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Thread: FET TESTER design by G0CWA

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  1. #1
    Join Date
    Apr 2012
    Location
    Near Manchester in UK
    Posts
    120

    Default FET TESTER design by G0CWA

    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

    http://makearadio.com/visitors/nick-fet-tester.php

    in Daves visitors section.
    I am following this with designs for other items of home brew test equipment.
    Happy testing de Nick G0CWA
    [CENTER]It is a hobby just enjoy building your radios, don't be afraid to have a go yourself.

    You can always put the magic smoke back
    into a component that goes bang to make it work again !!!! [/CENTER]

  2. #2
    Join Date
    Sep 2011
    Posts
    618

    Default

    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. #3
    Join Date
    Sep 2011
    Posts
    618

    Default

    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. #4
    Join Date
    Apr 2012
    Location
    Near Manchester in UK
    Posts
    120

    Default

    Quote Originally Posted by G0HZU View Post
    I can't remember for sure when I made it **** and you can see it was built in a hurry
    Now thats what I call home rolled equipment

    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 by G0CWA; 03-19-2013 at 08:03 PM.
    [CENTER]It is a hobby just enjoy building your radios, don't be afraid to have a go yourself.

    You can always put the magic smoke back
    into a component that goes bang to make it work again !!!! [/CENTER]

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