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Old 19th January 2013, 10:20 AM   #1
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Default 6av5ga distortion spectrum

Hi all.

I'm throwing together a push pull amplifier with parts from my stash. It's got the cheapest danbury 6k6 20 w opt in at is but these will be replaced next month. This amp is going to be a test bed as 310v and 6k6 seems to be ok for lot of tubes 6c4c 6av5 6p13s 6p20s el360 etc

Any how, its got 12av5's in at the minute triode strapped g2 to anode with 470r ad a soft bias of -60 for now, and d3a diff pair input/driver.

Anyhow.... The spectrum seems to be dominated by 3rd harmonic, anyone else found this?

Also any recommendations re opt, nothing too boutique as this is not my main amp, I was thinking of the better danburys or hammond 1650 etc

Enzo
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Old 19th January 2013, 11:22 AM   #2
DF96 is offline DF96  England
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A push-pull amplifier dominated by 3rd harmonic - who would have thought it?

If you prefer it to be dominated by 2nd then you just have to unbalance either the phase splitter or the output stage.
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Old 19th January 2013, 11:34 AM   #3
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Doh! Spent too long on the dark side, what a prat!
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Old 19th January 2013, 11:35 PM   #4
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Anyone have an opinion on the hammond 1650g? seems very affordable and has lots of options with the secondarys?

enzo
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Old 22nd January 2013, 10:19 AM   #5
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This is obviously not a popular thread, but please indulge me sharing some results?

After a lot of bias fiddling and tube swapping (only have 4 12av5, 15 6av5 on their way from states) I seem to have hit a sweet spot, i think some cancellation or something in the mix.

6P52s 10ma 12k5 load 300vht, 12av5 -65-67v 310vht 6k6 load

1W 0.076% 3rd harmonic 4 db higher than 2nd
8W 1.28% using same driver ballance setting as the 1w or 1.1% if adjusted.

the 1W figure impressed me zero feedback.

enzo
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Old 22nd January 2013, 10:30 AM   #6
SY is offline SY  United States
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This looks like a good candidate for a harmonic equalizer tweak.
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Old 22nd January 2013, 05:16 PM   #7
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Whats that?

enzo
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Old 22nd January 2013, 10:25 PM   #8
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I managed to get visual analyser working again tonight...


1% @ 8W
Click the image to open in full size.



0.065% @ 1W
Click the image to open in full size.


1khz

Click the image to open in full size.

Last edited by enzoastro; 22nd January 2013 at 10:27 PM.
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Old 22nd January 2013, 10:36 PM   #9
SY is offline SY  United States
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Quote:
Originally Posted by enzoastro View Post
Whats that?

enzo

See page 184 forward in "Valve Amplifiers," 4th edition, as well as the Bulwer-Lytton amplifier described in the same book. Also US patent 1,970,325.
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Old 22nd January 2013, 10:41 PM   #10
kevinkr is offline kevinkr  United States
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The distortion levels are low enough compared to typical tube practice that I doubt the typical waterfall plot which imo does not really apply to pp amplifiers anyway is something to shoot for..

How does it sound or have not yet listened to it?

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