New B2 for complete rebuild.

Discussion in 'Yamaha' started by belgianbrain, Oct 6, 2017.

  1. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    So, I received Moron's B2 today (see other thread for its genesis).

    He did double box it, but he did not pack it securely or with a inch of bubble wrap around the B2 and around the first box as I ordered. There was maybe 1/4" of padding on part of it on the inner box and just a bunch of junk around the first box in the second box. It arrived in good condition, except for a broken meter switch on the rear. But, based on the packing job, I think this B2 survived a near death experience. :thumbsdown:

    So, "Moron" seems like an appropriate assessment by Rottalpha in the other thread. ;)

    The B2 is in nice shape. A bit of oil soap and I think it could look nearly brand new!


    IMG_20171006_155626.jpg
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    IMG_20171006_155748.jpg
     
    Last edited: Oct 6, 2017
    fishondwan, zaibatsu and Cosmin2000 like this.
  2. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    This B2 will get a complete rebuild over the winter as I have time.

    First things first. I tried to turn it on briefly. It powers up. No protection light. No relay click. After 5 seconds of not hearing the relay click, I killed the power.

    What is the appropriate approach to diagnose this without endangering VFETS that are hopefully in working condition?

    I have the parts to do a complete recap of the power supply section and install new relays. Should I just start there?

    ...or is the best approach to pull the VFET boards and test those and rebuild those first?
     
    Last edited: Oct 6, 2017
  3. Saint Johnny

    Saint Johnny Bon Ton Roule Subscriber

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  4. Vint Age

    Vint Age B-1 With Yamaha

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    Hey congrats again! Is it possible that the speaker on off switch was in the off position when you tried it? It looks like it's in the off position in your first picture but it's hard to tell from here. If so the protection relay wouldn't click ...
     
  5. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    :rflmao:BINGO. Relay clicks. I have never turned the speakers off on my other B2 and never noticed this.

    I'll give it a quick try later this weekend when I get a chance to see if I get sound. It'd be really cool if I can just start the rebuild with it in working order and not have to troubleshoot it first.
     
  6. OMGCat!

    OMGCat! AK Subscriber Subscriber

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    That got me on my B2x as well. No click made me unhappy until I realized that there's a relay for each speaker set.
    Great that it made it to you in good shape. Looking forward to watching the resto thread.
     
  7. rottalpha

    rottalpha Yamaholic

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    or the meter switch was not really meant to sustain the amp's weight during the potoshoot ;)
     
    Last edited: Oct 7, 2017
  8. rottalpha

    rottalpha Yamaholic

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    glad to hear all OK in that department. This unit is going to clean up nicely...it seems mostly dirty, but otherwise a nice unit.
     
    Last edited: Oct 7, 2017
  9. Mark B

    Mark B Yamaha Fan Subscriber

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    Very fortunate that the B-2 arrived in fairly good shape. :thumbsup:
     
  10. Bert 1100

    Bert 1100 Super Member

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    Planquiri !
    Great news !
    :lurk: :lurk:
     
  11. Vint Age

    Vint Age B-1 With Yamaha

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    If it were mine I'd start by checking the PS voltages, bias, and offset on the bench first. They'll be good indicators of the amp's current condition ... :thumbsup:
     
  12. zaibatsu

    zaibatsu Active Member

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    Congratulations!

    They say fortune favours the brave, this seems like a golden example.
     
  13. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    Power supply = 85.0V / -85.3V

    Bias and offset were close and just required a tiny nudge of the potentiometers to get right on spec. :thumbsup:
     
  14. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    Hooked it up and....sweet VFET sound. :rockon:

    Unit is now off until it meets its new self. First to come...complete power supply section rebuild, including the 18,000 uF main caps..
     
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  15. Bert 1100

    Bert 1100 Super Member

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    Woohoo !
     
  16. amr2

    amr2 Active Member

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    Congratulations! :beerchug:
     
  17. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    First up...power supply board. Here it is before.

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    Last edited: Nov 7, 2017
  18. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    The glue on the board used for some of the larger caps and heat sinks is used sparingly and does not appear to be causing havoc with surrounding components. Any point to trying to remove this, other than aesthetic?
     
  19. Mr. Yamaha

    Mr. Yamaha Not so much Yamaha lately... Subscriber

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    I can't think of one good reason why you would leave the glue on the boards while you are doing a 'complete rebuild'. Or maybe one: laziness :p

    Other than the aesthetic aspect (important enough as sole reason), the glue is known for it's corroding powers over time. So, while (it looks like) it did not affect any surrounding components, it can in in the future.

    Really a no brainer if you ask me :thumbsup:
     
  20. belgianbrain

    belgianbrain AK Subscriber Subscriber

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    Power supply board is almost done. I remove some of the glue where possible, but I don't see much point to risking damage of the board or exposing myself to funky chemicals where there is no practical benefit to doing so.

    I will do the large electrolytic capacitor board at the same time, but I am awaiting arrival of the Mundorf AG capacitors I decided to try this time around.

    First serious question: I am eying L201 and L202 suspiciously.

    I understand the L201/R237 and L202/R238 output filter is there to decouple any speaker crossover reactance from the Amp's internal feedback network (or something like that - close enough, I hope). My research suggests that with some speakers, the reactive load can present a problem.

    On my other B2, I tried shorting this output filter to assess the effect on sonics. I noticed a noticeable improvement right away, especially in the high range. This did not appear to create a problem with the NS-1000 speakers attached to the amp, but in theory maybe it could with other speakers, or maybe it does and it's not noticeable. Who knows.

    The point is, I would like to leave the filter intact in this rebuild. However, since the audible frequency spectrum passes through that inductor and not the resistor, obviously the inductor must be degrading the sonics.

    Now I notice in this B2 that inductor is a very small wire wound inductor. Other amplifiers I have worked on, like my Bryston 3BSST, uses a 2uH coil, which is a THICK wire wound inductor that has only a few turns. Actually, it looks like a twisted piece of 14 AWG wire.

    I'd like to replace the L201/L202 in the B2 with this sort of inductor. Now, when I search mouser for 3uH inductors, I find nothing that looks like these inductors used in newer power amplifiers.

    Where to get them?
     
    Last edited: Oct 21, 2017

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