Introduction: Building a Stereo Tube Amp

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.

Step 1: First Things First: Tubes

Picture of First Things First: Tubes
Quick Intro to Tubes

A project such as this one can teach you a lot of about electricity and electronics. In order to appreciate what more or less goes on in this amplifier, we need to take a look at how a few things work, and first up are the vacuum tubes themselves.

A vacuum tube is just a glass tube that's had all the air sucked out of it. A good example is the early lightbulb, inside of which a filament was subjected to a current which caused it to produce energy in the form of light and heat. If the interior of the lightbulb were not a vacuum, the filament would experience combustion due to the high temperature in the presence of oxygen and be destroyed.

The Diode

The most basic vacuum tube is a diode, so named because of the two electrodes which it contains. Vacuum tubes are said to be thermionic, meaning that heat is used to encourage the emission of electrons from an electrode. If a negatively charged electrode (as in it has an excess of electrons, in tubes it's called the cathode) is heated by a filament, the electrons in it become 'excited' and, if a sufficient electric potential difference or voltage is present, they will actually be emitted from the electrode. The potential difference is due to another electrode, called the anode or plate, which is positively charged and therefore exerts an attractive force on these enthusiastic little particles, causing them to whip across the vacuum from the negatively charged cathode. Since electric current flows from negative to positive and never the other way around, the current can only flow one way in a diode. However, this isn't much good for amplification, so let's move on to the next step in the vacuum tube hierarchy: the triode.

The Triode

In a triode, there is a third electrode in addition to the anode and the cathode, called the grid. The grid carries a negative voltage and is connected to an input source, which, in the case of this amp, is a fluctuating audio signal. The negative voltage on the grid repels a certain amount of the electrons leaping off of the cathode, and how many electrons it repels depends on how negative it is, which in turn depends on the amplitude of the audio signal. This is by definition amplification: using a small amount of electricity to control a large amount. The audio signal is quite small, and it is effectively controlling the flow of however many electrons we choose to saturate the cathode with. The base voltage of the grid, the voltage that is present whether there is a signal or not, is referred to as the bias voltage. The bias determines how much current the tube draws when there is no input signal.

The Tetrode

Add yet another electrode and you get a tetrode. This new electrode is called the screen or shield. Basically, the screen prevents the flow of electrons across the tube to be affected too much by the anode, and instead be totally controlled by the changes occurring in the grid. It has a smaller positive voltage than the anode. When the electrons initially break free from the cathode, they can only 'see' the screen, and so they rush towards it, and upon reaching it notice the anode and continue on towards that.

The Pentode

Now we come to the pentode. In a pentode there is, obviously, a fifth electrode that wasn't there before. This is the suppressor. The suppressor sits between the anode and the screen and is somewhat negative in charge. Its purpose is to make sure any electrons that might bounce off the anode don't escape for too long by repelling them back into it.


Pentodes are not the end of the road when it comes to tubes, there are many other kinds, and if you're interested in them, check out the links step. There are two kinds of tubes used in this amp: triodes and tetrodes. The triodes are used in the preamplifier stage, where the audio signal is stepped up to a certain level suitable for further amplification by the tetrodes of the main amplifier.

Also, check out this fantastic old-fangled movie about tubes and how they are made:

Step 2: Parts: What You'll Need

Picture of Parts: What You'll Need


The guy who originally designed this amp, Poindexter of Audiotropic , has a wealth of information on his site about the parts he used. His device, called the Musical Machine, is made up of some very nice, but very expensive audiophile-type components (high quality specialty hookup wire, extra fancy solder). These components may well make for great sound, but somehow I just can't bring myself to spend $35 on a capacitor that I can have a reasonable facsimile of for two bucks, and my uneducated ears probably can't tell the difference anyway. So, for that reason, I have built the same circuit as Poindexter, but with cheaper and more available parts.

What You'll Need

The amp consists of two sections, the audio circuit and the power supply. Let's look at the parts in both.


You're going to need something to put your amp in, and there are definitely certain considerations to be taken when picking an enclosure. Transformers and especially the tubes themselves can get very hot, and so need to be in a well ventilated kind of area, preferably jutting out the top of the case. Unfortunately, in my case, I foolishly chose an enclosure purely for its looks, which ended up being a bit of headache. I picked an old wooden cutlery case, which just happened to have rather thick panels, making it painful to mount components that were designed to be mounted on circuit boards or thin metal project boxes. So, unless you want to spend the time making that kind of case work, I'd say go with something more conventional.


What to Buy

You'll be making the audio circuit twice over since this is a stereo amp, after all, and so you'll need two output transformers. Poindexter uses very fancy special order transformers that are way out of my price range, so I settled for a Hammond 125D, which, as far as I can tell, works fine.

There are four transformers in the power supply, one for the heating filaments in the tubes (Hammond 166N6), one for the main positive supplies (Hammond 167G120), one for the negative supplies (an Amveco toroid), and a 'choke' transformer (Hammond 158Q). A choke isn't really a transformer but an inductor. Basically, the function of a choke is similar to that of a capacitor in parallel, it resists sudden changes in current, and so acts as a filter.

Where to Buy It

I got these transformers from Angela Instruments which has a ton of old high quality audio components. Another good place is Parts Connexion . The Amveco toroid I ordered from Digi-Key (part no. TE62045-ND).


What to Buy

The tetrodes used in the main amplifier section are four Electro-Harmonix 6V6EH tubes, which are pretty easy to find. For the preamp tubes, we have two 5965 tubes which are double triodes, meaning each tube actually contains two triodes. If you look at the guts of the tube you will notice two separate metal sheaths; these are the triodes. Tube sockets are also essential for affixing the tubes to the case.

