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 Im 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 tubes 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 isnt 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. Dont harden your brains 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 tubes plate is attached to the OP transformer), class A or B (how the op tubes grid is biased), ultralinear, ultrapath (how an op tubes screen grid is attached to the power supply or the op transformers primary.) etc all describe the output tube in one way or another and so it generally is thought of as the defining stage. But Im 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 its own unique signature in this way. Thats right, a tubes sound is mostly related to its imperfections. If a tube has a perfectly linear response, that is, its output is an exact copy of its 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
There are lots of things that add to the sound and Im 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 tubes 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 isnt 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. Dont harden your brains 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 tubes plate is attached to the OP transformer), class A or B (how the op tubes grid is biased), ultralinear, ultrapath (how an op tubes screen grid is attached to the power supply or the op transformers primary.) etc all describe the output tube in one way or another and so it generally is thought of as the defining stage. But Im 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 its own unique signature in this way. Thats right, a tubes sound is mostly related to its imperfections. If a tube has a perfectly linear response, that is, its output is an exact copy of its 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