Not stupid, but not logical. You can get better performance by taking the output from the lower anode in that case, as this creates a very symmetrical circuit with very predictable properties. See the first stage of the Aikido:
http://www.tubecad.com/2004/NewLineStage.gif
There is little point in taking the output from the upper cathode, like an SRPP, when the stage is DC coupled.
Hi,
First you say it acts like a resistor, which I clearly say it cannot, then you agree with me that it presents a non-linear resistance (which was my point). As result of the non-linearity the load line is no longer straight and the overall circuit behaves more linear than a CCS loaded common cathode stage.
So we agree.
The rest is semantics.
I have not seen any reference to "shunt regulated push pull" in Artzt's 1940 Patent. He calls it "Balanced Direct and Alterntaing Current Amplifier". the patent does not exclude the case of Zload = oo
I guess we should rename SRPP to BDACA.
Ciao T
PS, I am familiar with V&W, thank you. But not all written in books is true.
First you say it acts like a resistor, which I clearly say it cannot, then you agree with me that it presents a non-linear resistance (which was my point). As result of the non-linearity the load line is no longer straight and the overall circuit behaves more linear than a CCS loaded common cathode stage.
So we agree.
The rest is semantics.
I have not seen any reference to "shunt regulated push pull" in Artzt's 1940 Patent. He calls it "Balanced Direct and Alterntaing Current Amplifier". the patent does not exclude the case of Zload = oo
I guess we should rename SRPP to BDACA.
Ciao T
PS, I am familiar with V&W, thank you. But not all written in books is true.
SRPP Not
That series triode thing documented post war by V&W needs a name You two just agreed that it is not Push Pull.
I think that it should be called SRAR for Shunt Regulated Active resistor.
Just for grins let’s take it to the lab pick some parameters and test it and log the results. Now with everything the same pull the top tube (figuratively, I know there are two triodes in the same glass envelope) and cathode resistor. Replace the triode with a resistor and adjust for the same voltage drop as was across the original triode. Test and log as was done the first time. My bet is that gain, gm and anything you care to measure looks and walks like a resistor in the top triode position.
If that top triode does not pull its load we should rename it.
Done: SRAR
DT
All just for fun!
That series triode thing documented post war by V&W needs a name You two just agreed that it is not Push Pull.
I think that it should be called SRAR for Shunt Regulated Active resistor.
Just for grins let’s take it to the lab pick some parameters and test it and log the results. Now with everything the same pull the top tube (figuratively, I know there are two triodes in the same glass envelope) and cathode resistor. Replace the triode with a resistor and adjust for the same voltage drop as was across the original triode. Test and log as was done the first time. My bet is that gain, gm and anything you care to measure looks and walks like a resistor in the top triode position.
If that top triode does not pull its load we should rename it.
Done: SRAR
DT
All just for fun!
I would prefer a common cathode stage loaded on a CCS with positive feedback by AC that depends on load resistance. And with negative feedback by voltage on DC (like a gyrator with negative losses).
What can be more linear?
Nothing. A tube loaded by a tube can't be linear, since a loading tube is a tube, but not an anti - tube. It does not have a mirrored curve. Period.
What can be more linear?
Nothing. A tube loaded by a tube can't be linear, since a loading tube is a tube, but not an anti - tube. It does not have a mirrored curve. Period.
The SRPP has had lots of names over the years, and Artzt wasn't the first to patent it either.
Hi,
Actually, if you look closer you will find that the grid signals for upper and lower tube in the BDACA are 180 degrees out of phase, so it is not an anti-tube, but a tube operating at opposite polarity, so in the mathematical sense it does become an "anti tube". Actually, it has no choice in the matter.
That is the beauty of the BDACA, which is often overlooked. Sometimes I think only John Broskie understands how the BDACA really works and no-one reads what he writes about it (probably because of his unhealthy preoccupation with PSRR)...
Ciao T
Actually, if you look closer you will find that the grid signals for upper and lower tube in the BDACA are 180 degrees out of phase, so it is not an anti-tube, but a tube operating at opposite polarity, so in the mathematical sense it does become an "anti tube". Actually, it has no choice in the matter.
That is the beauty of the BDACA, which is often overlooked. Sometimes I think only John Broskie understands how the BDACA really works and no-one reads what he writes about it (probably because of his unhealthy preoccupation with PSRR)...
Ciao T
Hello,
Several years ago after reading about the mislabeled 6DJ8's I bought some Tunsgram PCC189’s (variable mu). The idea was to make an effects/line stage between the CD player and SS amplifier in the garage. My point here is that it was difficult to get a signal voltage amplifier to sound sweet and tube like. I ended up starving a common cathode stage and putting a stepped attenuator before and after the line stage tube. Turn up the input attenuator to get 25 + volts out and then knock it down to feed the power amplifier then it sounded like a tube. At 1 or 2 volts out it was difficult to tell even if you knew. Now that I have the FFT setup on a computer the thing may be fun to test.