Where to Buy It

I got the tetrodes from [htttp:// Tube Depot] and the double triodes from Antique Electronic Supply . The sockets came from Antique Electronic Supply , eight-legged ones for the 6V6's and miniature nine-legged ones for the 5965's.


What to Buy

For the most part I just used regular metal film resistors, although there are a couple of high-quality Kiwame's in there just because I had them. The 60K and 62.5 4W resistors that you see in the schematic, called the plate load resistors are actually each two 2W resistors in parallel, two 120K's for the 60K and a 120 and 130 for the 62.5K. A few nice resistors are pretty cheap and most people insist on using good ones for the plate load, but they aren't necessary everywhere. The 100 ohm resistors connected to the 6V6 screen are rated at a 1/2W and I didn't bother with anything special, just regular old resistors. Same goes for the 100K bias resistors, 1/2W, metal film.

Where to Buy It

You can get metal film resistors at various ratings at any electronic supply store in your neighbourhood, or you can order them online from a variety of suppliers like Digi-Key . For the fancy stuff try Parts Connexion , Angela Instruments , or Percy Audio . Of course, there are lots of other good suppliers, as Google will tell you.


What to Buy

The two 0.33uF capacitors in the circuit are meant cut off any DC coming through and allow only the AC audio signal to pass. While expensive capacitors would be nice here, I'm cheap and so I just used 630V Mylar capacitors (the ones that look like big red rectangles). Actually, the ones in my amp right now are 0.47uF, but that just means I'll get a little more bass. All the capacitors in the power supply are standard components, except for the few that I replaced with some orange drop-style caps that I had.

Where to Buy It

I just bought the 0.47uF filter caps from a local store, but if you want the shmancy ones, you'll have to try places like Angela Instruments . The power supply capacitors were all ordered from Digi-Key .


What to Buy

I just used the UF1007 1000V 1A diodes recommended by Poindexter. Nothing expensive is really necessary I think, unless of course you choose to use tube diodes. Tube diodes will cost you extra and require a power supply for their heaters, though.

Where to Buy It

You can get them from Digi-Key or Parts Connexion and probably lots of other places.

Potentiometers, Switches, and Jacks

What to Buy

There are only three potentiometers in the amp, one for volume, and two for adjusting the bias on either channel. The one for volume is a double deck pot. There are two switches, one for the main power supplies and one for the tube heaters. Regular old single-pole double-throw switches are fine here. Since I only have one input in my amp, I don't have a DPDT to change between inputs like Poindexter. You'll also need two sets of speaker winding posts, so you have something to hook the speakers up to, as well as a set of stereo input jacks, and a plug for the power cord.

Where to Buy It

I personally didn't splurge on an expensive volume pot, but lots of people think it's an important part, so if you have the money feel free to splurge. Again, try Parts Connexion , Angela Instruments , or Percy Audio . For switches, posts, and jacks, try Radioshack or any other electronic supply store. The plug/fuse box for the power cord was from Digi-Key , and its part no. is Q201-ND. You will of course need a fuse for this, I think a 1A one, which you can get from any electronics supply store.

Other Stuff

You will need some screws, nuts, and bolts and those sorts of things, which you can get at any hardware store. As for hookup wire, Poindexter uses some pretty fancy stuff, but being the cheapo that I am I just used regular hookup wire form Radioshack.

Step 3: The Audio Circuit: What's Going On

Picture of The Audio Circuit: What's Going On


The basic principle behind this amp is pretty cool and worth taking a look at. This amp is called a 6V6 Push-Pull amp, the 6V6 being the tube model, but what's this push-pull business? It refers to a special case of differential circuits, where a whole signal is made up of the difference of two voltages, a negative and a positive (technically speaking, only the output stage is push-pull, but both are differential). Simply put, one tube produces to the positive half of the AC audio signal, pushing the speaker out, while the other one produces the negative half, pulling the speaker cone in, and as a result sound waves are created. Take the two triodes in the preamp, for example. Their cathodes are connected together and the signal goes to the grid of only one of the tubes. So, when the signal goes high, the grid on the one tube repels less of the electrons jumping off the cathode, and so more rush across, and since the cathodes are connected together, electrons also rush out of the cathode of the other tube as well. This results in current flowing in one direction through the circuit and eventually through a transformer which produces a current forcing the speaker cone outwards. When the signal goes low, the opposite occurs. The grid repels electrons back to the cathode and these electrons go to the cathode of the other tube, sending current in the opposite direction as before. When this current goes through the primary coil of the output transformer, it induces a current in the secondary coil which causes the speaker cone to move inwards.

Before it does go to the speakers, though, the signal is filtered through the two .33uF capacitors (DC can't pass through these, since a capacitor is technically a break in the circuit, but AC can) and makes its way on to the output stage, or the main amplifier section. Then, everything happens all over again, except this time with the 6V6's and to a greater extent. The -20 DC voltage in the middle there is for the bias on the grids of the 6V6's. The shield of the 6V6's is connected through a resistor to the anode, so that it has a fraction of the anode voltage.

Step 4: Layout/Planning

This is probably the most important step of the whole project, as Poindexter points out. Just putting everything in the right place to begin with can make the experience so much nicer. Being new to the while tube amp thing, mine isn't exactly pristine, far from it. But it works, so there.

