When a webpage loads that looks like it was made in the 90’s, no ads, and is too wide for mobile so I have to drag from side to side, I know the content is gonna be legit.
Yeah...and I like how if you hit the 'hide ad' arrow, it veeeery slowly scrolls out of the way. Keep it classy. And don't put a 'donate' button and then pack the page with so many ads I have to use an adblocker[1] to actually view the content in a non-rage-inducing way.
I was a tube amp tech for several years, have built multiple guitar amps from scratch, and still dabble in it.
What may not be obvious is that modern tube amp designs are an evolutionary branch from 1930's technology, with only a little coming across from the transistor->digital tech tree. The amps of the 40s and 50s were pretty closely based on reference designs that came from RCA and other tube manufacturers.
Modern passive components (resistors, diodes and caps) are made to a far higher tolerance and are better understood, but tubes and transformers are a mixed bag. The older designs were somewhat overbuilt and can be more reliable or have tonal characteristics that are not available in modern parts.
I always found fascinating the power section of valve amp for guitar will always be made of a very basic rectifier circuit to convert AC to DC that requires a expensive transformer and produce power with a terrible efficiency compared to more modern SMPS. Why is it nobody interested in valve amp never go the SMPS path? Is it all because sag is a desirable sound distortion?
You mean a modern construction with semiconductor-based SMPS, but tube for output? If so, plenty of those, here is hit #2 in my google search for "guitar tube amplifier": "Orange Micro Terror" [0]. This one take 15V DC input - no way you can get this to tubes without some sort of SMPS.
Or do you mean why people who do period-authentic tube amps don't use SMPS? That's because tube-based SMPS is very complex, often as complex as amplifier itself, and needs unusual parts [1].
The rectifier is an audible part of the circuit, you can definitely tell e.g. between tube rectifiers and diode based ones.
SMPS have been somewhat problematic with audio circuits when they were new, especially when it comes to noise and "musicality". A overdimensioned toroid transformer with a rectifier is inefficient, but an extremely simple design which allows people without too much electrical engineering knowledge to get a decent result without expensive measurement equipment.
This is a bit similar to early PCB-use in guitar amplifiers. Back then some manufacturers did a shit job with their PCBs and since then guitarists think hand-wired is always superior to PCBs.
Guitarists are traditionalists and thus the amount of innovation in that space moves slower than elsewhere.
I noticed the same thing. Like, why not at least use a fullwave rectifier with semiconductor diodes? Surely nobody believes that a tube diode in the power supply makes any audible difference.
Sometimes it does, for example, just like gp mentions, a tube rectifier in a single ended amp can have a voltage “sag” that interacts with the rest of the system and causes an interactive “color” in the output, especially when amplifying larger voltage swings of bass notes and chords.
There are quite a few effects like this. In a modern design this would be eliminated, but sometimes “bad” is good :)
Let me rewrite that without the condescending tone: Artists that output sound invest time and money into crafting how they are heard. Is there tube amp elitism? Absolutely. Do tube amps "sound better"? I dunno. But clearly the market for them and the demand for inefficient circuits that sound different than more efficient circuits stays seemingly consistent and may even go up.
A guitarist who plays electrified isn't just playing the guitar; the entire signal chain becomes the instrument. Everything from the room to the fingers of the player alter the sound and how a person plays their instrument and for some even the temperature of the room makes a concrete, quantifiable difference.
Music appreciation is largely cultural as well. The history of music is full of people hearing sounds, becoming accustomed to them and reproducing them with a novel variation. This is exemplified by many recent genres like hip hop, rap, jazz, rock, folk music and so on. There were and are entire genres of music and specific artists that revolve around certain tools. For example the Sunn brand of amplifier, especially the Model T which is venerated by some subgenres of metal or Jimmy Hendrix and his Fuzz Face pedal (and his wah and octaver and amp, and .....)
Naturally, musicians seek to pay homage to and recreate the atmosphere and feel of a specific song, instrument, artist, genre or time period. Until fairly recently, modeling and digital tools had a lot of trouble replicating the sound and interaction of these vintage, analog circuits and even today the most straightforward way to achieve a specific style is often to simply buy or clone the old-school original instruments and equipment.
While digital modelling has come a long way, arguably surpassing most of the original equipment, the rarity, variation and uniqueness leads players to continually seek out the Real Deal in order to achieve an authentic style or sound.
An example of this entire idea is the DRUMETRICS collective, whose entire purpose is to write and record new and modern performances with original vintage instruments and recording equipment. Heres a link to one: "Pale Horse" https://www.youtube.com/watch?v=vZqoFf859Xw
The key diagram is the one that shows the signal path through the amplifier. Input feeds grid, plate feeds next grid, final output is from plate. Everything else is supporting circuitry.
Note that between each stage there's a capacitor in the signal path. That's to block DC. If you want an amp that amplifies DC, each stage has to run at a higher voltage than the previous stage. The plate must be above the grid in voltage.
This was a huge headache in tube computers, both analog and digital.
Transistor circuits don't have the increasing voltage problem. Outputs and inputs are in the same voltage range. That's because transistors are current gain devices, not voltage gain devices.
> Note that between each stage there's a capacitor in the signal path. That's to block DC. If you want an amp that amplifies DC, each stage has to run at a higher voltage than the previous stage. The plate must be above the grid in voltage. This was a huge headache in tube computers, both analog and digital.
You can also stick a voltage divider (and probably some diode clamping) in there to pull the signal off of the plate down to a grid compatible voltage for the next stage if you're just doing digital computing. That was the most common setup I've seen in tube based computing. They tended to play pretty nice with the resistors needed for the plate current anyway so it wasn't that much extra RC constant delay.
It's not exactly what I'd call a rounding error, but it's manageable. But yeah, tube computing in general is an exercise in building a really fancy space heater.
I'm trying to keep my tube computer I'm building down to ~3KW, and that's probably the biggest actual constraint on design complexity.
> The key diagram is the one that shows the signal path [...] Everything else is supporting circuitry.
