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Old 5th March 2011, 01:55 AM   #321
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Quote:
Originally Posted by jcx View Post
although "single ended pentode" is likely a pretty good aproximation to a "no feedback amp" - as long as you don't use a cathode R (and bias up those "extra" grids like the tube designers intended)[/url]
You can't have it both ways.

If triodes have internal feedback, then so do pentodes,
since they exhibit a finite plate impedance due to their
"feedback".

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Old 5th March 2011, 04:34 AM   #322
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As engineers we can perhaps argue over what defines "good approximation" in terms that make sense to both of us

I am happy to engage in the original meaning "dialectic" - not that I think we really have uniformly "opposing" positions or that every engineering issue can be reduced to simplistic "two sided" sets of propositions with simple binary true/false resolutions

(which doesn't mean that there's no definitions, standards that have to be agreed - and are agreed by the EE community - some statements can be "nonsense" or "true/false" by the rules that a community like professional EEs use to "construct"/express/represent knowledge )

for tube internal feedback we could continue in my thread in the tube forum?

the better measure of internal feedback in vacuum tubes is probably (inverse) "mu" - "mu" is easily 100x higher in pentodes vs triodes

so pentodes would seem to at least qualify as ~ "100x better approximations" to "no (internal) feedback" amplifying devices by having ~100x less internal feedback?

my tube expertise is pretty limited to having been the only one with any idea of how to replace/rebias/maintain a Dynaco tube amp in a community music room in my college days so I could easily be wrong – care to put up some numbers to compare or point to some good tube modeling sites?
In one of those life ironies George Valley hung around the undergrad program I was in but before I realized I wanted to do electronics he fully retired

Since my education in control theory started with Mech E courses and my career has involved motion control with a variety of motors, hydraulic valves as well as electronics I do think I can figure out diverse "gain device" parameters if anyone wants to “put some numbers” on the floor to debate

this source kind of fades away before reaching pentode properties: Tubes 201 - How Vacuum Tubes Really Work


last 2 posts added to Triode plate resistance == internal negative feedback? if Nelson really wants to keep this thread closer to the subject of his article tube internal feedback debate should continue there

Last edited by jcx; 5th March 2011 at 04:50 AM.
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Old 5th March 2011, 05:14 AM   #323
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I sense a bit of a condescending attitude.
There is no need for it here.
The Pass Labs forum is last place you want to come if you are going to take yourself too seriously.
No one cares for it.
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Old 5th March 2011, 05:24 AM   #324
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hopefully the units are still just "milli-Rollins"?
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Old 5th March 2011, 06:49 AM   #325
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By the way Nelson is a Scientist not an Engineer.
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Old 5th March 2011, 09:45 AM   #326
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according to implication of mR , seems that you're fighting for mJCX acclamation ?

we are pretty good in neglecting units ...........

ignorance above all !!

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Old 5th March 2011, 10:22 AM   #327
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Quote:
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[snip]some others here have as Jan points out apparently have gotten hung up on detailed "semantic analysis" of simplified "feedback" definitions that require "feeding back" the OUTPUT signal to the input ("in anti-phase" seems to be another stumbling block)
[snip]
Linear Audio Vol 1, which will be published 1 April, has an article by Bruno Putzeys under the apt title: "The F-word".

His definition:

“Feedback is an arrangement where an amplifier is made to respond to its own output signal in addition to the wanted input signal and any unwanted disturbances. When the response to an unwanted disturbance is smaller with feedback applied than without it, we call it negative feedback.”

Now I fully realize that if you're not coming from an engineering discipline, if you enjoy building audio amps for a hobby, you most probably aren't interested in such a formal definition. But it seems to me that anybody would benefit if we all speak the same language. Suppose you go to Spain and start to talk about your ''carro" to the car dealer. After much confusion they tell you that in Spain they use 'coche' for car. Are you going to insist that they follow your 'carro' because that's what you think it is?

Quote:
Originally Posted by jcx View Post
[snip]it can be seen as consistent in a very fundamental way when you apply Blackmann's relations to calculate input and output impedance as a function of "loop gain", when you use Bode's sensitivity analysis, calculate bandwidth, or the distortion reduction/harmonic order multiplication (as explained yet again, at length in the Cordell Feedback thread)

then you can go o the lab and see these behaviors in real circuits do follow the theory

its worth repeating: "there is nothing so practical as a good theory"
[snip][/B]
That was my point also. If you assume it's feedback, and you calculate and measure, and it acts as if its feedback, it seems folly to persist it isn't. Except for marketing reasons

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[snip]"there is nothing so practical as a *really* good theory"[snip]
Ludwig Bolzmann IIRC?

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Old 5th March 2011, 10:26 AM   #328
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It is really getting boring at the solid state forum.




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Old 5th March 2011, 10:35 AM   #329
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yeah

triode and pentode couldn't care less what ppl wrote .......

heptode too

and diode ....

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Old 5th March 2011, 12:38 PM   #330
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Quote:
Originally Posted by Ila View Post
Amplifiers with immeasurable THD figures and other hyper specs never saw a lasting success.
In all friendship, is it OK if i beg to differ with that.


Quote:
Originally Posted by janneman View Post
After much confusion they tell you that in Spain they use 'coche' for car. Are you going to insist that they follow your 'carro' because that's what you think it is?
Ouch => The Pass Pub: The High-End Off Topic Thread
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