Picture of Building A Stereo Tube Amp
Ever wanted to build a highly dangerous, inefficient, yet awesomely retro 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. Going through the process of purchasing parts, planning, and executing is a useful experience for any maker. Keep in mind that I am just a dude on the internet - take everything I say with a grain of salt. Except, of course, for these next few sentences. This project is dangerous in a very serious way. It involves high voltages and a lot of current that can make you feel decidedly unpleasant or even decidedly dead. If you decide to work on it with the power on, be careful. Some of the capacitors in this amp will hold onto a charge for a long while after the power has been switched off. Discharge all capacitors through a resistor connected to ground, preferably with a voltmeter across it to be absolutely sure the cap has completely discharged. When testing the amp out for the first time, use something like a twelve volt power brick instead of plugging directly into the wall, just to be safe, as well as to prevent things from exploding or melting. An old trick is to keep your left hand in your back pocket all the time, so if you do get shocked, it hopefully won't reach your heart.

Also, you'll need to know how to read a schematic, solder, and use a hand drill.

****UPDATE****: Kits are now available on my site!
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emuñoz61 year ago
Hello! I live in Florida, any idea were can I learn electronics in order to build a beauty like this? Thanks!

online!!!! lol look up "Uncle Doug" on youtube he literally takes you though the steps of building one including troubleshooting and how the whole thing works!! and by your definition of "Learn", tube amps have a HUGE amount of allowed error in them compared to transistors thus trial and error is a VERY good way to learn... just pull up an old fender guitar amp schematic (ex: the simplest 5F1 that "I" learned with) and build one!!! and if you have any problems email ppl on forums if you cant find help I have a guy who used to engineer tube broadcast stations in korea and I can ask him questions so just email me ( or ( and id be glad to help

davidm2004 days ago

the transformer hum is literally from the 60Hz (mains electricity frequency) hum which vibrates the transformer quite a bit to the point where you can fell it by touching it (kinda feels like your phone vibrating) which just means your laminations for your transformer core isn't solid enough or youre using an air coil (saw it in a photo up there ^) second using copper sheets for the grounding plane will result in hum due to ground loops that can lead to hum or even modulation of the sound waves. By experience the unmatched tubes for the PP (Push Pull) system doesn't have that much of a significant effect although the PP will be a source of modulation if not correctly designed. Also the hum might be through the induced frequencies from power lines etc. Thus cross all wires at right angles and have everything neat and tidy (trust me.... i built tube amps for a while and It helps to be OCD when building tube amps...mods repairs and fighting hum just gets so much more easier) and one more point that not many people know.... have the transformers all on different planes meaning to put the power transformer upright then the output transformer laying down etc. so that the core of the magnetic field does not interfere with each other. happy building :)

davidm2002 months ago

the hum is
A: from the preamp circuit picking up on the AC frequency
B: bad capacitor lineup (Especially in the filter capacitors for the DC power)
C: unmatched output tubes in a push-pull style amp
D: poor placement of ground point or buss thus creating a "loop effect"

For the transformer hum IDK what the problem is. Most high end audio transformers are encased in tar for this exact reason.... new "Better" transformer maybe? switch from a toroid to a iron core?

HeS15 months ago

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jackricci7 months ago

how are you determining the Vdrop resistiors?

paler311 year ago
Hi great tutorial I was toying with the idea of building one of these. However I am in the UK which has a mains voltage of 240V as opposed the the lower american 115V. Would i just need to change the hammond 167G120 for one of the hammond 229 series transformers?