This is also very misleading in that all this supporting circuitry AND the stuff not even shown, such as wires routing with respect to each other and with respect to the inside or outside of a metal case ALSO contribute. All this stuff contributes to basic functionality ("noise", "hum", etc) and to finer performance (frequency response, dynamic, distortion, crosstalk, etc).
It's easy to confuse the map for the territory, the schematic for the physics of the thing. And common electronics schematics abstract away much that does matter. Engineers and builders with some experience will pay attention to this without bothering to include it in the schematic.
Pay attention when following a magazine article for example: most of the time it will point out the why of several decisions. Why they placed this and that away from each other. Why these wires are routed this way...
Transistors in principle have the same issue as tubes with bias stacking in that they only operate biased in one way and so the bias potentials necessarily add up (of course we're talking about much smaller voltages, both in absolute terms and in relation to usual supply voltages). But p-type transistors are practical, unlike p-type vacuum tubes. Well, you could build every other tube out of antimatter.
I will second your recommendation and also recommend all of his ‘Tested’ videos. The microphone ‘Tested’ video was also an absolute delight.
The delivery style gets to some people (i.e. “I’m not ___ I just play guitar…”) but i find it absolutely fine.
I moved on from tube amps about 15 years ago and now really enjoy a variety of different solid state amplification stages with varying EQ and ‘dirt’ options at various places. Turns out a lot like were Jim’s Video goes.
Thanks for that. I hadn’t come across Jim Lill before. For someone who’s “just a performer”, he knows a lot (about circuits). I found the comparisons of different order of Equalisation and Distortion to be interesting and I loved his Tacklebox. I’ll definitely check some of his other videos.
Echoes of vacuum tubes in my memories: seeing tube testers in drug stores as a child (thinking they looked like either scientific equipment or else science-fiction props—and accidentally left just feet from the penny-candy), as well as peering into the back of our small B&W TV growing up (and marveling at the "city of light" inside there: all the orange glowing filaments from the tubes…).
And gone by the time I was old enough to be interested in electronics.
Nonetheless, my curiosity about them remained and I did eventually seek out books to understand how they worked. I have since built perhaps a dozen hi-fi stereo and mono-block tube amplifiers—some from kits, some from scratch. I've built a handful of guitar amps as well (even sold some as kits for a bit). Point to point, tagboard, PCBs…
Anyone that likes to tinker in electronics I recommend they try their hand at at least one tube project (probably an amp of some kind).
>Anyone that likes to tinker in electronics I recommend they try their hand at at least one tube project (probably an amp of some kind).
Only if they are aware of the voltages and current often associated with tube setups. One bad move can be painful, or fatal in some cases.
I used to work on guitar amplifiers, doing modifications on tube amps. Messing around with the internals demanded my focus, a level of attention most "tinkerers" aren't likely ready for. Not trying to gatekeep here, just suggesting it may not be something for "anyone that likes to tinker".
This is what has kept me from working on amps. I'm comfortable working inside of pedals (9v) or with USB-powered circuits, but anything with a large transformer just seems a lot scarier.
It depends on the "power" of the project. I was building ½ Watt Darling hi-fi amps that never had more than about 225 VDC or so running through them.
But by all means, you never touch it when plugged in, you use chopsticks if you need to poke/debug a live circuit (you keep one hand in your pocket, etc.).
225VDC will kill a person, but it entirely depends on the current that can be delivered. As little as 50mA can kill. Your 1/2 watt amp probably won't but I don't know the details of the power supply.
Fun vacuum tube history fact: the humble vacuum tube actually traces its origins back to Edison’s incandescent light bulbs. Those early bulbs would mysteriously blacken over time, and for years nobody could figure out why. It wasn’t until 1904 that John Ambrose Fleming connected the dots — the darkening came from metal burned off the filament, and in studying it, he created the first true vacuum tube. So the vacuum tube, the heart of early electronics, was born from the same simple light bulb that first lit our homes.
A complementary resource for learning about tube amps is the YouTube channel Fazio Electric. Colleen Fazio does a nice job of repairing old amps and explaining various aspects of their construction, history, and significance. Plus she has a very calming voice and is probably one of the loveliest amp repair technicians out there.
it's a bit weird that I never thought about it before this, when I already had the facts in my head: the triode tube amplifier was invented by Lee de Forest, but he had no idea how it worked or even what it was capable of. then 45 years later, the solid state transistor amplifier was invented, and they had no idea how it worked either.
for people who have not had much EE education, what is important about triodes and transistors is that they amplify. you can put a signal in (a signal like from a microphone responding to your voice), and put some power in (like from a battery) and these amplifiers can make an output "copy" of the signal which is more powerful/"louder" than the original.
from this basic function, everything that we think of as "electronic" flows. we would still have electric things like light bulbs, heaters, spark plugs, electromagnets, but basically just electric steam punk frankenstein machines, and nothing subtle. Amplifiers are termed "active" electronics; without them, we'd simply have passive electricity.
I didn't read this article because I already know how these things work, and the article looks extremely confusing, and I've already read my fill of explanations that don't explain anything and (not saying this is one of those) I don't want to even risk that again. it is very difficult to find explanations for how transistors work that make any sense at all.
> he solid state transistor amplifier was invented, and they had no idea how it worked either.
That cannot possibly be true. Not knowing what exactly is going on with the charge carriers at the subatomic and quantum levels is not the same as not knowing how the amplifier works: like if we fiddle with the voltage at the base, we can influence the collector current, and all the rest.
What is true is that some early transistor designs of audio amps treated transistors like tubes: they featured a phase inverter transistor that fed two non-complementary push-pull stages whose output was combined by a center-tapped output transformer.
The excuse that well-matched complementary PNP transistors were not readily available at that time rings hollow, because it's possible to create an push-pull output stage with just NPN transistors. This is called "quasi complementary" (lots of search results for this).
Output transformers, if they have multiple taps in the secondary winding, do allow for different impedances. If the end users expect to be able to plug a 16 ohm speaker into a 16 ohm output jack and a 4 ohm into 4 ohm, then they will understand that kind of amp better.
