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Old 17th July 2012, 06:41 PM   #6751
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Actually, "purple" feedback is nested: it combines feedback by current through emitter of the 1'st transistor (voltage on the resistor is proportional to the emitter current) and by voltage (through the resistor from collector of the 2'nd transistor, proportional to the voltage on it's collector). However, according to Wayne's classification the feedback through that resistor can be called "Current" since currents sum on the emitter, but it is misleading term that I don't use.
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Old 17th July 2012, 06:57 PM   #6752
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When at college I was taught about theoretical pentodes . I wish I had kept my notes . It was quickly said no such device existed .

As I understood it the linearity of a triode is by conduction between cathode and anode due to effects of secondary emission or " related " . Admittedly an RAF college so perhaps not top scientists . The words are important . However others will be confused and not understand there is no magic in this . I always saw the pentode as vastly superior .

My speculation about ECC 82 and 81 is that within reason the parts are the same size and current similar . I suspect the distortion and gain to be very similar if shunt feedback is used on an ECC81 . Neither are especially linear . It strikes me that someone adjusts one to get the other when laying down these designs .

I have some of the D series battery valves . Are they worth trying ?
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Old 17th July 2012, 07:53 PM   #6753
dvv is offline dvv  Serbia
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Quote:
Originally Posted by Wavebourn View Post
No. The question is like whether you car uses diesel engine, or it is green in color. Because green car can use both engines. Nested feedbacks mean more than one loop, with loops inside loops. Current feedback is description of a single loop: whether the designer calculates feedback current, or feedback voltage. As you see, the question is irrelevant: nested feedbacks can include either current feedbacks, or voltage feedbacks. You can't answer the question, what is better, nested or current feedback, because the question is irrelevant, like what is better, green car, or diesel car.

Do you hear me now?
When you make yourself clear, yes, I do. No idea why we always have to prod you to make yourself as clear to others as you are to yourself.
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Old 17th July 2012, 07:55 PM   #6754
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Quote:
Originally Posted by dvv View Post
When you make yourself clear, yes, I do. No idea why we always have to prod you to make yourself as clear to others as you are to yourself.
I have no talents to prove neither definitions nor axioms. Sorry.
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Old 17th July 2012, 08:00 PM   #6755
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Quote:
Originally Posted by DF96 View Post
Where is the fourth option: shunt application of current feedback? Would raise output impedance and reduce input impedance - I admit I can't think of a useful purpose for it.
Ideal BJT!

(Waiting for theoreticians to argue that BJT is controlled by voltage)
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Old 17th July 2012, 08:01 PM   #6756
dvv is offline dvv  Serbia
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Originally Posted by Wavebourn View Post
I have no talents to prove neither definitions nor axioms. Sorry.
Wave, I'm serious. I love reading your posts most of the time, but every now and then you simply assume the reader perfectly follows your line of reasoning.

Thus, some of the illustrations you provide can be very confusing sometimes, sidetracking one in an irrelevant direction.

But your second time round explanations are usually crystal clear.
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Old 17th July 2012, 08:03 PM   #6757
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Originally Posted by Wavebourn View Post
Ideal BJT!

(Waiting for theoreticians to argue that BJT is controlled by voltage)
Hell, no, BJTs are controlled by my soldering iron in my home!
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Old 17th July 2012, 08:06 PM   #6758
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Originally Posted by tsiros View Post
of course... it has soul.
Like, helicopters are souls of killed tanks! :S
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Old 17th July 2012, 08:07 PM   #6759
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Hell, no, BJTs are controlled by my soldering iron in my home!
Now you got it!
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Old 17th July 2012, 08:21 PM   #6760
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by Wavebourn View Post
No. The question is like whether you car uses diesel engine, or it is green in color. Because green car can use both engines. Nested feedbacks mean more than one loop, with loops inside loops. Current feedback is description of a single loop: whether the designer calculates feedback current, or feedback voltage. As you see, the question is irrelevant: nested feedbacks can include either current feedbacks, or voltage feedbacks. You can't answer the question, what is better, nested or current feedback, because the question is irrelevant, like what is better, green car, or diesel car.

Do you hear me now?

Finally an answer .....

Quote:
Originally Posted by Wavebourn View Post
Here is the chart that I drew for students long time ago. I hope it helps. What Bob taught you, is parallel feedback by voltage (output voltage applied to input in parallel with the signal).

(The typo in the 3'rd picture description, should read "Parallel feedback" instead of "parallel input".)

Click the image to open in full size.
Ahhh more, like pulling teeth huh ......
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