You'll want to keep the power supply and the audio circuit as two separate sections/sides. All the tubes should go together in one area, and the output transformers somewhere nearby. Putting transformers too close together can apparently cause hum, but I'm not picky enough to complain about it, so mine are pretty close together. Some of the hum issues can be solved by putting metal covers over the transformers and grounding their cases properly. In this amp, the bolts fixing the transformers to the case are firmly attached to the ground plate by nuts. Apparently, the positioning of transformers relative to one another also helps to eliminate hum. If you rotate the transformers 90 degrees, so that they are not in line with each other, you get a certain decrease in hum. The angle isn't always 90 degrees though, so if you're very picky and patient, carefully adjusting the angle until it is optimum is definitely an option.

The circuitry in many tube amps is implemented a little differently than in other electronic projects. printed circuit boards are not always used, and they weren't here. It's more of a free-form circuitry type thing, with components soldered directly to each other, and terminal strips as little hubs of connections. This isn't the most organized way to do things, but it's faster than designing and ordering PCB's, and proto-boards can take up more room than is available in your enclosure (although now that i think of it they might work just fine).

Step 5: The Build: Enclosure

Picture of The Build: Enclosure

The enclosure that I picked was an old cutlery box. Honestly, I wouldn't recommend this kind of case, since, as good as it looks, it is a hassle. The sides and top are quite thick, making it difficult to mount components meant for thin metal or plastic cases without tediously grinding away at the thing. Also, a metal enclosure makes it easier to ground things since you can just connect ground to the chassis and ground anything in the circuit by connecting it to the chassis. With the cutlery box, I had to put copper-coated plates in there to solve this problem. But, if you want a cool looking wood enclosure and you don't mind the extra work, go for it.

Step 6: The Build: Getting Started

Picture of The Build: Getting Started

So I put the power supply on one side and the audio circuit on another. On the inside of the case, I attached a copper-coated plate that would serve to ground anything connected to it. This makes it easy to ground the exteriors of the transformers and hopefully reduce some hum. The transformers aare firmly connected to the plate with nut and bolts, and so fix the plate itself to the inside of the case.

Step 7: The Build: the Power Supply

Picture of The Build: the Power Supply

As long as you can read a schematic and solder, you should be able to put everything together. However, if you're like me, you'll do it wrong the first few times. As you can see, there are two copper plates, one for the power supply and one for the audio circuit. It would have been even better to have one big plate covering the entire surface, but I didn't have one big enough, so I had to make do. In this first picture, I was just getting a feeling for the layout of the rest of the amp, figuring out where to put the tubes and how to bridge the gap between the audio circuit and power supply.

In the later pictures, there's some of the 'free-form' circuitry I was talking about. There are these little clumps of components soldered directly to one another, which is a little more confusing than using a PCB, but it's quick and does save you the trouble of worrying about making space for and possibly designing a circuit board (and it's hardcore). The terminal strips keep most of them anchored fairly securely to the case, anyway.

The Amveco toroid is wired a little strangely, but never fear, there's a very handy diagram.

Step 8: The Build: the Audio Circuit

Picture of The Build: the Audio Circuit

The audio circuit might seem a bit messy. I was soldering components to the legs of the tube sockets, there were wires criss-crossing, and so on. Thankfully, though, it works.This is a first-time kind of project, but it's also one that you can go back to again and again and improve and update, and I think I probably will.

Those red capacitors there are supposed to be 0.33uF, but they're actually 0.47uF, which isn't really a problem, it just means I'll get more bass. They also happen to hold on to a big charge, and so you should be extra careful with them and remember to discharge them. These components are ones that are probably worth replacing with high-quality parts at some point in the future, since most people agree they are very important to the sound of the amp. (Oh yeah, and don't forget, you're building the audio circuit twice - this is a stereo amp, after all!)

Step 9: The Build: Testing and Finishing Up

Picture of The Build: Testing and Finishing Up

So once you've put it all together it's time to see if it actually works. However, don't plug it in directly into the wall at first, because if you do and you've made some wiring mistakes, you could end up frying some components. If smoke comes out of it, that's probably not a good sign. You could use a power adapter for a phone or some other low-ish voltage device to check everything first. Connect this to the terminals of the power socket and use a multimeter to test the points on the schematic where the voltage is indicated. With a power adapter like the one pictured, the voltages should be off by about a factor of ten or so. If everything looks basically right, go ahead and plug it in and hope that nothing bursts into flame. Once the power supply is behaving, hook up some speakers and see how it sounds. Keep poking around until it works, but be very careful (check the Intro if you don't know what I'm talking about).

Step 10: Conclusion

Picture of Conclusion

It works, dammit. And it's pretty.

(The big 167G120 transformer does hum a little I've noticed, any ideas on what to do about that? I think it's most likely just the construction of the transformer itself, so maybe I just need to upgrade)

Step 11: Links and Notes

Picture of Links and Notes

Poindexter's Musical Machine

All About Circuits' Introduction to Tubes How Vacuum Tubes Work

Fun With Tubes is an amazing resource. (thanks satman!)

There's always Wikipedia

There are lots of good books too, such as Valve Amplifiers by Morgan Jones, which thoroughly covers all the fundamental tube concepts as well as amplifier design. Jones has a companion book called Building Valve Amplifiers which covers all of the physical design considerations that go into building a good tube amp, including component layout, enclosure design/construction, and performance testing and troubleshooting.

The Power Vacuum Tubes Handbook is a great, detailed textbook on tubes.


Poindexter has since updated his design, and was kind enough to provide the schematics, pictured below.


kcrow11 (author)2013-08-21

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.

kcrow11 (author)kcrow112013-09-07

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!

