Doctor Dave,
You asked me to compare Black’s classic feedback model to Graeme’s op-amp feedback and Graeme’s op-amp feedback model to the triode feedback model that I am speaking of. The detail of the comparisons will develop as we dig deeper into the process.
Black’s classic model does not address the op-amps inverting connection.
Graeme’s op-amp feedback model does not address the inverting output of the triode model.
Even if I am completely wrong in the above assessment I intend to draw the triode feedback loops and feedforward loops including completed math blocks. We want model and math to match measured triode performance.
Some things I have observed as this begins:
For op-amps all the local inputs and feedback nodes are inside the plastic box. We cannot touch or see them. They are out of sight and for the large part out of mind. Only the 2 inputs and single output stub to the outside the plastic box. If there is any additional feedback applied is done with real circuit traces and or voltage dividers.
DT
You asked me to compare Black’s classic feedback model to Graeme’s op-amp feedback and Graeme’s op-amp feedback model to the triode feedback model that I am speaking of. The detail of the comparisons will develop as we dig deeper into the process.
Black’s classic model does not address the op-amps inverting connection.
Graeme’s op-amp feedback model does not address the inverting output of the triode model.
Even if I am completely wrong in the above assessment I intend to draw the triode feedback loops and feedforward loops including completed math blocks. We want model and math to match measured triode performance.
Some things I have observed as this begins:
For op-amps all the local inputs and feedback nodes are inside the plastic box. We cannot touch or see them. They are out of sight and for the large part out of mind. Only the 2 inputs and single output stub to the outside the plastic box. If there is any additional feedback applied is done with real circuit traces and or voltage dividers.
DT
People who are new to a topic often draw false distinctions between things which are actually the same, or fail to see distinctions between things which are different. Standard feedback theory does not need extending.
Please don't say "we" when you mean "I, DualTriode,". Please don't pretend that you are doing anything new and innovative; you can't "dig deeper" until you have begun to learn the basics and start from true premises instead of false premises.
I think I will go and find a mech eng website and tell them how I am going to dig deeper into the theory of levers and explain how they have misunderstood them for millenia.
Please don't say "we" when you mean "I, DualTriode,". Please don't pretend that you are doing anything new and innovative; you can't "dig deeper" until you have begun to learn the basics and start from true premises instead of false premises.
I think I will go and find a mech eng website and tell them how I am going to dig deeper into the theory of levers and explain how they have misunderstood them for millenia.
I am going fishing
Doctor Dave,
This is a ME site perhaps you are interested in posting.
I am going fishing, be back in a few.
Applying heat exchanger control strategies|Control Engineering
DT
Doctor Dave,
This is a ME site perhaps you are interested in posting.
I am going fishing, be back in a few.
Applying heat exchanger control strategies|Control Engineering
DT
exeric , you are correct. As a SS guy I tried a 12AX7 vs 2N5551 as a voltage gain stage and found a huge difference that is difficult to detect on a scope but instantly apparent when listened to.
BTW exeric, you do not have to clip the SS amp to hear the difference between the two pre stages
new system = 12AX7 preamp > volume pot > SS tone controls > 6922 prestage > SS output
BTW exeric, you do not have to clip the SS amp to hear the difference between the two pre stages
new system = 12AX7 preamp > volume pot > SS tone controls > 6922 prestage > SS output
Last edited:
Does the classic Black model give us the answer?
Hello,
I am back from the south east of Alaska, My wife made me go. Way too much fish to eat.
Looking at this DIYaudio site the degree of dogma and hostility is amazing to me. The head butting between solid state and vacuum or between open baffle and box speakers just to start.
I am looking at this concept of single triode and feedback / feedforward for my interest and anyone else that wants to join in. The classic Black theory address noninverting feedback, however it does not address inverting feedback. Somewhere along the way if you think that I am mistaken please provide an alternate thought or a reference. This will not be a daily adventure. I will measure things on the bench and ask how it fits the feedback model and or adjust the model as I understand it so that things fit together.
As a contrast Graeme and his crew have developed / documented feedback theory that addresses operational amplifiers, including inverting and noninverting inputs. The conceptual feedback loops and voltage dividers are all drawn external to the triangular amplifier block that is shown with a inverting and a noninverting inputs plus a single output. It is curious to me how the op-amp feedback theory is simpler than looking than looking at a discrete FET and a couple of resistors.
Now back to the triode, say we have a triode configured as a voltage follower (CF). The classic Black model tells us that there is 100% feedback and that output voltage will never exceed input voltage. This is a hard wired feedback loop. Now we add a resistor at the anode, intuitively we suspect that there is additional local feedback at the anode. We (I) ask if this is the same or different feedback loop that is operational at the cathode.
I say that there are 2 separate resistors and 2 separate feedback loops.
Now, intuitively we need feedback math blocks that when applied match the performance measured on the bench.
Does the classic Black model give us the answer?
DT
Hello,
I am back from the south east of Alaska, My wife made me go. Way too much fish to eat.
Looking at this DIYaudio site the degree of dogma and hostility is amazing to me. The head butting between solid state and vacuum or between open baffle and box speakers just to start.
