Think of it as characteristic trade offs and compromises. Also, you're confusing Tube characteristics (triode, pentode, etc.) and amplification toplogies.
I hope this makes sense in the context of REAL information you hopefully get here soon.
Way too much to ask from a single reply. (Remember Google is your friend.) But here is a very quick & dirty response.
SET = single ended triode. A tube amp with only one output tube per channel that handles both the + and - sides of the waveform. Tend to be lower power but highly beloved by their followers.
Push-Pull = has two output tubes per channel. One tube handles the + side of the waveform and the other handles the - side. Easy to get more power from than an SET.
Triode = the simplest amplification tube type. The cathode (filiment/heater) emits electrons to be picked up by the plate. A grid in the middle regulates the flow. The 3 elements = triode.
Pentode = five elements. A cathode, plate and 3 grids. Gives better control of the tube for certain conditions.
Ultralinear = a push-pull tube circuit that helps reduce certain types of distortion.
Class A = a bit tough to describe simply, but the output circuit is always on. They are very linear but waste a lot of power so the design tends to be used for lower wattage amps. SET amps are Class A operation.
As far as sound goes, triodes sound the best but make the least power. Class A also sounds the best, but makes the most heat.
Ultra-linear is an attempt to get a pair of pentodes to behave a little more like triodes, without sacrificing too much power- a compromise. If done right, it can be fairly successful, although no ultra-linear sounds like a triode amp.
SETs make less power than push-pull. They also sacrifice bandwidth, in return get *extremely* low distortion at low power levels. Most push-pull designs have an audible *increase* in distortion at low power levels. Low power levels is where detail resides- SETs can be a lot more detailed. Their qualities can only be tapped by high efficiency speakers however (those who say otherwise have yet to hear what their amp is capable of....).
All of the above types of amps use output transformers. The output transformer can be bypassed with audibly and measureably increased performance including low level detail and extreme bandwidth. The sacrifice is the ability to drive low impedance loads, although bigger Output TransformerLess (OTL) amplifiers can drive some surprisingly low impedances! OTLs can be triode, tetrode or pentode and they can be class A to class B and anything in between.
Execution is important and can shoot down the best concept, or support the operation of the worst. All amplifiers are sensitive to load, so you always have to be careful. In general, all tube amps perform better on speakers that are 8 ohms or more, as opposed to 4 ohms, all other things being equal. But in the end you will probably have to compare different types of amps that you can afford to find what works for you and your speakers. Have fun! and keep asking questions.
Excellent replies from Mlsstl and Atmasphere. Here is a quick and dirty run-down of the different types of tubes.
A tube basically works by boiling off electrons from the cathode (-ve terminal) and accelerating the electrons to the anode (+ve terminal). The cathode may be indirectly heated (have a seperate heater element) or directly heated.
A DIODE is the simplest type of tube. The cathode and the anode are placed relatively close together so current can only flow in one direction.
In a TRIODE, the cathode and anode are placed further apart so no current will flow. A seperate grid, called a "control grid", is placed between the cathode and anode. A weak musical signal is fed to the control grid, which attracts electrons from the boiling cathode and accelerates it towards the anode. In this way, a small musical signal generates a larger current.
However, the amplification that triodes produce is not very much. So the TETRODE was invented. As the name implies, there are four grids. In addition to the three grids in the triode, the tetrode adds a "screen grid" between the control grid and the anode - making the configuration: cathode, control grid, screen grid, anode.
The screen grid is positively charged, and its effect is to accelerate even more electrons towards the anode thereby giving more amplification.
However, the electrons now have so much energy that some of them bounce off the anode, reducing overall efficiency and messing around with the musical system.
So the PENTODE was invented. In addition to the four grids in the tetrode, a pentode has a negatively charged "suppressor grid" between the screen grid and the anode - cathode, control grid, screen grid, suppressor grid, anode. The effect of the suppressor grid is to reduce the energy of the electrons bouncing off the anode, giving greater amplification and less wastage.
A Pentode can be made to function as a triode if you simply disconnect the screen and suppressor grids. Hence some Pentode based amps (like the Cary V-12R and Cary 120S) can be operated in triode or pentode mode.
In MY opinion (and this is a gross generalization), triode amps sound more delicate and have more of that tube "bloom". Pentode amps are more powerful and sound more "solid state" than triodes. Of course, not all amps are like this.
I'll let someone else explain Class A, etc. but hopefully this was of use to you.
Hi Mlsstl. An ultralinear amp in not necessarily push-pull. I have seen a circuit diagram for an ultralinear single ended amp.
An amp is ultralinear when the screen grid is biased from an center tap on the primary side of the output transformer. I think the only thing we can say definitively is that a ultralinear amp cannot be an OTL amp, but it most certainly can be single ended if you can source the right output trannies.
Hi BDChem, everybody posted some good info. Being vain, Ill post some more. ;-)
Vacuums tubes used for audio reproduction can be triodes, tetrodes or pentodes.
To make things a bit complex, tetrodes and pentodes can be wired to run in triode mode, pentode mode or ultralinear mode.
For all combinations of the above tube tubes and how they can be wired, they can be deployed in either single ended or push pull configuration in an amplifier.
So you could have a single ended tetrode amplifier or a push pull pentode wired in triode mode. I believe there are 10 possible configurations?
People like Ralph makes things even more complex by building tube amps that have no output transformers. So now you can have any combination running with or without output transformers. (Note. I dont believe it is possible to have an OTL amp that is ultralinear.)
And then some amps allow you to run in a hybrid mode. Carys V12 series amps can be run in partial ultralinear and partial triode mode.
I believe they all sound very different. I say I believe, as I have not heard all the possible configurations and probably never will.
To summarize the responses - it's all in how it handles the signal! I can tell you that the Triode will be the most honest, but you will have to look at Pentode if you want to wake the neighbors! What the vacuum tube does so well? Realism! You can have a great sounding stereo with transistors - but nothing does realism like a vacuumtube.
These are the choices we have in tube amplifier.
Topology in circuitry;
** tubes used,DHT/indirectly heated,,, like 300b,kt88,,211,,845.
**tube used DHT or not DHT,,300b,,kt88
3 types of topology of tube OTL
** tube used,,,like 300b,211 0r 6as7,6c33c,7242 kt88,etc.
***different tubes used in one of these amps have different sound and over 1000 combinations/sounds.
Realdeal, there are no practical OTLs using 300bs, 211s or KT88s; just for the record.
Ralph,I think Realdeal is right,I also made an OTL using single KR52B,5R4GYB tube rectified with 600V on the plate.,no feedback and what a transparency.
@amfibius Thank you so much for the nicely concise overview of how the tubes work. This was simple, and to the point. I hadn't come across something like this until just now. :)