Mr ross (author)kcrow112017-11-29

A current of around 30 mA (0.030 amperes) is potentially sufficient to cause cardiac arrest or serious harm if it persists for more than a small fraction of a second. Therefore it is mandatory that household wiring is fitted with ground fault circuit interrupters. Are your sure it was "only" 1 ampere?

pfred2 (author)2011-11-27

Thank God for William Shockley that we don't have to play with infernal tubes for much today. Certainly not for audio amplification. Tube audio amplifiers belong in museums next to the stone knife and bear skin display!

davidj53 (author)pfred22015-08-29

Often times, technology is used by the rich to make more money and customers are convinced the new technology is a further advanced and more convenient. Just look at the frequency reproduction differences between CD's and LP's. Same difference between Tubes and Transistors and with tubes you can fine tune the sound by changing out the tubes. But, it is all about how involved we want to be in what we do and the end result we wish to enjoy. Though, there are people that can not tell the difference in the sound reproduction differences between tubes and transistors!

pfred2 (author)davidj532015-08-30

What is stopping you from adjusting the sound by changing out transistors? Having character curved traced a number of transistors myself I can assure you they are NOT all the same! Ignorance like you're displaying now is what perpetuates the popularity of tubes today.

GregJ19 (author)pfred22015-12-02

As a former professional musician and lifelong audiofile, I promise you that IN GENERAL tube amps sound better than solid state. There's a reason that many amp manufactures have employed 'tube emulation' in their sound. Some even patented the name of their technology like "Transtube". Funny that tube amp manufactures have not tried to emulate the solid state sound.

pfred2 (author)GregJ192015-12-02

As a myriad of total harmonic distortion specifications plainly show vacuum tube technology cannot match the performance of solid state devices. So even if manufacturers of tube amplifiers tried to emulate solid state sound, they could not. The technical reasons why tube amps remain popular today are too complicated to get into here. It mainly boils down to a mixture of ignorance, and nostalgia though. With a healthy helping of simply being difficult thrown in, for good measure, of course.

Stym1e (author)pfred22017-06-27

Wow ! Ignorance ?? Sounds like you need to finish reading ALL the specs. Your blanket statement regarding solid state out-performing tubes is embarrassingly ignorant and wrong. I challenge you to find 1 commercial broadcast station, radio or television, that uses "solid state devices" to broadcast a 100,000 watt or more signal. A walk in the park for tubes, been doing since before Marconi invented the dipole. I admit, this is of little use in home audio amplification but tubes do have a place and that place is well respected by the solid state design engineers.

FirstL15 (author)pfred22017-06-08

I would take a Tube Amp over Solid State any day of the week! I simply let my ears decide which sounds better. My experience, and I've had several high-end SS Amps in the past, has been that Tubes simply reproduce a much warmer more natural sound with a lot more detail and a much wider sound-stage that no SS Amp has ever been able to. So for my critical 2-ch Stereo and Vinyl set-up, I use 2 Mono Tube Amps. For my Home Theater I still use Solid State.

GeneralIx (author)pfred22017-02-17

I would disagree pfred. Why a lot of people feel that tubes sound better has something to do not by THD in itself, but with the variety of THD. As you may or may not know, solid state amplifiers (SSA) mainly create uneven nth order distortion (e.g. 2263 hz, not full octaves). Tubes mainly create (and a lot more of it in total measured THD) eventh order harmonic distortion (full octaves). As we humans like full octaves better than uneven (hence why we don't like people who sing out of tune), tubes feel smoother.

So technically yes, SSA is better in terms of power delivered as well as lower THD. However, the THD produced can be more fatiguing. Note that this isn't always so, but there is a difference to be observed between the sound output between most tubes and SSA. Though arguably the tubes make for artefacts more than SSA and are therefore less 'honest', this doesn't mean they are worse. The music you hear has been processed many times over however you wish to put it, and its only goal should be your amusement.

So if you like a tube sound over SSA, that is perfectly valid, no matter how technically it could be seen inferior.

