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Old 14th February 2012, 08:37 PM   #201
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Why to heatsink cascodes?
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Old 14th February 2012, 10:27 PM   #202
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Quote:
Originally Posted by bobodioulasso View Post
Why to heatsink cascodes?
Bobo,
They're not heatsunk.
It just happens that the devices Papa specified are TO220 package and the only room I had for them was at the top of the board.

:-)
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Old 14th February 2012, 10:40 PM   #203
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Parralel imputs
There you have it.

AS far as I know paralel imputs give a bit more current and maybe same gain.

Imput impedance is given by R1/R2 (as far as I know as well )

They need to be close togheter for termal coupling / Traking
easy done just move close togheter or just put another set of pads close to existing ones.

I like the board wery much by fitting the Mosfets / diodes paralel to the board plane they can be bolted to the heat sink with the diodes on the botom Mosfets on top

Heath rise

what is the question about mono blocks?
board fit to one sink make monobloks with just one sink
Attached Images
File Type: jpg Fair Parralel1.JPG (119.5 KB, 691 views)

Last edited by Bksabath; 14th February 2012 at 10:44 PM.
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Old 14th February 2012, 11:08 PM   #204
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Quote:
Originally Posted by Bksabath View Post
Parralel imputs
There you have it.

AS far as I know paralel imputs give a bit more current and maybe same gain.

Imput impedance is given by R1/R2 (as far as I know as well )

They need to be close togheter for termal coupling / Traking
easy done just move close togheter or just put another set of pads close to existing ones.

I like the board wery much by fitting the Mosfets / diodes paralel to the board plane they can be bolted to the heat sink with the diodes on the botom Mosfets on top


Heath rise

what is the question about mono blocks?
board fit to one sink make monobloks with just one sink
Yes, I was thinking more about what would happen if the devices were badly matched. i.e. Would one pair conduct early and render its 'partner' inoperable'. It just doesn't 'feel' right to me. But hey I'm open to be convinced.

Last edited by UKToecutter; 14th February 2012 at 11:10 PM. Reason: My reply missing
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Old 14th February 2012, 11:17 PM   #205
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That is the difficoult part about building with mosfets in parralel

Papa pass published a paper about matching

I did same work by matching at given temperature.(VGS changes with temperature)

Papa had big advantagge of good batches from suplier
I got my 100 FQA12P20 and FQP19N20 from farnell and batch was all over the place.

You can adjust for a lazy mosfet by adjusting the source resistors As you got 2 in parralell it may be easy to keep a few low values ones just for purpose

Papa uses a 2.4 Homs in parralel in a picture posted here somewhere by migty Zen let me go and get link to Papa article
http://www.firstwatt.com/pdf/art_mos_test.pdf


On the sketch is what I meant by mounting board to parralel to sink
Attached Files
File Type: pdf F5 Board mounting.PDF (65.0 KB, 150 views)

Last edited by Bksabath; 14th February 2012 at 11:31 PM.
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Old 14th February 2012, 11:32 PM   #206
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Bksabath

I meant the input JFETs
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Old 14th February 2012, 11:38 PM   #207
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Quote:
Originally Posted by lhquam View Post
There is already a F5-turbo thread: F5 Turbo is posted
Yep. There certainly is. I know about that one. So, how about we:

1. Move the F5 Turbo stuff from this thread to the F5 Turbo is posted thread, or....

2. Start the F5 Turbo BUILD thread. With folks already discussing build components, and build PCBs......a thread for BUILDing would be nice. Months from now this will be a thread with a lot of inputs/variations/comments/etc.

How about it guys?
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Old 14th February 2012, 11:41 PM   #208
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CanAM Man
IMO start new tread
we can leave theoretical discussion on that one.

UKToecutter
Matching mosfet paper also good for imputs no source resistors there but easy enoug to get god matched Jfets from Blues (got my lot from him) or other members.
Jfets need matching for current (Ids Ithink)

Got to go and catch same Spatcha
Later Alligators

Last edited by Bksabath; 14th February 2012 at 11:49 PM.
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Old 14th February 2012, 11:57 PM   #209
labjr is offline labjr  United States
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Quote:
Originally Posted by Bksabath View Post
Parralel imputs
what is the question about mono blocks?
board fit to one sink make monobloks with just one sink
In the F5 Turbo article, Nelson stated that with V1 that "We are not in a good position to ask the original heatsinks to dissipate more, so if you increase the supply to 32 volts you may need to operate at a lower bias point"

And that's only to go beyond V1. The First Watt heatsinks appear larger than most everything I've seen for DIY.

If the output devices are doubled you would need a massive heatsink to have enough dissipation. Doesn't seem practical.

Last edited by labjr; 15th February 2012 at 12:00 AM.
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Old 15th February 2012, 12:13 AM   #210
NYCOne is offline NYCOne  United States
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Quote:
Originally Posted by EUVL View Post
>

But why not try 3497/681 ?


Patrick
I've been running the 3497/681 in a balanced cascoded amp for about a year now...
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