NPN Transistor Questions

F1nut
F1nut Posts: 50,647
edited July 2014 in DIY, Mods & Tweaks
I need to replace some NPN transistors. The original is a 2SC870 spec'd at 30V, 0.03A, 0.2W, 150MHz.

These are suggested new replacements.

http://www.mouser.com/ProductDetail/Central-Semiconductor/2N3707/?qs=%2fha2pyFadugSm4f7j2P5eC7hn5ON5G8x7%252bJtYJRzyFU%3d

http://www.mouser.com/ProductDetail/Fairchild-Semiconductor/KSC1845FTA/?qs=%2fha2pyFadujuRv8Fbx51XeLs97y508AFaz7wFPeqKuw%3d

These are suggested NOS, but I'm a bit concerned about their age even though they NOS.

http://www.ebay.com/itm/2SC1682-Original-Toshiba-Transistor-2-pcs-/291177243389


Which one is the better match/choice???
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Post edited by F1nut on
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  • WLDock
    WLDock Posts: 3,073
    edited June 2014
    I would just stick with the new recommended replacements. The ones on eBay seem a little pricey. Here is the same part number from MAT electronics:http://www.matelectronics.com/electronic-repair-parts/semiconductors/2sc-semiconductor/semiconductor-2sc1682/

    I don't remember their order minimum but they sell a lot of low cost odd items: http://matelectronics.com/content/catalog/mobile/index.html
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  • F1nut
    F1nut Posts: 50,647
    edited June 2014
    Thanks for the link, but they are out of stock.


    No one here knows what specs matter?
    Political Correctness'.........defined

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  • WLDock
    WLDock Posts: 3,073
    edited June 2014
    All the specs matter if you think about the fact that the best replacement is a new unit with the same model number. So, Breakdown Voltage, Max Current, Max Power, Max Frequency, Case type, and material are what you want to match to the reccomended replacements. I think these are general purpose amp units? So, theres no reason I can think ofwhy it should be more complex than that. What part of the circuit are these these located?
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  • F1nut
    F1nut Posts: 50,647
    edited June 2014
    All the specs matter if you think about the fact that the best replacement is a new unit with the same model number. So, Breakdown Voltage, Max Current, Max Power, Max Frequency, Case type, and material are what you want to match to the reccomended replacements.

    I agree and that makes sense to me, but it doesn't seem like one can find exact replacements for any transistor.
    I think these are general purpose amp units?

    These are low power, low noise.
    What part of the circuit are these these located?

    Pre amp board and headphone amp board.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • disneyjoe7
    disneyjoe7 Posts: 11,435
    edited July 2014
    The gain is different with the two transistors


    One is 200 and the other is 100

    DC Collector/Base Gain hfe Min: 200

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  • westmassguy
    westmassguy Posts: 6,850
    edited July 2014
    Jesse, I wouldn't worry about the NOS part. Transistors don't age or breakdown sitting on a shelf. Electro-Migration isn't a problem, since they've never had current applied other than the initial testing done at the factory. Whatever the Silicon is encapsulated in may breakdown over time, but that's usually heat related. If they're a critical part, sometimes you have to bite the bullet and pay a premium for an original part.
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  • SCompRacer
    SCompRacer Posts: 8,505
    edited July 2014
    The TO-92 package has no standard pinout so you gotta check your replacements data sheet and stick the leads in the right hole. You can have E-B-C, E-C-B or B-E-C.
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  • F1nut
    F1nut Posts: 50,647
    edited July 2014
    disneyjoe7 wrote: »
    The gain is different with the two transistors


    One is 200 and the other is 100

    DC Collector/Base Gain hfe Min: 200

    Ah, now that is one spec that I didn't pay attention to.

    So, the 2SC870 has a forward current transfer ratio (hFE), min: 250, but doesn't state if that is the hFE1 or hFE2 spec.

    The 2N7307 lists the hFE1 spec at minimum 100, maximum 400, but lists nothing for the hFE2 spec.

    The KSC1845 lists the hFE1 at minimum 150, typical 580 and the hFE2 spec at 200 minmum, 600 typical.

    Still confusing as hell.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

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  • ViperZ
    ViperZ Posts: 2,046
    edited July 2014
    NTE makes equivalents for a lot of old transistors.

    Here is an example:
    http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=2SC870

    I haven't had problems with NTE transistors (used about a dozen different replacements), but check the specs to be 100% sure.
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  • F1nut
    F1nut Posts: 50,647
    edited July 2014
    ViperZ wrote: »
    NTE makes equivalents for a lot of old transistors.

    Here is an example:
    http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=2SC870

    I haven't had problems with NTE transistors (used about a dozen different replacements), but check the specs to be 100% sure.

    Indeed they do, but everyone else has said their products are not good quality, so I ruled them out.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • WLDock
    WLDock Posts: 3,073
    edited July 2014
    NTE is just over priced IMO. Why would I pay $10 for their version of a component that everyone else sells for $1?
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