>That cannot possibly be true. Not knowing what exactly is going on with the charge carriers at the subatomic and quantum levels is not the same as not knowing how the amplifier works
since everything that happens inside a transistor is exactly what is going on in a quantum sense, you've described "not knowing how it works". You cannot understand a bipolar transistor without quantum effects, it's the thing that creates the transistor effect.
the theory of amplifiers you go on to talk about was well developed at that time because it's the same theory for vacuum tubes.
You can empirically drive the equations that apparently govern the macroscopic behaviors, right down to details like temperature sensitivity, and the Early effect, without having a detailed model of what is going on at the atomic and subatomic level.
Then what makes an amplifier work is explained by those equations. And for that not even the full detail of them is necessarily required, depending on what aspect of the amplifier we need to explain. Like basic operation versus concern for thermal runaway.
What makes the amplifier work and what makes the transistor work are separate concepts.
That's why understanding translates from tube circuits to transistors. A transistor circuit maybe an emitter follower, which has a counterpart in tube circuits known as the cathode follower. The cathode resistor creates local negative feedback similarly to an emitter resistor. Early op amps where tube circuits. They have the same differential input stage and the same basic theory of operation. You program their game the same way with resistors. The familiar Sallen-Key filter topology was first described with the help of tube circuits for reference, back in 1955. To undestand it, we don't even need the details like how amplifiers work at the component level except when we get into design parameters in which certain issues matter, like frequency-bandwidth product, or input offset current or whatever.
Radio Shack sold PA amplifiers with an output transformer well past the age of the tube, like the MPA series, e.g. MPA-40, a 20 W mplifier. On that thing you can obtain the raw amplifier output using the "70V" terminal. Then it has a number of through-the-trafo outputs labelled with nominal ohmages of speakers.
The Owner's manual extols the advantages of using transformers for speakers and describes how to use the 70V output in conjunction with external transformers.
Quote:
For complex multiple-speaker arrangements that require many speakers and
long runs of connecting wire, we recommend you use a line transformer (not
supplied), available at your local RadioShack store.
[...]
There are several advantages to using
transformers.
• You can connect speakers with different impedances without causing
differences in output between the
speakers.
• You can add or remove a speaker
without having to recalculate the
entire system’s impedance.
• You can reduce signal loss when
you use speaker wire over 50 feet
long.
Sound masking systems still use 70V audio output with output transformers at each speaker, voltage drop is rough when your signal is only a few volts and you’re using small conductors. Last time I sold a sound masking install we used 14/2 cable for the 70V audio signal.
They're quite popular for distributed audio systems in general (of which sound masking is one type). "Constant voltage audio" comes in a few flavors and 70v is very common in the US, other parts of the world often use 100v. Background music systems in retail, voice paging systems, etc use constant voltage hardware because its much better technology for very long cable runs, daisy-chained speakers, and centrally located amplifiers.
The cost is fidelity. Full-range audio transformers aren't cheap, so these systems usually make some compromises because your announcements or smooth jazz over the pasta aisle don't need to be true hi-fi.
Its cool technology. Most of the speakers have variable power taps, so you can run a bunch of them in parallel on a single line and control the actual volume as-needed based on where the speaker is deployed by varying the transformer tap on each speaker.
Nowadays, for things like the Las Vegas Sphere, the whole audio distribution is fully digital: put an amp close to each speaker, distribute the audio over a network, and have that do all the very precise delay compensation for the shape of the space.
Some colleagues of mine are looking at the same thing for cars.
Eh? 70v PA is really common stuff and has been for a very long time. You probably hear it every time you're in a department store, amusement park, stadium, or other public space.
There's no need to LOL. It's useful tech.
By using a (~nominal maximum) 70v intermediate voltage, low-impedance PA systems become high-impedance. Compared to low-impedance systems at any power level, current through the wire feeding that system is reduced. Increasing impedance reduces the size of the copper wire required, and makes things easier for practical amplifiers to drive.
This is Really Useful in systems that may have dozens or hundreds of speakers distributed over a wide area.
Just to pick an example: Let's say we have 24 8-Ohm speakers to drive in a place like a grocery store. The system never needs to get proper-loud, so we'll budget 1 Watt for each speaker (24 Watts total).
If they're wired in parallel[1], then that's an impedance of 0.33 Ohms. Most power amplifiers can't drive that kind of impedance. It's also 8.5A of current, which isn't too daunting but is significant.
But if we add transformers and run things at 70v? Things get a lot easier.
Let's say we pick a 50 Watt amplifier just so we get some headroom instead of maybe running it at 100%, and that this amplifier's output power is rated at 8 Ohms.
That amplifier produces a maximum output of about 20v. Suppose we step that up to ~70V with a 1:4 transformer (which actually gives us a maximum of 80V, but again: headroom), and drive our grocery store full of 24 1-Watt 70v speakers with it.
With the same 24 Watts, our current on the speaker line drops from 8.5A to ~0.34A -- it goes from significant, to very nearly unimportant.
Our amplifier is happy: Rather than 0.33 Ohms, it sees an impedance of 12.75 Ohms.
That's an amplifier that runs cool and quiet, probably for decades. The wire can be small (18AWG seems common-enough in the grocery store overhead PA systems I've worked on; much smaller than that, and things become harder to deal with inside of ceilings). The speakers, which are all simply wired in parallel, can be replaced, removed, or added -- and also be individually adjusted in output level by changing transformer taps -- as time moves on without thinking much about the greater system architecture.
That's a lot of words, but in practice: 70v is easy. It works. We use this technique all over the globe: Some countries use 100v, and both 140v and 25v also exist as standards, but using transformers in PA-world is ridiculously common.
The usual method doesn't involve much thought at all: Add up the total power of the 70v speakers in Watts, pick an appropriate 70v amp that can drive at least that number of Watts, and send it. It's dead-simple to get right.
70v is not common in stage or musical instrument use, or in home hifi, but it doesn't have to be. It solves problems that don't exist in those spaces.
