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Old 10th March 2012, 05:03 PM   #1
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Default is this idea worth looking at ?

one of my employees was reading the pass article about this amp that is made from i don't recall how many small J fet

so he said to my why not do the same with bjt transitors ore make one that has 10X BD139 +10X BD 140 for outputs

anyone thinks that this is an idea worth looking at ?
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Old 10th March 2012, 11:30 PM   #2
Bigun is online now Bigun  Canada
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This has been discussed before, I can't remember where - but somebody did build something on the forum and said they really liked the results.

I think modern BJT power transistors are very good - not sure it's worth the effort to make massively parallel small power BJTs.
For JFETs there aren't many power devices available.
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Old 11th March 2012, 05:21 AM   #3
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Jan Didden had a 200W design in Audio Amateur using the 40Mhz/4A MJE243/253 pair.
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Old 11th March 2012, 06:58 AM   #4
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quick look on the net i couldn't find much about the article ...it could be nice if you had some more info

Thanks
sakis
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Old 11th March 2012, 08:07 AM   #5
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Old 11th March 2012, 08:19 AM   #6
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Quote:
Originally Posted by djk View Post
Jan Didden had a 200W design in Audio Amateur using the 40Mhz/4A MJE243/253 pair.
MJE200/210, cascoded with 2N3773 IIRC ...

jan
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Old 11th March 2012, 08:39 AM   #7
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i had no trouble finding the Pass article ...still it seems that i cannot find the Jan Didden article
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Old 11th March 2012, 09:42 AM   #8
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Paralelling those small BD's works very well but carefully matching is needed. And this is a serious effort. TO220 devices are better from POV of cooling than TO126's.
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Old 11th March 2012, 12:14 PM   #9
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"MJE200/210, cascoded with 2N3773 IIRC ..."

Ah, the author speaks!

You are of course correct, the MJE200/210 being 65Mhz/5A devices.

"TO220 devices are better from POV of cooling than TO126's. "

The real heat is handled by the 2N3773s.
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Old 11th March 2012, 12:44 PM   #10
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Would not the base drive get unmanageable pretty quick?
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