Need to understand a transistor part marking

Discussion in 'The Projects Forum' started by JerryEngineer, Nov 30, 2015.

  1. JerryEngineer

    Thread Starter New Member

    Nov 30, 2015
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    I'm working on a project for a friend where he has an old organ (4140 Wurlitzer) that was built in the 1960's. The schematics for it are no longer available. I've isolated the functionality problem to several TO-92 transistors on one of the tone generators. There is no part marking on the devices except for "891". Does anyone have an idea how to cross reference this to a part number? If not, is there an easy way to identify a potential replacement part?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Chances are its silicon, if you can compare it with others on the pcb, use a multimeter on diode test, or remove the transistor and put it into a dvm/transistor tester.

    Could be 2sd891, 2sc891, or it could be a unijunction fet, the list is endless....

    Any pictures?
     
    Last edited: Dec 3, 2015
  3. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    @JerryEngineer

    Likely a 2n891

    A small silicon controlled Rectifier (SCR). Google for limited old-school datasheet.
     
  4. recklessrog

    Member

    May 23, 2013
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    It could also be a 2SA891 which is listed as similar to BC327A, BC638, BC640, 2SB647.
    Silicon pnp 60v 0.5A 0.35W 100MHz
    Info from VRT comparison table vol 2
     
  5. Brevor

    Active Member

    Apr 9, 2011
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    I serviced organs many years ago, many transistors used in organs can be subsituted with generic NPN and PNP transistors. I suggest you trace out the part of the circuit the transistor is used in and also measure a good transistor in order to determine which type it is. (NPN, PNP or other) Then replace the bad ones with a generic 2N3904 or 2N3906 transistor.
     
  6. Brevor

    Active Member

    Apr 9, 2011
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    No, Wurlitzer didn't use foreign transistors in their products.
     
  7. SLK001

    Well-Known Member

    Nov 29, 2011
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    In the 60's, there were plenty of American made transistors that would have been used in American products. Your transistor was probably marked with a house number, so unless you have the original schematic or detailed parts list, you're going to have to characterize a functional "891" device to find a modern substitute.

    If you find many "891" devices on the boards, you can probably just measure the VCC and select a generic version that has a voltage rating above your VCC measurement.
     
  8. JerryEngineer

    Thread Starter New Member

    Nov 30, 2015
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  9. JerryEngineer

    Thread Starter New Member

    Nov 30, 2015
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    Thanks all for your valuable input. I was able to figure out the transistor type that I needed (2N3904) and the board is now functional again. Thanks again!
     
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