WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
There are nearly an infinite number of opinions on this subject. It realy comes down to personal preference. You need to listen to some good tube gear and deside for you self. You can build or by, new or used. Some of the older used equipment can be a great choice for up grading or rebuilding into a compleatly different design.
Reliability is not a problem with most tube gear unless the tubes are pushed hard. Conservitive design and correct biasing will yield long life in most cases. I have tube amps. that have run for many years with daily use and required zero maintanince (an old Harmon Karden made in the 60s and I just replaced the output tubes for the first time, one was a little weak).
The type of amp to use is more determined by the speakers power requirements and how they react with the amp and the kind of music you listen to.
In my opinion the major difference in tubes is in the highs. Tubes and SS are going to distort and I find the distortion of tubes to be much more pleasant. I have heard that the order of harmonics of the human voice and that of tube amplication are the same while SS is not. I don't know what that means but I have and do notice that even high quality SS the highs can be piercing while with tubes they tend not to be. There are so many factors to consider when choosing audio gear and cables etc. What kind of music you like and how loud, how much you want to spend and whether or not you might want to DIY and build your own. You want to end up building your own amps then I recommend tubes. A bit easier, more dangerous and some tubes sound better than others so you can feel great about buying those Telefunkin 12AX7s on Ebay.
To tell you the truth I really can't say I can tell the difference between tubes or SS in low bass. Both sound good. I use both. Some speakers sound like crap with tubes but sound fine with SS and the other way around. I will say this though, the little things can mean much more with tubes, especially Single Ended amps because of the very low wattage. The SPL of your speakers, the cables you use, the rest of your componants become much more critical. Single ended and you are going to hear everything and will then only be able to listen to some of your old favorites in the car because the recording wasn't as good as you thought it was. It is lots of fun and it won't quit. Like great wines and automobiles. Never get tired of playing.
Cons...the ones not open to argument:
Heat--set aside the operating class, the filaments produce heat. It's the nature of the beast. Good in the winter. Bad in the summer.
Low damping factor--this can be improved somewhat by using good transformers, but tube amps simply do not get the kind of damping factor that solid state amps can do, at least not without a zillion dB of negative feedback (which is part of how solid state amps get such high damping factors), but then you're throwing away one of the better aspects of tube design. (Note that there's no agreement as to how much damping factor is 'enough.' Some tube amps [almost always high powered ones] are quite good in the bass in spite of having low damping factors. Go figure.)
Tubes--you have to replace them at intervals. How long? Depends on hard they're biased.
Cons...the ones open to interpretation:
Weight & size--this one almost evens out. Both tubes and solid state need power transformers, but only tube amps need output transformers. (Unless you want to go OTL...I'm working on it as fast as I can. If you're in a hurry, go find a published design out on the web.) However, solid state amps need heatsinks, which brings things nearly to parity. (Note that tubes have built-in heatsinks.)
High voltage--yes, this can be a nuisance, dangerous, even. On the other hand, you're not going to stick your finger in there, are you? On the other, other hand, I've been hit with jolts numerous times, and am still here. It hurts. You cuss. You go on to the next thing. Just be careful, and when you're not careful...cuss quietly.
Distortion--tube amps distort, and so do solid state amps. Tube amps generally (there are exceptions) measure as having higher conventional distortion than solid state (just for reference, a good tube amp will measure less than 1% distortion without trouble). But...tube distortion is of lower order harmonics, which are easier on the ear (no one disputes this part). Tube detractors invariably seize upon this and declare that people who like tube equipment 'like euphonic distortion.' There's no easy answer here, just make a choice. Hint--go listen to live music and choose the circuit that sounds more like the concert hall. Music is the benchmark, not measurements.
Pros (note that tube detractors will bitch about some of these):
Sound quality--exquisite, if the circuit is done properly. Tubes image like there's no tomorrow, something that solid state amps can approach, but have never equalled. If you like imaging, tubes are for you. If it ranks lower on your priority list, then the battle is somewhat more evenly balanced.
They look cool--some people don't like the look of glowing filaments. Personally, I think they need their heads examined.
They automatically protect your speakers--this is the flip side of using transformers. Even if a tube flames out, the most you get is a quiet pifft through the speakers. When a transistor amp goes down, it can sometimes take drivers with it.
Tubes clip more gracefully--this is sometimes expressed as 'tubes sound more powerful than equivalent power solid state amps.' When a solid state amp clips, it generally sounds pretty rough. Most tube circuits clip so softly that people don't even realize that they've hit the wall.
I use both solid state and tubes in my system. I like both, for what each does best. But don't let folks kid you, what tubes do, they do really, really well.
I understand it's all a matter of taste, so all I can do is speak for myself. After purchasing a pretty good high-end ss system, after several years I found that I was listening less and less. For me, a relatively inexpensive EL-34 push-pull tube amp brought back the magic. Less harsh, not fatiguing. Since then, I've gone to hell in a handbasket, less and less power, more and more pleasure. Douglas Self would spit on me, but I don't care!
