher amplification where
the details pop out more.

Class A uses tubes, and works in the simplest and most accurate way by
amplifying the complete signal. It maintains the most important characteristic
needed to perfection - linearity of waveform amplification. When you try and
get extra juice out of it, instead of the annoying clipping you get from
digital amplification, you get a nicer sounding and more gradual reaction. The
main drawback is energy efficiency. There's a theoretical peak efficiency of
50% to Class A amps, and what's worse is that it's usually less than half
that. It makes tube amps that aren't small require massive heat sinks, and
increases the BOM.

Class D is totally different. It dumps linearity out the window in favor of
energy efficiency. It basically outputs a bunch of pulses, and then applies a
low-pass filter to remove the annoying artifacts. While you might say that
it's close enough - it isn't for high fidelity systems, especially in
production studios, live performance, and audiophile cases. While competitive
in quality with the low end of amplifiers (under $200), if you are looking for
accurate detail reproduction there is no replacing linear amplification yet.
The advantage is that even at the worst use scenarios, Class D amps have over
50% energy efficiency, and usually manage over 90% for higher volumes, making
them need far less in the way of heat sinks which allows for leaner designs,
and a better price/performance ratio.

The Class D amps will eventually win out. Class A amps have decades of R&D as
an advantage, but Class D is improving by leaps and bounds. Eventually, Class
D will become "good enough" and replace Class A altogether because of the
advantages in price and energy efficiency. But that day has not yet come.

That being said, I use a class D amp for my home set up. It's close enough,
and my power bill thanks me monthly.

~~~
gsteinb88
>Class A uses tubes...

Class A amplifiers can be made in solid state as well, very easily. As a truly
simple, DIY example:
[http://headwize.com/?page_id=31](http://headwize.com/?page_id=31)

There's nothing about solid state that requires a circuit that "outputs a
bunch of pulses, and then applies a low-pass filter" \-- true linear
amplification exists in the transistor domain just as well.

And even if solid state did require quantization (beyond the shot noise that
vacuum tubes suffer from also), given that we can do direct digital synthesis
up to the 100's of MHz regime pretty easily these days (i.e. beyond the
bandwidth of most audio tube amplifiers), with 24+ bits of resolution, there's
no reason that a solid DSP system couldn't emulate a vacuum tube response well
enough to be electrically indistinguishable from the actual tube.

But, as the grandparent post notes, it's one heck of a lot easier/cheaper to
just use vacuum tubes. Which is why I'm staring at a tube-based headphone
amplifier on my desk right now. Though it does use solid state buffers, which
incidentally are way more linear than the typical ways -- capacitors,
transformers, etc. -- of removing the DC offset inherent to tubes...

------
Semiapies
"Maybe the magnetron is really not the last vacuum tube product"

Not by far. A more obvious example than the ones the article gives would be
tube amplifiers.

------
burnte
I dunno, I think a microwave with a vacuum tube will make my food sound warmer
and trued to the original analog food I remember as a kid.

------
webnrrd2k
Am I wrong, or is this a press piece for Freescale's new transistor?

------
lkrubner
I think this article is focused on consumer products? Last time I checked,
large scale items such as radar were still using vacuum tubes. I know there
were huge breakthroughs in solid-state radar back in the 1990s, but I don't
think that technology has seen a wide commercial roll-out.

~~~
AnimalMuppet
I went to college with this guy who was on a scholarship to study tube design.
(This would have been 1981 or 1982.) I said, "What are you studying that for?
Semiconductors are going to make tubes obsolete." He said, "You have 6000 amps
you're trying to control. Try that in a transistor." I mean, yes, there are
schemes that try to use multiple high-current transistors in parallel, but...
6000 amps is a _lot_ of current for semiconductors, even today.

~~~
Animats
There's been a lot of progress since then.

One IGBT pair. 1200 amps. 4500 volts. 140x190 mm housing:

[http://www.infineon.com/dgdl/Infineon-FZ1200R45HL-
DS-v03_01-...](http://www.infineon.com/dgdl/Infineon-FZ1200R45HL-
DS-v03_01-en_de.pdf?folderId=db3a304412b407950112b4095b0601e3&fileId=db3a304345087709014516f875431b4b)

~~~
wtallis
Impressive, except that the times are listed in units of microseconds, so it's
completely irrelevant to microwave use.

------
georgebonnr
I think more than a couple of people still buy guitar amps!

