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Old 24th June 2004, 06:43 PM   #21
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Quote:
Originally posted by Frank Berry
If you have a non-linear tube in a circuit, you can not make the circuit linear by simply adding more of the same non-linear tubes.
I'd be willing to bet money you're wrong on that one.

EDIT

I mean, I bet paralleled tubes amplify more linearly than a single tube.
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Old 24th June 2004, 07:53 PM   #22
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Default parallel tubes

Putting more tubes in parallel will just get the deviations between the tubes to average out, but you will be left with the design average which is generally not linear. In fact, tubes are 3/2 power devices, not linear at all, triodes manage to come close to linear via plate feedback with a high impedance load, but as soon as you connect a real load they are not linear either. Pentodes require feedback networks to get any linearity.

P-P designs only get the even harmonics to cancel out, leaving the odd harmonics, which many people seem to consider the most damaging to the sound.

This leaves one with only a few choices: feedback, inherent feedback (like triode or cathode follower) , unity error feedback (like the Hawksford error correction scheme), class A with very limited signal swing (or conversely very high idle current) or complementary predistortion.

Don
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Old 24th June 2004, 08:47 PM   #23
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Yes, PP cancels the second order nonlinearities. Third order, and all other odd errors for that matter, are still present however. Theoretically, you might be able to preamplify a signal to give it inverse distortions which cancel with those in the power amp, but that might make IMD up the ying-yang or something.

Oh. You just mentioned that. You people are phasing me out!!!

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Old 24th June 2004, 08:53 PM   #24
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Quote:
Originally posted by serengetiplains


I'd be willing to bet money you're wrong on that one.

EDIT

I mean, I bet paralleled tubes amplify more linearly than a single tube.

Come by and measure Hept'AU7. Especially with bias backed off, I dare you to find any linearities for large signals in any half of the PP stage.

The simplest way to put it is "paralleling nonlinearity with more of the same nonlinearity is still going to produce the SAME DANG NONLINEARITY". Sorry if you can't comprehend that, but the universe is what it is due to simple logic as this.

It'll average out inconsistencies between tubes but it isn't known if those alone are detrimental or advantageous. (Statistics and averages. Some will fall above and below the average value.) Heck, you may well have several exceedingly linear tubes in the bunch that are being wasted!

Tim
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Old 24th June 2004, 09:58 PM   #25
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Default Damn Statistics

Quote:
Originally posted by Sch3mat1c
The simplest way to put it is "paralleling nonlinearity with more of the same nonlinearity is still going to produce the SAME DANG NONLINEARITY". Sorry if you can't comprehend that, but the universe is what it is due to simple logic as this.
No dang need to be sorry, Tim, it's I don't think any two tubes have the *same* non-linearity, which leaves the question whether averaging operational differences using a multi-tube setup produces greater linearity. I'm betting it does. Think: throw ten darts onto a dart board; now average the location of each dart relative to the other .... seems to me the "average" gets you closer to the bulls-eye which, in our case, is best-case non-linearity. Just my view of the statistics of things.
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Old 24th June 2004, 10:08 PM   #26
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As the valves age, a number of them will change characteristics in a non-typical way. This will alter overall linearity and cause distortion to increase. I think you'll need to keep a valve tester next to the amp
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Old 24th June 2004, 11:53 PM   #27
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Quote:
Think: throw ten darts onto a dart board; now average the location of each dart relative to the other .... seems to me the "average" gets you closer to the bulls-eye which, in our case, is best-case non-linearity. Just my view of the statistics of things.
You stubbornly refuse to read or comprehend the page above and your analogy is completely off the mark. If you like the sound of paralleled tubes that's fine but trying to invent quasi statistical explanations is simply no good.
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Old 25th June 2004, 12:15 AM   #28
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Default really only completely wrong

Quote:
Originally posted by analog_sa
... stubbornly ... completely ... simply ...
Nice use of adverbs. Using adverbs is among the first things one is taught to quit in Writing 101 as adverbs replace persuasive explanation, which requires hard work, with emphatic-ness, which doesn't. I'll show you. By *completely* off the mark, do you really mean I'm a bright, clear 100% wrong? (C'mon, is anybody ever clearly 100% wrong?)

My sense is that multi-tube amps can have a certain clarity that might be attributable, perhaps in part, to multi-tube operation. The best hypothesis I can conjure suggests that amusical quirks of a given tube blah blah blah.
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Old 25th June 2004, 12:40 AM   #29
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Hi,

Quote:
My sense is that multi-tube amps can have a certain clarity that might be attributable, perhaps in part, to multi-tube operation.
IMO, if there were to exist a single tube with all the electrical properties (the good ones such as some linearity ) of those multiple parallel tubes it will quite likely sound better still.

On the other end of the scale, if we all had half decent loudspeakers with healthy effeciency, low colouration and acceptable levels of distortion we wouldn't be needing those huge power mongers anyway.

It seems to me that the mistake one tends to make is that two wrongs make a right when adding tubes in parallel.

Unfortunately nature is cruel and in a bunch of paralleled tubes the weakest link is going to determine what you'll have, after that things will only get worse as time goes by.

In my mind, the less tubes one needs to put in parallel for a preset result the better.
If we'd return to the OTL analogy, a 100W class AB amp using 4 6C33-Cs is likely to yield better results than say, 10 6080s disregarding the fact that the two tubes are of course not the same.

Cheers,
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Old 25th June 2004, 12:56 AM   #30
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Quote:
On the other end of the scale, if we all had half decent loudspeakers with healthy effeciency, low colouration and acceptable levels of distortion we wouldn't be needing those huge power mongers anyway.
Frank, I meant to thank you for your previous post above, so do so now.

Re your comment, North America was long ago bitten by the bigness bug: big amps, big cars, big houses, big power cords, big capacitors, big burgers, big buildings, big companies, big computer screens, big bath tubs, big foreign policy, big big big big big. Check out the new Chrysler 300 automobile: 350hp hemi in a car weighing about a billion pounds. My god.

We have almost forgotten the fine art of knowing the importance of all that is either not or is before big, like the first watt coming out of an amp.
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