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Old 10th April 2012, 02:30 PM   #171
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Back in the day, Ed Dell would publish a picture of your handiwork in the back of "The Audio Amateur". Nice work!
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Old 10th April 2012, 02:39 PM   #172
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Originally Posted by mogliaa View Post
If greater phase correction is needed, shall I try adding an RC stage before the 100k and 50nF Phase correction circuit?

Any ideas?
Thanks
Ale
Hi Ale,

Has your DC balance of the AC sine wave changed? This should affect your adjustment range as the edge detection shifts. Mine uses a zero detect comparator so had to inject the common potential into a fake center tap built by using two resistors.

Alfredo
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Old 10th April 2012, 02:48 PM   #173
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Originally Posted by Michael Koster View Post
Yes, you are getting the same result as Schade, and it's working the way it does in circuit. You could draw a load line.

You've built a nice instrument, congratulations!

Michael
Thanks Michael,

I have never experimented with parallel feedback in a real amp circuit. Implementing it may be more difficult as in probably will need a DC blocking cap and some FR tuning. I can see that it increases the drive requirements significantly and would add complexity in many cases. I am going to check out a very sensitive TV sweep tube to see what the Parallel feedback does to its drive requirements.

Alfredo

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Old 10th April 2012, 02:48 PM   #174
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Originally Posted by jackinnj View Post
Back in the day, Ed Dell would publish a picture of your handiwork in the back of "The Audio Amateur". Nice work!
Thanks
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Old 10th April 2012, 02:50 PM   #175
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by avincenty View Post
Hi Ale,

Has your DC balance of the AC sine wave changed? This should affect your adjustment range as the edge detection shifts. Mine uses a zero detect comparator so had to inject the common potential into a fake center tap built by using two resistors.

Alfredo
Hi Alfredo,
No, just changed transformer secondary from 12V to 6V... Shouldn't be this?
Great curves plotted BTW!
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Old 10th April 2012, 04:56 PM   #176
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Originally Posted by mogliaa View Post
Hi Alfredo,
No, just changed transformer secondary from 12V to 6V... Shouldn't be this?
Great curves plotted BTW!
Thanks.

Yes, it could be the culprit as your edge detection window should be narrower now.

Alfredo
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Old 10th April 2012, 05:20 PM   #177
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Default $1 Compactron 6AH9

Here is the pentode section of a 6AH9 (sames as 12HL7 in 9 pin). The feedback amount was determined by moving the pot until the 150V grid signal fit within the 600V Plate range. This gave me 717K. Used a 100K grid resistor. Less feedback can be used and the drive requirements are more reasonable and still look like a pretty good triode. Looks good, doesn't it? I think the drive requirement eliminates making a spud out of it. Maybe putting two in parallel and using the two medium mu stages may be enough doubling the power to 6.6 Watts. If using a 12HL7 then any other driver could be used.


I wonder if something like this will ever be stable in the real world...

Alfredo
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File Type: jpg 6AH9 Parallel Feedback load lines.jpg (129.7 KB, 179 views)
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Old 10th April 2012, 06:11 PM   #178
mogliaa is offline mogliaa  United Kingdom
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Originally Posted by avincenty View Post
Thanks.

Yes, it could be the culprit as your edge detection window should be narrower now.

Alfredo
Hi Alfredo,
You are probably correct as is the only thing I changed (in addition to final wiring and layout). I stole one 6V winding of my 6V+6V for one of the LCD meters as need to be floating. didn't think I would end up with a limited sync capability. Attached is my current circuit. What is not drawn there is the 100K pot and 50nF RC network between the transformer and the rectifier bridge. I can go back to the 12V winding but will need to think of a workaround for the LCD.....

Actually P1 needs to be set to one of the ends. I suspect it may be better to wire P1 to +15V rather than +5V for a greater pulse width support, but that will require PCB hacking which I want to avoid where possible.


Thoughts?
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File Type: png Curve tracer - grid step generator.png (173.0 KB, 168 views)
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Old 10th April 2012, 06:53 PM   #179
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What about lifting the rectifier output by connecting the left side of the bridge to 5V rather than ground?

Alfredo
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Old 10th April 2012, 07:11 PM   #180
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That would be a minor pcb hacking but could give it a try if you think it would make a difference...
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