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Output classes A and AB
"Patrick Turner" wrote in message ... In class AB, each man pulls the saw about 1/2 way across the stroke then lets go, and the other guy grabs his saw handle and pulls the saw back the other way. Each man only mainly pulls the saw in turn, and applied force is jerky, and frankly, a difficult way to work; the Union will be down soon to have a go at the boss who told the men to saw the log that way. So speaks someone who obviously has no experience cutting wood with a cross-cut saw. You can pull on a saw, but pushing on it can easily cause it to bend and bind. When 2 men use a cross-cut saw, each man pulls far more than he pushes. Class AB verging on pure class B is the preferred mode of operation for a cross-cut saw. |
Output classes A and AB
"Eeyore" wrote in message ... John Byrns wrote: Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. I'd love to know how that happens. There's no cancellation of ANYTHING once one side has ceased conducting ! Actually, there is cancellation regardless of whether one side has ceased conducting or not, because the cancellation comes from the fact that the transfer functions of the two sides are identical but opposite. During the portion of the wave where both sides conduct, there may be cancellation of odd order distortion. In school I was taught the law of half-wave symmetry. Any wave, no matter how distorted, that has matching halves has no even-order distortion. A wave that is composed of one half of any kind and the other half is zero, has only even-order distortion. |
Output classes A and AB
"Don Pearce" wrote in message ... On Thu, 25 Oct 2007 15:40:55 +0100, Eeyore wrote: John Byrns wrote: Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. I'd love to know how that happens. There's no cancellation of ANYTHING once one side has ceased conducting ! Graham Because if you add an even harmonic to a signal, you have to make it asymmetrical. You always get a peak coinciding with a trough on one half cycle, followed by a peak coinciding with a peak on the next. If you modify the signal to remove any asymmetry, you must by definition remove the even harmonics. Agreed. |
Output classes A and AB
On Thu, 25 Oct 2007 13:43:56 GMT, John Byrns
wrote: In article , (Don Pearce) wrote: Can you overdrive a class A amp to cutoff? Yes, it is painfully easy. In my experience what happens when you overdrive a class A amp is that one device saturates, and the other sticks with its normal bias condition. No, the coupling capacitor charges up as a result of grid current shifting the bias point so that cutoff becomes even easier. There is no circumstance in which I have ever managed to put a class A amplifier output device into cutoff. You haven't tried very hard then. The designs I have used must have been better matched in drive level between the driver and output stages. They tended to limit almost simultaneously so that the drive level to the output stage did not go on rising as the input signal increased, just squared off. As I say, I never saw an output valve go into cutoff. d -- Pearce Consulting http://www.pearce.uk.com |
Output classes A and AB
In article ,
"Arny Krueger" wrote: "Eeyore" wrote in message ... John Byrns wrote: Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. I'd love to know how that happens. There's no cancellation of ANYTHING once one side has ceased conducting ! Actually, there is cancellation regardless of whether one side has ceased conducting or not, because the cancellation comes from the fact that the transfer functions of the two sides are identical but opposite. During the portion of the wave where both sides conduct, there may be cancellation of odd order distortion. Are you sure about this? I guess I will have to do some homework. In school I was taught the law of half-wave symmetry. Any wave, no matter how distorted, that has matching halves has no even-order distortion. Aren't there two symmetry laws, I can never remember the second one, or is it the first? A wave that is composed of one half of any kind and the other half is zero, has only even-order distortion. Could you say that again please? Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
Output classes A and AB
In article ,
"Arny Krueger" wrote: "Patrick Turner" wrote in message ... In class AB, each man pulls the saw about 1/2 way across the stroke then lets go, and the other guy grabs his saw handle and pulls the saw back the other way. Each man only mainly pulls the saw in turn, and applied force is jerky, and frankly, a difficult way to work; the Union will be down soon to have a go at the boss who told the men to saw the log that way. So speaks someone who obviously has no experience cutting wood with a cross-cut saw. You can pull on a saw, but pushing on it can easily cause it to bend and bind. When 2 men use a cross-cut saw, each man pulls far more than he pushes. Class AB verging on pure class B is the preferred mode of operation for a cross-cut saw. I was going to call him on that, maybe they don't have many trees in OZ. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
Output classes A and AB
In article ,
(Don Pearce) wrote: On Thu, 25 Oct 2007 13:43:56 GMT, John Byrns wrote: In article , (Don Pearce) wrote: Can you overdrive a class A amp to cutoff? Yes, it is painfully easy. In my experience what happens when you overdrive a class A amp is that one device saturates, and the other sticks with its normal bias condition. No, the coupling capacitor charges up as a result of grid current shifting the bias point so that cutoff becomes even easier. There is no circumstance in which I have ever managed to put a class A amplifier output device into cutoff. You haven't tried very hard then. The designs I have used must have been better matched in drive level between the driver and output stages. They tended to limit almost simultaneously so that the drive level to the output stage did not go on rising as the input signal increased, just squared off. As I say, I never saw an output valve go into cutoff. That sounds like a dangerous way to go, I would think that running the drivers that close to "limiting" would create a lot of distortion in the driver stage before the output stage starts clipping. I think Patrick just posted, expressing his dislike for this sort of wimpy driver. Regards, John Byrns -- Surf my web pages at, http://fmamradios.com/ |
Output classes A and AB
On Oct 25, 7:40 am, Eeyore
wrote: John Byrns wrote: Patrick Turner wrote: Cancelation of even order harmonics occurs in amps working in class AB during that part of the wave forms which are in class A, ie, the bits either side of the zero crossing. But once each tube moves into cut off, nothing is cancelled. Patrick, I'm surprised to hear you say this. What are you trying to tell us, that the even order harmonics are only cancelled during those parts of the cycle when both tubes are conducting, but that the even order distortion components reappear during those parts of the cycle when only one tube is conducting? If you actually believe that you should go back to the books and study the theory of harmonic distortion more carefully. I hope you didn't get this notion from the RDH4, I haven't read the RDH4's harmonic distortion explanation, but if this is what it says I have just lost any respect I had for the book. In a perfectly balanced PP amplifier the even order harmonic distortion is completely cancelled even when the tubes are cut off for parts of the cycle. I'd love to know how that happens. There's no cancellation of ANYTHING once one side has ceased conducting ! Graham Holy ****! Did I say yet that Poopie is ignorant and incompetent? Nah, nobody can be that stupid and uninformed about tube basics. Poopie must be cracking a joke. For the first time in his life. Good on yer, cobber! If you can't be smart and informed, at least you can try to be a clown, give people a giggle. Andre Jute Entertainer |
Output classes A and AB
Coupla superbly detailed posts here, Patrick, that I've copied to save
the calculations if I ever sink so low as to build a Class AB amp... Andre Jute Class A1 rules the waves! |
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