Matching JFets for first time

[Aentons]

I have bread boarded a few of the jfet matcher circuits including geofex and the similar one in the nom-nom doc and I'm not having much luck. They either give me the same reading for all trannies or always measure half voltage whether a trannie is connected or not.

I tried the runoff groove tester for Vp and it seems to give each one a slightly different reading but the trannie gets really hot, really quickly.
http://runoffgroove.com/fetzertech10.png

I have seen a lot of folks over the years that have issues with the geofex one and the solution is usually just to build the similar one at runoff groove.

Also, I just have a cheap digital multimeter. Trying to match J113's

What am I doing wrong? Any tips or tricks?

[jkokura]

I built my own jfet tester years and years ago, and if I remember right, getting the transistor pinout right is very integral. Could you maybe show your setup to us with a picture, including the design you're using, and then let us help verify you have the jfet pins correct?

Jacob

[Aentons]

Sorry, It's bit messy. Bottom is the one from runoffgroove. The j113 datasheet says the source and drain are interchangable

[Aentons]

I re-did it to be a little cleaner and using the nom-nom schematic.

I'm using a one spot outputting 9.45v.
With no trannie loaded I'm getting a reading -3.69v.

[Aentons]

I re-did it again with power on just one side and the source and drain swaped. Getting +3.9 with the trannie and -3.72 without.

[jkokura]

I can't quite see that there's an issue. The thing I would suggest is maybe trying my version out. I know it works, and I've attached.

The other thing might be that your JFets might be fake, which is why you're not getting good readings.

Jacob

[Aentons]

I can't quite see that there's an issue. The thing I would suggest is maybe trying my version out. I know it works, and I've attached.

The other thing might be that your JFets might be fake, which is why you're not getting good readings.

Jacob

Thanks, I'll try yours. All the JFets came recently from Mouser.

[Aentons]

Nope, same result. I tried wiring it a couple of different ways. I tried a new opamp this time also.

[Aentons]

The Arrow datasheet is newer (2020) and has the J113 pins listed as GSD. This is what I was using.
https://static6.arrow.com/aropdfconversion/ef7ceb2eaee61dd6eec61a61475125d8ab985b66/mmbfj113-d.pdf

I actually bought 100 of them from Mouser so I took a look at their datasheet, which is from 2001, and it has them as DSG. Wtf
https://www.mouser.com/datasheet/2/308/J113-1120625.pdf

https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/J113/?qs=ljbEvF4DwONIvgQL%2FiOeMA%3D%3D

Mine all have a date code of A21

[Aentons]

I measured them using the diode setting and they do appear to be DSG so that's good to know for sure.

I bought another multimeter that is advertised as having a 10M ohm impedance and tested the other multimeter. It has 1M ohm impedance, which I thought might be a factor causing the trouble.

I connected the new multimeter and initially got a -0.6v reading. Great! But then, I disconnected my leads and then reconnected, and now it back to about 3.8v. not sure what the deal is...

[jimilee]

Measure the jfets using the dc voltage setting, that's what I do.


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[Aentons]

Measure the jfets using the dc voltage setting, that's what I do.


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I have been using the dc volt setting for the matcher circuit. I was just using the diode setting to verify which pinout the j113 uses because of the datasheets that seem to conflict

[jimilee]

Ah. I should read more closely. And you're powering the jfet matcher of course? Do mind attaching some pictures of your set up?


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[Aentons]

Here are new pics of a new rebuild using the new multimeter and a TL071 and a new battery.
Trannie inserted or not it reads -3.9v. What am I doing wrong?

[jimilee]

Nothing, that sounds accurate, does another one read about the same?


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