Dual JFET 2N5565 How to test it ?

Hello friends, I don't have much experience with JFETs.
I assembled a couple of amplifiers with dual JFET input, 2N5565 / IFN5565, no problems.
But I have this case in which I was not lucky last time and the amp didn't work.
I need a very simple test circuit for this specific device in order to know if both halves of the dual JFET are working fine.
Any idea will be very much appreciated.:)
Using a breadboard,
(1) put 100 Ω resistor in series with each S (source) lead.
(2) Tie G to the tail of that resistor.
(3) put a 9 V battery's + lead on D (drain)
(4) and the – to the tail of resistor.
(5) relative to the – lead and the S pin of the VFET, measure voltage.​
It should be roughly 0.3 - 0.7 volt.
1.5+ too high.
0.2 V … marginal.
0 V, then VFET is bad (open).

At least those are the numbers for the 2n5565

⋅-=≡ GoatGuy ✓ ≡=-⋅
Last edited:
Thank you very much GoatGuy.
I think this picture shows your solution, please correct me if I'm wrong.
I'll will test this guy right away.


  • JFET TEST.jpg
    JFET TEST.jpg
    123.2 KB · Views: 222
Yap… that's the number. If you have a bunch of the now nearly-obsolete 2N5565's, you could also test 'em all, to see what the nominal range for VRs is. My calculations were educated guesses based on using a lot of JFETs in a lifetime of fiddling around. However, nothing is better than a larger body of statistically significant measurement. Good Luck! ⋅-=≡ GoatGuy ✓ ≡=-⋅
Ohhhhh yessss !:D
I have many of those here in my lab and the price in Argentina is really low $6 to $10 depending on size and quality.

It is just that I had my soldering iron hot and that I pulled out the DJFET from the faulty board one minute before. I straighten the leads and took just one minute to test.

I would have definitely used a protoboard if the device was brand new.
Thank you for the tip !:cheers: