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Old 22nd January 2010, 06:52 PM   #6711
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by bobodioulasso View Post
Bad idea, i think.
pretty much
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Old 22nd January 2010, 07:13 PM   #6712
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I know that NP frowns on the idea, but I've been able to get the amplifier to work into the ham bands -- and I found that it was more stable with some decoupling.
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Old 22nd January 2010, 07:31 PM   #6713
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"decoupling"
Are you talking about the same
The suggested looks just like a "small" onboard 1000uf supply cap to me
Will that be fit fore classA? one reason I may have my doubts about such
Without knowing enough about, I would rather try and have the main supply caps closer to amp curcuit

"more stable" ? maybe best not say that
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Old 22nd January 2010, 07:35 PM   #6714
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Well that is what decoupling is. But it is true that NP has expressed strong opinions against decoupling on the F5.
I would assume that this is highly dependent on the actual implementation, but since decoupling can give you better high frequency performance at best, I think it is very much irrelevant for this amp, unless you as jack use it in the ham bands.
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Old 22nd January 2010, 10:03 PM   #6715
tinitus is offline tinitus  Europe
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Oh, I thought "decoupling" was about small filmcaps

But ok, I see it now, theres a small 20ohm resistor added, in the suggested schematic
I my "common logic" and understanding of english, "DEcoupling is the resistor, more than the exstra cap, I guess

Well, I admit to have suggested similar a while back, to have seperate supply fore jfet
And it was explained to me that jfet and outputs are so very closely coupled, so that any differential imbalance from supply may cause severe problems
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Old 23rd January 2010, 07:37 AM   #6716
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Is it possible to use these fet's IRFP9240 and IRFP240
They are easy to get for me.

john
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Old 23rd January 2010, 08:40 AM   #6717
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They are mostly used!
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File Type: jpg F5 circuit.jpg (53.1 KB, 551 views)
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Old 23rd January 2010, 10:43 AM   #6718
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Thanks,
I had ordered fqpf19nc and fqp12p20 before but they are in a to220 case so I can't use them.
regards John
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Old 23rd January 2010, 11:32 AM   #6719
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Quote:
Originally Posted by gervenja View Post
Thanks,
I had ordered fqpf19nc and fqp12p20 before but they are in a to220 case so I can't use them.
regards John
You can use them. The Id and max power dissipation are a bit lower.
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Old 23rd January 2010, 11:49 AM   #6720
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Rjc of those TO-220 Fairchilds is already over 1C/W, but Rjc + Rcs can get messy with insulators.
Only way to keep temperature of the dies under 100C would be to mount them either straight to the heatsink or use an L-bracket with a large mounting area on the heatsink side.
(for 24Vdc rails and 1.3A bias)
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