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.
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.
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.
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.
> 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...
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.
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.
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:
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).
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.
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.
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.
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.
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.
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.
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.
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.
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.
28 comments
[ 3.0 ms ] story [ 62.4 ms ] threadfor 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.
* Please don't suggest I install an Ad blocker.
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.
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...
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.
Just his list of 5E3 mods (Fender Deluxe) is awesome:
https://robrobinette.com/5e3_Modifications.htm
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).
https://www.youtube.com/watch?v=wcBEOcPtlYk
I promise you it does not contain AC when unplugged :)
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.
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.
[1] yes, yes...I know...always use an ad blocker.
https://www.youtube.com/@FazioElectric
A reversal, which occurs in the vaccum chamber compresses electrodes, tagging battery terminal from the +/- amplifier schema AC electricity is transformed.