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transistor subs

Discussion in 'Radio Circuits, Repair & Performance' started by K9UR, Nov 30, 2021.

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  1. K9UR

    K9UR Subscriber QRZ Page

    Looking for the following transistor substitute options

    1) C9112
    2) 2N3904

    These are used in an MFJ 407B keyer.
     
  2. KB0MNM

    KB0MNM Ham Member QRZ Page

    Item 2 see attached files. Long ago, this might have been an excuse for a trip to AEI Inc. in Golden Valley, Stark Electronics in Minneapolis, or even Digi-Key in Thief River Falls. I may have a few 2N2222a or P2N2222a parts here near Houston. I have no financial interest in AEI Inc., Stark Electronics, nor Digi-Key(R/TM)- just fond recollections. 73
     

    Attached Files:

  3. W1NJC

    W1NJC Ham Member QRZ Page

    3904's should be available literally anywhere. In that circuit it's probably just used as a switch anyway so you could likely replace with many other NPNs.
    I've never heard of a C9112 though....are you sure that is the correct part number?
     
  4. K9UR

    K9UR Subscriber QRZ Page

    That’s what I think. Second opinions please ? See photos.
    3F898CF4-A10E-4685-B61D-63EE74A47368.jpeg 3D391564-EA44-4407-9B75-17B36FAA757A.jpeg 3F898CF4-A10E-4685-B61D-63EE74A47368.jpeg
     
  5. KB0MNM

    KB0MNM Ham Member QRZ Page

    Joe, The VN10KM and shape might indicate something a bit more exotic than a regular BJT. I think that this may be of the MOSFET class of semiconductors. Many were in larger cases, and did include the metal for heatsinking. If I had an old RadioShack catalog handy, I could give you an example of a VN part number that was a MOSFET and used for handling a bit more power. You might want to look up the 2SC9112 transistor ( if there is one ) and compare the package outline. Most of the 2SC-series BJTs were in the same case as the 2N3904- TO-92.
     
  6. KB0MNM

    KB0MNM Ham Member QRZ Page

    Take a look at what I just found by searching on just VN10KM ( attached ).
    It appears that the manufacturer logo on the Jameco part matches, for what little that is worth. 73
     

    Attached Files:

    K9UR likes this.
  7. W1NJC

    W1NJC Ham Member QRZ Page

    That's a VN10KM. The C9112 is a date code. That part is a N-channel MOSFET, datasheet here: https://pdf1.alldatasheet.com/datasheet-pdf/view/26693/TEMIC/VN10KM.html
    An NTE491T looks like a drop-in replacement https://www.nteinc.com/specs/400to499/pdf/nte491t.pdf Digikey has stock in their "marketplace" which says it would ship in 5 days...
    A 2N7000 could also work here (they're ubiquitous), though the original FET is rated for more power dissipation (but the on-resistance "Rds-on" is lower on the 2N7000). Do you have a schematic of the circuit? If so, we could probably estimate how much power dissipation it would have.
     
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  8. W1NJC

    W1NJC Ham Member QRZ Page

  9. KB0MNM

    KB0MNM Ham Member QRZ Page

    Also, look at:
    https://ac0c.com/main/page_gear_mods_mfj407b_dds_sidetone.html
    It may be difficult to find another Curtis chip, so you may want to be very careful about modifications. If the output of your Curtis chip connects directly to the N-Channel MOSFET- you may wish to check in with MFJ to see if it is the stock part. They may have a diagnostic clue or two to give about expected voltages or signals.
     
  10. W1NJC

    W1NJC Ham Member QRZ Page

    The appnote calls for a series 1k on pin 18 (the output of that Curtis 8044). A schematic would be great, maybe OP can confirm if the unit he's working on is in fact the MFJ407B. I'd hazard a guess that the Curtis is driving the 3904 which in turn drives the gate of the FET. In this case, the current through the FET would be limited by the KEY circuit in the radio...
     
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