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Old 8th November 2010, 09:03 PM   #11
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Quote:
Originally Posted by Zen Mod View Post
I made my Babelfish J2 ;

but I have o intention to go in public with even poor Babelfish version of Papa's current product

boyz - please go with that in closed circles
Any comment on how it sounds? Or do you prefer to wait until Nelson says OK on that, too? If so, I understand.
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Old 8th November 2010, 09:22 PM   #12
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I think you can see significant improvement by simply
dropping the Jfet in on the negative side - the IRF240
on the top (aleph) side can be left as is.

To bias it properly you will need to drop the value of the
resistor from the Drain of the input transistor (and Gate
of the Jfet) to the negative rail to a lower value - I
recommend a 500 ohm pot.

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Old 8th November 2010, 09:32 PM   #13
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Quote:
Originally Posted by bdbender View Post
Any comment on how it sounds? Or do you prefer to wait until Nelson says OK on that, too? If so, I understand.


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Last edited by Zen Mod; 8th November 2010 at 09:35 PM.
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Old 8th November 2010, 10:09 PM   #14
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Quote:
Originally Posted by Nelson Pass View Post
I think you can see significant improvement by simply
dropping the Jfet in on the negative side - the IRF240
on the top (aleph) side can be left as is.

To bias it properly you will need to drop the value of the
resistor from the Drain of the input transistor (and Gate
of the Jfet) to the negative rail to a lower value - I
recommend a 500 ohm pot.

Outstanding!

That is probably the exact thing that Buzz needed to hear.

Thank you very much for your input.
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Old 8th November 2010, 10:44 PM   #15
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N Kelson and Bill,
Thank you both for the advice. I found myself on this latest trail because of the reviews at 6moons. His reviews of the F5, J2 and Aleph J are what made me want to go this route. I think I will biuld the modified Aleph J and F5 first and then maybe I will know enough to stumble through the J2. That is, if I even need to. Hey Nelson, where do you get your heatsinks?
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Old 9th November 2010, 11:06 AM   #16
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The best bang for the buck in heatsinks is probably HeatsinkUSA. Russ is in the vendors section of the forum. I've been using his monster extrusions for a while, and he will cut them to any length and width you desire. You just have to finish them, he has no machining or anodizing facilities. A couple light coats of flat black paint works wonders.
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Old 9th November 2010, 12:49 PM   #17
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THanks Bill. I have seen those heasinks on the forum and on his external site. I was hoping for something pretty like what Pass uses. I have seen extruded HS that look cool but they are usually limited in length to about 4 inches. They cold be doubled up, but then you have fets attached to seperate sinks and may have some thermal differences which may lead to altered performance. At least that is what i have read,...I think!
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Old 9th November 2010, 05:07 PM   #18
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I had these extruded for me.

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Old 25th January 2011, 01:36 PM   #19
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I am looking for opinions/experience on the wattage/temperature limits of IRFP 240. I am wanting to build an ALeph J with bias set at around 2.4 or slighlty higher, using two fets with 28V rails. Nelson, if your willing to comment, how hard have you pushed these things and how much is too much in terms of reliabilty. Rad somewhere that 50W per fet is really pushing it. Looking at using Heatsink USA 10" x 2.85" x 6". claims C/W/3" rating of .70, but unable to verify.
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Old 25th January 2011, 03:49 PM   #20
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50W per mosfet is max you'll find anyone is using around ;

but - use more robust ones - IRFP150 , and be sure that heatsink isn't hotter than 50C , with good thermal contact between mosfet and hsnk

buy Keratherm pads from Zhoufang

best thing after invention of wheel
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