FET TESTER design by G0CWA

Discussion in 'Homebrew and Kit Projects' started by G0CWA, Mar 17, 2013.

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  1. G0CWA

    G0CWA Ham Member QRZ Page

    Hi all this is a companion tester to my earlier crystal tester and again it is made from "junk box" parts.
    Most DVM's available now can test bipolar transistors but a tester for FET's is rare.


    A detailed write up is available on


    in Daves visitors section.
    I am following this with designs for other items of home brew test equipment.
    Happy testing de Nick G0CWA
  2. G0HZU

    G0HZU QRZ Member

    Looks good :)

    I made a FET tester when I was a student and I think I still have it in the loft somewhere. it was built in an old tobacco tin and I fitted an old CB S meter to it for the indicator.

    From memory I used a crystal oscillator to drive the FET under test with a small RF signal. I then used a similar detector circuit as your own to measure the output level.

    I made it so I could select and match JFETs for use in balanced circuits etc. I think it could do MOSFETs as well (eg 40673) as I remember using a 4 hole test socket and I probably biased the spare hole for gate 2.

    I really should look for it one day and I think there should still be a little piece of paper inside the tin with all the common FET pinouts written on it...
  3. G0HZU

    G0HZU QRZ Member

    I had a quick rummage today and found it...

    It also tests dual gate mosfets like the BF981 by soldering to the 4 little posts around the 4 way skt.

    It does the testing at RF and was at its most useful when cherry picking FETs for best Gm or matching them.

    I can't remember for sure when I made it but I think it would have been mid 1980s and you can see it was built in a hurry :)

  4. G0CWA

    G0CWA Ham Member QRZ Page

    Now thats what I call home rolled equipment :D

    Who cares about appearance, it does its job, that's the important thing.

    Thanks for your comments and sharing your build, good to know others still build their own equipment and don't just buy, sorry for swearing, expensive black boxes ;)

    I still miss the old tobacco tins for building projects and am still wishing I had some for shielded enclosures.

    All the best de Nick G0CWA
    Last edited: Mar 19, 2013
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