I am looking at this concept of single triode and feedback / feedforward for my interest and anyone else that wants to join in. The classic Black theory address noninverting feedback, however it does not address inverting feedback. Somewhere along the way if you think that I am mistaken please provide an alternate thought or a reference. This will not be a daily adventure. I will measure things on the bench and ask how it fits the feedback model and or adjust the model as I understand it so that things fit together.
As a contrast Graeme and his crew have developed / documented feedback theory that addresses operational amplifiers, including inverting and noninverting inputs. The conceptual feedback loops and voltage dividers are all drawn external to the triangular amplifier block that is shown with a inverting and a noninverting inputs plus a single output. It is curious to me how the op-amp feedback theory is simpler than looking than looking at a discrete FET and a couple of resistors.
Now back to the triode, say we have a triode configured as a voltage follower (CF). The classic Black model tells us that there is 100% feedback and that output voltage will never exceed input voltage. This is a hard wired feedback loop. Now we add a resistor at the anode, intuitively we suspect that there is additional local feedback at the anode. We (I) ask if this is the same or different feedback loop that is operational at the cathode.
I say that there are 2 separate resistors and 2 separate feedback loops.
Now, intuitively we need feedback math blocks that when applied match the performance measured on the bench.
Does the classic Black model give us the answer?
DT
Well, inverting just means that you have a gain of -G instead of G. Any mathematical theory (of feedback) will cope with that without any problem. (A theory that cannot cope with negative numbers is not a mathematical theory).
I think what you are getting at is that when you look at bit of electronics (such as a triode valve) you sometimes think 'I am sure there is some negative feedback going on here' and it then can be a challenge to sort out 'what is the input variable', 'what is the output variable', 'how is the output variable being fed back to the input' etc.
I think what you are getting at is that when you look at bit of electronics (such as a triode valve) you sometimes think 'I am sure there is some negative feedback going on here' and it then can be a challenge to sort out 'what is the input variable', 'what is the output variable', 'how is the output variable being fed back to the input' etc.
some of us knowing the subject may have slight problems with your "framing"
Black wasn't the end of feedback theory until Graeme - everything Graeme popularized was textbook "Classical Feedback Theory" by the 1960's
"Classical Feedback Theory" includes Bode, Nyquist, Blackman, Mason, Hurwitz...
although by the '60s academic feedback theory had been redirected by the appearance in the west of Russian State Space abstract Linear Algebra methods gaining the title "Modern Control Theory"
not that even "Classical Feedback Theory" has been entirely static since the '60s - I like BJ Lurie's book http://luriecontrol.com/ClassicalFeedbackControl.htm
for its more modern perspective, but its not the 1st textbook to learn Classical Feedback from
also triode internal feedback isn't linear - tube cathode-grid and grid-plate both follow Langmuir-Child relations and are manipulated by setting the geometry of tube internals, gaps by the designers of the tubes
Black wasn't the end of feedback theory until Graeme - everything Graeme popularized was textbook "Classical Feedback Theory" by the 1960's
"Classical Feedback Theory" includes Bode, Nyquist, Blackman, Mason, Hurwitz...
although by the '60s academic feedback theory had been redirected by the appearance in the west of Russian State Space abstract Linear Algebra methods gaining the title "Modern Control Theory"
not that even "Classical Feedback Theory" has been entirely static since the '60s - I like BJ Lurie's book http://luriecontrol.com/ClassicalFeedbackControl.htm
for its more modern perspective, but its not the 1st textbook to learn Classical Feedback from
also triode internal feedback isn't linear - tube cathode-grid and grid-plate both follow Langmuir-Child relations and are manipulated by setting the geometry of tube internals, gaps by the designers of the tubes
Last edited:
mu ~ constant is evidence of triode internal V feedback - works down to DC
Miller multiplication of parasitic grid-plate C is there too, affects high frequency in typical circuits
shield grid also interrupts the DC V feedback - which is why tetrode/pentode have much higher mu for similar geometry
Miller multiplication of parasitic grid-plate C is there too, affects high frequency in typical circuits
shield grid also interrupts the DC V feedback - which is why tetrode/pentode have much higher mu for similar geometry
Last edited:
How about hi mu? those curves looking more like tetrodes. (no g2,no hi-knee at low Up)
I understand this as plate being a "electron magnet", force is growing with voltage. (1/distance)
Loose grids will pass easily electrons, near cutoff dht is more like x^5/2 or 7/2 they say. (electrons in middle between wires will sneak through)
Tight grids hold better them in place, better shielding from "plate magnet". Curves more horizontal - plate magnet is shielded better.
Very old dht´s have long distances; p-g increases µ; likewise does the g-k. Longer distances gives linear curves, but low gm is not fun to use.
i wonder why modern dht tubes are not made with big piece of thin foil, instead of few small cathode wires.
could use some higher resistivity alloys, to meet heater dcr.. emission area could be huge, and increasing distances/low gm is not problem anymore.. plate linearity..
instead asking 500€ for some mesh plates, and bigger glass.. that isn´t a improvement!
could use some higher resistivity alloys, to meet heater dcr.. emission area could be huge, and increasing distances/low gm is not problem anymore.. plate linearity..
instead asking 500€ for some mesh plates, and bigger glass.. that isn´t a improvement!
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.