------
userbinator
_They often cook unevenly and typically lose power over time as the magnetron
filament and cathode deteriorate. At last it is possible to replace the
magnetron with solid state devices._

My microwave is several decades old now and its magnetron hasn't ever needed
replacement, and I haven't noticed any degradation in power level either. I
wonder if these new "all-solid-state" ovens will last nearly as long - I've
read plenty of reports about the "inverter" types (essentially an HV SMPS)
that use many more components which are often operated near their maximum
limits and fail sooner, compared to the older design with a simple (but more
expensive) large HV transformer.

~~~
wtallis
Magnetrons are rated for thousands of hours of operating time, and the
degradation is gradual. Unless you use your microwave oven to the exclusion of
all other heating sources, a 40 year old oven should still be doing alright if
it was well built to begin with. It's only industrial uses that have to worry,
and even so the amortized cost is tiny. (I've seen an estimate of $1/hour for
a 100kW industrial heating magnetron with a rating of 8000 hours, which is
quite a bit smaller than the operating cost.)

------
sam
Don't forget about the krytron,
[http://en.wikipedia.org/wiki/Krytron](http://en.wikipedia.org/wiki/Krytron)
If you need to switch thousands of amps in under a nanosecond you'll probably
need one.

~~~
sitkack
I know I made the mistake of ordering these and Beryllium sphere at the same
time. Oopsie!

------
myth_buster
Vacuum Tubes are very popular in high fidelity audio spectrum.

[http://www.head-fi.org/t/655961/pictures-of-your-high-end-
sy...](http://www.head-fi.org/t/655961/pictures-of-your-high-end-system-ii-
same-rules-apply)

------
jhallenworld
There are some very interesting stories in the history of vacuum tubes. One is
the 416A planar triode for the Bell Labs TD-2 microwave relay network:
[http://long-lines.net/tech-equip/index.html](http://long-lines.net/tech-
equip/index.html) (I like especially the story of the terrorist attack on the
microwave relay station by the "American Republican Army")

Another is John Pierce on Klystrons and TWTs:
[http://www.smecc.org/john_r__pierce____electron_tubes.htm](http://www.smecc.org/john_r__pierce____electron_tubes.htm)

------
lmg643
TWTs are going to be around for a long time. There are only a handful of
companies in the world that make them, and there are no real alternatives to
producing high power microwave signals.

~~~
wtallis
Well, TWTs are just one member of a family of vacuum tubes that can do things
solid state devices can't. There are also IOTs, klystrons, and BWOs, and their
cousins from the gyrotron side of the family. There's a lot of territory for
solid-state devices to conquer before vacuum tubes are obsolete, and solid-
state devices can't even operate in most of those regions, let alone
outperform vacuum tubes.

------
mikestew
Even within the article under "Related" there's a link to a story titled "Long
Live Vacuum Tube Amps" from earlier this year. Perhaps a more accurate title
would be "...Last Mass-Market Vacuum Tube Product". Because even just last
year I bought a nice little desktop tube guitar amp, and it looks like the
Fender Greta is still being sold. (Which I'd recommend if you're looking for a
tiny amp to noodle around with and still get crunchy tube goodness.)

------
georgebonnr
I think more than a couple of people still buy guitar amps.

------
rbc
Consider the array of new tube combo guitar amps carried by Guitar Center
right now:

[http://www.guitarcenter.com/Tube-Combo-Guitar-Amplifiers-
Com...](http://www.guitarcenter.com/Tube-Combo-Guitar-Amplifiers-Combo-Guitar-
Amplifiers,New-Gear.gc?ipp=25)

------
richieb
There are plenty guitar amplifiers still made with tubes. Look up Fender Twin
for example.

------
Immortalin
[http://spectrum.ieee.org/semiconductors/devices/introducing-...](http://spectrum.ieee.org/semiconductors/devices/introducing-
the-vacuum-transistor-a-device-made-of-nothing)

------
bitwize
Are you kidding me? People who are serious about music swear by an all-analog
mastering process with tube amps. The even harmonics make for a warmer sound
than the harsh odd harmonics of transistors.

~~~
kibibu
The only reason you get _any_ harmonics is if you drive them to nonlinear
distortion though.

If you have enough headroom, you can get near-zero transistor distortion and
then apply your tube modelling digitally.

Audiophiles are often stuck in the 1970's with this stuff.

------
hapless
Aren't vacuum tubes still used in photomultipliers?

~~~
mng2
A photomultiplier is a special kind of vacuum tube, but it's a pretty niche
market. Plus avalanche photodiodes are making inroads.

------
pistle
Virtually every kitchen has a built in microwave? I'm not so sure about that
monsieur.

------
allworknoplay
Um, vacuum tube diodes?

