John Curl's Blowtorch preamplifier part II - Page 1337 - diyAudio
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Old 4th July 2011, 10:43 PM   #13361
SY is offline SY  United States
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Originally Posted by simon7000 View Post
Go ahead, but I think you understand the reasoning!
Keep plate load high, cathode impedance low.

You could reduce that tube count and get far better performance without adding feedback or rely on very imperfect cancellation. 12AX7-oids are incredibly linear under high plate load/ constant cathode voltage conditions. You just need to buffer them a bit to keep the plate load high.


Horshak, not Epstein.
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Old 4th July 2011, 10:47 PM   #13362
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And how would you reduce the distortion in a triode stage without feedback?
There is no need to reduce the distortion in well designed triode stage. Some of the best tube pre-amps and phono stages do it with a great success, without negative feedback. Even SY did it in his phono stage.
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Old 4th July 2011, 10:49 PM   #13363
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Ooooh, oooooh, Mistah Kottah, Mistah Kottah!!!!
I understand only English and Hebrew.
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Old 4th July 2011, 11:08 PM   #13364
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There is no need to reduce the distortion in well designed triode stage. Some of the best tube pre-amps and phono stages do it with a great success, without negative feedback. Even SY did it in his phono stage.
once again - that would be more exactly stated as "without external linear feedback" - the triode has built in negative feedback

as the tube experts explained in the thread I linked the internal feedback from the anode V being visible to the grid has a similar nonlinear power law as the gm, giving a low distortion, internally feedback fixed mu
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Old 4th July 2011, 11:11 PM   #13365
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I understand only English and Hebrew.
Reference to an American TV show in the late 1970's - "Welcome Back Kotter" More detail here: Welcome Back, Kotter - Wikipedia, the free encyclopedia

Horshack the character referenced had a particular way of addressing Kotter when he didn't get things.

Your English/American is just fine.. Anyone born after about 1980 probably would not catch the reference either. It is very specific to the era, I can't bear to watch the reruns.. John Travolta rather unfortunately got his start as an actor on this show... (OK, he really isn't that bad. )
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Old 4th July 2011, 11:43 PM   #13366
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once again - that would be more exactly stated as "without external linear feedback" - the triode has built in negative feedback

as the tube experts explained in the thread I linked the internal feedback from the anode V being visible to the grid has a similar nonlinear power law as the gm, giving a low distortion, internally feedback fixed mu
How what you said contradicts in any way what I said above?

Once again: "There is no need to reduce the distortion in well designed triode stage".
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Old 4th July 2011, 11:46 PM   #13367
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Originally Posted by kevinkr View Post
Reference to an American TV show in the late 1970's - "Welcome Back Kotter" More detail here: Welcome Back, Kotter - Wikipedia, the free encyclopedia

Horshack the character referenced had a particular way of addressing Kotter when he didn't get things.

Your English/American is just fine.. Anyone born after about 1980 probably would not catch the reference either. It is very specific to the era, I can't bear to watch the reruns.. John Travolta rather unfortunately got his start as an actor on this show... (OK, he really isn't that bad. )
Thanks Kevin.
It's an enigma to non-Americans.
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Old 5th July 2011, 12:18 AM   #13368
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Thanks Kevin.
It's an enigma to non-Americans.
I thought it might be, hence the post..
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Old 5th July 2011, 12:21 AM   #13369
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Originally Posted by jcx View Post
some suggest "inherently linear" triodes get that way from internal negative feedback

Triode plate resistance == internal negative feedback?

pentode's shield grid intecepts/blocks the feedback influence of the anode V and are better aproximations to "no feedback" amplifying devices than triodes
Bipolar Junction Transistors also have some emitter resistance.

However in this circuit I want distortion! The issue is how does feedback reduce distortion.

Anyone game for the question, Is distortion from feedback the same as distortion from additional stages of amplification?

If so how? If not how?

Interesting answers tomorrow.
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Old 5th July 2011, 01:48 AM   #13370
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Hi,

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Originally Posted by simon7000 View Post
That one is what many would expect, but it is not what you get! (The advantage of actually doing measurements!)
Interesting, looking forward to the measurements.

My guess was based on "gain of each stage is padded down to unity", which may not be quite the case. I guess it's time to get this circuit simulator up and running...

Ciao T
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