This tester works pretty well as a basic tester. I use it all the time. Its manufactured in China I do believe and you will see them on ebay. These testers test ESR in
capacitors, FETs, transistors, SCRs and other components. There are only 3 terminals. Good for a JFET..Source Drain Gate..but not for a DG mosfet ..BUT..i
KNOW you can tie both gates of a dual gate mosfet together and use it in a circuit as an ordinary FET. So I did that here with these BF981s. All the old stock I
had consistantly tested good just like a JFET would..HOWEVER..all the new ones from the batch of 30 I just recently ordered..tested as UNKNOWN COMPONENT
OR DAMAGED COMPONENT with the tester above.
I just rigged up this tester using common prototyping leads and sockets that are used in the Ardinio prototyping systems (lot of this stuff on ebay). I bent the pin  
socket (used to hold the leads of the BF981s) using a common pair of needle nose pliers. (note: I am going to improve this simple test station with time). IT DID
the job today. The FELLOW who reported that the 5 BF981s I sent him were defective..was right..they all are defective (the black ones-- the silver faced ones (my
old stock) ALL TESTED GOOD-- NOT ONE TESTED bad. NOW I'm sending this fellow 5 replacement GOOD BF981s FREE OF CHARGE. That is the way my little
SHOP WORKS..by GENTLEMANS AGREEMENT.
While testing the BAD devices I experimented with the lead configurations. I thought to
myself..maybe the device was internally wired different from what it was supposed to be. A
factory error. A bonding error. Easy enough to do. Wire up something backwards or the wrong
way. So I shorted the G1 to the Source (instead of wiring G1 and G2 together) and wired the
device up to the tester..AND IT TESTS THE DEVICE NOW as a good known JFET type device.
HOW GOOD?? Is it really a good BF981 only the pinout is different. Tommorrow or the next
day..WHEN I HAVE MORE TIME. I will solder on some little leads and make a
What I am going to do is modify these BAD DG MOSFETS like the one
above. I can then use my FT301 radio (it has transistor sockets in the RF
stage of the reciever) and I can test these bad DG MOSFET and actually
see if they perform like a BF981 would.
This all relates to my previous work with testing DG Mosfets in radios
(FT301 specifically).

BOTTOM LINE IS NOW..THE Bad DG Mosfets are under Quarantine. If
they are not wired to a standard configuration (like the data sheet
drawings show)..then people could end up soldering them into
circuits and having all sorts of difficulties because of this.