Edge59 (author)pfred22017-06-16

There's plenty of tubes still being offered today, why do so many guitarists prefer them to solid state, cause Solid state sounds like poop in your desert ale-mode, compared to tubes. I know transistors are getting better tone wise, I like their longevity, and consistency but Tubes in a power amp, makes everything warm and smooth, do you prefer diet drink to naturally sweetened? One might be better for you but which has the endorphin effect that you prefer? if you have a design for a solid state power amp that blows every tube amp out of the water tonally clean and over driven, I'm listening :) I've searched for years. Clean tones are fine with solid state, over driven guitar tones (for lead guitar) just don't totally cut it with all transistors without a thin raspy harshness, and I build solid state pedals that many consider to sound very tube like, but still require a power tube at the end of the chain. I even have modded several hybrid Solid state/tube guitar amps to get more of this tubey vibe, but ultimately power tubes always come through with the tones musicians hear in their head, even the average listener can hear the difference in many play tests. The even order harmonics are very present in tubes, The odd order harmonics are very present in solid state, so when a solid state amp clips, it has a very harsh distortion, one way of getting around this is higher wattage/headroom amps that dont get to their clipping point with most use (more wattage than your going to use). A few have come close over the years, but the inefficiencies of a tube relates more to the human ear, then again some peoples hearing cannot appreciate the difference. I have looked endlessly for a all Solid State amp that did it for me, and I always end up going back to something with tubes in it, at least power tubes, as they filter out most of the odd harmonics, and have more even, not to mention us guitar players love the % of THD that tube output transformers produce, put that in your I-pod am smoke it!. Music Man had a great idea back in the 70's, combining the best of both worlds, but now components are available to further enhance the guitars tones, but even still, good power tubes are hard to beat, they compress just enough to not pierce your ear drums, but can, they are just more musical, if your not a musician, then you have no clue as to the sound and FEEL of tubes when playing an instrument, especially live, tubes have a life to them that solid state just cannot compare. Granted, there are some great sounding modeling amps available today, but even those sound better going through a tube power amp! Many Metal heads love solid state because of the transient attack and brighter edge it has, but many classic styles prefer the sound and dynamics of tubes, and so many companies build solid state gear as mentioned by another poster here, try to emulate tubes in their design not transistors... :D See, when driving cascaded stages in a preamp, then into a power amp, all stages that are tube based, add so much to the tone, and overdrive as it is perceived as great tone to the player and the feel and dynamic response is more forgiving with tubes, where certain registers on the guitar neck may produce unpleasing harsh results due to the nature of the frequencies of the electric guitar in general where a acoustic guitar will usually sound best through a solid state amp or PA system, as you dont want to color the acoustics of the guitar in most cases. The electric guitar is one instrument that if played clean it's one thing to use solid state and sound great, some of my favorite clean electric players use solid state, but the ones that use tubes or combinations of tubes, usually will implement a tube or more to achieve their signature tones. One very rare guitarist extraordinaire, Allan Holdsworth (God rest his soul!) got different but incredible tones using solid state and modeling devices with great success! Allan used both Tubes and Solid State over the years, but in the last days he was spotted using either Yamaha Magic Stomp pedals that had extensive programming capabilities to dial in a complicated tone as his, along with the Axe Fx II which is another amazing piece of gear, mostly the effects are out of this world, the amp modeling is decent, but the Kemper Profiler is said to be one if not the best Amp profiler (Modeler?) today, not to mention the Bias Grid and other new technologies that are doing very well. It is possible in time that they will come very closely matching the tubes sonic dynamic qualities us guitarist/musicians are listening for, if not already. But Digital still has a % of artifacts that tend to be audible to one who has an experienced ear. SO what I find that works for me is to combine Analog with digital, maybe use a good overdrive pedal that has the overdrive dynamics, run that into a quality modeler set to a fairly clean setting, with a mild breakup, then a warm power amp. There are some amp companies building hybrid power amps with a 12ax7 type input or preamp to warm up the dynamic response to a lesser degree, Koch is one of those, and they do sound very good!

I can see where someone might want un-colored tone/sound quality, for playing back music, but why do you think a lot of people are going back to Analog tape, vinyl and it is so dated and inefficient compared to today's technology, but the listener prefers it for the most part, and if money is not an issue, most always go with good vintage gear. The problem with a lot of modern gear is that they are designed to discard after they break, non fixable items, where vintage gear can still be repaired and will outlast most modern gear today! Not trying say your wrong and Im right, but people have opinions like buttholes!

Edge59 (author)Edge592017-06-16

So if a guy likes his tube amp, let him like and toot his tube amp, if you dont like it and prefer your Solid State amp, enjoy your Solid State amp, to each his own, and damnit, Im glad people are different, this world would be really boring if everyone was the same!

bp_968 (author)davidj532015-11-05

the thing is, ears and brains are notoriously bad at judging subjective sound quality. It's why I'm a firm believer in "listen to what makes you happy in the manner that makes you happy"! If you think LPs sourced through tube amps and paper speakers sounds better then a digital audio file then listen to it that way and be happy! For example, I personally think the blues sound horrific but plenty of people would call me insane and love the stuff.

That said, I think tubes as a technology are amazing and awesome. I mean, can you take a silicon based electronic component and repurpose it as an X-ray emitter and make your own simple Xray machine? You can do that with some old vacuum tubes! Of course, it's a fair bit harder to kill yourself with silicon diode then it is with a big old vacuum tube, but hey that's part of the fun!

Edge59 (author)pfred22017-06-16

Maybe to your ears, some people might be better off in museums as well... :/ Some people cant hear the nuamces, some dont care, for those who do, all the tube power to them! :D :P

SergioL41 (author)pfred22016-02-07

You have a problem here.. When you mesure a tube amp their characteristics, seems ugly, they are insane bad compared with a transistor, or even a mosfet amplifiers giving a distortion 10 or even 100 times more, reaching 5% of THD, and so on. You are right, you mesure it.. But than, you feed your good music source in the transistor amp, and in the old bad, nostalgic, archaic, inefficient, power consuming, ugly, tube amp, lets say a good japanese stereo 300B SE with a power output of 10W per channel, or a more powerful Macintosh 450, without ANY tone control, and play a Toccata, or some Bach, recorded from an OLD 4 track tape..played from an AKAY 4000DS... in a good OLD fashioned pair of speakers, yes, 2 channels, 2 speakers...

Play, than pay close attention to the sound, of every instrument that is in the music, you will hear the noise of the arc touching the strings in the violin, the hammer beating in the piano,sometimes nail hitting the keys, the sound of the wood vibrating in the celo... the wispper in the trumpet, and the hand that dumped the thunder from the drums.... than you will UNDERSTAND, that music is for HUMAN EARS and HUMAN BRAIN, is not for a THD meter... Music is SUBJECTIVE, one likes, others not, but for the majority of people that LIKES classical, TUBE rules, seems like it is the DISTORTION of the tube that gives that "high" in the music played... No feedback, no phase compensation, no tone control, just the sound, its like the amplifier is some kind of instrument, that takes part in the show, not simple a block of components that reproduces the sound... the Tube amp is PART of the music...