get2john1 year ago
Slightly off topic here but can someone put my mind at rest and tell me the name of the piano music that plays during the video of the chap making hand made valves?
kcrow111 year ago
thobson - I am in the process of building this exact amp based on your instructable and info from Poinzie's DIY Audio Pages (Poindexter's Website with the 2002 design). I ordered mostly all the parts you used except I had Edcor make me some custom Audio Out Transformers and I used a high dollar caps for the coupling caps. I am planning on building Poindexter's Moebius Linestage that was made as the counterpart for this Amp once I finish the Amp and get it working. I have tried relentlessly to get a hold of Poinz but AudioTropic seems to no longer exist and all of the emails address I find for him come back undeliverable. I was hoping you could answer a question about the Amplifier that I have, as this is my first Tube Amp project (but not my first electronics project). The Hammond Power Transformer supplies 120V to the power does the half-wave diode bridge and the couple capacitors increase the voltage to the req'd 320V for 'A' and 305V for 'B'? I have not finished wiring the power supply up yet so I have not had a chance to test the circuits to see what the voltages are but I am just curious because Poindexter mentions using Transformers with 275Vac or 300Vac HV Secondaries for the main power supply in his 2002 schematic. I just want to make sure that this circuit will achieve the correct voltages in order to power the amp to its fullest capacity. I am aware the Vdc is equal to 1.4 times the Vac but with that said - 120Vac x 1.4 = 168Vdc. Do the diodes and caps in this main power supply circuit somehow double this voltage again?? Thanks in advance for any insight you can provide. I figured you would be the guy to ask since you built this same design I am working on and have already tested the voltages and have seen what is going on.
Nevermind....Since I posted this, I have built this particular tube Amp and the Line Stage. I have learned many things about Tube Amp Building and Designing Tube Amp Power Supplies now. I am actually working on a modified version of the 2006 Musical Machine - a 12AX7 driven 6550 Ultralinear design. Obviously, the entire power circuit will have to be redesigned to power the "bigger" 6550's. Using Thobson's Walk-through posted above, I am achieving 9.2Watts on each channel for a total of 18.4Watts MAX with my 6V6 Musical Machine. This is a little more power than is typical with this design but my voltages are a little hotter but not out of spec from what is listed on the 6V6's Data Sheets. I am hoping with the 6550 Machine I can achieve an output power of double what the 6V6 Machine is capable of. For those wondering, this amp (the 2006 6V6 Musical Machine) has plenty of power to fill a large room or small house with sound. Currently I have two Definitive Technology 6.5" Bookshelf Speakers connected to it. These are the rear speakers for my Home Theater Surround Sound System, but are doubling in use as my main speakers for the Tube Amp at this moment. I am using these as they are the highest sensitivity speakers I have at the house (93dB). In a 1450sq ft house, at full volume this amp is too loud to listen to when sitting in front of it, but perfect if I'm doing chores and cleaning the house up. You will want some sensitive speakers for this Amp as they will make it louder. I will be building some Folded Horn Enclosures soon to put a 6.5" 97-101dB speaker in and these will become the dedicated speakers for my Tube Amps. Thanks Thobson for an awesome write-up....good luck to everyone else who is embarking on this journey and building their first Tube is an educational experience and very exciting, mine was also quite shocking (literally), so be careful when testing the power supplies. I took 400Vdc to the wrist and elbow several times (grounded my arm accidentally while working on the amp). Fortunately it's not the voltage that kills but the amperage and in the case of this amp we are only dealing with 1Amp or less (not enough to kill but definitely enough to not feel good). Be smart and be careful! Good Luck!
batfish551 year ago
Transformers can conduct large amounts of current. Current produces a magnetic field. A magnetic field affects current. Thus, if transformers are close enough to one another, each transformer's magnetic field will affect the current of the other one. That affectation will be evident in the output audio signal.

How to avoid this? Mu metal. It has an extremely low magnetic permeability. This means that if you build a shield of mu metal around the transformer(sort of like a faraday cage), the magnetic field produced by that transformer will be conducted through the Mu metal instead of the air. It will also insulate the transformer from external magnetic fields (ie: the other transformers).

In short: build a shield of Mu metal around each of the transformers, and each transformer will not be affected by any magnetic fields around them. No foreign magnetic influence = no audible distortion.
nice job I was looking online for a push pull schematic this one is the one for me, the others online were using parts that all together costed <$500
thanks for posting,
p.s. when all said and done i will upload some pics of the amp
lloydrmc3 years ago
Sweet! Fantastic job! Well done, end to end.
Xellers6 years ago
(removed by author or community request)
wupme Xellers6 years ago
You know, thats exactly what i asked myself when i saw commercial iPod Tube Amps... What a waste..
REA wupme6 years ago
Thats apple! Ripping people off since the iPod!
thatonekid REA5 years ago
it has nothing to do with apple its just that compressing music into mp3 format looses lots of quality, you can easily convert tracks off of a cd to .wav files that sound much better but are ten times the size of an mp3. apple doesnt rip people off.
No it is apple. Other Companys create MP3 Players that sound better, have more features and no Copyprotection. Of course you can't compare an MP3 to an actual CD, but there is still a hughe difference on how the same MP3 sounds on an iPod or lets say an iRiver Player. Apple products is 50% of the price just for being Apple, to have some kind of symbol that you can show of with.
na your all just haters, apple puts top of the line audio processors in their products and you can easily transfer music off someones ipod onto your computer, just show hidden files in explorer, and on a mac there is 3rd party software that lets you copy music back and forth. and just about every piece of technology is marked up at least 2x what it costs to build when you buy it retail, not just apple. and trust me you get what you pay for when it comes to apple computers, they are not marked up any higher than any other brand computer with the same specs. and they use the highest quality parts for they're pcs and laptops, where else can you get a laptop with dual video cards, one being a dedicated 512mb GeForce 9600M GT, 4GB of DDR3 1066mhz ram and a 3.06GHz Intel Core 2 Duo processor with 6MB L2 cache, with a 1066mhz fsb, all protected by a single piece of billet aluminum.
"highest quality parts" -> See: Foxconn