DT
All just for fun!
Indeed. This illustrates an important point about electronics and the ear, as well as the excellence of conventional common cathode stages. If one is to believe the SP article that Thorsten references, a simple common cathode amplifier will give an order of magnitude lower distortion than an SRPP, and with a considerably better harmonic distribution. Couple it with a cathode follower and for the same bottle count, you've also got lower output impedance.
The home FFT is an amazing tool! Wish I had one 20 years ago.
edit: You could probably do what you were trying and do it better with Wavebourn's clever Variable Harmonizer circuit.
Hi Stuart,
You did not actually read the article, did you, or look at the figures, did you?
If you look again, the author shows an optimum in his curves that approaches 0.01%.
Show me a common cathode stage that (alone, not with cancelling harmonics in the cathode follower) is ONE MAGNITUDE (that is by a factor 1:1000) lower.
Oh what the heck, show me ANY common cathode stage that offers 0.00001% THD even with cancellation in the follower.
Ciao T
You did not actually read the article, did you, or look at the figures, did you?
If you look again, the author shows an optimum in his curves that approaches 0.01%.
Show me a common cathode stage that (alone, not with cancelling harmonics in the cathode follower) is ONE MAGNITUDE (that is by a factor 1:1000) lower.
Oh what the heck, show me ANY common cathode stage that offers 0.00001% THD even with cancellation in the follower.
Ciao T
Do you understand what the words "order of magnitude" mean? I'll be a nice fellow and help you out here:
Order of magnitude - Wikipedia, the free encyclopedia
Hi,
You are right of course. Some confusion between the english and a similar german term that does mean 1:1000. Happened to me before, sorry.
But to be honest, show me one with 0.001% THD either.
Does not even matter that I was two orders of a magnitude out... Either way you cannot.
Ciao T
You are right of course. Some confusion between the english and a similar german term that does mean 1:1000. Happened to me before, sorry.
But to be honest, show me one with 0.001% THD either.
Does not even matter that I was two orders of a magnitude out... Either way you cannot.
Ciao T
Wrong again. Look at ECC88, common cathode, CCS load, ip = 10mA, the same 2V out. 0.002%, nearly entirely 2nd order. And unlike the figures shown in the Evers article, it isn't relying on a sharp null in the 2nd order distortion which is unlikely to be maintained with thermal drift, warm up, and tube aging. And also unlike the Evers data, which is dominated by second order distortion nulling, the resulting spectra have second order dominating, with third and higher below -100dB.
For yet another example, look at the 6J5 (6SN7 equivalent) SRPP vs. mu follower data that Morgan published (and again, unlike your rather vague claims, he is explicit about levels, test circuits, loads, and test conditions). 15dB distortion difference, which, not coincidentally, is about an order of magnitude.
Where the SRPP is useful, it is very useful- high voltage swings. But the trade-off is distortion, and that cannot be escaped. If you try to minimize the distortion as Evers did, you lose the ability to swing high voltages and end up with a circuit that is still worse than a conventional one as regards distortion.
Hi,
Really?
Surely an order of magnitude bigger or smaller in German means exactly the same as it does in English, does it not?
Cheers,
Really?
Surely an order of magnitude bigger or smaller in German means exactly the same as it does in English, does it not?
Cheers,
Hi Sy,
You could of course claim that going from 0.01% to 0.009% gives a change of an order of magnitude. This would be technically correct but meaningless, so I took you to mean factor of ten. But you can keep weasel around. BTW, you would not happen to have a reference to the source for the common cathode stage that has 0.002% THD, would you.
Fred, I mistook "Order of Magnitude" which is "Groessenordnung" in german for a colloquial use of the term magnitude in german. As mentioned, my fault. I some times get languages mixed up. Of course, never happens to you.
Ciao T
You could of course claim that going from 0.01% to 0.009% gives a change of an order of magnitude. This would be technically correct but meaningless, so I took you to mean factor of ten. But you can keep weasel around. BTW, you would not happen to have a reference to the source for the common cathode stage that has 0.002% THD, would you.
Fred, I mistook "Order of Magnitude" which is "Groessenordnung" in german for a colloquial use of the term magnitude in german. As mentioned, my fault. I some times get languages mixed up. Of course, never happens to you.
Ciao T
True, I don't know the Yiddish words for "order of magnitude." Not something that was said in my childhood home since my parents were artists, not tech folk.
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