(And yeah, our grocery store needs a ~25:1 transformer on each 8 Ohm speaker. That's fine. 70v speakers that are intended to mount overhead and that include transformers with multiple secondary taps are very, very common and are still made every day in places like Chicago and Dayton[2] -- and again, you hear them all the time when you're out in public.)
[1]: We could use series-parallel arrangements to get around this, but those wiring configurations turn both arduous and easy to screw up, and loudspeakers have non-linear impedances so mixing-and-matching them in series as time moves on becomes problematic. Series-parallel isn't broadly practical.
I had a 1971 Marshall tube amp land in my lap, for free. I'm not a guitar player, but wanted to get it fixed it up before either selling it or learning guitar. There's a lot of "magic" there - the amp guy asked if I wanted to swap the tubes for some "more authentic" tubes that were used in England at the time. Pro tip - don't ask the internet for advice for making your tube amp sound nice, you'll get every opinion possible.
Guitar amps are all about getting the right kind of harmonic distortion, so of course the guy had opinions. But tube rolling is madness, avoid it at all costs.
You don’t even need to ask! Generally speaking, you don’t want a guitar amp to sound nice, you want it to sound good, good being a function of many things.
For clean sound, use compatible radio preamp tubes and bias the power tubes conservatively.
For distorted sound, use the lowest overhead preamp tubes you can find, and bias the power tubes as hot as you dare without them breaking within the hour. You can always change them after a gig, or between sets. :-)
Excellent website, I'm an electrical engineer by trade, and play guitar. Back in college tube amps were long, long gone for anything other than microwave engineering.
My first real amp was a JCM800 2203 (technically a JMP "Mk 2 master model", which is just a cascaded JMP/Plexi, which Marshall then later re-released as JCM800 when their export deal expired...but I digress), and when I got into modding this website was my first real encounter with easy explained guides of the circuits.
Neat to see a Rob Robinette article pop up here, his website is a fantastic resource for guitar amp work. His articles on Amp Startup and Troubleshooting were particularly helpful when I built a tube amp for the first time. I hadn't heard of using an incandescent bulb as a current limiter in startup before, I was glad to have additional options for trying to make the troubleshooting process a bit safer given the high voltage involved.
Tangential question: Does anyone know of a basic large-signal equation for a triode (or any other vacuum tube type) like the simplified Ebers-Moll equation for BJTs or the square law equations for the linear and saturation regions of a MOSFET? It would really help my understanding, but whenever I google it I only see academic papers, like it's a weird thing to search for.
The intractability of the Triode is part of the reason why the Pentode exists. And, you will note, the Pentode curves in certain modes looks a lot like your bog standard MOSFET.
"All models are wrong, but some are useful." -- George Box
With that said, a N type JFET is not a bad start. The main rules of thumb work: The grid draws negligible current. The tube will pass enough current from plate to cathode, to maintain a roughly constant cathode voltage above the grid.
If I understand them correctly, Ebers-Moll equations are based on the exponential relationship between voltage and current in a BJT.
But tubes aren't current amplifiers, they're voltage amplifiers, like FETs.
You can look at the "characteristics curves" of tubes (plate curves and transconductance curves), which tell the story of current against plate-to-cathode voltages for fixed grid voltages.
Vladimirescu, Andrei. The SPICE Book. John Wiley & Sons, 1994.
Gives overview equations for MOSFET device simulations which are probably sufficient for most purposes in Section 3.5, and COMPLETE mathematical descriptions of the SPICE MOSFET implementation in Appendix A.3. Not for the weak.
Tube amplifiers function using compression test or where voltage alternates into a unitary current.
A reversal, which occurs in the vaccum chamber compresses electrodes, tagging battery terminal from the +/- amplifier schema AC electricity is transformed.
Rob Robinette is a great guitar-amp resource; knows just about everything about Fender amps in particular. He has many mods to many common/not-so-common Fenders.
Just his list of 5E3 mods (Fender Deluxe) is awesome:
Tubes are definitely inferior to transistors in a lot of ways, but nothing sounds like them (FETs come close). Plus, there's the comforting glow of those little glass bottles that just seems right.
Ok, I suggest that you install the "Stoutner, privacy browser", which treats seeing text, as the default, with the ability to allow other content as optional, though certain sites that are still hand coded, show, as they always have....adds and all.
Sorry, but adblock is a genuine quality of life hack for everyone online. Since you don't want to install anything, how about working at the DNS level and/or hosts level? https://adguard-dns.io/en/welcome.html will change your mind. https://github.com/Ultimate-Hosts-Blacklist is another option for doing it in the hosts file.
When a webpage loads that looks like it was made in the 90’s, no ads, and is too wide for mobile so I have to drag from side to side, I know the content is gonna be legit.
I got two ads that took up 2/3rds of the screen :(
Yeah...and I like how if you hit the 'hide ad' arrow, it veeeery slowly scrolls out of the way. Keep it classy. And don't put a 'donate' button and then pack the page with so many ads I have to use an adblocker[1] to actually view the content in a non-rage-inducing way.
[1] yes, yes...I know...always use an ad blocker.
[dead]
I was a tube amp tech for several years, have built multiple guitar amps from scratch, and still dabble in it.
What may not be obvious is that modern tube amp designs are an evolutionary branch from 1930's technology, with only a little coming across from the transistor->digital tech tree. The amps of the 40s and 50s were pretty closely based on reference designs that came from RCA and other tube manufacturers.
Modern passive components (resistors, diodes and caps) are made to a far higher tolerance and are better understood, but tubes and transformers are a mixed bag. The older designs were somewhat overbuilt and can be more reliable or have tonal characteristics that are not available in modern parts.
I always found fascinating the power section of valve amp for guitar will always be made of a very basic rectifier circuit to convert AC to DC that requires a expensive transformer and produce power with a terrible efficiency compared to more modern SMPS. Why is it nobody interested in valve amp never go the SMPS path? Is it all because sag is a desirable sound distortion?
You mean a modern construction with semiconductor-based SMPS, but tube for output? If so, plenty of those, here is hit #2 in my google search for "guitar tube amplifier": "Orange Micro Terror" [0]. This one take 15V DC input - no way you can get this to tubes without some sort of SMPS.