In my time they used to say that transistor amp performs heavenly in the THD meter but sounds like HELL when you try to hear music on it.. and that is true, that is why they made POP, and FUNK, RAP... That kind of NOISE is not music, its is compressed, to have be played as loud as possible and so does not have a Dynamic range... this site explains:

Transistor amp have high noise (that ssssshhhhh in the speakers...) , so the music must be played at some volume higher than the noise they produce... so for things work, music must be compressed... and today it is very difficult you find a music that was not compressed, so the classics from the 1950, and 1960 that was recorded in analogic, does not have compression, because as at that time the amp was all Tubes, there was no need to compress it...

Today, I think it is impossible, unless YOU RECORD the music...

Cliffystones (author)SergioL412017-02-26


I've been in electronics since i was a kid in the 60s. The "tube sound" I grew up with consisted of a 1940-era table radio and various televisions with a single 3-4 inch speaker. Combine that with the fact that I was raised by a Missourian (The "Show Me State") and you'll understand why my first reaction to tube audiophiles was "surrrreeee they're better. Now go with that nice man in the white coat".

A few years back I decided to buy and restore an old Jukebox. While it's amp was soild state, my EBay searching showed me just how much these folks (I thought of as fools) would spend on a tube amp. This was the kind of simple electronics I had build as far back as the 8th grade. I decided to have a second look at what all of the fuss was about. I figured that if I couldn't hear the difference at least i could make a mint repairing old guitar amps like the one the 'American Pickers" bought and re-sold for several thousand dollars.

I finished my first 6V6-SE amp and boy! I was impressed for exactly the reasons you list. Depth, detail and 'texture" unheard of in even the more expensive "Wave Radios". Tube amps are a personal choice, not necessarily for everyone. But if you actually love to "LISTEN" to "MUSIC", not just have noise to fill in the background, then you WILL notice a difference.

I suppose I will never understand folks like "pfred" who want to tell you how bad something you love is and if they think that they are somehow correct. Music, just like the human brain and the definition of a beautiful woman, is subjective. If freddie likes his Waveradio or i-pod better, more power to him. I'll put one of Bruce Heran's Oddwatts up against anything in a blind listening test and it will win every time.

Tinkerer1351 (author)SergioL412016-05-17

I could hardly have said it better myself, most young people just find them to much trouble to fiddle with but if they would take the time and really listen (as my youngest daughter now finally has done) they would would easily be convinced of the superiority of the sound quality. (now she want's my Tube system) ;-)

EdgarD21 (author)pfred22016-10-02

I am not an expert. But i'm 55 years old and have listened to vacuum tube amplifiers as well as solis state amplifiers....... I will say that vacuum tube amplifiers sounded better then. Presently, solid state amplifiers sound better not because of the amplifiers but because of the technology involved in sound processing, Therefore, if these new technologies are applied to vacuum tube amps, it will definitely be better. You will not appreciate vacuum tube when you grew up at an era where solid state amplifiers are becoming prevalent. Papers specs aren't always a reliable gauge for appreciation. Just my take based on experience.

AndrewB86 (author)pfred22015-09-23

When someone is this closed minded, beware. The reason that many still enjoy tube amplification certainly isn't they are a bunch of tone deaf fools.

Aadieu (author)pfred22015-07-10

I wouldn't mind a bear skin coat...growing up with -35°C winters really makes you appreciate good ol furs and leathers

as to stone knives, dunno about those...but properly sharpened, even some hardwoods outdo the crap you see in stores these days

tube amps rawk

Edge59 (author)2017-06-16

I love tubes because of the even order harmonics that are musical in nature to our analog human ears, they are easier on the ears, not so piercing on the attack of the note and I've heard more nuances come through with tubes than with any solid state power amp. I have a great Fisher solid state power amp that is very powerful, but I dug out my inherited vintage Pioneer tuner/receiver that has 20 watts per side, EL-84/6BQ5 power tubes, and various preamp tubes including 12AX7's. That Pioneer needs new tubes and caps, but for a 60's built amp, it has an amazing sound quality to it! I heard more detail and nuances on Santana's Abraxas album that I never heard before! I plan on restoring this unit and replacing the caps and tubes, what ever may have gone out of tolerance, these are great amps!

Edge59 (author)Edge592017-06-16

Amazingly at 20 watts per side, it gets pretty loud too! No solid state amp at 20 watts gets that loud with such tone to boot! :)

LesB (author)2011-07-07

Regarding tubes vs digital/solid state distortion discussion from early on in this forum:
Tubes certainly do distort the signals they amplify. But the two mediums distort the signal differetnly, and to many music lovers, the tube type of distortion is less offensive. For example, tube electronics generally produce more harmonic distortion than SS/digital. But, our ears themselves have harmonic distortion. The sound your brain percieves has some harmonic distortion produced by the ear drum and its likages. So, you could say that harmonic distortion is a sort of "natural" distortion and is less offensive than other types. Digital/SS electronics is good at throwing a lot of random hash into the signal. Think scraping fingernails on the blackboard. Not a musical or natural form of distortion.
MP3 is a whole other deal. These super-compressed audio flles mash the life out of music. (Never use the "MP" word around a self-respecting audiofile.)

