I am pilforing this info from the Web:
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. They 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.
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.
Tetrode - The Tetrode and Pentode have 4 elements that are externally assessable (Anode, Screen. Grid, Cathode). The extra screens described as suppressor screens and beam plates are internally connected and are not externally assessable. Variations of Tetrodes and Pentodes evolved as a means of getting around each others patents. A KT88 is a beam powered tetrode, whereas a 6CA7 (EL34) is a power pentode.
Ultralinear - a push-pull tube circuit that helps reduce certain types of distortion. It s 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.
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.
-----------------------------------------------------------
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.
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.
Generally 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.
Facebook
Twitter
Instagram