# J201 Measurements



## chongmagic (Feb 21, 2020)

I have some J201s that I have and want to measure before I use them in a build. I took some screenshots of one that I measured. 









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						New item by Jonathan Freeman
					






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						New item by Jonathan Freeman
					






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						New item by Jonathan Freeman
					






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						New item by Jonathan Freeman
					






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From what I have read and looking at the datasheet, these should have a IDSS should be between 0.2 to 1mA and I am getting 1.33mA on this. I am guessing this is already a bad sign?

The VGs (off) seems and VGS (on) seem ok. What are the key measurements I should be looking at to see whether or not the JFET is worth using?


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## tcpoint (Feb 21, 2020)

They look off.  The runoffgroove article on the Fetzer valve is an interesting read.  Right at the end they show some measurements of various jfets (incl the J201).

Here's the Link.


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## chongmagic (Feb 21, 2020)

tcpoint said:


> They look off.  The runoffgroove article on the Fetzer valve is an interesting read.  Right at the end they show some measurements of various jfets (incl the J201).
> 
> Here's the Link.



Yeah I think they are not worth using. I ordered some SMD J201s for the sake of having more consistency as well.


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## tcpoint (Feb 21, 2020)

I finally went to smd.


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## Chuck D. Bones (Feb 21, 2020)

Maybe try measuring Idss using the ghetto technique: 9V power supply and a 1K resistor.  See if that measurement validates the DCA75's measurement.  In any event, I would not scrap a JFET for having Idss 0.33mA higher than spec. The Vp and yfs numbers are good.  I expect these would work fine in most, if not all pedals.


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## music6000 (Feb 21, 2020)

This is what I Knocked up & use for Idss, It has not let me down.
You get a measurement with DMM & *X* by 10 =  ma.
I didn't use it when building the M800 & it was average. When I pulled them out, I used this and they were all out of spec.
I replaced with Siliconix J201's with white Dot that Idss were 0.55 to 0.65 ma on this device. 
Learned my Lesson with J201's!


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## music6000 (Feb 22, 2020)

Here it Is
Resistor & Links on Underside :


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## music6000 (Feb 22, 2020)

I see Mouser has around 1500 Interfet J201's @ $5.50 US each.


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## Idroj (Dec 14, 2020)

music6000 said:


> Here it Is
> Resistor & Links on Underside :
> View attachment 3191


Hi, I am trying to measure Vp and Idss on some J201s and have never done this before. Could you please explain the* absolute simplest way* to get those readings?  I can't read schematics yet... I'm very new at this... Thanks!


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## temol (Dec 15, 2020)

You have to learn how to read schematics before you can use *absilute simplest way .  *
I've already posted a link in your M800 thread. DMM, battery.
http://www.runoffgroove.com/fetzervalve.html (11. Measurement of Vp and Idss)








						jFET Characterization Technique using only 9v Battery and DMM - viva Analog
					

As mentioned in my other post about accurately characterizing a large lot of (TO-92 package) 2n5457 transistors, jFET device characteristics are primarily defined by two numerical constants: the Idss current, and the Vgs(off) voltage (sometimes referred to also as Vp).…Read more ›



					viva-analog.com


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