wirving (author)LesB2011-07-09

It's not that simple! Harmonic distortion measurements typically are stated as "THD," or "Total Harmonic Distortion." What exactly IS harmonic distortion? It is called "harmonic" distortion because it is the addition - by the audio gear - of multiples or "harmonics" of the original fundamental tone. For example, an "A" of 220 Hz will be amplified as desired, but the amplifier will add its own artifacts or "distortion products" to the original, including the multiple of two - 440 Hz, the multiple of three - 660 Hz, four - 880 Hz, five - 1,100 Hz, six - 1,320 Hz, etc., etc. - all the way up to the limits of human hearing and beyond. Conventional tube and solid state amplifiers add greater or lesser amounts of harmonic distortion to any signal fed to them. Most people can tolerate higher amounts of distortion from tube amps because tube amps mostly add low-order, even harmonics. That is, the harmonic distortion consists almost entirely of second, fourth, sixth and eighth harmonics, which are musically related to the signal; they represent octaves and fifths above the original tone, which blend musically with the original tone. They make the original sound "richer," to many peoples' ears, even pleasing. On the other hand, solid state amps - besides the low-order even harmonics - add more of the higher-order odd harmonics; seventh, ninth, eleventh, thirteenths, fifteenths, etc. These are often NOT musically euphonious; they represent dissonant intervals of seconds, fourths and sevenths. And the higher in frequency they are, the more AUDIBLE they are. SO, a person may listen to a tube amp with 2% low-order even harmonic distortion and not be irritated by it - may not even notice it. But that same person listening to a solid state amp with 2% high-order odd harmonic distortion will be driven from the room holding his ears! Double-blind listening tests have shown that a wide cross-section of people can detect high-order odd harmonic distortion at MUCH lower levels than low-order even harmonic distortion. In fact, the difference is greater than TWO whole orders of magnitude! A factor of ONE HUNDRED! And with all respect, your statement, "Digital/SS electronics is good at throwing a lot of random hash into the signal" is mostly hogwash! Whatever "hash" there is is certainly NOT random. Well... MOST of it isn't. As I explained, "harmonic" distortion" is related to the signal in a very precise and mathematical way. Likewise, the other kind of distortion plaguing amplifiers, "inter-modulation distortion," is ALSO related to the signal in a very precise and mathematical way. The ONLY random thing (technically, even this is not mathematically truly random) is the white noise that all electronic equipment adds to any signal. This white noise is all around us; it is literally the background echo of the Big Bang, the very explosion that created the universe as we know it today. As for MP3's, your statements about those are also a bit misinformed. "Mash the life out of music"? What the hell does THAT mean? I would agree with you that "super-compressed" MP3's sound bad. But not all MP3's are "super-compressed." Most that one would buy online ARE highly compressed, with bit-rates typically 128 Kb/s to 192 Kb/s. But MP3's can be encoded up to 320 Kb/s. In controlled listening tests - on MOST musical material - even self-appointed "golden-eared audiophiles" can't reliably and consistently hear the difference between uncompressed audio and 320 Kb/s MP3's. I can hear the difference MOST of the time, but the difference is not that huge, not night-and-day - not even over a good audio system. Well-ripped and encoded MP3's CAN sound quite reasonably good except with the most critical program material that is particularly sensitive to digital compression artifacts. For example, classical music with lots of high percussion. Things like triangle, wood block, snare drum, xylophone, can display digital pre-echo very noticeably under some conditions. But at higher bit-rates, even this effect is usually unnoticeable except rarely. But I will give you that "super-compressed" MP3's (I've seen some music MP3's encoded at the abysmal 64 Kb/s) as well as typical Apple iTunes MP4's, are awful and for that reason, I don't buy stuff online very much. But there ARE places online that do sell decent quality MP3 downloads as well as lossless FLACs. Now, let's talk about digital electronics - specifically digital "class D" amplifiers. They introduce their own kinds of distortion, but most of them aren't "random hash" either. Like with all things human-made, some Class D amplifiers are well-designed and executed, others are not. They tend to get a bad name because they are used in things like cheap portable MP3 players and the like. Why are they used in cheap things like this? Because they are not only inexpensive to make, they consume very little power - an important consideration with battery-powered devices. Class D amplification is - by its nature - EXTREMELY efficient; for every 100 watts in, you get 95-97 watts out. I have listened to good class D equipment, built by dedicated DIYers who know what they are doing and use the very best quality components for their builds. These amps are VERY impressive, especially for their relatively (compared to comparable quality tube amps) low cost. Categorical and sweeping statements like yours are misleading at best, propagating even more mythology among the buying public than there already is. The bottom line is, LISTEN!! Regardless of what kind of media are being played, or what kind of electronics is in the box driving your loudspeakers, what SOUNDS good, IS good!

techspec (author)wirving2017-05-16

Thank you for that analysis! It is absolutely true, and a good solid state system can produce rich and amazing sounds. MP3 is a file-format, and to your point, the level of audio compression varies. It definitely does not deserve the hatred or derision that it gets.

pfred2 (author)wirving2015-12-02

That is all well, and good, but tube amplifier distortion is typically in the 2-3% range, while solid state distortion is more in the 0.005-0.01% range. So solid state distortion is generally orders of magnitude less than tube distortion.

vicweast (author)pfred22016-05-23

The point is: The nature of the distortion is DIFFERENT. It is more NATURAL with TUBES and more HARSH with SOLID STATE. ...So much so that if you turn the volume UP to the point where it no longer sounds good because of the distortion, your solid state gear will likely DAMAGE your speakers due to the difference in the distortion. Note: That is NOT the case with tube distortion.

You seem to have lost your soul reading specs, and not actually explored the real world. I consider that similar to claiming you are a great traveler and know the local customs when all you have done is carefully study many maps... That my friend is delusion.

LesB (author)vicweast2016-05-24

Remember, back when CDs first came out? I am that old, i.e. ancient. The digital hype
(DH) at the time was that this tech reproduced sound "perfectly", and
they had the engineerNumbers to prove it.