Or do you mean why people who do period-authentic tube amps don't use SMPS? That's because tube-based SMPS is very complex, often as complex as amplifier itself, and needs unusual parts [1].
[0] https://www.sweetwater.com/store/detail/MicroTerror--orange-...
[1] https://www.righto.com/2018/09/glowing-mercury-thyratrons-in...
The rectifier is an audible part of the circuit, you can definitely tell e.g. between tube rectifiers and diode based ones.
SMPS have been somewhat problematic with audio circuits when they were new, especially when it comes to noise and "musicality". A overdimensioned toroid transformer with a rectifier is inefficient, but an extremely simple design which allows people without too much electrical engineering knowledge to get a decent result without expensive measurement equipment.
This is a bit similar to early PCB-use in guitar amplifiers. Back then some manufacturers did a shit job with their PCBs and since then guitarists think hand-wired is always superior to PCBs.
Guitarists are traditionalists and thus the amount of innovation in that space moves slower than elsewhere.
I noticed the same thing. Like, why not at least use a fullwave rectifier with semiconductor diodes? Surely nobody believes that a tube diode in the power supply makes any audible difference.
What, like a 5Y3? Listen to Neil Young’s tone on Cinnamon Girl. That’s the sag and compression of a cranked tube rectifier.
Sometimes it does, for example, just like gp mentions, a tube rectifier in a single ended amp can have a voltage “sag” that interacts with the rest of the system and causes an interactive “color” in the output, especially when amplifying larger voltage swings of bass notes and chords.
There are quite a few effects like this. In a modern design this would be eliminated, but sometimes “bad” is good :)
Tube amp people will believe anything that helps them justify their product ownership.
Let me rewrite that without the condescending tone: Artists that output sound invest time and money into crafting how they are heard. Is there tube amp elitism? Absolutely. Do tube amps "sound better"? I dunno. But clearly the market for them and the demand for inefficient circuits that sound different than more efficient circuits stays seemingly consistent and may even go up.
There is a little more than that.
A guitarist who plays electrified isn't just playing the guitar; the entire signal chain becomes the instrument. Everything from the room to the fingers of the player alter the sound and how a person plays their instrument and for some even the temperature of the room makes a concrete, quantifiable difference.
Music appreciation is largely cultural as well. The history of music is full of people hearing sounds, becoming accustomed to them and reproducing them with a novel variation. This is exemplified by many recent genres like hip hop, rap, jazz, rock, folk music and so on. There were and are entire genres of music and specific artists that revolve around certain tools. For example the Sunn brand of amplifier, especially the Model T which is venerated by some subgenres of metal or Jimmy Hendrix and his Fuzz Face pedal (and his wah and octaver and amp, and .....)
Naturally, musicians seek to pay homage to and recreate the atmosphere and feel of a specific song, instrument, artist, genre or time period. Until fairly recently, modeling and digital tools had a lot of trouble replicating the sound and interaction of these vintage, analog circuits and even today the most straightforward way to achieve a specific style is often to simply buy or clone the old-school original instruments and equipment.
While digital modelling has come a long way, arguably surpassing most of the original equipment, the rarity, variation and uniqueness leads players to continually seek out the Real Deal in order to achieve an authentic style or sound.
An example of this entire idea is the DRUMETRICS collective, whose entire purpose is to write and record new and modern performances with original vintage instruments and recording equipment. Heres a link to one: "Pale Horse" https://www.youtube.com/watch?v=vZqoFf859Xw
SMPS do output high-frequency noise, and the PSRR of tube amps is very bad.
That's a cute little article.
The key diagram is the one that shows the signal path through the amplifier. Input feeds grid, plate feeds next grid, final output is from plate. Everything else is supporting circuitry.
Note that between each stage there's a capacitor in the signal path. That's to block DC. If you want an amp that amplifies DC, each stage has to run at a higher voltage than the previous stage. The plate must be above the grid in voltage. This was a huge headache in tube computers, both analog and digital.
Transistor circuits don't have the increasing voltage problem. Outputs and inputs are in the same voltage range. That's because transistors are current gain devices, not voltage gain devices.
> Note that between each stage there's a capacitor in the signal path. That's to block DC. If you want an amp that amplifies DC, each stage has to run at a higher voltage than the previous stage. The plate must be above the grid in voltage. This was a huge headache in tube computers, both analog and digital.
You can also stick a voltage divider (and probably some diode clamping) in there to pull the signal off of the plate down to a grid compatible voltage for the next stage if you're just doing digital computing. That was the most common setup I've seen in tube based computing. They tended to play pretty nice with the resistors needed for the plate current anyway so it wasn't that much extra RC constant delay.
That won't help with the power consumption though, I guess. (Or is that a rounding error compared to everything else?)
It's not exactly what I'd call a rounding error, but it's manageable. But yeah, tube computing in general is an exercise in building a really fancy space heater.
I'm trying to keep my tube computer I'm building down to ~3KW, and that's probably the biggest actual constraint on design complexity.
> The key diagram is the one that shows the signal path [...] Everything else is supporting circuitry.
This is also very misleading in that all this supporting circuitry AND the stuff not even shown, such as wires routing with respect to each other and with respect to the inside or outside of a metal case ALSO contribute. All this stuff contributes to basic functionality ("noise", "hum", etc) and to finer performance (frequency response, dynamic, distortion, crosstalk, etc).
It's easy to confuse the map for the territory, the schematic for the physics of the thing. And common electronics schematics abstract away much that does matter. Engineers and builders with some experience will pay attention to this without bothering to include it in the schematic.
Pay attention when following a magazine article for example: most of the time it will point out the why of several decisions. Why they placed this and that away from each other. Why these wires are routed this way...
Transistors in principle have the same issue as tubes with bias stacking in that they only operate biased in one way and so the bias potentials necessarily add up (of course we're talking about much smaller voltages, both in absolute terms and in relation to usual supply voltages). But p-type transistors are practical, unlike p-type vacuum tubes. Well, you could build every other tube out of antimatter.
