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F5 power amplifier
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Old 5th June 2008, 06:11 PM   #1041
jackinnj is offline jackinnj  United States
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I am still intrigued by using 2 different resistors/voltage dividers on the gates of the JFET's as well. You can go as low as some 10's of ohms here.

Here's the results using 100pf, 160pF and 470pF cap on the front end. I note that Borbely used 560pF on the input of the Servo-50 and the DC-102.

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Old 5th June 2008, 06:56 PM   #1042
jackinnj is offline jackinnj  United States
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Here's how the amp looks with 3.3nF compensation caps on R5/8 and no input capacitor:

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Old 5th June 2008, 07:39 PM   #1043
EUVL is offline EUVL  Europe
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What is dark blue and what is light blue on the oscilloscope plots ?

And what is the vertical scale (dB / div) on the freq response plot ?
Is it possible to see the response a bit further upscale (say to 5MHz) to see what happens now with your previous peaks and valleys ?


Patrick
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Old 5th June 2008, 07:58 PM   #1044
jackinnj is offline jackinnj  United States
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Dark blue is the sq wave oscillator output (input to JFET). Light blue is the amplifier output.

The network analyzer output is 5dB/div from 10kHz to 5MHz -- the absolute reference isn't relevant as I have an attenuator on the "A" channel -- but overall the amplifier gain is 15.4dB.

The real screw up on my part was not recognizing that the Vcc/Vee at the trimpot nodes had to be bypassed right then and there.

I'm leavin' for a bike ride ...
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Old 5th June 2008, 08:32 PM   #1045
Nelson Pass is offline Nelson Pass  United States
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F5 power amplifier
Quote:
Originally posted by jackinnj
I am still intrigued by using 2 different resistors/voltage dividers on the gates of the JFET's as well. You can go as low as some 10's of ohms here.
One limitation here is that you can't assume too much about
the output impedance of the preamp that will drive it. Most
products are a couple hundred ohms to a Kohm or so.
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Old 5th June 2008, 08:38 PM   #1046
steve jones is offline steve jones  United States
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Default Heatsinks.

Did a search, but not much help.

I've got the parts for a F5, and the Plitron xformer is on its way.

All I need is some heatsinks.

Does anyone have any current recommendations on where to get heatsinks with part number for the F5 ?

TIA,
-Steve
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Old 5th June 2008, 09:36 PM   #1047
MEH is offline MEH  United States
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Quote:
Originally posted by Nelson Pass


One limitation here is that you can't assume too much about
the output impedance of the preamp that will drive it.
Uhhhh... maybe you can't, but those of us who know exactly which preamp will be driving it certainly can.
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Old 5th June 2008, 11:09 PM   #1048
SCD is online now SCD  Canada
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Default Heatsinks

Hello Steve Jones:
I recommend the Conrad heat sinks. There is a group buy getting started right now. There are some troubles at Conrad that are getting sorted out. Once things get going these sinks are the stuff. For me at least.
Which Plitron transformer did you order?
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Old 5th June 2008, 11:33 PM   #1049
steve jones is offline steve jones  United States
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Hi SCD,

Another DIYAUDIO member has emailed me offline with some surplus 8X12x1 heatsinks. So I believe that problem will be solved.

I ordered the Plitron 18V+18V@8.33A (300VA) p/n 077014201.

I'll be sure to check out the Conrad heatsinks when I build the F6. Thanks for the tip.
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Old 6th June 2008, 02:51 AM   #1050
vdi_nenna is online now vdi_nenna  United States
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Some heat sinks here: www.apexjr.com

http://www.apexjr.com/images/GOLDHEATSINK3.JPG

Ask for matching color heat sinks.
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