Presumably in response to the public's bitching about the
sound of CDs, the engineers did some tweak to the tech, and the DH of this new
day was that the new tech make it even better than the original. BETTER THAN PERFECTION!!

LISTEN!! to the hype.

I have done a measure of my LISTEN!!ing in concert halls. During a musical rest, if one is really
LISTEN!!ing, the sound decays gradually until it fades below the biological
limen of the auditory apparatus.

The engineerNumbers for CDs tell us that CDs have a "wider"
dynamic range than the vinyls. But the
CD tech considers the top of the noise floor to be the bottom of the dynamic
range, the end of the world, where below that one sails off the edge of the
world, like poor Columbus did while trying to
find India.

The really bad news here is that in actuality, the limen of the auditory
system is somewhere down there in the murky depths BELOW the top of the noise

Listening to a CD recorded in a concert hall, if you LISTEN!! during a musical
rest, you will hear the sound decay to a certain point, then abruptly disappear.

That is the "sound" of the das Commendant Herr Digital
Algorithm commanding all the transistors to turn off. Or face certain death. It's ugly.

"Mash the life out of music"

I realize that in popular music some angelic level of aural purity is sometimes not issue. Crank in your Aphex Aural
Exciter! The singer can't sing, crank in
your Autotune! And sh*t who listens to
classical any more anyway?

For sure the engineerNumbers have some value, but paying religious
homage to them produces the DH that is like putting faith a survey promoted by a
party with interest in the results. Or
maybe it is exactly that.

YesItsMeJimmy (author)LesB2016-07-20

There I disagree, Digital auto recordings are VERY clean and the bit rate can be off the wall CDs are held down to 44,100, 16. While digital files can be much much higher. It still does not replace vinyl which has the music imprinted, no 1s and 0s. With a good record player and an undamaged record it blows away the quality of CD even considering the hiss, which you ignore quickly enough.

techspec (author)2017-05-16

Thank you for compiling this information into one place! FYI, the humming may be an issue with the transformer, or it could be an imbalance with your electrical system. A quick and dirty solution is to use a ground-lift. If the humming goes away, it could point to an issue with an improperly-grounded residence. If you can, use the outlet face-panel as an ad-hoc ground to avoid minor shock from touching components.

I have worked in audio, video, and lighting now for the better part of two decades, and even if you have not, most people can tell the difference when they listen to uncompressed or vinyl music recordings via transistor (AKA solid state) or tube (AKA valves) amplifiers in the prosumer arena. Well, unless you have $30,000 laying for a top of the line audio rig. Don't get me wrong, transistors have come a long way, and they have revolutionized entire industries with cheaper, more sustainable, and efficient technology. I love them, but like everything else, they have their limits when it comes to certain applications. With some notable, expensive exceptions, most solid state (i.e. transistor) amps produce shrill, high-pitched tones in output audio. When I'm listening to 8-bit Chip-Tunes, 70's and 80's Punk, Hardcore/Thrash and Metal, that shrill/high-pitched tone is actually welcome! However, if you like rich, warm and dynamic tones, tube amps are definitely preferred. For example, when I'm listening to Jazz/Swing, Blues/R&B, Mo-Town, Bluegrass, or Ska, I generally prefer tube amps.

evelluchia (author)2016-10-13

Hello everyone ive been considering building one of these vacume tube amplifiers for some time now i find these are intreging devices (vacume tubes are far beyond my time ive never had the pleasure of working with them before) now heres the canumdrum how would i know the output power of the amp or what impedance for the speakers? Im not very experienced with scematics so any reccamindations?

ZachR32 (author)evelluchia2016-10-28

I believe this amplifier outputs between 6-8 watts. It is fairly low power, so I'd suggest a sensitive speaker. I'm using the amp on a speaker with 4 ohm impedance and 96db sensitivity if that helps.

AdamBombBaby (author)2016-09-29

If one wanted to to use a tube rectifier instead of solid state rectifier, how would he go about that?

The reason electrons flow negative to positive is Ben Franklin got the flow backwards, as his description had gotten into general use when the error was found no one bothered trying to change the labels as it would have lead to a lot more confusion.

If you still have hum from the 6.3 filament wires you can use a wire shield over them and ground it or use a ferrite bead to cut down on the radiation.

SzabolcsK (author)2016-08-05

Rotate the output trannys in 90° to cancel hum from the power transformer! Also twist the 6,3 V filament wires together! Since they carry AC they induce hum.

LEDAC (author)2016-03-22

Very Nice

Alf Riston (author)2016-03-17

The website for this commercial amplifier explains "tube sound" simply and exhibits good design principles.

Alf Riston (author)Alf Riston2016-03-17

AbhishekB5 (author)2016-02-21

How would I wire up the amp/output transformer to a speaker.

MichaelB233 (author)2015-10-16

Could you just connect a wire to a lightbulb filiament and get binary in light?

red_dr4gon1 (author)2015-05-28

What are some safety tips for me when working on it?

emuñoz6 (author)2014-01-27

Hello! I live in Florida, any idea were can I learn electronics in order to build a beauty like this? Thanks!

davidm200 (author)emuñoz62015-04-12

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

davidm200 (author)2015-04-12

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 :)

davidm200 (author)2015-01-21

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?

jackricci (author)2014-09-03

how are you determining the Vdrop resistiors?

paler31 (author)2013-11-20

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?



get2john (author)2013-10-18

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?

batfish55 (author)2013-07-27

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.

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