B-1 Quickie

Discussion in 'Yamaha' started by rottalpha, Dec 11, 2017.

  1. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    YES this is a part of many mysteries in parts list of service manual

    B1-parts-list.JPG


    a MPSU60 can't replace a FET or VFET
    A FET or VFET can't be replaced by a bipolar transistor
     
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  2. rottalpha

    rottalpha Yamaholic Subscriber

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    oh, I know that is not why the SK-180s failed. They failed due to operator error 100%. I have one dead on each channel. .The remaining most likely not a pair.
    The TJ08s are probably NOT original Yamaha replacements. The reason the original J24s were replaced is probably opertor error as well.
     
    Last edited: Jan 24, 2018
  3. rottalpha

    rottalpha Yamaholic Subscriber

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    Thank you Patrice,
    that is why I am checking in with you guys. I have six B-1s with only one has the green boards and the TJ8s...but you all helped me confirm my hypothesis about the TJ8s.

    I would like to point out is that not all boards look like the one you are showing. As Alex and Nick pointed out, and as I was able to observe on one of my units, some of the boards can be green.
    View attachment 1096637

    one more observation Patrice:
    in these green boards, the LK15 and the LJ13 have rank letters, where on all other units I see color markings for rank.
     
    Last edited: Jan 24, 2018
  4. clinic-audio

    clinic-audio all on YAMAHA untill 1990

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    OK
    What kind of 2SK75 do you have on all your driving boards (green PCB and others) ?

    LK15A IDSS 8,00 to 9,00 mA color code RED
    LK15B IDSS 9,00 to 10,00 mA color code BLUE
    LK15C IDSS 10,00 to 11,00 mA color code ? Did not made any measurements yet

    As you can see 1mA difference , very very tight

    LJ13A IDSS 2,5 mA to 3,5 mA color code RED
    LJ13B IDSS 3,5 mA to 4,5 mA color code YELLOW
    LJ13C IDSS 4,5 mA to 5,5 mA color code BLUE
     
  5. rottalpha

    rottalpha Yamaholic Subscriber

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    the SK75s are all the same...
    A-rank for the ones on the center
    B-rank for the ones on the heatsink

    thank for providing the ranks for the smaller fets. I did not make any measurements yet...still in the discovery mode
     
  6. rottalpha

    rottalpha Yamaholic Subscriber

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    J13 - rank A
    K15 - rank B

    matched pairs on each board, both boards are the same. I am going to make the assumption they are original
     

     

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  7. rottalpha

    rottalpha Yamaholic Subscriber

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    what is the IDSS / color rank for the J24?
     
  8. vintagejapan

    vintagejapan AK Member Subscriber

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    I was surprised myself when I saw it. The board was a early revision also.
     
  9. vintagejapan

    vintagejapan AK Member Subscriber

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    I installed the SK77 yesterday and after adjustments had a good listening. I am using a tube pre and the direct in inputs. To my ears the K180 has a smidgen more extension on the high. All the rest is identical.

    The only issue I have is that this B-1 does get very hot. The fact that there is around 30 degrees celsius everyday surely does not help. So after running it for a couple of hours the amp need to cool off before can be turned back on. Is this normal?

    Here is a close up of the drive boards.
     

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  10. vintagejapan

    vintagejapan AK Member Subscriber

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    Gave it a fresh coat of paint also, installed some better speaker connectors and a IEC power connector.
     

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  11. Vint Age

    Vint Age B-1 With Yamaha

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    Thanks for the comparison!

    Yes the B-1 runs quite hot. So much so that in my case I rotate in my B-2 in the late spring here because of how much heat the B-1 contributes to our already very hot home during the summer; that and I also love the sonics of the B-2 and this way I get to enjoy both. Albeit moving a B-1 around is a real pain in the back ... and a few other places! ;)

    Very nice indeed! :thumbsup:
     

     

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  12. vintagejapan

    vintagejapan AK Member Subscriber

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    My pleasure Nick,
    At list now I can keep this one going. To my ears, B-3 run as 2 mono blocks would be next in line after the B-1. And they do run quiet cool.
     
  13. vintagejapan

    vintagejapan AK Member Subscriber

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    The K180’s that we’re in before.

    And a pic of some unmarked SK75 ‘s
     

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  14. Vint Age

    Vint Age B-1 With Yamaha

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    Thanks!
    YB1_a.jpg
     
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  15. rottalpha

    rottalpha Yamaholic Subscriber

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    what is very hot? if the thermo switches are puting the amp in thermal protection, that is not normal
    the unit I worked on for this thread was getting extremely hot, but not turning off. It was obviously on its last legs and most likely out of adjustment.
    My understanding it that the balance pot will help balance out minor differences within a output v-fet pair. That will ensure that one of the devices does not work more than the other and overheat. It will also bring down THD.

    edit: while testing the unit I did let it on hooked to the generator for a long period of time at 75w otput. The heatsinks weare at a toasty 160deg F, but everything seemed normal. But again, if you do not need a room heater when you have 30deg C outside, do not play your B-1 :D
     
    Last edited: Jan 25, 2018
  16. rottalpha

    rottalpha Yamaholic Subscriber

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    I meant to say, Thank you for the close-ups. I see the fets rank marked with letter.
     
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  17. rottalpha

    rottalpha Yamaholic Subscriber

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    nice job bringing that bad boy to prime again:thumbsup:
     
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  18. rottalpha

    rottalpha Yamaholic Subscriber

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    :thumbsup: Where did you come up with all this stuff?

    so bunch of "strange" fets and v-fets in there ...and the TJ08 mistery solved. Tried to find informaion on it and I found nothing.

    so interesting. I am willing to bet that the Y304/405 devices were from your green boards? correct?

    if my assumption is correct, the Y304/405, the TJ08 and the letter ranked J13/K15 devices were used in the earler B-1 units.
     
  19. Beau Geste

    Beau Geste Addicted Member

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    I see an IEC320 socket on the back of the Power Amp. Is there a special tool to cut it out of the sheet?Thanks.
     
  20. vintagejapan

    vintagejapan AK Member Subscriber

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    “Cannot held hand on top of the heat sink” hot.

    The unit does not turn off, but if I turn off will not turn back on until cooled a little.

    I will check the p-p balance settings again.
     

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