I'd like to plug the YouTube Video by Jim Lill - "Tested: Where Does The Tone Come From In A Guitar Amplifier?"
https://www.youtube.com/watch?v=wcBEOcPtlYk
I will second your recommendation and also recommend all of his ‘Tested’ videos. The microphone ‘Tested’ video was also an absolute delight.
The delivery style gets to some people (i.e. “I’m not ___ I just play guitar…”) but i find it absolutely fine.
I moved on from tube amps about 15 years ago and now really enjoy a variety of different solid state amplification stages with varying EQ and ‘dirt’ options at various places. Turns out a lot like were Jim’s Video goes.
Thanks for that. I hadn’t come across Jim Lill before. For someone who’s “just a performer”, he knows a lot (about circuits). I found the comparisons of different order of Equalisation and Distortion to be interesting and I loved his Tacklebox. I’ll definitely check some of his other videos.
Echoes of vacuum tubes in my memories: seeing tube testers in drug stores as a child (thinking they looked like either scientific equipment or else science-fiction props—and accidentally left just feet from the penny-candy), as well as peering into the back of our small B&W TV growing up (and marveling at the "city of light" inside there: all the orange glowing filaments from the tubes…).
And gone by the time I was old enough to be interested in electronics.
Nonetheless, my curiosity about them remained and I did eventually seek out books to understand how they worked. I have since built perhaps a dozen hi-fi stereo and mono-block tube amplifiers—some from kits, some from scratch. I've built a handful of guitar amps as well (even sold some as kits for a bit). Point to point, tagboard, PCBs…
Anyone that likes to tinker in electronics I recommend they try their hand at at least one tube project (probably an amp of some kind).
>Anyone that likes to tinker in electronics I recommend they try their hand at at least one tube project (probably an amp of some kind).
Only if they are aware of the voltages and current often associated with tube setups. One bad move can be painful, or fatal in some cases.
I used to work on guitar amplifiers, doing modifications on tube amps. Messing around with the internals demanded my focus, a level of attention most "tinkerers" aren't likely ready for. Not trying to gatekeep here, just suggesting it may not be something for "anyone that likes to tinker".
This is what has kept me from working on amps. I'm comfortable working inside of pedals (9v) or with USB-powered circuits, but anything with a large transformer just seems a lot scarier.
It depends on the "power" of the project. I was building ½ Watt Darling hi-fi amps that never had more than about 225 VDC or so running through them.
But by all means, you never touch it when plugged in, you use chopsticks if you need to poke/debug a live circuit (you keep one hand in your pocket, etc.).
225VDC will kill a person, but it entirely depends on the current that can be delivered. As little as 50mA can kill. Your 1/2 watt amp probably won't but I don't know the details of the power supply.
Fun vacuum tube history fact: the humble vacuum tube actually traces its origins back to Edison’s incandescent light bulbs. Those early bulbs would mysteriously blacken over time, and for years nobody could figure out why. It wasn’t until 1904 that John Ambrose Fleming connected the dots — the darkening came from metal burned off the filament, and in studying it, he created the first true vacuum tube. So the vacuum tube, the heart of early electronics, was born from the same simple light bulb that first lit our homes.
A complementary resource for learning about tube amps is the YouTube channel Fazio Electric. Colleen Fazio does a nice job of repairing old amps and explaining various aspects of their construction, history, and significance. Plus she has a very calming voice and is probably one of the loveliest amp repair technicians out there.
https://www.youtube.com/@FazioElectric
Also https://www.youtube.com/@UncleDoug
it's a bit weird that I never thought about it before this, when I already had the facts in my head: the triode tube amplifier was invented by Lee de Forest, but he had no idea how it worked or even what it was capable of. then 45 years later, the solid state transistor amplifier was invented, and they had no idea how it worked either.
for people who have not had much EE education, what is important about triodes and transistors is that they amplify. you can put a signal in (a signal like from a microphone responding to your voice), and put some power in (like from a battery) and these amplifiers can make an output "copy" of the signal which is more powerful/"louder" than the original.
from this basic function, everything that we think of as "electronic" flows. we would still have electric things like light bulbs, heaters, spark plugs, electromagnets, but basically just electric steam punk frankenstein machines, and nothing subtle. Amplifiers are termed "active" electronics; without them, we'd simply have passive electricity.
I didn't read this article because I already know how these things work, and the article looks extremely confusing, and I've already read my fill of explanations that don't explain anything and (not saying this is one of those) I don't want to even risk that again. it is very difficult to find explanations for how transistors work that make any sense at all.
> he solid state transistor amplifier was invented, and they had no idea how it worked either.
That cannot possibly be true. Not knowing what exactly is going on with the charge carriers at the subatomic and quantum levels is not the same as not knowing how the amplifier works: like if we fiddle with the voltage at the base, we can influence the collector current, and all the rest.
What is true is that some early transistor designs of audio amps treated transistors like tubes: they featured a phase inverter transistor that fed two non-complementary push-pull stages whose output was combined by a center-tapped output transformer.
The excuse that well-matched complementary PNP transistors were not readily available at that time rings hollow, because it's possible to create an push-pull output stage with just NPN transistors. This is called "quasi complementary" (lots of search results for this).
Output transformers, if they have multiple taps in the secondary winding, do allow for different impedances. If the end users expect to be able to plug a 16 ohm speaker into a 16 ohm output jack and a 4 ohm into 4 ohm, then they will understand that kind of amp better.
>That cannot possibly be true. Not knowing what exactly is going on with the charge carriers at the subatomic and quantum levels is not the same as not knowing how the amplifier works
since everything that happens inside a transistor is exactly what is going on in a quantum sense, you've described "not knowing how it works". You cannot understand a bipolar transistor without quantum effects, it's the thing that creates the transistor effect.
the theory of amplifiers you go on to talk about was well developed at that time because it's the same theory for vacuum tubes.
You can empirically drive the equations that apparently govern the macroscopic behaviors, right down to details like temperature sensitivity, and the Early effect, without having a detailed model of what is going on at the atomic and subatomic level. Then what makes an amplifier work is explained by those equations. And for that not even the full detail of them is necessarily required, depending on what aspect of the amplifier we need to explain. Like basic operation versus concern for thermal runaway.
