Harman Kardon A-402 speaker protetors no relay

Discussion in 'DIY' started by sssboa, Nov 14, 2017.

  1. sssboa

    sssboa Active Member

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    383
    Hi

    HKs have those spekaer protectors and no relay.
    Do they require cleaning (is it possible)? Are new (modern) drop-in replacements available?

    HK1.jpg HK2.jpg
     
  2. avionic

    avionic " Black Knights " Subscriber

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    Circuit breakers- thermal resetable ? I can't make out the make and model number in your photo.
     
  3. sssboa

    sssboa Active Member

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    383
    What I can read on it:
    50W
    BC 201-1-
    Hosiden 125v 50.60Hz
     
  4. avionic

    avionic " Black Knights " Subscriber

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    Do these OEM breakers have a reset button on them ?
     
  5. I LIKE MUSIC

    I LIKE MUSIC Super Member

    The 2.5 A might mean that it is rated at 2.5 amps.
     
  6. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Good question. According to my catalog, they are available as auto reset or manual reset.

    Edit, I should have mentioned that my catalog does not show that exact part number, but does show similar devices.
     
  7. restorer-john

    restorer-john Super Member

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    They are 2.5A and they are pretty reliable.

    If you want to test it, hook it up to to a small NiMh battery pack- it should trip really fast.

    HK used to use push to reset circuit breakers and then moved to auto reset at one point, before dropping them altogether.

    The Owner's Manual for the A-402 has this:

    a402.JPG

    It says it needs a manual reset when tripped, but I would confirm that. The buttons should protrude from the back panel when tripped.
     
    I LIKE MUSIC likes this.
  8. I LIKE MUSIC

    I LIKE MUSIC Super Member

    ^^^^^Good information.


    My catalog shows pictures that look the OP's picture for both auto and manual reset, of course the auto reset does not have reset button.
     
  9. sssboa

    sssboa Active Member

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    Yeah. There are buttons protruding at the back from the speaker protectors.
     
  10. avionic

    avionic " Black Knights " Subscriber

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    So does mouser and digikey.
     
  11. I LIKE MUSIC

    I LIKE MUSIC Super Member

    Again, that is good information. I have not looked there, but from the pictures in my catalog, it looks like he might be able to find an exact replacement, depending on this measurements.
     
  12. avionic

    avionic " Black Knights " Subscriber

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    Reuse the originals.Unless they are no longer serviceable.
     
  13. sssboa

    sssboa Active Member

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    Do you guys think these switches guarantee safety for speakers? I mean in comparison to a usual relay.
     
  14. restorer-john

    restorer-john Super Member

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    Less safety for the speakers, more protection for the output stage.

    Those breakers trip with excess current- not voltage, so transients can pass without premature tripping. Excess current can come from too many paralleled speakers, low impedance speakers turned up too high for too long, or simply a shorted speaker lead.

    The 'usual relay' you mention can be various things. It can be simply a delay at turn on, an overpower/overcurrent arrangement or detecting and protecting against DC (output stage failure) and, most often, a combination of all three.

    HKs implementation using circuit breakers is valid, reliable, and simple. In the case of the A-402, there is no DC protection implemented, however there is turn-on delay thump protection implemented by a simple AC detect/delay which turns on the differential pair (input stage) after a few seconds.

    HK's attitude was always to protect their amps, not your speakers.
     
    Last edited: Nov 15, 2017 at 6:34 PM

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