greg.trice@canremote.uucp (GREG TRICE) (10/03/90)
Does anybody know any computer programs (preferably Unix based) that would assist in the design of vacuum tubes, e.g. tell you what shapes and spacings are required for the electrodes to achieve a particular characteristic? Also any recommendations for a good book on tube design? I'm also interested to know whether there are any good SPICE models available for vacuum tubes that really take into account the various non-linearities and account for things like the kink in the Va/Ia curve of some tetrodes at low anode voltages.
siegman@sierra.STANFORD.EDU (siegman) (10/16/90)
>Does anybody know any computer programs (preferably Unix based) that >would assist in the design of vacuum tubes, e.g. tell you what shapes >and spacings are required for the electrodes to achieve a particular >characteristic? Also any recommendations for a good book on tube design? Wow, that goes back to the old days! My impression would be that tubes went out before computer design came in; but I don't know what some of the surviving tube manufacturers might have in their boxes of tricks. In any event, wasn't Spangenberg one of the important vacuum tube textbooks? Plus maybe some of the old MIT Rad Lab series volumes?
cgordon@vpnet.chi.il.us (Crash Gordon) (10/18/90)
>Author: [siegman] >Wow, that goes back to the old days! My impression would be that >tubes went out before computer design came in... I've seen a CD player (California Audio, I think) which uses tubes for its audio output. Mucho $$$. Hardcore audiophiles claim that a tube amp sounds better than solid state. ----------------------------------------------------- Gordon S. Hlavenka cgordon@vpnet.chi.il.us Disclaimer: Yeah, I said it. So what?
henry@zoo.toronto.edu (Henry Spencer) (10/21/90)
In article <271c8c45-4b1.2sci.electronics-1@vpnet.chi.il.us> cgordon@vpnet.chi.il.us (Crash Gordon) writes: >Hardcore audiophiles claim that a tube amp sounds better than solid state. Yeah, it's so hard for a transistor circuit to reproduce all those warm fuzzy nonlinearities. -- The type syntax for C is essentially | Henry Spencer at U of Toronto Zoology unparsable. --Rob Pike | henry@zoo.toronto.edu utzoo!henry
wolfgang@wsrcc.uucp (Wolfgang S. Rupprecht) (10/22/90)
>In article <271c8c45-4b1.2sci.electronics-1@vpnet.chi.il.us> cgordon@vpnet.chi.il.us (Crash Gordon) writes: >>Hardcore audiophiles claim that a tube amp sounds better than solid state. In sci.electronics you write: >Yeah, it's so hard for a transistor circuit to reproduce all those warm >fuzzy nonlinearities. ;-) Actually the truth is probably that it is much easier to design a *bad* transistor amp than a bad tube amp. The real problem is that a transistor stage with high gain and no local loop feedback (ie. no emitter resistor) is *very* nonlinear. Much more so than a tube stage constructed similarly. Many of cheap transistor amps run each stage at close to open loop gain of the transistor. They then fix the strong nonlinearities with a feedback loop around the whole amp. This is what I call the Phase Linear approach - shove a 741 in there to get .00000000000000001 % distortion. It works quite well for carefully selected test conditions, that is ones that leave the every stage biased in a linear enough region of its curve (eg. 1khz sine wave). Unfortunately the first stage, the one that does the error difference subtraction, is very easy to overload if we task it with the chore of multiplying any error by 10**5. How does one overload the input stage? Simplest case inputting a square wave. For the time that the output slews from low to high the amplifier is *not* modelable as a linear system. Any small change in input will not result in *any* change in the output. This is the "transistor" sound. The sound of a bone-headed designer that just learned which end of a transistor went to which rail. ;-) The solution? Do a good job on feedback on each stage, and keep each one of the stages linear by using lots of local feedback. Don't try to patch it all up in the end. Tube amps all have very limited gain in all the stages, and little or no global feedback. This is all becaues tubes have very limited gains at best. Notice how they force you to do a good job. You still need to add the "tube distortion curves" is you want the transistor amp to sound like real tube amp while clipping. You can probably use a large bag of diodes and resistor ladder to model this. ;-) -wolfgang -- Wolfgang Rupprecht uunet!{nancy,usaos,media!ka3ovk}!wsrcc!wolfgang Snail Mail Address: Box 6524, Alexandria, VA 22306-0524
myers@hpfcdj.HP.COM (Bob Myers) (10/23/90)
>Hardcore audiophiles claim that a tube amp sounds better than solid state.
