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.
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.
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.
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.
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).
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".
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.
E.g. to a metalhead, any tone that doesn't "chug" is useless, including something useable to a jazz fusion player.
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. :-)
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.
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.
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.
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.
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.
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!
https://www.atlasied.com/speech-privacy-speakers?srsltid=Afm...
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.
Just his list of 5E3 mods (Fender Deluxe) is awesome:
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.
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.
"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/