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Can RF transistor junction be used as a diode?

Discussion in 'Radio and Communications' started by Sinedup, May 17, 2017 at 7:38 AM.

  1. Sinedup

    Sinedup New Member

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    It it possible to use some ancient vintage NPN germanium transistors' base/emitter as a 2-lead germanium diode?
    What about the higher-frequency BFY90?
    I have been given a "scrap" box full of old OC76 and (OC90?).
    Simply for experimentation in RF filters & tanks.
     
  2. JimB

    JimB Super Moderator Most Helpful Member

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    Probably, but they will probably be poor performers.

    Probably better to use as a transistor and buy some real diodes.

    OC76 is PNP not NPN.
    Never heard of an OC90 though.
    The cynic in me says that being given a box full of old germanium transistors is like winning third prize in a beauty contest.

    How will this lot help in experimenting with filters and tanks (tuned circuits ?).

    JimB
     
  3. Mikebits

    Mikebits Well-Known Member

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    • Informative Informative x 1
  4. dave

    Dave New Member

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  5. ci139

    ci139 Member

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    found from web about https://wiki.analog.com/university/courses/electronics/electronics-lab-3

    basically if you have a proper diode for intended operation you don't need transistor substitutes

    for some very specific situation you may have to combine different diodes in series / reverse /parallel ... with transistor substitutes either using BE , CE (with 3-rd electrode not connected) or EC-B or CB-E or BE-C

    for example : for a simulation -- i found -- the weak signal driven bjt booster-comepensation(/opener-(junction-discharger)) diode (a reverse from E to B) to be a diode from the very same transistor in B-EC configuration e.g. Si-NPN as P-NN (E & C shorted together)

    PS! most likely the transistor-diodes have much larger junction capacity (depends on I.FW) and series resistance than "conventional" diodes but they may provide lower voltage drop , higher power e.c. as fuzzily hinted above
     
    Last edited: May 17, 2017 at 4:22 PM
  6. RichTheDude

    RichTheDude Active Member

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    To the OP and Jim, try looking at the prices of OC76s etc on eBay. Sell your box on a piece by piece basis for megabucks and buy some modern diodes, transistors and other electronics gear with the proceeds.
     
  7. JimB

    JimB Super Moderator Most Helpful Member

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    OK, the cynic in me says sell them on eBay and buy some decent stuff!

    JimB

    PS, anybody want to buy some 2N404s ?
     
  8. ci139

    ci139 Member

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    Last edited: May 20, 2017 at 3:06 AM

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