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Old 9th January 2004, 10:59 PM   #1
akb1212 is offline akb1212  Norway
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Lightbulb DIY MOSFET tester

A colleague of mine just showed me an Elector article describing a power MOSFET tester/matcher made for testing and matching fets for power amps (and smaller devices to).

It works by feeding an increasing voltage to the tested devices and showing the curves on a scope. It is doing this in intervals, and are capable of showing the curves for 2 P-channel and 2 N-channel fets at the same time.
That way it is possible to match either the same type devices or equal devices.

It is possible to test at currents up to 13 A (enough for even the most daring amp builder I would suspect.... ). The way it does this is by sending that current through it 1/100 th of the time. The rest of the time the device is left in off state to cool down, so there is no need for heatsinking. You would have to heat the transistor to the expected working temp if you wanted to test it at that temp. I think I'll try to do that.

Oh well, I ordered the PCB for it through www.thepcbshop.com (this is the card: http://www.thepcbshop.com./ArticleDe...ArticleID=2121 ). They have a service offered at www.elektor-electronics.co.uk for making one of PCB's not currently stocked. It costed me €52 including shipping.

This was presented in number 9 1993 (I think) in the English version, but the copy I have is from the Swedish version (and is therefore readable only to those of you capable of reading Swedish) and there it was presented in number 5 1994. So in a while I'll be able to build it and see how good it is for testing fets for Pass amps.

I just wondered if this sounds interesting to any of you guys??

I won’t present the schematic here since that would be violating copyrights..... or.... anyways, I don’t have a scanner. Too bad it is from before they started making CD's of one year of the magazine.

Anders
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Old 9th January 2004, 11:38 PM   #2
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Extremely interesting to me!

Bartek
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Old 10th January 2004, 06:03 PM   #3
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You can also find schematics and an article on Mosfet
testing at www.passdiy.com
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Old 10th January 2004, 08:11 PM   #4
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As well as the latest Audioexpress (mighty interesting article )
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Old 13th January 2004, 10:49 AM   #5
akb1212 is offline akb1212  Norway
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Quote:
Originally posted by rwagter
As well as the latest Audioexpress (mighty interesting article )

Yep it is! Most informing Great as an introduction, or even more experienced amp builders. Teaches sides of this not talked about other places.

But the tester is a natural step further to this. That's why I posted about it here. But this discussion isn't going further until I can present a schematic, so Cobra2 is going to help me scan it (I have sent him a photocopy to do it yesterday). To bad about the language though, and the age of it.

But anyway, it is made in a way just begging for DIY'ers to take it apart and make other more sophisticated versions. Putting in a PIC or something would also be a nice thing to do. And then of source there is digitising of the curves. This opens up a whole new world in matching

But then again there is the testing/listening dilemma. As Pass also have explained, perfect match is no guaranty that it sounds good....

Oh, and to those of you that mailed me about the direct link to the PCB doesn't work. You are right, but if you go through their homepage and find the Elector PCB's and then go to 1993 and number 9 (next last that year) you'll find it. But remember this is ONLY the PCB, no kit! I have the BOM (parts list) (I hope Cobra2 remembers to scan that to from the article to), and all parts should be readily accessible and cheap (only some 4000 logic and some transistors and some passive parts).

Ok, we'll only have to wait for Cobra2 to scan them then.....

Anders
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Old 28th January 2004, 01:01 PM   #6
akb1212 is offline akb1212  Norway
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Here is the working principal of the tester:


Anders
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File Type: jpg tester1.jpg (16.5 KB, 2133 views)
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Old 28th January 2004, 01:14 PM   #7
akb1212 is offline akb1212  Norway
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And here is the complete chematic.

The image is large, but I compressed it as much as I could to make file size small. It became unreadable if I used smaller image size.

And there was a limitation to 800x1200 (and NOT possible with 1200x800. Why ???). Therefore I rotated it to get as much as possible details to make it readable.
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File Type: jpg tester4.jpg (99.5 KB, 2110 views)
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Old 28th January 2004, 01:52 PM   #8
akb1212 is offline akb1212  Norway
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Sorry, but the component list was unreadable in the scanning Cobra2 helped me with. I have to do it again. I have found a scanner at the IT department so no problem to do it, except finding the time while at work......

I don't feel like typing it in by hand, as that always (or way to often) leads to errors..... I'll find a way soon.

And to get the PCB all you have to do is to visit www.thepcbshop.com and click on their Elector PCB link (bottom of page). Then go to November 1993 and you'll find it. It costs something like 45€ (don't remember exactly) plus shipping.

I'm still waiting for the PCB, but I'll keep you posted when I receive it.

Except for the PCB I have everything needed for 10 channel (at least) AlephX' now. And the Group buy PCB's are soon to arrive I hope

And I picked up 4 halogen transformers (proper iron core ones) on 300VA 11.5 V for free at work the other day. And on top of that I found ceiling aluminium roofing there too (0.5 mm thick), so now I have all the materials I need for testing and making the “psalmbook” heatsinks from this thread: http://www.diyaudio.com/forums/showt...477#post292477 . The downside is that they are only 12cm wide (after straightening the profile bends), so I have to improvise a bit. But since I can have absolutely as much as I want there is room for testing (except for the time to actually do it…..).

Since I have some old computergrade caps lying around rated for 15-30V (that I haven't been able to use earlyer because of the low voltage) I can actually make some amps for almost nothing

Anders
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Old 30th June 2010, 09:02 AM   #9
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Ok, my patience has run out - 6 years...I've been waiting for you to do that rescan - there must be one helluva queue for your office scanner.
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Old 30th June 2010, 09:35 PM   #10
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They have an updated product
Transistor Curve Tracer - ELEKTOR.com | Electronics: Microcontrollers Embedded Audio Digital Analogue Test Measurement

The pcb is about $40, or about $90 for populated and tested pcb.
If it was me I would buy the finished product. I would rather spend my time (which is very limited) building amplifiers etc.
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