What makes the amplifier work and what makes the transistor work are separate concepts.
That's why understanding translates from tube circuits to transistors. A transistor circuit maybe an emitter follower, which has a counterpart in tube circuits known as the cathode follower. The cathode resistor creates local negative feedback similarly to an emitter resistor. Early op amps where tube circuits. They have the same differential input stage and the same basic theory of operation. You program their game the same way with resistors. The familiar Sallen-Key filter topology was first described with the help of tube circuits for reference, back in 1955. To undestand it, we don't even need the details like how amplifiers work at the component level except when we get into design parameters in which certain issues matter, like frequency-bandwidth product, or input offset current or whatever.
empirical equations are driven by data about devices. they didn't have any devices, they were inventing the first ones.
Radio Shack sold PA amplifiers with an output transformer well past the age of the tube, like the MPA series, e.g. MPA-40, a 20 W mplifier. On that thing you can obtain the raw amplifier output using the "70V" terminal. Then it has a number of through-the-trafo outputs labelled with nominal ohmages of speakers.
The Owner's manual extols the advantages of using transformers for speakers and describes how to use the 70V output in conjunction with external transformers.
Quote:
For complex multiple-speaker arrangements that require many speakers and long runs of connecting wire, we recommend you use a line transformer (not supplied), available at your local RadioShack store.
[...]
There are several advantages to using transformers.
• You can connect speakers with different impedances without causing differences in output between the speakers.
• You can add or remove a speaker without having to recalculate the entire system’s impedance.
• You can reduce signal loss when you use speaker wire over 50 feet long.
LOL!
Sound masking systems still use 70V audio output with output transformers at each speaker, voltage drop is rough when your signal is only a few volts and you’re using small conductors. Last time I sold a sound masking install we used 14/2 cable for the 70V audio signal.
https://www.atlasied.com/speech-privacy-speakers?srsltid=Afm...
They're quite popular for distributed audio systems in general (of which sound masking is one type). "Constant voltage audio" comes in a few flavors and 70v is very common in the US, other parts of the world often use 100v. Background music systems in retail, voice paging systems, etc use constant voltage hardware because its much better technology for very long cable runs, daisy-chained speakers, and centrally located amplifiers.
The cost is fidelity. Full-range audio transformers aren't cheap, so these systems usually make some compromises because your announcements or smooth jazz over the pasta aisle don't need to be true hi-fi.
Its cool technology. Most of the speakers have variable power taps, so you can run a bunch of them in parallel on a single line and control the actual volume as-needed based on where the speaker is deployed by varying the transformer tap on each speaker.
Nowadays, for things like the Las Vegas Sphere, the whole audio distribution is fully digital: put an amp close to each speaker, distribute the audio over a network, and have that do all the very precise delay compensation for the shape of the space.
Some colleagues of mine are looking at the same thing for cars.
Eh? 70v PA is really common stuff and has been for a very long time. You probably hear it every time you're in a department store, amusement park, stadium, or other public space.
There's no need to LOL. It's useful tech.
By using a (~nominal maximum) 70v intermediate voltage, low-impedance PA systems become high-impedance. Compared to low-impedance systems at any power level, current through the wire feeding that system is reduced. Increasing impedance reduces the size of the copper wire required, and makes things easier for practical amplifiers to drive.
This is Really Useful in systems that may have dozens or hundreds of speakers distributed over a wide area.
Just to pick an example: Let's say we have 24 8-Ohm speakers to drive in a place like a grocery store. The system never needs to get proper-loud, so we'll budget 1 Watt for each speaker (24 Watts total).
If they're wired in parallel[1], then that's an impedance of 0.33 Ohms. Most power amplifiers can't drive that kind of impedance. It's also 8.5A of current, which isn't too daunting but is significant.
But if we add transformers and run things at 70v? Things get a lot easier.
Let's say we pick a 50 Watt amplifier just so we get some headroom instead of maybe running it at 100%, and that this amplifier's output power is rated at 8 Ohms.
That amplifier produces a maximum output of about 20v. Suppose we step that up to ~70V with a 1:4 transformer (which actually gives us a maximum of 80V, but again: headroom), and drive our grocery store full of 24 1-Watt 70v speakers with it.
With the same 24 Watts, our current on the speaker line drops from 8.5A to ~0.34A -- it goes from significant, to very nearly unimportant.
Our amplifier is happy: Rather than 0.33 Ohms, it sees an impedance of 12.75 Ohms.
That's an amplifier that runs cool and quiet, probably for decades. The wire can be small (18AWG seems common-enough in the grocery store overhead PA systems I've worked on; much smaller than that, and things become harder to deal with inside of ceilings). The speakers, which are all simply wired in parallel, can be replaced, removed, or added -- and also be individually adjusted in output level by changing transformer taps -- as time moves on without thinking much about the greater system architecture.
That's a lot of words, but in practice: 70v is easy. It works. We use this technique all over the globe: Some countries use 100v, and both 140v and 25v also exist as standards, but using transformers in PA-world is ridiculously common.
The usual method doesn't involve much thought at all: Add up the total power of the 70v speakers in Watts, pick an appropriate 70v amp that can drive at least that number of Watts, and send it. It's dead-simple to get right.
70v is not common in stage or musical instrument use, or in home hifi, but it doesn't have to be. It solves problems that don't exist in those spaces.
(And yeah, our grocery store needs a ~25:1 transformer on each 8 Ohm speaker. That's fine. 70v speakers that are intended to mount overhead and that include transformers with multiple secondary taps are very, very common and are still made every day in places like Chicago and Dayton[2] -- and again, you hear them all the time when you're out in public.)
[1]: We could use series-parallel arrangements to get around this, but those wiring configurations turn both arduous and easy to screw up, and loudspeakers have non-linear impedances so mixing-and-matching them in series as time moves on becomes problematic. Series-parallel isn't broadly practical.
