Yamaha B-3 V-fet restoration

Discussion in 'Yamaha' started by vintagejapan, Feb 18, 2018.

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  1. vintagejapan

    vintagejapan AK Member Subscriber

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    I have in my posession this wonderful amplifier and am trying to bring it to its former glory.
    Looking for some guidance on replacements for the following transistors 2sc1775 and 2sa659 on the muting board. Thank you

    Here is the circuit
     

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  2. wmgwizard

    wmgwizard AK Subscriber Subscriber

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    You may want to moderators to move this to the Yamaha Board.

    Avionic and a few others are the Yamaha guru's and tend to lurk there.

    Be careful with those V-FET's, they are unobtainable.
     
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  3. Oilmaster

    Oilmaster Drillers go deeper Subscriber

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    That is really a big drafting mistake on that schematic.
    Listing a 2SA for a NPN device.....urgh!!
    Then double-erroring it to go from 1775 to 1175.....duh !

    As you may have noticed in reality, TR310/304/306 are indeed 2SC1775

    By default, 2SA1775(A) is normally subbed by KSC1845 (or 2SC2240)

    In case you can't get them, then the next step down are transistors that are rated 50V, such as KSC1815 and KSC945C (note the C suffix for correct leg order)

    Voltage-rating-wise (Vce of 2SC1775 ~ 90V), that is not really required for subs in that section there (rail voltage is 50V, with maximum 25V dropping over those transistors).

    2SA659 can be subbed by KSA1015
     
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  4. rottalpha

    rottalpha Yamaholic Subscriber

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    I thought your pair of B-3 running bridged are working. Is this a 3rd one?
     
  5. vintagejapan

    vintagejapan AK Member Subscriber

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    Awesome stuff,

    Thank you Oilmaster, the ones I pulled out were indeed 2SC1775’s

    I wanted to replace those because black legged and they didn’t measure to spec.

    Didn’t notice the mistake on the schematic and thank you for your eagle eyes

    I do have some new 1775 and will use 2sa1015 for the 2sa659.
     
  6. vintagejapan

    vintagejapan AK Member Subscriber

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    I originally did the 2 big filtering caps, all electrolytics, the double diodes Will do a complete restoration now.

    Also measured the fusible resistors on the drive board and some were slightly out of spec so will do those also. Then all the film caps.


    Last just for ease of use the speaker connectors and install a IEC power connector.

    May take a couple of pics on the way. Have not seen much info on the B-3 and although a bit less powerful than The B-2 personally think is a step above on sound quality. Especially when on BTL mode.
     
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  7. vintagejapan

    vintagejapan AK Member Subscriber

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    Just have the 2 original B-3’s
     
  8. Vint Age

    Vint Age B-1 With Yamaha

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    Yes please and thank you! :thumbsup: :)
     
  9. vintagejapan

    vintagejapan AK Member Subscriber

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    Ok, so powering on while waiting for some parts to arrive sorted the back panel. the speaker connectors are crap, replaced them with some modern ones that accept banana connectors. Volume pots are also on the back panel, the 2 pots in front are only for show and connect to the pots in the back via the long metal rods as seen. Ideally would like to change them but dont think would be easy to find drop in replacements. They are alps 30k pots but only go up to 25~26k on my meter. Gave them a good clean and lubricated them. Guess will leave them in for now.
     

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  10. vintagejapan

    vintagejapan AK Member Subscriber

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    The muting board. So far have replaced the 3X 2sc1775 and 2X 2sa695 transistors. Used some new 2sc1775's i had in hand and 2sa1015. Relay is a HC4a-PY 24VDC. Will also change the film caps with polypropylene caps.
     

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  11. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Looking very good, nice work :thumbsup:. Great idea on the speaker connector upgrade, many Yamaha'a from this era seem to have average connectors from the factory.
     
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  12. Oilmaster

    Oilmaster Drillers go deeper Subscriber

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    I guess the pots aren't a real issue when duly cleaned.
    Since you'll probably use a preamp, the pots are in the extreme position anyway, not using the track.
     
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  13. vintagejapan

    vintagejapan AK Member Subscriber

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    The heatsink is actually 2 pieces and they are in different shades of black. V-fets are 2SK76A(c) and 2SJ26A(c) Must be a special grade, I have come across a couple of times of the A only version on the Yamaha B-2. They did sound identical to my years with the non A version.
     

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  14. Oilmaster

    Oilmaster Drillers go deeper Subscriber

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    An "A" suffix (not rank) for Japanese transistors normally means a higher voltage rating of the non-A version.
    For example, look at the datasheet of the 2SC1775 (which exists in non-A and A version, Vce rating)
    Later production runs of the B-2 and all B-3 have the A version; probably as the higher voltage rating also means better SOA (stress resistance)
    In other words; better quality.
     
  15. rottalpha

    rottalpha Yamaholic Subscriber

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    IIRC, the original, non-suffix devices were more robust, not that it matters with B-2, since they will not see that voltage.
    2SK76 - VGDO 200V with IDSS = 5A
    2SK76A - VGDO 180V with IDSS = 3.5A

    not sure what the C suffix datasheet says, but I am curious
     
  16. Oilmaster

    Oilmaster Drillers go deeper Subscriber

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    Oh well, there must be exceptions to the rule :cool:
     

     

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  17. vintagejapan

    vintagejapan AK Member Subscriber

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    One more lonely electro here, just behind the RCA IMG_8680.JPG inputs board
     
  18. vintagejapan

    vintagejapan AK Member Subscriber

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    I have been swamped at work lately so not much time for the B-3. I decided to replace the Yamaha blue film caps on each driver board.. Using some nice polypropylene, if not happy with the results will put them back on.
     
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  19. vintagejapan

    vintagejapan AK Member Subscriber

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    Here is what have done so far. I admit the board does not appear pretty. Replaced all fusible resistors with Dale metal film, and all the film caps with polypropylene. Still waiting for a new NF2E relay and new trimmers for the Bias and DC adjustments. I am not sure if I want to start digging on all the transistors condition, on a couple couldn't even make the letters out.

    IMG_5518 2.JPG
     
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  20. Oldsansui441

    Oldsansui441 AK Subscriber Subscriber

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    Looking good! What axial polypropylenes did you use in the centre of the board? Did they replace radial polyesters?
     

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