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 NEW  Matt presents bias and operation data for the 6V6 tube in SE operation - 6V6 Single-Ended (SE) Ultra Linear (UL) Bias Optimization.

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PostPosted: 22 Apr 2016, 15:10 
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Matt, great work. It confirms some things I discovered in the past when using both SE U/L 6V6s and PP U/L 6V6s. There does seem to be a sweet spot at about 275 volts. The distortion levels also agree with what I found. I consider everything over 2% unacceptable and the power outputs you got at those distortion levels agrees with what I measured. It is one reason why I have not used 6V6s in any of the posted projects (6AQ5 and similar as well). All my systems need at least 5 watts (under 2%) and preferably 15 watts. Again great work and clearly a lot of effort.

Good listening
Bruce

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PostPosted: 22 Apr 2016, 16:54 
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I'm glad my results made sense to someone, your's is the first feedback I've received. I've always been willing to accept a little more distortion, so long as the harmonic envelope is to my liking, and it's proportional to output. I am currently looking at performing a 6V6 distortion study at optimized bias conditions as a follow up to the bias optimization study. I think the results should be interesting.

In addition, now that I know how to set up the experiment, it should be simple to do the same thing for other tubes (6L6, EL34, etc.). We'll have to see how much spare time I have to perform my investigations.

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PostPosted: 26 Apr 2016, 14:02 
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I love that you take the "witchcraft" and "because that's the way it's been done in the past" out of tube amps and replace it with the scientific method. As one engineer to another, I always look forward to you write ups.

So did you adjust your Lacewood 6V6 amp to take advantage of your new data?

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PostPosted: 26 Apr 2016, 16:09 
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RossD wrote:
So did you adjust your Lacewood 6V6 amp to take advantage of your new data?
Well... :blush:

So as you know, this would raise the bias to around 16v. This means that the driver stage needs more amplification to maintain overall sensitivity. So I ended up designing a whole new schematic for the Lacewood based on the new data. Now the question is to rewire, or build a new amp altogether? I think it will be a rewire, but it may be a while before I get around to it.

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PostPosted: 27 Apr 2016, 09:31 
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Please share the new design, as your 6V6 is an amp I'm planning on building in the future.

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PostPosted: 10 Nov 2016, 09:54 
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Matt,
I was reviewing your tests again, and was wondering if you can draw any conclusions/calculations/... from existing published data and get to the end results of your tests?

IE, can you extrapolate optimized UL design points from the old data sheets for other output tubes? Or would you have to go through the tests each time? I'm assuming the latter.

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PostPosted: 10 Nov 2016, 19:33 
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RossD wrote:
IE, can you extrapolate optimized UL design points from the old data sheets for other output tubes? Or would you have to go through the tests each time? I'm assuming the latter.
I tend to agree with you. I have dissected the data I measured and I don't think I can draw any firm conclusions for other tubes. It may be possible to do the same measurements on a different tube and begin to draw correlations, but I haven't gotten that far yet in my investigations.

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PostPosted: 15 Nov 2017, 03:05 
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Sorry to revive an old topic here, but after re-reading this wonderful article, I'd like to add that for guitar, a really unusual OP commonly used (RCA black plates only need apply here) in Trainwreck clones is 450V B+ with 300V screens and an idle Pa of about 7-8W per tube.

I duplicated a breadboard for HiFi at these voltages, but they were not suitable in the lower registers. The harmonic content was really complex - shifting with each step in output power level, rather than a continuous line :2c:

Cheers!

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