Well put Grey, accurate, to the point, succinct. I too have both valve and solid state, (BJT and FET) amps and like them all. I've got CDs, vinyl and 78s and love them all as well, (ok I have cassettes and reel to reel as well, hmm).
I tend to like the tight bass, clinically accurate sound that I get from solid state, if I want a friendly sound I go thermionic. I've never met some one who doesn't like the valve glow. I've got some bright red LEDs in my BJT amp, looks great, but it's not the same, (they do actually perform a legitimate function).
Pkgum, don't forget that speakers, room acoustics, and recording will make a larger difference than the amp selection!
Grey, could you tell me which is better red or white wine? Via la difference!
PS If I was starting out in DIY I'd go for a solid state amp.
The first duty of a great wine is to be red...
I forget who said it, but I agree wholeheartedly.
I no longer have a reel-to-reel, but enthusiastically support vinyl. I have some CDs, and am cautiously optimistic about SACD (which I've heard two or three times under decent, but not ideal circumstances), and DVD-A (which I've yet to hear).
Incidentally, something I forgot to put above...women, in my experience, respond much more positively to the glow of filaments than they do to LEDs. What follows is up to you.
Grey, when you say that you think tubes "image" better than solid state, do you know of any physical/operational differences between tubes, fets, or bjts that would account for the better imaging? different bias levels, levels of doping, etc?
I think good imaging comes from channel separation and accurate signal reproduction. I think we've been able to reasonably achieve both for quite some time. This makes me wonder how any modern amp could have an effect on imaging unless its being played past its limits.
I, along with many others, would love to know the "why's" of this stuff. You'd think we would have figured them out in 75+ years Do you know if they give masters or PhD's for this kind of research? Journals or papers from the AES maybe?
It almost seems like there is some unknown characteristic(the schwartz?!) that weighs heavily on sound reproduction. On the other hand, it also seems like it might all be in our heads. I don't think i've heard of one person who could consistantly identify one quality amp over another while blindfolded.
The biggest problem I see with imaging is that a lot of speakers/setups strive for the ideal point source model(our current recording methods do cater to it), when a symphony is anything but. Want better imaging?, set up a wall of drivers, each one corresponding to an instrument and its general location on the stage. (more frugal models might include a speaker for each section, instead of each instrument). Start recording 10-50 channels and stick it onto a DVD-A disc. Sure, its got an SAF of about zero, and, it might be expensive and ridiculous, but not nearly as crazy as the clowns who pay for a krell master reference and set of wilson WAMM's to get the "best" sound. There is a market for anything in audio.
Aye, stick fragile into my list above. Can't argue that one. Of course, I've seen many a bent heatsink fin, although that doesn't prevent the amp from being used.
Microphonic? Not necessarily. It depends on the tube. I've never had a microphonic 6550, although I'm sure they exist. 12AX7s are sometimes microphonic--depends on the manufacturer as much as anything. 6SN7s are never microphonic here, chez Bear (I use lotsa 6SN7s--love 'em). We can put that in an iffy category.
Bias? That's more a design problem. There's no need to put up with it. I use regulated bias supplies (most people don't go to the trouble, I guess). I check the bias about once a year. Sometimes I find it needs a whisker of adjustment; usually not. If you really don't want to fiddle with bias, there are two excellent options: cathode bias (meaning to use a resistor under the cathode), and current source. I chose fixed bias (an external voltage applied to the grid) because it's more efficient, but either of those other methods are certainly rock-solid as far as bias stability. Sorry, I don't view bias as a problem in a well-designed circuit.
I've heard people postulate that tube imaging is due to:
1) Distortion products. Bull. There's no distortion product that's going to bring the back wall of a concert hall into focus. Quite the opposite, I'd think.
2) Microphonics. Some think that there's a positive feedback loop going on between sound in the room and the tube. Again, I don't buy it. Anything of that nature would--because of the time/phase lag if nothing else--tend to blur the image, not bring it into clearer focus.
3) Greater linearity. If I say that one out loud, a solid state fan (usually bipolar, for some reason MOS/J/FET folks aren't as defensive--don't know why) will come rushing in complaining. This usually leads to discussions of comparative rates of...
4) Feedback. Generally, lower amounts of negative feedback lead to better imaging, although this is <i>not</i> a hard and fast rule. The idea here is that NFB gives with one hand and takes away with the other. Sure, you get greater bandwidth, damping factor, etc. but you lose imaging and inner detail. Choosing the right rate of feedback is an artform, not a science.
But the long and the short of it is...nobody knows why tubes do the things they do. You can theorize all day, but not get anywhere. The problem is that no one has yet figured out what (regardless of gain device) makes a piece of hardware image well. There are some who go so far as to deny that there is such a thing as depth of image (hopefully nobody argues about image width). Given what they listen to, they're probably right--for their system.
