Help measuring SMD JFETS

[Robert]

This is probably a stupid question, but wouldn't the magnetic field affect the readings on the fet?

I wondered the same thing, but apparently not. (if the clearly AI generated response I received to the question can be trusted)

 

[lrgaraujo]

Found a journal paper saying that high intensity fields should affect transconductance, depending on the orientation.

 

[Ginsly]

FWIW Peak now has their test leads on more flexible silicone wires that hold up much better than the stiff ones they used for years. They'll send you some if ya ask nicely.

 

[comradehoser]

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.

 

[Robert]

Hey @jwin615, does an MRI machine have JFETs?

Could you see if running it nearby affects your DCA75 readings?

 

[MichaelW]

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.

I can try that today. Stay tuned.

 

[MichaelW]

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.

 

[jessenator]

Searched a little for images, and even the manual doesn't specify, but could someone show where the USB cable connects on the device?

 

[MichaelW]

Searched a little for images, and even the manual doesn't specify, but could someone show where the USB cable connects on the device?

To which device? The Peak DCA75?

 

[jessenator]

To which device? The Peak DCA75?

Ope, I didn't say. Yes, the DCA75

 

[MichaelW]

To which device? The Peak DCA75?

Sorry for totally derailing your thread Rene.......

 

[comradehoser]

Sorry for totally derailing your thread Rene.......

Are you serious?? I LOVE THIS THREAD!!!!!