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How Tube Amplifiers Work

robrobinette.com

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Re: How Tube Amplifiers Work

#61

Post by pjc50 »

kazinator wrote: post #10
kazinator wrote: post #5

Earlier quoted context omitted.

> 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 tra…

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 70…

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.

Re: How Tube Amplifiers Work

#62

Post by marpstar »

leptons wrote: post #40
JKCalhoun wrote: post #22

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 o…

>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…

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.

Re: How Tube Amplifiers Work

#63

Post by TomMasz »

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.

Re: How Tube Amplifiers Work

#64

Post by santix »

yardshop wrote: post #47

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

Re: How Tube Amplifiers Work

#65

Post by formerly_proven »

Animats wrote: post #7

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…

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.

Re: How Tube Amplifiers Work

#66

Post by creer »

Animats wrote: post #7

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…

> 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...

Re: How Tube Amplifiers Work

#67

Post by krbaccord94f »

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.

Re: How Tube Amplifiers Work

#68

Post by Anthony-G »

WorkerBee28474 wrote: post #31

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

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.

Re: How Tube Amplifiers Work

#69

Post by JKCalhoun »

marpstar wrote: post #62
leptons wrote: post #40

Earlier quoted context omitted.

>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…

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.).

Re: How Tube Amplifiers Work

#70

Post by baylessj »

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.
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