One oddity is why some amps present an image that is further forward than others. The Aleph 2s I built image <i>behind</i> my tube amps by about a foot. Say what? I've heard amps do this before, but never had such an obvious case in my own home where I could play with it. I'm building a second pair of Aleph 2s (up late last night populating the front end boards) so as to try some experiments with this. Nelson and I wrote back and forth about it; his take was,'It's a mystery.' If I'm able to resolve any questions on this front, you guys will be first to know. Don't hold your breath. Nobody's been able to pin this down yet, and I doubt I'll be the one to do so.
There is one amplifiier that uses a small microprocessor and DAC to set tube bias automatically during each and every turn on/warm up sequence. It adjusts for the aging and different (EL34) brand/date of tubes. Neat huh?
Wolcott Prescence Monoblocks, 220 watts and 75 pounds each. But they cost about 10 grand for a pair. They will drive Sound Lab Electrostatics better than any other amp! Talk about sweet sound!
My problem with their strategy is that the tubes are read cold (at least as I understand it), which isn't going to give you an accurate bias setting. They ought to run for an hour or so first.
An even better way to do it if you want to go active bias is to use a sense resistor, monitored by an opamp with a lowpass filter set at, say, 1 Hz. The opamp drives the bias voltage. Voila, real-time bias adjustment, not just when you turn on the amp. I might incorporate something of this nature into the OTL I'm working on.
Supposedly, OTL amps are a wonderful match for electrostats, but I've never heard the combination.
Sound Labs M-1s are one of the two electrostats I've ever given serious thought to buying. (The other was the Stax F-81--a gloriously impractical speaker.)
The amp takes several minutes to completely turn on,
So it gives the tubes time to warm up, and you can press the autobias reset switch at any time while playing music, it temporarily mutes the music and starts the autobias cycle all over again. Smart, huh?
I'd give it an hour or more before trying to check the bias. It changes dramatically during that time (solid state does too, for that matter--this isn't limited to tubes). If you've got to go tell it to check the bias manually every time you listen (after an hour) then you're actually losing, rather than gaining. It'll start not knowing the bias, take a cold read (anything less than fifteen or twenty minutes minimum will be way off), and be wrong. After a bit, assuming that you want optimum performance, you'll have to rebias. Sounds like you're going to have to do this every single time you listen, whereas I only bias once every six months to a year. I dunno, seems like a lot of unnecessary fiddle factor to me.
Incidentally, I haven't heard the amp. I'm not saying that it doesn't sound good. It just seems like a flashy way to bias without much thought towards the practicality.
Put biasing, tube life, power etc all aside the first time I really heard my speakers, the first time I got great imaging and soundstage was when I hooked up a pair of 3.5 watt SE 6BQ5 mono blocks built on the old Mullard circuit to my humble but loveable Shahinian Obelisks which are by no means efficient in my book at 91-92 db. I do get out and listen to "High End" of the latest flavour( all the B&Ws, Martin Logan, Magnepan, Krell, Mac, AR, etc,etc)and recently went to a DIY Speaker Convention in Texas where tubes, SS, great cables and expensive interconnects were all there with about every type speaker represented in some fashion except Elecro Statics and I did not hear the kind of imaging that the SE tube amps provide. There was no SE tubes there. Most of the speakers were less than 90 db and had complicated crossovers and SE wouldn't have worked with them anyway. The point is that I have heard better sound reproduction with $2600 retail (I don't do retail)gear and speakers with DIY cables and interconnects than I have heard on $50K plus systems at dealers. That is the whole point to DIY isn't it? You want what sounds best for the least amount of $$ and the pride of DIY. And by the way I have hooked up Marantz, Carver, Phase Linear and other SS, and Dyna ST-70s, Fisher PP integrated amps and recievers and others to the same speakers without comeing close to the sound of the Mullard 3.3s which are not the best SE out there (well maybe for the money). The only draw back was because of the inefficiancy of my speakers I could easily clip the amps. That level was well above my normal listening
level so the only thing I could not do was really crank it. Bi amping would take care of that problem though. The best imaging of the soundstage I have heard with SS sounded artificial and like it was a thing the amp did and not necesarily something that was on the recording. These are only opinions, but I do want to say that the only way to measure the difference between the different types of amps is to listen to them. And listen to them correctly. Which means with the right type of speaker and cables etc. It really is apples and oranges.
I doesn't take a tube as long to warm up as solid state. Checking bias on solid state is sometimes real tricky, I know how fast it changes with temperature change. Take the cover off of the amplifier and the temperature along with bias changes immediately. Then put the cover back on and watch your adjustments drift again. Frustrating! i once set up a SS amp with external test leads so that I would not have to remove the cover, then adjusted the bias and offset over a two week period.
I've always assumed imaging is dependant on phase. With opt tubes you'd expect to be less able to image well but unless the performance is due to the phase errors this doesnt seem to hold as we've all had great imaging from tubes.
Distortion is another topic where measurements dont always reflect experience. Even within tube amps. My quad11's measured much better than my gm70se amp, but the gm70 is hands down the best amp i*ve had.
Re solid state, its been ages since ive had a serious ss amp to compare with. But i cant deny im drawn to the esoteric!
Ultimatly i still feel the speaker is by far the weakest link in any system.