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Old 11th September 2019, 01:56 PM   #1451
EUVL is offline EUVL  Europe
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Nice simple clean design.




Patrick
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Old 11th September 2019, 01:57 PM   #1452
EUVL is offline EUVL  Europe
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I wanted to know whether I can adjust the schematics such that it can be optimised to drive a 3R load without parelleling output devices.

Well, you can, by changing a few things, including to 16V rails and 2A bias.
And it would be useful also for 8R loads, even up to 10Vrms output.




Cheers,
Patrick

.
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File Type: asc J2 K3497 Amp 3R.asc (6.1 KB, 20 views)
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Old 11th September 2019, 02:05 PM   #1453
astromo is offline astromo  Australia
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Quote:
Originally Posted by oreo382 View Post
Quote:
Originally Posted by aspringv View Post

Are these legit? Has anyone bought and tried these?
I bought a pair earlier in the year but a screw up with the test rig I cobbled together fritzed one .. .. sux I know. I was planning to use them for an Aleph J but the store's board layout doesn't really lend itself to a straight forward fit from this style of component. One for the learning curve on my part.

Following that learning experience, I got myself a Peak DCA75. The unit was purchased without a calibration certificate but (according to Peak) all units are calibrated as part of the production QA process.

Refer the attached for the test runs that I logged of the surviving 2SJ109. There are 2 files. The A and B files relate to the respective JFETs in the monolithic component.

From use with the tester, I observed that there was little bit of drift in the results associated with subsequent tests. So, I ended up logging the results of the 5th consecutive test. That seemed to give stable results.

Best efforts to help but please be aware that I'm not a electrickery techo wunderkind.

My read of the results are that the component that I tested is legit. Here are the summary results (sheet marked "ID" from the attachment):
Quote:
P-Ch JFET
Green-G, Symmetrical Src/Drn
Vgs(off)=-0.49V at Id=4.6µA
Vgs(on)=-0.11V at Id=4.99mA
gfs=29.4mA/V at Id=3.0mA to 5.0mA
Idss=8.78mA at Vds=2.35V
Rds(on)=22.4Ω at Id=5.0mA and Vgs=0.0V

If I've misunderstood the data, I'm sure that those who know more will chip in with their advice.


Hope that helps..
Attached Files
File Type: zip 201902Feb02 Test Results J109BL.zip (193.4 KB, 10 views)
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Old 11th September 2019, 02:50 PM   #1454
JeffYoung is offline JeffYoung  Ireland
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FirstWatt J2
Case is looking nice, chromenuts!

Cheers,
Jeff.
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Old 11th September 2019, 03:35 PM   #1455
obh is offline obh  Norway
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Nice case!

I did not see any air inlet at bottom and outlet on top...
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Old 11th September 2019, 04:23 PM   #1456
chromenuts is offline chromenuts  United States
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Originally Posted by obh View Post
Nice case!

I did not see any air inlet at bottom and outlet on top...
Yeah...unfortunate result of “engineering on the fly”.

I planned on perforating the bottom plate along the sides with my mill.

As far as the top, I might try elevating the heat sink with some screw heads slightly to create a small gap that runs the length of the case on both sides.

Otherwise I’ll just have to mill some holes through the heat sink flanking where the board mounts on the bottom side.

Still a bit of finishing work to do too. Trying to get the casework done before cold weather prevents me from doing any work outside.
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Old 11th September 2019, 05:57 PM   #1457
obh is offline obh  Norway
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FirstWatt J2
Yes. Caseworking outside before snow arrives. :-)
Winter is coming.

It must be difficult to mount parts on heatsink while
keeping wire short and placed away magnetic field
of transformer. Maybe turn case upside down
and mount on heatsink with bottom as lid?

I guess convection must be better with flat top mounted
heatsink than side mounted. But will the heat in the heatsink be as distrubuted on heatsink as side mounted? Interesting? Maybe you can measure
heatsink temp either way?

Cheers!

Last edited by obh; 11th September 2019 at 05:58 PM. Reason: fix smileys
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Old 11th September 2019, 09:29 PM   #1458
Itsmee is offline Itsmee  England
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Quote:
Originally Posted by EUVL View Post
I wanted to know whether I can adjust the schematics such that it can be optimised to drive a 3R load without parelleling output devices...
Thank you Patrick, now I can use the second quad to make a another amp
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Old 12th September 2019, 12:52 AM   #1459
obh is offline obh  Norway
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Default Rth of

Quote:
Originally Posted by EUVL View Post
Hi, re-read your paper once more. Thanks for making it public!

Just a single detail: You write that
modern TO247 using Keratherm 86/82 has thermal resistance of
3.5C. I think you referred to 2SK1530 when you wrote this.
This device seems to have a rather large metal pad size.

But Vishay IRFP240, SJEP*R100 and 2SK3498 seems to have
much smaller pad size (I see about 170mm2, 190mm2, 250mm2
looking at specsheet/pictures) and thus I get a rather higher
thermal resistance of 6.5C, 5.7C and 4.5C of Keratherm for these.

Btw: I do totally agree with you conclusion that in the end one needs to measure
actual temperature on heatsink.
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Old 12th September 2019, 03:32 AM   #1460
EUVL is offline EUVL  Europe
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Originally Posted by Itsmee View Post
Thank you Patrick, now I can use the second quad to make a another amp
Yeh. One with 20V+ rails as the original.
And then you can compare.




Patrick
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