Of course, there are also hardcore audiophiles who claim they can
hear the color of the front panel of the pre-amp. :-)
Bob Myers | "The difference between science and the fuzzy subjects
myers%hpfcla@hplabs. | is that science requires reasoning, while those other
hp.com | subjects merely require scholarahip." - R. Heinleinankleand@mit-caf.MIT.EDU (Andrew Karanicolas) (10/24/90)
In article <1990Oct21.171736.9918@wsrcc.uucp> wolfgang@wsrcc.uucp (Wolfgang S. Rupprecht) writes: >>In article <271c8c45-4b1.2sci.electronics-1@vpnet.chi.il.us> cgordon@vpnet.chi.il.us (Crash Gordon) writes: >>>Hardcore audiophiles claim that a tube amp sounds better than solid state. > >In sci.electronics you write: >>Yeah, it's so hard for a transistor circuit to reproduce all those warm >>fuzzy nonlinearities. > >;-) > >Actually the truth is probably that it is much easier to design a >*bad* transistor amp than a bad tube amp. What does this mean? It takes a lot of knowledge to correctly design a reasonably complicated audio amplifier, regardless of the devices used. >The real problem is that a transistor stage with high gain and no >local loop feedback (ie. no emitter resistor) is *very* nonlinear. >Much more so than a tube stage constructed similarly. Sorry, but analog circuits used for operational amplifiers are considered weakly non-linear otherwise they would not be useful for many applications. Have you ever seen what happens if you run a vacuum tube amplifier into clipping? Try it, it's educational. Also, connect to a spectrum analyzer if you have one and you will see the rich collection of harmonic content. >Many of cheap transistor amps run each stage at close to open loop >gain of the transistor. They then fix the strong nonlinearities with >a feedback loop around the whole amp. This is what I call the Phase >Linear approach - shove a 741 in there to get .00000000000000001 % >distortion. One could only wich the distortion could ever be so low. What are you trying to say anyway? The whole *idea* is to use the *high* transconductance of bipolar devices in op-amp designs. This way, the loop transmission can be large leading to small closed loop errors. >It works quite well for carefully selected test >conditions, that is ones that leave the every stage biased in a linear >enough region of its curve (eg. 1khz sine wave). Unfortunately the >first stage, the one that does the error difference subtraction, is >very easy to overload if we task it with the chore of multiplying any >error by 10**5. How does one overload the input stage? Simplest case >inputting a square wave. For the time that the output slews from low >to high the amplifier is *not* modelable as a linear system. Any >small change in input will not result in *any* change in the output. Use a larger slew-rate. This is 1990. Stop using the 741 for everything. Open your eyes, and your ears, and LEARN what modern integrated-circuit processes can now accomplish. Also, check out the large signal square-wave response of a vacuum tube amplifier sometime into a purely resistive load. A non-ideal step response will be readily apparent. Try this with a reactive load also. >This is the "transistor" sound. The sound of a bone-headed designer >that just learned which end of a transistor went to which rail. ;-) > >The solution? Do a good job on feedback on each stage, and keep each >one of the stages linear by using lots of local feedback. Don't try >to patch it all up in the end. > Use a larger slew rate. Use modern op-amps. Do not use lateral p-n-p's. Do not compensate your op-amp for unity-gain if the closed-loop gain is 40. Do not use a 741 for every single op-amp job in the world. >Tube amps all have very limited gain in all the stages, and little or >no global feedback. This is all becaues tubes have very limited gains >at best. Notice how they force you to do a good job. > They do no such thing. Vacuum tube amplifiers sound more melodious than solid-state amplifiers and that is *all*. >You still need to add the "tube distortion curves" is you want the >transistor amp to sound like real tube amp while clipping. You can >probably use a large bag of diodes and resistor ladder to model this. ;-) > Why bother. Use vacuum tubes and you will be happier as will I. Personally, I prefer not to clip my audio amplifiers. If you use solid-state op-amps, get one designed recently that has a reasonable slew rate so the input stage worries are not important. This does not mean that 2000V/usec slew rate is needed for audio, unless the tweeter has to settle out within 25ns. >-wolfgang >-- >Wolfgang Rupprecht uunet!{nancy,usaos,media!ka3ovk}!wsrcc!wolfgang >Snail Mail Address: Box 6524, Alexandria, VA 22306-0524 Andrew Karanicolas MIT Microsystems Laboratory ankleand@caf.mit.edu
cbrandau@isis.cs.du.edu (carl brandauer) (10/24/90)
In article <1990Oct21.171736.9918@wsrcc.uucp> wolfgang@wsrcc.uucp (Wolfgang S. Rupprecht) writes: [much stuff deleted] >Tube amps all have very limited gain in all the stages, and little or >no global feedback. This is all becaues tubes have very limited gains >at best. Notice how they force you to do a good job. > Hogwash - there is not a single instance of a tube power amplifier without global feedback in such classic references as the 'Radiotron Designer's Handbook' by Langford-Smith and others.
jgk@osc.COM (Joe Keane) (10/31/90)
I think one of the toughest problems facing today's designer is that for people to like your equipment it has to add the right coloration. Digital recording almost eliminates noise and distortion due to the recording. With today's electronics you can get ridiculously low levels of non-linearity, so your THD and IMD figures are going to be much better than what hi-fi standards used to be. Also with careful design the frequency response of the amplifiers can be very flat. Then with many-band equalizers you can get rid of any variation frequency response due to speakers or room acoustics. Now we've got a technically superior system, where the sound produced is very close to the sound originally picked up by the microphone. Guess what? People don't like it, because it's `boring'. Vinyl has more `clarity'; tube amps are more `musical', some other system has more `presence'. So now to get a better product you have to go back and break some things you worked so hard to get right. Maybe add some white noise to sound like a record, add some second harmonic distortion to get the tube amp sound, boost some frequencies to sound like some other speaker system. Wouldn't it be nice if you could just buy boxes which do this for you? Then your amplifier wouldn't do anything to the sound, so they all would sound the same.
cgordon@vpnet.chi.il.us (Crash Gordon) (10/31/90)
I said: >>Hardcore audiophiles claim that a tube amp sounds better than solid state. Bob Myers said: >Of course, there are also hardcore audiophiles who claim they can >hear the color of the front panel of the pre-amp. :-) Hell, I can _smell_ the color WITH MY EYES CLOSED! ----------------------------------------------------- Gordon S. Hlavenka cgordon@vpnet.chi.il.us Disclaimer: Yeah, I said it. So what?