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Old 7th October 2011, 01:20 PM   #11
6L6 is offline 6L6  United States
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So can you use a diff pair of j74? Or does it have to be the j109?
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Old 7th October 2011, 02:32 PM   #12
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I paralleled the sj74's in my AJ monoblock's FE. I was running three output pairs. 109 is better of course, if you got them. ZM is always talking about liking lots of current. I believe Nelson says more current allows reduction of Rl and gain and better linearity. Don't quote me though, bad memory.
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Old 7th October 2011, 02:54 PM   #13
6L6 is offline 6L6  United States
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Here is a copy of the schematic that Nelson drew out for me at Burning Amp (well, he modified and made notes on an Aleph J schematic) Not significantly different than the original.

Click the image to open in full size.
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Old 7th October 2011, 03:12 PM   #14
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Looks great and plus, he drew it. No current limiting stuff on bottom end. I think the extra current/paralleled inputs in the J2 was for optimization of that circuit, so go with what he gave you. Cant get any better than a personalized schematic by the guru. You can use one matched pair of SJ74 unless you have and want to use a single 109. Phenomenal build diary on your other stuff. Very helpful for other interested in the DIY game.

Last edited by buzzforb; 7th October 2011 at 03:22 PM.
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Old 7th October 2011, 05:00 PM   #15
qusp is offline qusp  Australia
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Quote:
Originally Posted by Nelson Pass View Post
You can run enough current through the 2SJ109 to do the job - I paralleled
them just because I can.

cool, thanks, i selected some matched high idss j74 quads so i'll probably parallel them too

Quote:
Originally Posted by 6L6 View Post
So can you use a diff pair of j74? Or does it have to be the j109?
you can use either, i actually think thermally bonded well matched singles are better, j109 arent always a great match.
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Old 9th October 2011, 02:19 PM   #16
DUC985 is offline DUC985  Germany
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would you have any voltages, how to bias the PowerJfets correctly ?
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Old 9th October 2011, 03:27 PM   #17
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would the data sheet be helpful for establishing vgs?

judging from the curves (please forgive me if I am wrong), I'd say between 1-1.5V. (?)
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Old 9th October 2011, 06:29 PM   #18
Zen Mod is offline Zen Mod  Serbia
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more like 1V4 - 1V9 ;

at least from my experience .

but - nothing really to worry about .

it will work in any range of Ugs , if they are reasonably close matched inside one channel
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Last edited by Zen Mod; 9th October 2011 at 06:38 PM.
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Old 9th October 2011, 07:44 PM   #19
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Looking good.
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File Type: jpg 0203_1024x768.jpg (275.1 KB, 1534 views)
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Old 28th October 2011, 06:11 PM   #20
6L6 is offline 6L6  United States
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The saga continues...
Click the image to open in full size.

Here are my Peter Daniel boards I bought from a member in Holland. The only ones that anybody had for sale were stuffed, with tightly-matched 240's, and neat parts like Silmics and such. Saves me a digi-key order, I like that.

I will have to remove a few components (limiter circuit, the power Fets) and replace a resistor with a pot in order to match it to the schematic that Nelson drew.

Then it's off to chassis fabrication, I have the important parts, and am hopefully going to meet with a machine shop today.
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