Is there an advantage to more tubes in an amp?


I'm not really familiar with tube amp design, so I really don't have an understanding of how the number of tubes affect the sound of an amp.

Do more tubes allow you to minimize the sonic effects of a single tube within the group?

Do more output tubes give you more power?

Are amps with fewer tubes "more pure" and "cleaner"?

How do Current Source Tubes and Input Tubes affect the sound of an amp?

Thanks in advance.
Nicholas Renter
128x128nrenter

Showing 2 responses by clueless

said above >> I'm not really familiar with tube amp design, so I really don't have an understanding of how the number of tubes affect the sound of an amp.

There are lots of things that add to the sound and I’m not sure the “number of tubes” as such really is that important although, as you note below, some folks have a minimalist philosophy that “less is more” when it comes to the signal path. It can be confusing though. Generally tubes have different functions in an amp. They are used in different amp “stages” to amplify voltage, or power (current), split phase, provide buffers and/or match impedances, etc… I listed a few online articles that are general introductions at the bottom of this post if you are curious about tubes.

said above>> Do more tubes allow you to minimize the sonic effects of a single tube within the group?

I guess it depends. It is just as possible that one tube, if off a little or used with the wrong operating points, or not right for the job (that is, it does not give the tube in the next stage of the circuit what it needs) could change the sound of all the others too. The Q is a little stilted because generally, if you do not like the sound associated with a tube, you are going to take it out of the circuit and use one that sounds good in the mix. Everything is interrelated and it is hard to hide/bury something. Especially is a SET because there just is not much there to begin with.

>>Do more output tubes give you more power?

Generally, yes. If you use a push-pull (PP) circuit (at least 2 op tubes) you will usually have more power than a single ended one output tube amp or a single ended amp with more than one output tube. If you use more than one output tube in a SET they are connected in parallel. And if you are using a P-P amp you are getting more power not just because you have more tubes but because you are running them in a different, more efficient, manner (at least in terms of pure power). Of course, a given type of tube can only provide so much power. A 300b about 8w, a 2A3 about half of a 300b and a 45 about half of a 2A3 etc….If you want more power one usually goes to a different type of tube. If you like the sound of a low power tube you “compromise” for less power. Generally all triode amps make this compromise of gaining a certain sound for power. (yes, I know some do not think it a compromise at all) Power is closely associated with the tube’s capacity to dissipate power (as heat) from its plate.

>>Are amps with fewer tubes "more pure" and "cleaner"?

That would be Single Ended Triodes. Some think they are and that they sound better too. I like them very much but basically it isn’t about pentode vs. triode, or Push Pull vs. Single Ended, or even tube vs. SS. It's about making the right design compromises and choosing the right parts to build a well thought-out circuit. There are many roads to sonic purity grasshopper. Don’t harden your brain’s arteries before you have listened for yourself.

>>How do Current Source Tubes and Input Tubes affect the sound of an amp?

They are both important. Amps are generally named after the power output(op) tubes which I think you mean by the “current source tube.” I think most folks would say the power tube is the “most important.” They generally name tube amps after the power/output stage - 300bs and 2A3s (type of output tube), Push-pull, single ended (describes how the op tube’s plate is attached to the OP transformer), class A or B (how the op tube’s grid is biased), ultralinear, ultrapath (how an op tube’s screen grid is attached to the power supply or the op transformer’s primary.) etc…all describe the output tube in one way or another and so it generally is thought of as the “defining stage.” But I’m not entirely sure that is always true. You can make an intelligent argument that the transformers are most important or the circuit designed around the tube or the driver stage. It is very hard to isolate these things and tell what you are listening to in a tube amp sometimes. Some think that the coupling caps (used to attach stages to each other and block dc current) add the strongest sonic signature. In any event, all tubes “affect the sound of an amp” because they are not perfect. They do not amplify in an even/linear fashion and each tube has it’s own unique signature in this way. That’s right, a tube’s sound is mostly related to its imperfections. If a tube has a perfectly linear response, that is, its output is an exact copy of it’s input only bigger, it is basically sonically invisible. It’ the unique distortion pattern that to a great extent defines the sound.

A few things online to read.

1) ✔ A Taste of Tubes (50 pages), Sonic Frontiers: http://www.anthemav.com/OldSitev1/frames/tubesfr.html
2) ✮ The National (British) Valve Museum. http://www.r-type.org/static/.contents.htm
3) The Cool Sound of Tubes, E. Barbour: http://www.spectrum.ieee.org/select/0898/tube.html
4) How A Vacuum Tube Works, E. Barbour: http://www.svetlana.com/docs/tubeworks.html.
5) Vacuum Tube Valley FAXs, E. Barbour: http://www.vacuumtube.com/FAQ1.htm.
6) Vacuum Tube FAX, H. Pasternack: http://home.earthlink.net/~busenitz/vac.html.
7) A History of Tube Companies: http://vintagetubeservices.com/page8.html
8) Vacuum Tube Primer, R. Hamm: http://www.audioasylum.com/audio/faq/tubeprimer.html

Cheers
I remain
Hey thanks for the kind words folks. I learn more here than anything else and a lot from the folks in this thread.

above by Mark >> "The only thing I don't dig is how 300b or any pre-historic-triode SE amp can play MUSIC? To me it's the same as to build 1w radio that also can play music quite loud especially if placed soewhere in the corner of empty room..."

What do you mean you "don't dig" Mark? I'm not sure I get your point.? Do you think low powered tube amps are nonsense? I don't think they are for everybody but they do a lot of things quite well.

>> said above by Sean .."On top of this, i've found that tubes (even from the same manufacturer ) have a far wider level of operating tolerances than SS devices"

I thought that fets and mosfets were far less consistent than tubes? A 30% tolerance in transistors is fantastically good isn't it?

I'm not much re SS but I'm told the specs show that one transistor will have twice the capacitance of the other - thus half the speed...ie the NPN and PNP "complements" really aren't a true complement. MOSFETs being the worst in this regard. These capacitance nonlinearities get worse when you have more than two transistors in the output stage. You have large, and dissimilar, capacitances that are all over the place, and drifting slowly with temperature. It takes a lot of current to charge them. I’m not sure that SS is an answer to poor tolerances or stray capacitance issues. They are different problems but they are still there.

Anyway I’m really NOT that well informed about the SS stuff as I don’t really mess with it much. Really just asking. your comment re tolerance surprised me. Tubes have some weaknesses I wasn't sure that was one. I'll have to check it out.

There are lots of handy tricks to bring aging a tubes back into line such as simple cathode biasing which makes a stage almost self adjusting (if the current goes up in one it increases the bias which, in turn, decreases the current.)

Anyway
Cheers
I remain,