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Thread: Modern equivalent of MPS-U51 PNP transistor on Disk ][ analog board?

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    Default Modern equivalent of MPS-U51 PNP transistor on Disk ][ analog board?

    Not sure how to spec out a replacement for a long obsolete transistor. The Disk ][ & III analog board and the Apple III motherboard use MPS-U51 5W PNP transistors with base in the middle. What's the modern equivalent?

    MPS-U51 datasheet: https://datasheet.octopart.com/MPSU5...eet-105499.pdf

  2. #2
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    Plugging MPS-U51 into https://www.nteinc.com/search.php gives NTE189, which you could probably plug into further cross reference lookups for other manufacturers.

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    Worse comes to worst, you could always just do a lead swap on a BCE-type TO220 PNP or just use a TO5 version (e.g. 2N6191) assuming that the MPS-U51 weren't heatsinked. That way, the same lead ordering obtains.

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    Usually what I do with transistors is follow the same guidelines that we use for capacitors:

    ALWAYS go the same voltage values or higher (like 50v Collector-to-Emitter means 50v or higher, -40v means -40v to anything beyond 40 in the negative range [i.e. -50v]) as the previous component. NEVER go lower.
    Higher voltage values only means that the component is just that much more bolstered against failure in the circuit. And remember, you have at LEAST 3 values to contend with (Collector-to-base, Collector-to-Emitter, Emitter-to-Base). Also, don't forget the POLARITY. Match NPN with NPN, and PNP with PNP.

    I fixed my Sanyo's CRT control board following these guidelines.

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    Any of these are meet or exceed the electrical requirements.

    https://www.digikey.com.au/products/...=1&pageSize=25

  6. #6

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    I have always liked that range of transistors with the thin unique metal tab (fond of them). Sometimes they came in interesting colors like red-brown and green, as well as black and some SCR's came in that package.

    There are many replacement types that exceed the specs so there is no worry there. A common garden approx modern equivalent, a little smaller than a TO-220 package, but not identical to the TO202, would be the BD140, a very robust transistor.

    But there is another option to help it look original:

    A transistor with near identical physical specs is the MPSU52, same voltage and power dissipation , 1.5A rather than 2A max collector current, but I think if you check the application probably fine, because it is also complimentary to the MPSU01. You can get these still I think from Surplus Sales Nebraska for $5.50.

    https://www.surplussales.com/cgi-bin...ors-SCR-4.html
    Last edited by Hugo Holden; October 26th, 2020 at 08:57 PM.

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