Re: 2N3819 source
« Reply #21 on: July 07, 2019, 06:39:08 PM »
I am still struggling to hear/measure a difference between properly selected/biased tubes and FETs.

I couldn't imagine there would be any difference between widely available ones and 2N3819.

BladeSG

Re: 2N3819 source
« Reply #22 on: July 07, 2019, 11:22:24 PM »
I understand that there are components that can be subbed but I have a batch of 2n3819 I bought but don’t know how to verify that they’re authentic.

Khron

Re: 2N3819 source
« Reply #23 on: July 08, 2019, 04:18:10 AM »
I understand that there are components that can be subbed but I have a batch of 2n3819 I bought but don’t know how to verify that they’re authentic.

There's a Gibson Guitars joke in there somewhere ;D

That being said, JFETs aren't the tightest-tolerance parts at the best of times, so... If those 2N3819's you have, work as JFET (should), then, without specialized equipment (curve-tracer perhaps?), i'm not too sure if and how one could verify such things.
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

BladeSG

Re: 2N3819 source
« Reply #24 on: July 08, 2019, 04:44:52 AM »
There's a Gibson Guitars joke in there somewhere ;D

That being said, JFETs aren't the tightest-tolerance parts at the best of times, so... If those 2N3819's you have, work as JFET (should), then, without specialized equipment (curve-tracer perhaps?), i'm not too sure if and how one could verify such things.

Thanks.

I've spent quite some time trying to find a solution. I was told that if I put my DMM in diode mode and measured  drain with gate on one lead and source on the other I should get a reading around 0.75-0.80 and then the same results when doing source with gate on one lead and drain on the other. I'm not getting anywhere near this but I suspect its because my DMM only puts 3.3V out in diode mode.

Looking at the data sheet it looks as though I need a gate to source break down voltage 25V minimum to test, does that sound right?

I tried another method I read here (maybe in the U47 FET build thread) where you use a 9v battery and DMM in current mode but I don't get any reading at all. Maybe also because the gate to source breakdown voltage is 25V minimum?

Or you are right and it cannot be done and I'm not doubting you either.

ruffrecords

Re: 2N3819 source
« Reply #25 on: July 08, 2019, 06:13:28 AM »
The battery test should work. Connect gate to source. Connect battery neg to source. Connect one side of DMM to battery plus and the other end to drain. For typical 2N3819 the DMM should read in the region pf 20mA in current mode.

If you get nothing they are probably fake. You could try the J112 as a substitute:

https://uk.farnell.com/on-semiconductor/j112/transistor-jfet-35v-to-92/dp/1017712?rpsku=rel3:2N3819E3&isexcsku=false

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

rogs

Re: 2N3819 source
« Reply #26 on: July 08, 2019, 11:03:25 AM »
.... You could try the J112 as a substitute:

I've found the J113 to be a closer  match ---- especially IDSS wise. -- but I'm sure either should probably work well 

....And not forgetting the pin outs for the J112/J113 are in a different order.... the 2N2819 has the gate in the centre...

rickc

Re: 2N3819 source
« Reply #27 on: July 08, 2019, 01:37:09 PM »
how many do you need.

I have nos from vishay/siliconix

I can sell you a few (10),

--rick

BladeSG

Re: 2N3819 source
« Reply #28 on: July 09, 2019, 06:38:02 AM »
The battery test should work. Connect gate to source. Connect battery neg to source. Connect one side of DMM to battery plus and the other end to drain. For typical 2N3819 the DMM should read in the region pf 20mA in current mode.

If you get nothing they are probably fake. You could try the J112 as a substitute:

https://uk.farnell.com/on-semiconductor/j112/transistor-jfet-35v-to-92/dp/1017712?rpsku=rel3:2N3819E3&isexcsku=false

Cheers

Ian

I tried the 9V battery test again with 3 new ones and got reading between 12.1 - 13.4mA. Does this sound right?

Khron

Re: 2N3819 source
« Reply #29 on: July 09, 2019, 08:43:32 AM »
https://www.onsemi.com/pub/Collateral/2N3819-D.PDF

Idss (zero-gate-voltage current) is spec'd as anything between 2mA and 20mA, so... yes.

Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans


ruffrecords

Re: 2N3819 source
« Reply #30 on: July 09, 2019, 12:47:43 PM »
https://www.onsemi.com/pub/Collateral/2N3819-D.PDF

Idss (zero-gate-voltage current) is spec'd as anything between 2mA and 20mA, so... yes.

+1

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

BladeSG

Re: 2N3819 source
« Reply #31 on: July 09, 2019, 05:33:48 PM »
+1

Cheers

Ian
https://www.onsemi.com/pub/Collateral/2N3819-D.PDF

Idss (zero-gate-voltage current) is spec'd as anything between 2mA and 20mA, so... yes.

Thank you

Fuzz Face

Re: 2N3819 source
« Reply #32 on: July 10, 2019, 09:01:27 AM »
Is there a way to check if a 2n3819 is real?

My semiconductor analyser tells me its an N Channel JFET but cannot identify drain and source.
Drain and source are often interchangeable

You could look at the data sheet to identify pinout and use the test described above


 

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