BF862 is now End Of Life. Well that sucks.

A project log for Chymes

Cheap, nondestructive atomic analysis in real time.

A. M. AitkenA. M. Aitken 09/04/2018 at 13:412 Comments

NXP has restructured, spinning off standard products into a new company called Nexperia.  The BF862, beloved of physics projects, fiber optic bootstrap circuits and seemingly a particular favorite of WInfield Hill ("Art of Electronics") is not going along for the ride.  Some LHC preamp projects report a resolution of better than 1kev in Ge with a room temperature BF862 so this is/was a pretty good JFET even if it was only intended for the preamps of car radios.

The important thing of course is not to panic.

So after panic buying the next logical step is to look back and assess the situation. In 2013 the people on diyaudio became concerned that the noise knee had increased when stated production moved to china.  Some information came from the company that the chips were being fabbed in the same place and only the encapsulation point had changed.  This seems unresolved.  It's quite a difficult test to do and the small number tested may not be representative.  Could dielectric noise be a contributing factor? That would potentially be affected by a change in encapsulation.

Possible replacements suggested on usenet by Phil Hobbs; On Semi CPH3910. Lower capacitance but higher Idss and NSVJ2394.

For my purposes the BF862 was a little high in input capacitance and I spent some time chasing Sony 2SK152's (which I found in all Idss grades except -1) and 2SK300 (which so far I have failed to find in any grade).  These have 6 to 7 pf input capacitance versus the BF862's 10pf.  In the same way the BF862 bulk application was car radio preamps the 2SK152 was originally produced for the head amplifier circuit of the Betamax video recorder and found it's way into shortwave sets and the Amptek X-ray spectroscopy literature where is performs the best of all JFETs tested except for a narrow low capacitance range where it's just beaten by the Interfet "NJ14".  There are Interfet NJ14AL process JFETs, which may or may not be the same, available on mouser as the IF140, IF140A and IF142, but they are expensive.  They may be worth matching with low capacitance detectors if MMBF4416 (related, cheap, low capacitance JFET) designs do well.


alexandre zanol wrote 01/20/2021 at 11:53 point

I work with audio and landed here when searching "2sk152", and you provided some useful info. I imagine you will prefer to use available parts, since this is a hackaday project, but in case you need that missing grade of 2sk152 (Idss under 15mA) I have found some at a local supplier here in brazil. Their website says 48 units available, we can split them if you wish! It will likely be very cheap for you since our currency is so devalued. Thanks,

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chuck cooperman wrote 05/15/2019 at 21:04 point

I have recently had success using 2SK2394 in place of BF862. Specs aren't quite as good as BF862 but it is made for the same application and works well enough in my application (low-noise high-impedance audio frequency sensor amplifier). I also bought some BF862's on eBay that have the correct markings but I haven't tested them yet.

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