[2]: Chicago: https://quamspeakers.com/product-group/ceiling-loudspeakers Dayton: https://fourjay.com/background-speakers/
*output transformers
I had a 1971 Marshall tube amp land in my lap, for free. I'm not a guitar player, but wanted to get it fixed it up before either selling it or learning guitar. There's a lot of "magic" there - the amp guy asked if I wanted to swap the tubes for some "more authentic" tubes that were used in England at the time. Pro tip - don't ask the internet for advice for making your tube amp sound nice, you'll get every opinion possible.
Guitar amps are all about getting the right kind of harmonic distortion, so of course the guy had opinions. But tube rolling is madness, avoid it at all costs.
There is a whole range of useable distortions, so a lot of the opinions mainly boils down to genre bias.
E.g. to a metalhead, any tone that doesn't "chug" is useless, including something useable to a jazz fusion player.
In this case it was a very common swap, 6550->EL34 for Marshall JMP 50W. I ended up going for it (the existing tubes were damaged), it sounds great.
You don’t even need to ask! Generally speaking, you don’t want a guitar amp to sound nice, you want it to sound good, good being a function of many things.
For clean sound, use compatible radio preamp tubes and bias the power tubes conservatively.
For distorted sound, use the lowest overhead preamp tubes you can find, and bias the power tubes as hot as you dare without them breaking within the hour. You can always change them after a gig, or between sets. :-)
Goodness, I hope you weren't injured.
Excellent website, I'm an electrical engineer by trade, and play guitar. Back in college tube amps were long, long gone for anything other than microwave engineering.
My first real amp was a JCM800 2203 (technically a JMP "Mk 2 master model", which is just a cascaded JMP/Plexi, which Marshall then later re-released as JCM800 when their export deal expired...but I digress), and when I got into modding this website was my first real encounter with easy explained guides of the circuits.
Neat to see a Rob Robinette article pop up here, his website is a fantastic resource for guitar amp work. His articles on Amp Startup and Troubleshooting were particularly helpful when I built a tube amp for the first time. I hadn't heard of using an incandescent bulb as a current limiter in startup before, I was glad to have additional options for trying to make the troubleshooting process a bit safer given the high voltage involved.
Tangential question: Does anyone know of a basic large-signal equation for a triode (or any other vacuum tube type) like the simplified Ebers-Moll equation for BJTs or the square law equations for the linear and saturation regions of a MOSFET? It would really help my understanding, but whenever I google it I only see academic papers, like it's a weird thing to search for.
The Koren equations are the only thing I've found.
"Improved vacuum tube models for SPICE simulations" https://normankoren.com/Audio/Tubemodspice_article.html
The intractability of the Triode is part of the reason why the Pentode exists. And, you will note, the Pentode curves in certain modes looks a lot like your bog standard MOSFET.
This also discusses how the "constants" ... well, aren't. https://www.john-a-harper.com/tubes201/
That’s exactly what I’m looking for! Thank you very much!
"All models are wrong, but some are useful." -- George Box
With that said, a N type JFET is not a bad start. The main rules of thumb work: The grid draws negligible current. The tube will pass enough current from plate to cathode, to maintain a roughly constant cathode voltage above the grid.
If I understand them correctly, Ebers-Moll equations are based on the exponential relationship between voltage and current in a BJT.
But tubes aren't current amplifiers, they're voltage amplifiers, like FETs.
You can look at the "characteristics curves" of tubes (plate curves and transconductance curves), which tell the story of current against plate-to-cathode voltages for fixed grid voltages.
Vladimirescu, Andrei. The SPICE Book. John Wiley & Sons, 1994.
Gives overview equations for MOSFET device simulations which are probably sufficient for most purposes in Section 3.5, and COMPLETE mathematical descriptions of the SPICE MOSFET implementation in Appendix A.3. Not for the weak.
> WARNING: A tube amplifier chassis contains lethal high voltage even when unplugged--sometimes over 700 volts AC and 500 volts DC.
I promise you it does not contain AC when unplugged :)
Nope, probably not at all, and certainly not for very long.
Tube amplifiers function using compression test or where voltage alternates into a unitary current.
A reversal, which occurs in the vaccum chamber compresses electrodes, tagging battery terminal from the +/- amplifier schema AC electricity is transformed.
Rob Robinette is a great guitar-amp resource; knows just about everything about Fender amps in particular. He has many mods to many common/not-so-common Fenders.
Just his list of 5E3 mods (Fender Deluxe) is awesome:
https://robrobinette.com/5e3_Modifications.htm
Tubes are definitely inferior to transistors in a lot of ways, but nothing sounds like them (FETs come close). Plus, there's the comforting glow of those little glass bottles that just seems right.
I definitely came across this website back when I was learning how to fix and build tube amps. Glad to see nothing has changed.
This is an interesting topic, but the ads overlaying the content make this very hard to read :(
* Please don't suggest I install an Ad blocker.
OK, have your {dad|fifth grader|IT manager} install an ad blocker.
Ok, I suggest that you install the "Stoutner, privacy browser", which treats seeing text, as the default, with the ability to allow other content as optional, though certain sites that are still hand coded, show, as they always have....adds and all.
What ads? Install an ad blocker.
Firefox Reader View is really great. Worth giving a try if you use Firefox.
Sorry, but adblock is a genuine quality of life hack for everyone online. Since you don't want to install anything, how about working at the DNS level and/or hosts level? https://adguard-dns.io/en/welcome.html will change your mind. https://github.com/Ultimate-Hosts-Blacklist is another option for doing it in the hosts file.
Install an Ad blocker. I'd recommend uBlockOrigin on Firefox, or Firefox for mobile.
I mean just in general it makes the web less awful. Webpages are so much easier on the eyes without all the crap they try to stuff in there.
And it can prevent malware, especially for those less tech-inclined.
And it means you use less data/bandwidth, since the blocker prevents the request from ever being made in the first place.
If you want to support a site, just buy a subscription or donate to them or something.
id never do it, but you could install an ad blocker
very good article! i am surprised how such simple circuit was used in the 5f1!