vacuum tube amps vs. transistor amps?
okay, i see the tube amp versus solid state arguments everywhere, and from what i gather, tube amps create more distortion, but favorable distortion, while transistors produce far less distortion, but it is entirely unfavorable.
okay, great. but what does this sentence mean:
"Tube amplifiers could not use as much negative feedback (NFB) as transistor amplifiers due to the large phase shifts caused by the output transformers and their lower stage gains"
1. what is an output transformer and why does a vacuum tube require one? i thought the voltage was dc by the time it is amplifying a wave form that will go to the speakers and make sound...so how does a transformer work into this?
2. what are lower stage gains? what are large phase shifts?
3. why are tube amps the pre-amplification in hybrid systems and not the main output amp? aren't vacuum tubes better at handling more wattage than solid state? (which is why satellites, radio stations and microwave ovens use vacuum tubes and not transistors?)
4. what is total intermodulation distortion?
5. Why is solid state better for driving woofers and sub woofers? how does it provide better "bass control"?
Update:can someone please address the questions by answering in numbered format?
and now i have a 6th question
6. Why does the wave coming off of the vacuum tube directly require a transformer but an amplified wave coming out of a transistor does not?
Update 3:Can someone answer questions 3 and 6?
Comments
Tubes tend to generate second order harmonic distortion while transistors tend to generate third order harmonic distortion. Second order distortion is less objectionable to the human ear than third order.
Tubes tend to be more linear than transistor amplifiers so tube amplifiers don't require as much negative feedback as transistor amplifiers. Transformers have inductance, this inductance will cause a phase shift to the audio signal. If large amounts of negative feedback are used from amplifier output this could lead to the amplifier becoming unstable.
1. The tube amplifier needs an output transformer to match the high impedance of the tube output to the low impedance of the speaker. The transformer steps down the output voltage and steps up the output current, net effect lowers the output impedance.
2. An amplifier has several stages of amplification, most of them are fairly low voltage gain around 10 times or so. Phase shift is caused by reactive components like inductors and capacitors. As an audio signal pass through a reactive component, the audio signal's various components are delayed by various amounts. This causes the phase shift of the output audio signal.
3. Vacuum tubes do handle higher power than transistors, but most devices now use transistors as they are more reliable. Microwave ovens use a magnetron to generate microwaves. Magnetrons are vacuum tube devices but are far different from normal vacuum tubes.
4. Total intermodualtion distortion is the distortion caused by a non linear amplifier. A non linear amplifier will generate sum and difference intermodulation products when two non harmonically singles are applied to the input. If the input signals frequency are A and B, there will be a new signal generated that has a frequency A +B and frequency A- B ( assuming A>B) or B - A ( assuming B>A).
5. Solid state amplifiers tend to have lower output impedances than tube amps. This means the solid state amplifier will able to drive a woofer/ sub woofer with higher current than a tube amplifier. It also means that the dampening factor of a solid state amplifier is greater than a tube amplifier. This means the amplifier absorb the current from the moving speaker cone. These two factor leads to better bass control.
You also asked why a hybrid amplifier uses transistors in the output and not tubes. Transistors have become very reliable and can handle high enough power that a transistor amp can put out 100's and even a 1,000 watts. Vacuum tubes usually require output transformers which have become expensive for a high quality unit ($100 +). Tubes further require 300 + volts on their plates this means an expensive step up transformer.
Roger has done a nice job on 1-5 so I'm going to concentrate on #6. The output impedance of vacuum tubes (or valves as we Brits know them) is much higher then semiconductors such as BJTs and seriously higher than the likes of mosfets and so in most configurations either single ended or push pull tube amps a transformer is required to get the output impedance to match the speaker impedance.
However......there is a configuration of valve amplifier which doesn't require an output transformer and is known as the OTL (output transformer-less) tube amplifier. This is a totem pole arrangement with several tubes (three or more) tubes in parallel at the top and bottom of the pole (six in total) so the output impedances are reduced obviating the use of a transformer. Have a look at http://www.bonavolta.ch/hobby/en/audio/6as7_2.htm
and there's an example using 8 tubes in the output stage. The immediate disadvantage of the configuration is the obvious lack of DC isolation between the output and the speaker so not good for unwary fingers however because there's no transformer the fidelity and frequency response is better than a conventional valve amp configuration. Another downside is the design is only good for maybe up to 50W maximum and more usually 25W so not exactly capable of driving a 4 x 12" speaker "stack" very hard.
Quick word about high power applications. Much above 10KW the vacuum tube still rules the roost in RF applications with one of top of the pile being the CY1172 220KW transmitting tetrode http://cfile240.uf.daum.net/attach/156DA6494F20D3B... You won't find one of these in a satellite, it takes a small electricity substation all on its own to drive it.
Tube amps require output transformers because what comes out is wrong for driving the coils in the speakers. And of course it is not DC - it is music which is by definition alternating - sine wave mixes.
Microwaves use, I believe, a single tube, the klystron that actually produces the microwaves. The rest is solid state.
When transistor amplifiers were introduced, they were praised for their crisp clear sound and precise feed back of the recorded material. But people then discovered that the recorded material included stuff they didn't really want to hear - like mouthing instruments and clicks on the stage - and people divided into those that wanted cleaner recordings and those that preferred the "warm" sound of tubes which covered up the perfect errors.
Transistor amplifiers provide plenty of distortion. In music, some people prefer tube amps because they provide a "warmer" sound. Transistor amps provide a "harsher" distortion. Also, I do not know where you got the information that satellites or microwaves, etc use tube amps. They all use transistors if anything. Like I said, tube amps are used mainly for music.