Help measuring SMD JFETS

Well, it ain't called electromagnetism for nothing.

I think the only way to be really sure is to do the scientific thing and test a JFET with and without magnet to see if the readings shift in a significant way. Might be an argument for a weaker magnet as well.
 
comradehoser said:
Well, it ain't called electromagnetism for nothing.

I think the only way to be really sure is to do the scientific thing and test a JFET with and without magnet to see if the readings shift in a significant way. Might be an argument for a weaker magnet as well.
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I can try that today. Stay tuned.
 
Welp, there's good news and less good news.

1st, I tried testing the mmbf201 on both a magnetized pad and a non magnetized pad.
Since this thread is in the context of matching jfets for phasers, I was only looking at VGS off.

The magnet made no difference. See the readings on my Peak in the pics below.

The "not so good news" is that the magnet alone is not enough. The legs of the SMD's are not consistently on the same plane and you still doo need to put some pressure on them in order to get a correct reading. If not, it only see's two legs and thinks it's a resistor.

This is true for both the Keen tester and the Peak.

I dunno if this puts us back to square 1. I think the magnet definitely helps with the "Mexican jumping bean" issue.

But notice how I was pushing down on the jfet with the tip of my tweezers in both pics.



IMG_8245.JPG

IMG_8247.JPG
 
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Robert said:
So you're saying it's in there......... :D



These are always an (expensive) option...
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I'm sure there's plenty of jfet switching going on in a few devices.
I know there's a few hundred in our high end coils used for transmit receive switching. Those are probably the only ones that make it into the magnet.
 
MichaelW and the rest--

I don't think the magnet idea is dead yet. It just needs a less powerful field. The magnetic bits are the feet. I think with a strong magnet, it's double the force pulling down on the side with two feet than with one, so it lifts. If the pulling force isn't so great, then gravity can also get into the mix and hold things down.

I just tried this with a crappy magnetic door strip--the cheap flexible plasticy magnet that you put on fridges and whatnot. Works okay! The SMD doesn't "snap to", but it holds in place pretty well. The best thing is you can chop the strip up and try stacking the pieces to fine-tune the magnetic adhesion.

Full disclosure: I didn't test it in a rig like MichaelW to see if it lifts, so it still might. But I'm confident in my ignorance that this will work great!
 
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