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Thread: Acoustasonic Jr Outputs MJW21191/92

  1. #1
    T9c
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    Acoustasonic Jr Outputs MJW21191/92

    Working on a Fender Acoustasonic Jr and the outputs are MJW21191 & 92's per side (it's a stereo amp). Only one side has blown outputs and the drivers/predrivers/bias xistrs check ok onboard (none shorted/open). The 91/92's are no longer available.

    I can get MJW21193 & 94's, but their specs are double what the 91/92's are, except they have the same Vebo (5). Same case style.

    Do you think the 93/94 would replace the 91/92's without any circuit mod?

  2. #2
    Senior Member mozwell's Avatar
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    looking at the datasheets
    MJW21191 / 21192 are 150V 8A 1C/W hfe 25 @4A
    MJW21193 / 21194 are 250V 16A 0.7C/W hfe 60 @ 5A
    MJL21193 / 21194 are 250V 16A 0.7C/W hfe 60 @ 5A

    MJW21193 / 21194 and MJL21193 / 21194 are suitable replacements, no circuit mods required,
    21191 is PNP, 21192 is NPN, 21193 is PNP, 21194 is NPN
    Also, before replacing the transistors, check to see the speaker is ok & not shorted / blown

  3. #3
    T9c
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    Thanks, mozwell. that's what I thought/hoping for. Just puzzled me a bit that even though ON Semi site recommended them as replacements, but the max specs were so much higher. Checked the speaker too and it's good.



    Quote Originally Posted by mozwell View Post
    looking at the datasheets
    MJW21191 / 21192 are 150V 8A 1C/W hfe 25 @4A
    MJW21193 / 21194 are 250V 16A 0.7C/W hfe 60 @ 5A
    MJL21193 / 21194 are 250V 16A 0.7C/W hfe 60 @ 5A

    MJW21193 / 21194 and MJL21193 / 21194 are suitable replacements, no circuit mods required,
    21191 is PNP, 21192 is NPN, 21193 is PNP, 21194 is NPN
    Also, before replacing the transistors, check to see the speaker is ok & not shorted / blown

  4. #4
    Senior Member Enzo's Avatar
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    I agree, use them.

    Make sure to check those 100 ohm and the 0.22 ohm resistors. Even though they check OK, if I had to replace an output, I;d replace its driver too. It is not worth being cheap over.


    Note the MJW and MJL are different packages. I'd stick with the MJW
    Education is what you're left with after you have forgotten what you have learned.

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    I know this is a way-old thread, but I have a similar issue with an Acoustasonic Jr.

    Enzo, when you refer to the 100 ohm and 0.22 ohm resistors do you mean R117 and R119 (left power amp MJW21192 ), R116 and R115 (left power amp MJW21191), and R217 and R219 (right power amp MJW21192), R216 and R218 (right power amp MJW21191)?

    Thanks
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  6. #6
    Senior Member Enzo's Avatar
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    Uh...

    We were talking about failed output transistors, so I suggested always checking any associated resistors, so yes, those.
    Education is what you're left with after you have forgotten what you have learned.

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