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 tenderland 5th August 2004 01:03 AM

second harmonic distortion

I hope my question is not to rudimentary for Iam just starting to learn tube design(after reading throgh many posts I am discouraged by my lack of knowledge)

QUESTION I understand from reading Crowhurst that when the plate swing is not symetrical due to equal changes in grid voltage
there will be second harmonic distortion . The distortion is calculated by determinig how far the mid poing of the swing deviates from the operating point. I can not see how this waveform produces second order distortion, isnt second order a component with 2 times or .5 times the fundemental freq.
Jeff
try not to flame me to bad

 Sch3mat1c 5th August 2004 01:50 AM

Twice the frequency. To find out why you have to understand Fourier transforms and such. The basic idea is that at twice the frequency and the proper phase, the harmonic reinforces (adds to) one peak while degenerating the other. If you have a graphing program (heheh, I wrote my own in QuickBasic) this is easy to see.

Tim

 tenderland 5th August 2004 03:13 AM

second order

That explains it very well ,thank you tim I should be able to
research it from the information you gave .

Jeff

 jan.didden 5th August 2004 07:03 AM

If you draw a sine wave on graph paper, and in the same graph draw a sine with twice the ferquency but say a quarter of the amplitude, you can then add these two curves graphically to get to the combined wave. That one will show massive 2nd harmonics, but it will be very clear how the mechanism works.

Jan Didden

 Guido Tent 5th August 2004 09:34 AM

Quote:
 Originally posted by janneman If you draw a sine wave on graph paper, and in the same graph draw a sine with twice the ferquency but say a quarter of the amplitude, you can then add these two curves graphically to get to the combined wave. That one will show massive 2nd harmonics, but it will be very clear how the mechanism works. Jan Didden

Hi

Yes, very true

Steve Bench put that on his site

http://members.aol.com/sbench102/thd.html

cheers

 jan.didden 5th August 2004 12:29 PM

Quote:
 Originally posted by Guido Tent Hi Yes, very true Steve Bench put that on his site http://members.aol.com/sbench102/thd.html cheers

Yes, nice site.
Steve Bench, huh? That the guy from those Bench-tests??:D

Jan Didden

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