N-channel JFET info

[w2aew]

My google-foo is failing - can't seem to locate any data or replacement info for this N-channel JFET.  Most searches result in finding a Programmable Unijunction Transistor, but I know for sure that it is a N-channel JFET.  Of course, it pre-dates the internet...  Can anyone help?

[Chris56000]

Hii

It's Samsung coded but not a direct copy of a more well–known 2N–etc., device!

If you do need to replace it, PN4393, BF256, 2N3819, etc., would probably do!

Chris Williams

[w2aew]

Hii

It's Samsung coded but not a direct copy of a more well–known 2N–etc., device!

If you do need to replace it, PN4393, BF256, 2N3819, etc., would probably do!

Chris Williams

Thanks!  I'll have to see which of them come closest to what I measured on the curve tracer.

Where did you find the info?

[Chris56000]

Hi!

My own personal store of device specs and equivalents gained from over 35 years doing Audio, TV and Industrials!

There is also:–

2SK30, and the J100, J200 and J300 series as well! Most JFETs rarely require a voltage rating of more than about 25–30V!

As you have access to a C.T., it might be worth checking eBay, AliExpress, Bangood, etc., etc., for cheap "goodie bags" of 10–20 or so and trying a selection, then marking their tops with a little dot of paint from a paint marker and keeping 'em in a clearly labelled bag!

Chris Williams

PS!

If the FET you showed us came out of a meter or similar piece of T & M, you might require one with low leakage characteristics, in which case, the parameter to look at is "Igss".

The E200/E300 and J208/J209 are characterised for low gate–leakage, and there's others as well!

If you need to check Igss, bias the gate about –3V with respect to source and interpose a 10M resistor in series with the gate lead – 1nA leakage will drop 10mV across a 10M resistor!

You'd need a nanometer with an electrometer–type input amplifier to try and measure Igss directly – Keithley 616/617 for instance!

[CHexclaim]

BTW, from the picture, great PCB design! ... or not.

[w2aew]

BTW, from the picture, great PCB design! ... or not.

Yeah, NOT!  I bent the JFET over to get a better picture.  Single layer PCB, no silk-screen, but then again, the instrument is likely almost 40 years old.