Tube amps are specialized amplifiers that are known for their musical reproduction. Although distortion is generally higher to much higher in tube amps, the nature of the distortion is not generally displeasing.
It is amazing that, when a guitar amp is fed a source of hi-fi audio, and plugged into a hi-fi speaker, what a great job it does and how good it sounds!
The guitar amp has had a comparatively long history in modern technology, and it is surprising that the Vacuum Tube (Valve) Amp is still so much sought-after.
I'm not a guitar player. I'm a technician who loves the sound of guitars, especially when played through tube amps. So most of my time is spent on repair, design, and listening. I've been doing technician work since the mid-70's, in audio, digital, radio, and computer electronics.
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Speakers and Power - techy article from Antique Electronics and tubesandmore.com!
Speakers and Power Explained
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Good Video... No narration - watch the screen for tips.
Article: Tube Biasing - How it contributes to Amp Tone, and other considerations.
Copyright webmaster@TubeModules.com 7/2010
Output tube biasing effects two major things: Clean Headroom and Breakover.
These can be balanced out so that half of the usable volume level is clean and the upper half is compressed and breaks over easily.
What contributes to this is the type of circuit (Class A or AB), the B+ voltage, output transformer resistance.
A Little Theory...
Class A operation makes both halves of the push-pull output section draw current constantly. This reduces crossover distortion, increases linearity, and makes the tubes stay close to the point where hard playing runs them into the rounded-top distortion that makes that "tube-y" sound tubes are famous for.
Class AB, on the other hand, is a good compromise when done right. One tube is always drawing current, and sometimes both, but always in a small amount. AB is more like an electronic see-saw, where when one tube is up, the other is down. Careful adjustment of distance from the ground (bias) and position of the balance of the see-saw board (bias balance) can make for a wonderful result.
In the world of amp tone seekers, though, there is a big difference in the Class A and Class AB structure when it comes to tone.
The Class A amp has a fuller sound (my opinion) and breaks over sooner.
The Class AB amp is cleaner for a wider range and breaks over with difficulty. You can bias a Class AB "Hot" and get more of a Class A sound, but usually the supporting circuit isn't able to carry the extra load.
The next consideration is the tone stack. That is where many amps get their distinctive sound. On amps that do analog modeling, the tone stack is one of the sections of the amp they switch out.
For a comparison of the response curves of different tone stacks, Duncan Amps has a Tone Stack simulator the is really nice. I've used it to experiment with responses BEFORE I even build the circuit. Its accurate, and FREE!
See Tone Stack Calculator for the Win version. You can run it in Linux if you are using Wine.
There are lots of sites that list great discussions and tutorials about tone. One that comes to mind is the Tone Lizard site Tales from the Tone Lounge. Be aware, it is not for the faint of heart. If you can't bear to hear a few well-placed cuss words about the stuff some people put out as truth about tone, do not click on their link... but I really enjoy the way the author presents his case for BS standing in for truth.
Warning, some of the links have expired. In fact, the home page itself announces that this site may soon expire, but that announcement was in 2009! All the same, get there quick and get the knowledge.
R. G. Keen has been on my list of references for a while. His site at www.geofex.com is full of electronic stuff, all good, but I want to point to one section in particular, the Tube Amp FAQ page. Lots of learning experiences there.
More to come later...
Search the web for examples of the tone you want, then you have something to show someone when words fail. Send me the links to your clips at Design Your Next Amp on my site.
If nothing else, just leave the link in the link place, so I can get an idea of what people like.
Be safe. Observe rules about measuring high voltages, which can absolutely kill you or at least ruin your day.
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I have to point you to Michael Hoffman, BSEE, at Amptone.com. I saw his site years ago but couldn't find it again. His site may have been my inspiration for starting this one. Be sure and give him a visit. His site is really complete and full of good info, suggestions and tips.
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