Their pricing might be on point, that is if you count the extra $1000 for the aluminum casing.
@ thatonekid: That's nothing, there are laptop PCs with MUCH better hardware.
REA LkArio5 years ago
i have a Toshiba tablet PC. lets see Apple beat that.
REA thatonekid5 years ago
> can easily transfer music off someones ipod onto your computer, just show hidden files in explorer, and on a mac there is 3rd party software that lets you copy music back and forth...

ahem. for zune. connect, open zune software, rightclick the song, select "add to collection." no folders, no hassle.

>...where else can you get a laptop with dual video cards, one being a dedicated 512mb GeForce 9600M GT, 4GB of DDR3 1066mhz ram and a 3.06GHz Intel Core 2 Duo processor with 6MB L2 cache, with a 1066mhz fsb, all protected by a single piece of billet aluminum...

let me ask you something. yes they do have good specs, but what about the every-day person who doesnt know/give a damn about whats in there? let say i want a lappy that i will just be using to check my twitter or facebook or whatever it is kids check these days. am i going to go for a quad-core lappy with a NVIDA Gforce 2.5 tb graphics card (over-exagerated) and 3 pb memory (impossible), or am i going to get the lappy with a nice big screen and is easy to use? its not about quantity and quallity, its about what you need. and, no im not being a fanboy. honestly, i hate WinVista and am going to get OS X when i get the money, but i know what i need and what i dont, and Apple has what i dont need.
REA thatonekid5 years ago
lol hat?
wupme REA6 years ago
I think that amps are not even made by apple, was some 3rd party company. But still, you're right. iPod, iPhone all just to ripp people off. Other companys give you more, with higher quality, for less. Well except that they don't got an apple as logo...
REA wupme6 years ago
the only 3 things the did right: Apple I Apple II iTouch
Kasm279 REA5 years ago
 you forgot the older iMacs
If you factor in the piece of mind of not worrying about viruses, the resale value of macs being far greater than pcs (which have virtually no resale value), not having to buy virus software, the fact that you can run virtually everything on macs now since they switched to the intel chip and that OSX is profoundly better than vista and xp...macs come out on top.
You can only update the ram... That only gets you so far. Actually you can update everything in the Mac Pro (the desktop), but that computer's starting price is..... Unspeakable....
with some know how the hard drive and processor is upgradable in all the current macs
 the CPUs are soldered in on all of the current Macs except for the Mac Pro. The last iMac to have a removable CPU was thr tray loading G3, last laptop was the iBook G3 Clamshell and the PowerBook G3.
Xellers wupme6 years ago
Hmmmmm.... I'm going to have to disagree with you, I like Apple products such as the iPod because they are very easy to use (and hack), and because everything is kept simple and tidy (Although they cost much more than they should...). There simply isn't any MP3 player out there yet that can truly compete with the iPod (although I would really like an iPod like MP3 player that isn't made by Apple). But then again, I hate Apple computers because unlike PCs, their OS isn't very useful to me, they use non-standard parts (and are thus DIY proof for the most part), and they are way overpriced.
wupme Xellers6 years ago
Other companys MP3 Player are also easy to use, if you know how to move a file. You're not forced to use the stupid iTunes Software (I got all my 400 CDs digitalized and stored on a NAS, imagine to import that too iTunes..). I know there is 3rd party Software you can use for that, but there's also 3rd Party Software for other Players. There have always been MP3 Players that can compete with the iPod. Some Time Ago the iRiver Models beat every iPod, especially when it comes to Sound. Today is Archos. And even cheaper MP3 Players by other companies run out the iPod. Its just a novelty item, and besides the iPhone (wich is in my opinion a really bad mobile that didn't bring anything new ...) hyped more than anything else. If People would start to directly compare them, they would stop using it, well except those who only look for Design.
REA wupme6 years ago
you have brought a very good argument to the table.
But I thought this was an instructable, not an I HATE APPLE forum....... just kidding. They make nifty computers, if that counts for anything...
apple is good for recording studios and some gaming (large screen; built in NVIDA G-Force graphics card). for people who want it for normal things, coding, and visual customization, its hell to work with.
Mac just takes some getting used to and a large pocketbook...
i dont think ▼this▼ would be concidered a "pocket-book"
Xellers wupme6 years ago
That's true, but I got all of my iPods broken or obsolete and for free from people who didn't know what to do with them, so when I have a collection that works well, I can't complain.
digital amps will cause a further loss in audio quality
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