MOSFET Source Follower Headamp

Founder of XSA-Labs
Joined 2012
Paid Member
Founder of XSA-Labs
Joined 2012
Paid Member
I read in a post here that the BF862 is recommended to run at 2/3 of the IDSS value ? Is there a reason for this ? What happens if the BF862 runs at a lower value than 2/3 of IDSS ? Will it still work ?

I tried testing the BF862 using a JFET tester circuit like this SMD jfet test jig and I got about 25ma IDSS.

You can run a bit lower but these things are operating in Class A so try to keep some current flowing for best sound.
 
There’s no equivalent. Close in performance and higher voltage is 2SK170BL but those are even harder to find. Plenty still available from Aliexpress or eBay. They are too small and cheap to fake so will be genuine as far as I have seen.

e.g., 10PCS BF862 JFET N-CHAN 20V SOT-23 ZETEX NEW | eBay

100 for $16:
Free shipping 100pcs/lot BF862,215 BF862 JFET N CHAN 20V SOT 23 Best quality-in Integrated Circuits from Electronic Components & Supplies on Aliexpress.com | Alibaba Group

Sad reason to dredge up an old thread, but...

I recently purchased two lots of BF862 off of Ebay, from different sellers, and both were fakes.

Clearly visible under the microscope were the striations and gloss of the sanded & painted tops in place of the usual pebbled texture consistent with the other package surfaces, complete with sharp shoulders instead of the expected slight radius around the four edges. Laser markings were more inconsistent in alignment from part to part than they should have been - another subtle tell.

A few seconds under the flame of a butane torch, and the tiny die is easily liberated to the telling eye of the same microscope... the die look nothing like the genuine die photos posted elsewhere online:
 

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  • Counterfeit BF862 die.jpeg
    Counterfeit BF862 die.jpeg
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I took another part out of the packaging today to photograph, so that people can see what a counterfeit / re-marked salvage part looks like.

The photos and details are posted on the other related thread here: Bf862 purchased on ebay - labeled as 2AW2?

Yes, I cross-posted to a second thread on this topic, hoping to increase exposure of this issue. It is a sad situation, but I think it's important to raise awareness and help prevent more people getting burned.

If anyone does know of a reliable source for genuine "NOS" BF862, I am still looking to purchase a handful. Please PM me.

In the meantime, I'll be looking for current-production alternatives which can be sourced from the Tier-1 vendors.
 
I recently purchased two lots of BF862 off of Ebay, from different sellers, and both were fakes.
Sad indeed. Is it even worth faking them? Who would be interested – maybe a few hobbyists?

A fine sounding JFET. I have them running in my Pass B1 Buffer, PCA headamp and AKSA Lender preamp.

I might have a few (less than 10 probably) left. Will check this weekend and send a PM.